@article{petters_pujiastuti_satheesh_kasparoglu_sutherland_meskhidze_2024, title={Wind-driven emissions of coarse-mode particles in an urban environment}, volume={24}, ISSN={["1680-7324"]}, DOI={10.5194/acp-24-745-2024}, abstractNote={Abstract. Quantifying surface–atmosphere exchange rates of particles is important for understanding the role of suspended particulate matter in radiative transfer, clouds, precipitation, and climate change. Emissions of coarse-mode particles with a diameter greater than 0.5 µm provide giant cloud condensation nuclei and ice nuclei. These emissions are critical for understanding the evolution of cloud microphysical properties yet remain poorly understood. Here we introduce a new method that uses lidar retrievals of the elastic backscatter and Doppler velocity to obtain surface number emissions of particles with a diameter greater than 0.53 µm. The technique is applied to study particle number fluxes over a 2-month period from 1 June to 10 August 2022 during the TRACER campaign at an urban site near Houston, TX, USA. We found that all the observed fluxes were positive (upwards), indicating particle emission from the surface. The fluxes followed a diurnal pattern and peaked near noon local time. Flux intensity varied through the 2 months with multi-day periods of strong fluxes and multi-day periods of weak fluxes. Emission particle number fluxes peaked near ∼ 100 cm−2 s−1. The daily averaged emission fluxes correlated with friction velocity and were anticorrelated with surface relative humidity. The emission flux can be parameterized as F= 3000 u*4, where u* is the friction velocity in m s−1 and the emission flux F is in cm−2 s−1. The u* dependence is consistent with emission from wind-driven erosion. Estimated values for the mass flux are in the lower range of literature values from non-urban sites. These results demonstrate that urban environments may play an important role in supplying coarse-mode particles to the boundary layer. We anticipate that quantification of these emissions will help constrain aerosol–cloud interaction models that use prognostic aerosol schemes.
}, number={1}, journal={ATMOSPHERIC CHEMISTRY AND PHYSICS}, author={Petters, Markus D. and Pujiastuti, Tyas and Satheesh, Ajmal Rasheeda and Kasparoglu, Sabin and Sutherland, Bethany and Meskhidze, Nicholas}, year={2024}, month={Jan}, pages={745–762} }
 @article{sutherland_burton_hostetler_ferrare_hair_park_oak_meskhidze_2023, title={Application of DIAL/HSRL and CATCH algorithm-based methodologies for surface PM2.5 concentrations during the KORUS-AQ campaign}, volume={301}, ISSN={["1873-2844"]}, DOI={10.1016/j.atmosenv.2023.119719}, abstractNote={Particulate matter with an aerodynamic diameter of equal to or less than 2.5 μm (PM2.5) has been found to have a serious adverse effect on human health and the environment. While the importance of measuring PM2.5 has been demonstrated, doing so remotely remains challenging. In this study, methodologies for the assessment of aerosol PM2.5 and chemical composition based on a combination of regional and global models and active remote sensing were evaluated against surface observations from the KORUS-AQ campaign. The model outputs from the Community Multiscale Air Quality (CMAQ) and GEOS-Chem were used and were available at the KORUS-AQ campaign data archive. For remote sensing, aerosol extinction and derived aerosol types available from NASA Langley Airborne Differential Absorption Lidar (DIAL)/High Spectral Resolution Lidar (HSRL) flying onboard DC-8 aircraft were used. A revised version of the algorithm, which incorporates size-specific aerosol dry mass extinction efficiencies for sulfate, nitrate, and ammonia as well as organic matter, is also presented. The PM2.5 concentration estimates were compared with measurements taken at the ground stations. The estimated mean absolute error between the ground station measurements and the remote-sensing-based methodologies was significantly lower compared to the models. The data analysis has shown that uncertainties in relative humidity values, the presence of particles larger than 2.5 μm in diameter, and the abundance of black carbon and organic matter in Asian aerosol were unlikely to explain the differences between measured and predicted surface PM2.5. Local meteorology was found to play a key role influencing the spatiotemporal variability of aerosols and the most important factor determining the agreement between the estimated and ground site-measured PM2.5. The lowest mean absolute error was found for the May 1–16 period, when aerosols were well mixed within the mixing layer and homogeneous across the temporal (1 h) and spatial (8 km) scales used in this study. Under these conditions, the methodologies presented here could give reasonable estimates of PM2.5 concentration and derived chemical composition over South Korea when HSRL data are available.}, journal={ATMOSPHERIC ENVIRONMENT}, author={Sutherland, Bethany and Burton, Sharon and Hostetler, Chris A. and Ferrare, Richard A. and Hair, Johnathan and Park, Rokjin J. and Oak, Yujin J. and Meskhidze, Nicholas}, year={2023}, month={May} }
 @article{al-abadleh_kubicki_meskhidze_2022, title={A perspective on iron (Fe) in the atmosphere: air quality, climate, and the ocean}, ISSN={["2050-7895"]}, DOI={10.1039/d2em00176d}, abstractNote={As scientists engage in research motivated by climate change and the impacts of pollution on air, water, and human health, we increasingly recognize the need for the scientific community to improve communication and knowledge exchange across disciplines to address pressing and outstanding research questions holistically. Our professional paths have crossed because our research activities focus on the chemical reactivity of Fe-containing minerals in air and water, and at the air-sea interface. (Photo)chemical reactions driven by Fe can take place at the surface of the particles/droplets or within the condensed phase. The extent and rates of these reactions are influenced by water content and biogeochemical activity ubiquitous in these systems. One of these reactions is the production of reactive oxygen species (ROS) that cause damage to respiratory organs. Another is that the reactivity of Fe and organics in aerosol particles alter surficial physicochemical properties that impact aerosol-radiation and aerosol-cloud interactions. Also, upon deposition, aerosol particles influence ocean biogeochemical processes because micronutrients such as Fe or toxic elements such as copper become bioavailable. We provide a perspective on these topics and future research directions on the reactivity of Fe in atmospheric aerosol systems, from sources to short- and long-term impacts at the sinks with emphasis on needs to enhance the predictive power of atmospheric and ocean models.}, journal={ENVIRONMENTAL SCIENCE-PROCESSES & IMPACTS}, author={Al-Abadleh, Hind A. and Kubicki, James D. and Meskhidze, Nicholas}, year={2022}, month={Aug} }
 @article{kasparoglu_islam_meskhidze_petters_2022, title={Characterization of a modified printed optical particle spectrometer for high-frequency and high-precision laboratory and field measurements}, volume={15}, ISSN={["1867-8548"]}, DOI={10.5194/amt-15-5007-2022}, abstractNote={Abstract. The printed optical particle spectrometer (POPS) is a lightweight, low-cost
instrument for measurements of aerosol number concentrations and size
distributions. This work reports on modifications of the Handix Scientific
commercial version of the POPS to facilitate its use in multi-instrument
aerosol sampling systems. The flow system is modified by replacing the
internal pump with a needle valve and a vacuum pump. The instrument is
integrated into closed-flow systems by routing the sheath flow from filtered
inlet air. A high-precision multichannel analyzer (MCA) card is added to
sample the analog pulse signal. The MCA card is polled at 10 Hz frequency
using an external data acquisition system and improves upon the count-rate
limitation associated with the POPS internal data acquisition system. The
times required to change the concentration between 90 % and 10 % and vice versa
for a step change in concentration were measured to be 0.17 and 0.41 s at
a flow rate of 5 cm3 s−1. This yields a sampling frequency of
∼ 1–2 Hz, below which the amplitude of measured fluctuations is
captured with > 70 % efficiency. The modified POPS was
integrated into the dual tandem differential mobility analyzer system to
explore the coalescence of dimer particles. Results show that the
pulse-height response increases upon dimer coalescence. The magnitude of the
increase is broadly consistent with the change in light-scattering amplitude
predicted by the T-matrix method. It is anticipated that this modified
version of the POPS will extend the utilization of the technique for a range
of field and laboratory applications.
}, number={17}, journal={ATMOSPHERIC MEASUREMENT TECHNIQUES}, author={Kasparoglu, Sabin and Islam, Mohammad Maksimul and Meskhidze, Nicholas and Petters, Markus D.}, year={2022}, month={Sep}, pages={5007–5018} }
 @article{islam_meskhidze_satheesh_petters_2022, title={Turbulent Flux Measurements of the Near-Surface and Residual-Layer Small Particle Events}, volume={127}, ISSN={["2169-8996"]}, DOI={10.1029/2021JD036289}, abstractNote={According to recent field studies, almost half of the New Particle Formation (NPF) events occur aloft, in a residual layer, near the top of the boundary layer. Therefore, measurements of the meteorological parameters, precursor gas concentrations, and aerosol loadings conducted at the ground level are often not representative of the conditions where the NPFs take place. This paper presents new measurements obtained during the Turbulent Flux Measurements of the Residual Layer Nucleation Particles, conducted at the Southern Great Plains research site. Vertical turbulent fluxes of 3–10 nm‐sized particles were measured using a sonic anemometer and two condensation particle counters with nominal cutoff diameters of ≥ $\ge $ 3 nm and ≥ $\ge $ 10 nm mounted at the top of the 10‐m telescoping tower. Aerosol number size distribution (5–300 nm) was determined through the ground‐based Scanning Mobility Particle Sizers. The size selected (15–50 nm) particle hygroscopicity was derived with the Humidified Tandem Differential Mobility Analyzer. The ground level observations were supplemented by vertically‐resolved measurements of horizontal and vertical wind speeds and aerosol backscatter. The data analysis suggests that (a) turbulent flux measurements of 3–10 nm particles can distinguish between near‐surface and residual‐layer small particle events; (b) sub‐50 nm particles had a hygroscopicity value of 0.2, suggesting that organic compounds dominate atmospheric nanoparticle chemical composition at the site; and (c) current methodologies are inadequate for estimating the dry deposition velocity of sub‐10 nm particles because it is not feasible to measure particle concentration very near the surface, in the diffusion sublayer.}, number={17}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, author={Islam, M. M. and Meskhidze, N. and Satheesh, A. Rasheeda and Petters, M. D.}, year={2022}, month={Sep} }
 @article{cheng_wang-li_meskhidze_classen_bloomfield_2021, title={Partitioning of NH3-NH4+ in the Southeastern U.S.}, volume={12}, ISSN={2073-4433}, url={http://dx.doi.org/10.3390/atmos12121681}, DOI={10.3390/atmos12121681}, abstractNote={The formation of inorganic fine particulate matter (i.e., iPM2.5) is controlled by the thermodynamic equilibrium partitioning of NH3-NH4+. To develop effective control strategies of PM2.5, we aim to understand the impacts of changes in different precursor gases on iPM2.5 concentrations and partitioning of NH3-NH4+. To understand partitioning of NH3-NH4+ in the southeastern U.S., responses of iPM2.5 to precursor gases in four seasons were investigated using field measurements of iPM2.5, precursor gases, and meteorological conditions. The ISORROPIA II model was used to examine the effects of changes in total ammonia (gas + aerosol), total sulfuric acid (aerosol), and total nitric acid (gas + aerosol) on iPM2.5 concentrations and partitioning of NH3-NH4+. The results indicate that reduction in total H2SO4 is more effective than reduction in total HNO3 and total NH3 to reduce iPM2.5 especially under NH3-rich condition. The reduction in total H2SO4 may change partitioning of NH3-NH4+ towards gas-phase and may also lead to an increase in NO3− under NH3-rich conditions, which does not necessarily lead to full neutralization of acidic gases (pH < 7). Thus, future reduction in iPM2.5 may necessitate the coordinated reduction in both H2SO4 and HNO3 in the southeastern U.S. It is also found that the response of iPM2.5 to the change in total H2SO4 is more sensitive in summer than winter due to the dominance of SO42− salts in iPM2.5 and the high temperature in summer. The NH3 emissions from Animal Feeding Operations (AFOs) at an agricultural rural site (YRK) had great impacts on partitioning of NH3-NH4+. The Multiple Linear Regression (MLR) model revealed a strong positive correlation between cation-NH4+ and anions-SO42− and NO3−. This research provides an insight into iPM2.5 formation mechanism for the advancement of PM2.5 control and regulation in the southeastern U.S.}, number={12}, journal={Atmosphere}, publisher={MDPI AG}, author={Cheng, Bin and Wang-Li, Lingjuan and Meskhidze, Nicholas and Classen, John and Bloomfield, Peter}, year={2021}, month={Dec}, pages={1681} }
 @article{cheng_wang-li_classen_meskhidze_bloomfield_2021, title={Spatial and temporal variations of atmospheric chemical condition in the Southeastern U.S.}, volume={248}, ISSN={0169-8095}, url={http://dx.doi.org/10.1016/j.atmosres.2020.105190}, DOI={10.1016/j.atmosres.2020.105190}, abstractNote={Animal feeding operations (AFOs) are the largest ammonia (NH3) emission sources in the United States (U.S.). However, the impact of NH3 emissions from AFOs on the formation of secondary inorganic PM2.5 (iPM2.5) has not been well understood and systematically assessed. Under the Southeastern Aerosol Research and Characterization (SEARCH) Network, the hourly concentrations of iPM2.5 chemical compositions and its precursor gases as well as meteorological data were measured at eight urban/nonurban sites labeled as JST/YRK, BHM/CTR, GFP/OAK, and PNS/OLF during 1998–2016. Using the SEARCH data, this research investigated the spatiotemporal variations of atmospheric chemical conditions in those rural and urban areas. The spatiotemporal variations of atmospheric chemical conditions at the eight sites are characterized by four parameters, including (1) gas ratio (GR), (2) gas-phase NH3 molar fraction (NH3/NHx), (3) total available NH3 (gaseous ammonia + aerosol ammonium) to sulfate (SO42−) molar ratio (TA/TS), and (4) PM2.5 ammonium + nitrate to total PM2.5 mass ratio (AN/PM2.5). Results indicate that the NH3 emissions from AFOs may explain the greater values of GR, NH3/NHx, and TA/TS in the wind directions coming from AFOs at YRK and OAK rural sites than the other wind directions. In the wind directions coming from AFOs at YRK and OAK, NH3 was in excess of fully neutralizing acidic gases, more NH3 stayed in gas phase than those in other wind directions, and both ammonium sulfate and ammonium nitrate existed in iPM2.5. The upward trend in NH3/NHx indicates that gas-particle partitioning ofNH3–NH4+shifted toward gas phase, while the downward trend in AN/PM2.5 may implicate that smaller fraction of PM2.5 was directly NH3 sensitive. Understanding of the spatiotemporal variations of atmospheric chemical condition provides insights to improve our understanding of iPM2.5 formation under rural and urban conditions, the reduction in sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions resulted in the reduction of iPM2.5 formation despite the increase in NH3 emissions in the Southeastern U.S.}, journal={Atmospheric Research}, publisher={Elsevier BV}, author={Cheng, Bin and Wang-Li, Lingjuan and Classen, John and Meskhidze, Nicholas and Bloomfield, Peter}, year={2021}, month={Jan}, pages={105190} }
 @article{sellegri_nicosia_freney_uitz_thyssen_gregori_engel_zaencker_haentjens_mas_et al._2021, title={Surface ocean microbiota determine cloud precursors}, volume={11}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-020-78097-5}, abstractNote={Abstract One pathway by which the oceans influence climate is via the emission of sea spray that may subsequently influence cloud properties. Sea spray emissions are known to be dependent on atmospheric and oceanic physicochemical parameters, but the potential role of ocean biology on sea spray fluxes remains poorly characterized. Here we show a consistent significant relationship between seawater nanophytoplankton cell abundances and sea-spray derived Cloud Condensation Nuclei (CCN) number fluxes, generated using water from three different oceanic regions. This sensitivity of CCN number fluxes to ocean biology is currently unaccounted for in climate models yet our measurements indicate that it influences fluxes by more than one order of magnitude over the range of phytoplankton investigated.}, number={1}, journal={SCIENTIFIC REPORTS}, author={Sellegri, Karine and Nicosia, Alessia and Freney, Evelyn and Uitz, Julia and Thyssen, Melilotus and Gregori, Gerald and Engel, Anja and Zaencker, Birthe and Haentjens, Nils and Mas, Sebastien and et al.}, year={2021}, month={Jan} }
 @article{zimmerman_petters_meskhidze_2020, title={Observations of new particle formation, modal growth rates, and direct emissions of sub-10 nm particles in an urban environment}, volume={242}, ISSN={["1873-2844"]}, DOI={10.1016/j.atmosenv.2020.117835}, abstractNote={Ultrafine particles with diameters less than 100 nm suspended in the air are a topic of interest in air quality and climate sciences. Sub-10 nm particles are of additional interest due to their health effects and contribution to particle growth processes. Ambient measurements were carried out at North Carolina State University in Raleigh, NC between April to June 2019 and November 2019 to May 2020 to investigate the temporal variability of size distribution and number concentration of ultrafine particles. A mobile lab was deployed between March and May 2020 to characterize the spatial distribution of sub-10 nm particle number concentration. New particle formation and growth events were observed regularly. Also observed were direct emissions of sub-10 nm particles. Analysis against meteorological variables, gas-phase species, and particle concentrations show that the sub-10nm particles dominated number concentration during periods of low planetary boundary layer height, low solar radiation, and northeast winds. The spatial patterns observed during mobile deployments suggest that multiple temporally stable and spatially confined point sources of sub-10 nm particles are present within the city. These sources likely include the campus utility plants and the Raleigh-Durham International Airport. Additionally, the timing of data collection allowed for investigation of variations in the urban aerosol number size distribution due to reduced economic activity during the COVID-19 pandemic.}, journal={ATMOSPHERIC ENVIRONMENT}, author={Zimmerman, Alyssa and Petters, Markus D. and Meskhidze, Nicholas}, year={2020}, month={Dec} }
 @article{meskhidze_salter_sellegri_elliott_2019, title={Ocean Contributions to the Marine Boundary Layer Aerosol Budget}, volume={10}, ISSN={["2073-4433"]}, DOI={10.3390/atmos10020098}, abstractNote={Projections of future climate remain an important scientific goal for much of the Earth science community [...]}, number={2}, journal={ATMOSPHERE}, author={Meskhidze, Nicholas and Salter, Matthew and Sellegri, Karine and Elliott, Scott}, year={2019}, month={Feb} }
 @article{meskhidze_voelker_al-abadleh_barbeau_bressac_buck_bundy_croot_feng_ito_et al._2019, title={Perspective on identifying and characterizing the processes controlling iron speciation and residence time at the atmosphere-ocean interface}, volume={217}, ISSN={["1872-7581"]}, DOI={10.1016/j.marchem.2019.103704}, abstractNote={It is well recognized that the atmospheric deposition of iron (Fe) affects ocean productivity, atmospheric CO2 uptake, ecosystem diversity, and overall climate. Despite significant advances in measurement techniques and modeling efforts, discrepancies persist between observations and models that hinder accurate predictions of processes and their global effects. Here, we provide an assessment report on where the current state of knowledge is and where future research emphasis would have the highest impact in furthering the field of Fe atmosphere-ocean biogeochemical cycle. These results were determined through consensus reached by diverse researchers from the oceanographic and atmospheric science communities with backgrounds in laboratory and in situ measurements, modeling, and remote sensing. We discuss i) novel measurement methodologies and instrumentation that allow detection and speciation of different forms and oxidation states of Fe in deliquesced mineral aerosol, cloud/rainwater, and seawater; ii) oceanic models that treat Fe cycling with several external sources and sinks, dissolved, colloidal, particulate, inorganic, and organic ligand-complexed forms of Fe, as well as Fe in detritus and phytoplankton; and iii) atmospheric models that consider natural and anthropogenic sources of Fe, mobilization of Fe in mineral aerosols due to the dissolution of Fe-oxides and Fe-substituted aluminosilicates through proton-promoted, organic ligand-promoted, and photo-reductive mechanisms. In addition, the study identifies existing challenges and disconnects (both fundamental and methodological) such as i) inconsistencies in Fe nomenclature and the definition of bioavailable Fe between oceanic and atmospheric disciplines, and ii) the lack of characterization of the processes controlling Fe speciation and residence time at the atmosphere-ocean interface. Such challenges are undoubtedly caused by extremely low concentrations, short lifetime, and the myriad of physical, (photo)chemical, and biological processes affecting global biogeochemical cycling of Fe. However, we also argue that the historical division (separate treatment of Fe biogeochemistry in oceanic and atmospheric disciplines) and the classical funding structures (that often create obstacles for transdisciplinary collaboration) are also hampering the advancement of knowledge in the field. Finally, the study provides some specific ideas and guidelines for laboratory studies, field measurements, and modeling research required for improved characterization of global biogeochemical cycling of Fe in relationship with other trace elements and essential nutrients. The report is intended to aid scientists in their work related to Fe biogeochemistry as well as program managers at the relevant funding agencies.}, journal={MARINE CHEMISTRY}, author={Meskhidze, Nicholas and Voelker, Christoph and Al-Abadleh, Hind A. and Barbeau, Katherine and Bressac, Matthieu and Buck, Clifton and Bundy, Randelle M. and Croot, Peter and Feng, Yan and Ito, Akinori and et al.}, year={2019}, month={Nov} }
 @article{ito_myriokefalitakis_kanakidou_mahowald_scanza_hamilton_baker_jickells_sarin_bikkina_et al._2019, title={Pyrogenic iron: The missing link to high iron solubility in aerosols}, volume={5}, ISSN={["2375-2548"]}, url={https://doi.org/10.1126/sciadv.aau7671}, DOI={10.1126/sciadv.aau7671}, abstractNote={Air pollution creates high Fe solubility in pyrogenic aerosols, raising the flux of biologically essential Fe to the oceans.}, number={5}, journal={SCIENCE ADVANCES}, publisher={American Association for the Advancement of Science (AAAS)}, author={Ito, Akinori and Myriokefalitakis, Stelios and Kanakidou, Maria and Mahowald, Natalie M. and Scanza, Rachel A. and Hamilton, Douglas S. and Baker, Alex R. and Jickells, Timothy and Sarin, Manmohan and Bikkina, Srinivas and et al.}, year={2019}, month={May} }
 @article{meskhidze_royalty_phillips_dawson_petters_reed_weinstein_hook_wiener_2018, title={Continuous flow hygroscopicity-resolved relaxed eddy accumulation (Hy-Res REA) method of measuring size-resolved sodium chloride particle fluxes}, volume={52}, ISSN={["1521-7388"]}, DOI={10.1080/02786826.2017.1423174}, abstractNote={ABSTRACT The accurate representation of aerosols in climate models requires direct ambient measurement of the size- and composition-dependent particle production fluxes. Here, we present the design, testing, and analysis of data collected through the first instrument capable of measuring hygroscopicity-based, size-resolved particle fluxes using a continuous-flow Hygroscopicity-Resolved Relaxed Eddy Accumulation (Hy-Res REA) technique. The Hy-Res REA system used in this study includes a 3D sonic anemometer, two fast-response solenoid valves, two condensation particle counters, a scanning mobility particle sizer, and a hygroscopicity tandem differential mobility analyzer. The different components of the instrument were tested inside the US Environmental Protection Agency's Aerosol Test Facility for sodium chloride and ammonium sulfate particle fluxes. The new REA system design does not require particle accumulation, and therefore avoids the diffusional wall losses associated with long residence times of particles inside the air collectors of traditional REA devices. A linear relationship was found between the sodium chloride particle fluxes measured by eddy covariance and REA techniques. The particle detection limit of the Hy-Res REA flux system is estimated to be ∼3 × 105 m−2 s−1. The estimated sodium chloride particle classification limit, for the mixture of sodium chloride and ammonium sulfate particles of comparable concentrations, is ∼6 × 106 m−2 s−1. Copyright © 2018 American Association for Aerosol Research}, number={4}, journal={AEROSOL SCIENCE AND TECHNOLOGY}, author={Meskhidze, N. and Royalty, T. M. and Phillips, B. N. and Dawson, K. W. and Petters, M. D. and Reed, R. and Weinstein, J. P. and Hook, D. A. and Wiener, R. W.}, year={2018}, pages={433–450} }
 @article{elliott_burrows_cameron-smith_hoffman_hunke_jeffery_liu_maltrud_menzo_ogunro_et al._2018, title={Does marine surface tension have global biogeography? Addition for the Oceanfilms package}, volume={9}, number={6}, journal={Atmosphere}, author={Elliott, S. and Burrows, S. and Cameron-Smith, P. and Hoffman, F. and Hunke, E. and Jeffery, N. and Liu, Y. N. and Maltrud, M. and Menzo, Z. and Ogunro, O. and et al.}, year={2018} }
 @article{phillips_royalty_dawson_reed_petters_meskhidze_2018, title={Hygroscopicity‐ and Size‐Resolved Measurements of Submicron Aerosol on the East Coast of the United States}, volume={123}, ISSN={2169-897X 2169-8996}, url={http://dx.doi.org/10.1002/2017JD027702}, DOI={10.1002/2017JD027702}, abstractNote={Abstract}, number={3}, journal={Journal of Geophysical Research: Atmospheres}, publisher={American Geophysical Union (AGU)}, author={Phillips, B. N. and Royalty, T. M. and Dawson, K. W. and Reed, R. and Petters, M. D. and Meskhidze, N.}, year={2018}, month={Feb}, pages={1826–1839} }
 @article{myriokefalitakis_ito_kanakidou_nenes_krol_mahowald_scanza_hamilton_johnson_meskhidze_et al._2018, title={Reviews and syntheses: the GESAMP atmospheric iron deposition model intercomparison study}, volume={15}, ISSN={["1726-4189"]}, url={https://doi.org/10.5194/bg-15-6659-2018}, DOI={10.5194/bg-15-6659-2018}, abstractNote={Abstract. This work reports on the current status of the global modeling of iron (Fe)
deposition fluxes and atmospheric concentrations and the analyses of the
differences between models, as well as between models and observations. A
total of four global 3-D chemistry transport (CTMs) and general circulation
(GCMs) models participated in this intercomparison, in the framework of
the United Nations Joint Group of Experts on the Scientific Aspects of Marine
Environmental Protection (GESAMP) Working Group 38, “The Atmospheric Input
of Chemicals to the Ocean”. The global total Fe (TFe) emission strength in
the models is equal to ∼72 Tg Fe yr−1 (38–134 Tg Fe yr−1)
from mineral dust sources and around 2.1 Tg Fe yr−1 (1.8–2.7 Tg Fe yr−1)
from combustion processes (the sum of anthropogenic
combustion/biomass burning and wildfires). The mean global labile Fe (LFe)
source strength in the models, considering both the primary emissions and the
atmospheric processing, is calculated to be 0.7 (±0.3) Tg Fe yr−1,
accounting for both mineral dust and combustion aerosols. The
mean global deposition fluxes into the global ocean are estimated to be in the range
of 10–30 and 0.2–0.4 Tg Fe yr−1 for TFe and LFe, respectively,
which roughly corresponds to a respective 15 and 0.3 Tg Fe yr−1 for the multi-model ensemble model mean. The model intercomparison analysis indicates that the representation of the
atmospheric Fe cycle varies among models, in terms of both the magnitude of
natural and combustion Fe emissions as well as the complexity of atmospheric
processing parameterizations of Fe-containing aerosols. The model comparison
with aerosol Fe observations over oceanic regions indicates that most models
overestimate surface level TFe mass concentrations near dust source
regions and tend to underestimate the low concentrations observed in remote
ocean regions. All models are able to simulate the tendency of higher Fe
concentrations near and downwind from the dust source regions, with the mean
normalized bias for the Northern Hemisphere (∼14), larger
than that of the Southern Hemisphere (∼2.4) for the ensemble model
mean. This model intercomparison and model–observation comparison study
reveals two critical issues in LFe simulations that require further
exploration: (1) the Fe-containing aerosol size distribution and (2) the
relative contribution of dust and combustion sources of Fe to labile Fe in
atmospheric aerosols over the remote oceanic regions.
                    }, number={21}, journal={BIOGEOSCIENCES}, publisher={Copernicus GmbH}, author={Myriokefalitakis, Stelios and Ito, Akinori and Kanakidou, Maria and Nenes, Athanasios and Krol, Maarten C. and Mahowald, Natalie M. and Scanza, Rachel A. and Hamilton, Douglas S. and Johnson, Matthew S. and Meskhidze, Nicholas and et al.}, year={2018}, month={Nov}, pages={6659–6684} }
 @article{royalty_phillips_dawson_reed_meskhidze_petters_2017, title={Aerosol Properties Observed in the Subtropical North Pacific Boundary Layer}, volume={122}, ISSN={["2169-8996"]}, DOI={10.1002/2017jd026897}, abstractNote={Abstract}, number={18}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, author={Royalty, T. M. and Phillips, B. N. and Dawson, K. W. and Reed, R. and Meskhidze, N. and Petters, M. D.}, year={2017}, month={Sep}, pages={9990–10012} }
 @article{dawson_meskhidze_burton_johnson_kacenelenbogen_hostetler_hu_2017, title={Creating Aerosol Types from CHemistry (CATCH): A New Algorithm to Extend the Link Between Remote Sensing and Models}, volume={122}, ISSN={2169-897X}, url={http://dx.doi.org/10.1002/2017JD026913}, DOI={10.1002/2017JD026913}, abstractNote={Abstract}, number={22}, journal={Journal of Geophysical Research: Atmospheres}, publisher={American Geophysical Union (AGU)}, author={Dawson, K. W. and Meskhidze, N. and Burton, S. P. and Johnson, M. S. and Kacenelenbogen, M. S. and Hostetler, C. A. and Hu, Y.}, year={2017}, month={Nov}, pages={12,366–12,392} }
 @article{meskhidze_hurley_royalty_johnson_2017, title={Potential effect of atmospheric dissolved organic carbon on the iron solubility in seawater}, volume={194}, ISSN={["1872-7581"]}, DOI={10.1016/j.marchem.2017.05.011}, abstractNote={Atmospheric aerosols are an important source of soluble iron (sol-Fe) to the global oceans. After deposition to seawater, sol-Fe will either complex with Fe-binding marine organic ligands and enter the ocean dissolved Fe (DFe) pool, or form oxyhydroxide particles (PFe) and precipitate out. Since oceanic DFe is commonly assumed to be bioavailable, the importance of atmospheric sources of sol-Fe for ocean biogeochemistry is determined by both: total fluxes of sol-Fe and the fraction of sol-Fe that is converted to DFe in the ocean. The results from these laboratory studies show that in 20 min from the time of mixing with seawater, nearly all sol-Fe gets oxidized and converted to PFe. The addition of dicarboxylic acids (oxalic and malic) had minor influence on the conversion rate of sol-Fe to PFe. However, the addition of α-hydroxy-carboxylic acids (citric and tartaric) to Fe solutions prior to mixing with seawater was found to considerably increase the concentration of seawater DFe. After 10 days of the experiment, 15% and 50% of the sol-Fe in citric and tartaric acid solutions, respectively, remained in a DFe form. Numerical simulations for sol-Fe laden dust deposition events to the ocean show that if α-hydroxy acids are present in aerosol solution upon deposition to the surface ocean, over 95% of sol-Fe can potentially bind with marine organic ligands; this fraction reduces to < 20% in the absence of atmospheric organics. A possible mechanism is provided to explain the differences in binding strength between aerosol sol-Fe and atmospheric dissolved organic carbon species commonly found in maritime aerosols.}, journal={MARINE CHEMISTRY}, author={Meskhidze, N. and Hurley, D. and Royalty, T. M. and Johnson, M. S.}, year={2017}, month={Aug}, pages={124–132} }
 @article{ito_nenes_johnson_meskhidze_deutsch_2016, title={Acceleration of oxygen decline in the tropical Pacific over the past decades by aerosol pollutants}, volume={9}, ISSN={["1752-0908"]}, DOI={10.1038/ngeo2717}, number={6}, journal={NATURE GEOSCIENCE}, author={Ito, T. and Nenes, A. and Johnson, M. S. and Meskhidze, N. and Deutsch, C.}, year={2016}, month={Jun}, pages={443-+} }
 @article{dawson_petters_meskhidze_petters_kreidenweis_2016, title={Hygroscopic growth and cloud droplet activation of xanthan gum as a proxy for marine hydrogels}, volume={121}, ISSN={["2169-8996"]}, DOI={10.1002/2016jd025143}, abstractNote={Abstract}, number={19}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, author={Dawson, K. W. and Petters, M. D. and Meskhidze, N. and Petters, S. Suda and Kreidenweis, S. M.}, year={2016}, month={Oct}, pages={11803–11818} }
 @article{meskhidze_johnson_hurley_dawson_2016, title={Influence of measurement uncertainties on fractional solubility of iron in mineral aerosols over the oceans}, volume={22}, ISSN={["2212-1684"]}, DOI={10.1016/j.aeolia.2016.07.002}, abstractNote={The atmospheric supply of mineral dust iron (Fe) plays a crucial role in the Earth’s biogeochemical cycle and is of specific importance as a micronutrient in the marine environment. Observations show several orders of magnitude variability in the fractional solubility of Fe in mineral dust aerosols, making it hard to assess the role of mineral dust in the global ocean biogeochemical Fe cycle. In this study we compare the operational solubility of mineral dust aerosol Fe associated with the flow-through leaching protocol to the results of the global 3-D chemical transport model GEOS-Chem. According to the protocol, aerosol Fe is defined as soluble by first deionized water leaching of mineral dust through a 0.45 μm pore size membrane followed by acidification and storage of the leachate over a long period of time prior to analysis. To estimate the uncertainty in soluble Fe results introduced by the flow-through leaching protocol, we prescribe an average 50% (range of 30–70%) fractional solubility to sub-0.45 μm sized mineral dust particles that may inadvertently pass the filter and end up in the acidified (at pH ∼ 1.7) leachate for a couple of month period. In the model, the fractional solubility of Fe is either explicitly calculated using a complex mineral aerosol Fe dissolution equations, or prescribed to be 1% and 4% often used by global ocean biogeochemical Fe cycle models to reproduce the broad characteristics of the presently observed ocean dissolved iron distribution. Calculations show that the fractional solubility of Fe derived through the flow-through leaching is higher compared to the model results. The largest differences (∼40%) are predicted to occur farther away from the dust source regions, over the areas where sub-0.45 μm sized mineral dust particles contribute a larger fraction of the total mineral dust mass. This study suggests that different methods used in soluble Fe measurements and inconsistences in the operational definition of filterable Fe in marine environment and soluble Fe in atmospheric aerosols are likely to contribute to the wide range of fractional solubility of aerosol Fe reported in the literature.}, journal={AEOLIAN RESEARCH}, author={Meskhidze, Nicholas and Johnson, Matthew S. and Hurley, David and Dawson, Kyle}, year={2016}, month={Sep}, pages={85–92} }
 @article{meskhidze_sabolis_reed_kamykowski_2015, title={Quantifying environmental stress-induced emissions of algal isoprene and monoterpenes using laboratory measurements}, volume={12}, ISSN={["1726-4189"]}, DOI={10.5194/bg-12-637-2015}, abstractNote={Abstract. We report here production rates of isoprene and monoterpene compounds (α-pinene, β-pinene, camphene and d-limonene) from six phytoplankton monocultures as a function of irradiance and temperature. Irradiance experiments were carried out for diatom strains (Thalassiosira weissflogii and Thalassiosira pseudonana), prymnesiophyte strains (Pleurochrysis carterae), dinoflagellate strains (Karenia brevis and Prorocentrum minimum), and cryptophyte strains (Rhodomonas salina), while temperature experiments were carried out for diatom strains (Thalassiosira weissflogii and Thalassiosira pseudonana). Phytoplankton species, incubated in a climate-controlled room, were subject to variable light (90 to 900 μmol m−2 s−1) and temperature (18 to 30 °C) regimes. Compared to isoprene, monoterpene emissions were an order of magnitude lower at all light and temperature levels. Emission rates are normalized by cell count and Chlorophyll a (Chl a) content. Diatom strains were the largest emitters, with ~ 2 × 10−17 g(cell)−1h−1 (~ 35 μg (g Chl a)−1 h−1) for isoprene and ~ 5 × 10−19 g (cell)−1 h−1 (~ 1 μg (g Chl a)−1) h−1) for α-pinene. The contribution to the total monoterpene production was ~ 70% from α-pinene, ~ 20% for d-limonene, and < 10% for camphene and β-pinene. Phytoplankton species showed a rapid increase in production rates at low irradiance (< 150 μmol m−2 s−1) and a gradual increase at high (> 250 μmol m−2 s−1) irradiance. Measurements revealed different patterns for time-averaged emissions rates over two successive days. On the first day, most of the species showed a distinct increase in production rates within the first 4 h while, on the second day, the emission rates were overall higher, but less variable. The data suggest that enhanced amounts of isoprene and monoterpenes are emitted from phytoplankton as a result of perturbations in environmental conditions that cause imbalance in chloroplasts and force primary producers to acclimate physiologically. This relationship could be a valuable tool for development of dynamic ecosystem modeling approaches for global marine isoprene and monoterpene emissions based on phytoplankton physiological responses to a changing environment.
                    }, number={3}, journal={BIOGEOSCIENCES}, author={Meskhidze, N. and Sabolis, A. and Reed, R. and Kamykowski, D.}, year={2015}, pages={637–651} }
 @article{dawson_meskhidze_josset_gasso_2015, title={Spaceborne observations of the lidar ratio of marine aerosols}, volume={15}, ISSN={["1680-7324"]}, DOI={10.5194/acp-15-3241-2015}, abstractNote={Abstract. Retrievals of aerosol optical depth (AOD) from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite sensor require the assumption of the extinction-to-backscatter ratio, also known as the lidar ratio. This paper evaluates a new method to calculate the lidar ratio of marine aerosols using two independent sources: the AOD from the Synergized Optical Depth of Aerosols (SODA) project and the integrated attenuated backscatter from CALIOP. With this method, the particulate lidar ratio can be derived for individual CALIOP retrievals in single aerosol layer, cloud-free columns over the ocean. Global analyses are carried out using CALIOP level 2, 5 km marine aerosol layer products and the collocated SODA nighttime data from December 2007 to November 2010. The global mean lidar ratio for marine aerosols was found to be 26 sr, roughly 30% higher than the current value prescribed by the CALIOP standard retrieval algorithm. Data analysis also showed considerable spatiotemporal variability in the calculated lidar ratio over the remote oceans. The calculated marine aerosol lidar ratio is found to vary with the mean ocean surface wind speed (U10). An increase in U10 reduces the mean lidar ratio for marine regions from 32 ± 17 sr (for 0 < U10 < 4 m s−1) to 22 ± 7 sr (for U10 > 15 m s−1). Such changes in the lidar ratio are expected to have a corresponding effect on the marine AOD from CALIOP. The outcomes of this study are relevant for future improvements of the SODA and CALIOP operational product and could lead to more accurate retrievals of marine AOD.
                    }, number={6}, journal={ATMOSPHERIC CHEMISTRY AND PHYSICS}, author={Dawson, K. W. and Meskhidze, N. and Josset, D. and Gasso, S.}, year={2015}, pages={3241–3255} }
 @article{johnson_meskhidze_2013, title={Atmospheric dissolved iron deposition to the global oceans: effects of oxalate-promoted Fe dissolution, photochemical redox cycling, and dust mineralogy}, volume={6}, ISSN={["1991-9603"]}, DOI={10.5194/gmd-6-1137-2013}, abstractNote={Abstract. Mineral dust deposition is suggested to be a significant atmospheric supply pathway of bioavailable iron (Fe) to Fe-depleted surface oceans. In this study, mineral dust and dissolved Fe (Fed) deposition rates are predicted for March 2009 to February 2010 using the 3-D chemical transport model GEOS-Chem implemented with a comprehensive dust-Fe dissolution scheme. The model simulates Fed production during the atmospheric transport of mineral dust, taking into account inorganic and organic (oxalate)-promoted Fe dissolution processes, photochemical redox cycling between ferric (Fe(III)) and ferrous (Fe(II)) forms of Fe, dissolution of three different Fe-containing minerals (hematite, goethite, and aluminosilicates), and detailed mineralogy of wind-blown dust from the major desert regions. Our calculations suggest that during the year-long simulation ~0.26 Tg (1 Tg = 1012 g) of Fed was deposited to global oceanic regions. Compared to simulations only taking into account proton-promoted Fe dissolution, the addition of oxalate and Fe(II)/Fe(III) redox cycling to the dust-Fe mobilization scheme increased total annual model-predicted Fed deposition to global oceanic regions by ~75%. The implementation of Fe(II)/Fe(III) photochemical redox cycling in the model also allows for the distinction between different oxidation states of deposited Fed. Our calculations suggest that during the daytime, large fractions of Fed deposited to the global oceans is likely to be in Fe(II) form, while nocturnal fluxes of Fed are largely in Fe(III) form. Model sensitivity simulations suggest Fed fluxes to the oceans can range from ~50% reduction to ~150% increase associated with the uncertainty in Fe-containing minerals commonly found in dust particles. This study indicates that Fed deposition to the oceans is controlled by total dust-Fe mass concentrations, mineralogy, the surface area of dust particles, atmospheric chemical composition, cloud processing, and meteorological parameters and exhibits complex and spatiotemporally variable patterns. Our study suggests that the explicit model representation of individual processes leading to Fed production within mineral dust are needed to improve the understanding of the atmospheric Fe cycle, and quantify the effect of dust-Fe on ocean biological productivity, carbon cycle, and climate.
                    }, number={4}, journal={GEOSCIENTIFIC MODEL DEVELOPMENT}, author={Johnson, M. S. and Meskhidze, N.}, year={2013}, pages={1137–1155} }
 @article{meskhidze_petters_tsigaridis_bates_o'dowd_reid_lewis_gantt_anguelova_bhave_et al._2013, title={Production mechanisms, number concentration, size distribution, chemical composition, and optical properties of sea spray aerosols}, volume={14}, ISSN={1530-261X}, url={http://dx.doi.org/10.1002/ASL2.441}, DOI={10.1002/ASL2.441}, abstractNote={Production mechanisms, number concentration, size distribution, chemical composition, and optical properties of sea spray aerosols}, number={4}, journal={Atmospheric Science Letters}, publisher={Wiley}, author={Meskhidze, Nicholas and Petters, Markus D. and Tsigaridis, Kostas and Bates, Tim and O'Dowd, Colin and Reid, Jeff and Lewis, Ernie R. and Gantt, Brett and Anguelova, Magdalena D. and Bhave, Prakash V. and et al.}, year={2013}, month={Jun}, pages={207–213} }
 @article{meskhidze_petters_tsigaridis_bates_o'dowd_reid_lewis_gantt_anguelova_bhave_et al._2013, title={Production mechanisms, number concentration, size distribution, chemical composition, and optical properties of sea spray aerosols}, volume={14}, number={4}, journal={Atmospheric Science Letters}, author={Meskhidze, N. and Petters, M. D. and Tsigaridis, K. and Bates, T. and O'Dowd, C. and Reid, J. and Lewis, E. R. and Gantt, B. and Anguelova, M. D. and Bhave, P. V. and et al.}, year={2013}, pages={207–213} }
 @misc{gantt_meskhidze_2013, title={The physical and chemical characteristics of marine primary organic aerosol: a review}, volume={13}, ISSN={["1680-7324"]}, DOI={10.5194/acp-13-3979-2013}, abstractNote={Abstract. Knowledge of the physical characteristics and chemical composition of marine organic aerosols is needed for the quantification of their effects on solar radiation transfer and cloud processes. This review examines research pertinent to the chemical composition, size distribution, mixing state, emission mechanism, photochemical oxidation and climatic impact of marine primary organic aerosol (POA) associated with sea-spray. Numerous measurements have shown that both the ambient mass concentration of marine POA and size-resolved organic mass fraction of sea-spray aerosol are related to surface ocean biological activity. Recent studies have also indicated that fine mode (smaller than 200 nm in diameter) marine POA can have a size distribution independent from sea-salt, while coarse mode aerosols (larger than 1000 nm in diameter) are more likely to be internally mixed with sea-salt. Modelling studies have estimated global submicron marine POA emission rates of ~10 ± 5 Tg yr−1, with a considerable fraction of these emissions occurring over regions most susceptible to aerosol perturbations. Climate studies have found that marine POA can cause large local increases in the cloud condensation nuclei concentration and have a non-negligible influence on model assessments of the anthropogenic aerosol forcing of climate. Despite these signs of climate-relevance, the source strength, chemical composition, mixing state, hygroscopicity, cloud droplet activation potential, atmospheric aging and removal of marine POA remain poorly quantified. Additional laboratory, field, and modelling studies focused on the chemistry, size distribution and mixing state of marine POA are needed to better understand and quantify their importance.
                    }, number={8}, journal={ATMOSPHERIC CHEMISTRY AND PHYSICS}, author={Gantt, B. and Meskhidze, N.}, year={2013}, pages={3979–3996} }
 @article{johnson_meskhidze_kiliyanpilakkil_2012, title={A global comparison of GEOS-Chem-predicted and remotely-sensed mineral dust aerosol optical depth and extinction profiles}, volume={4}, ISSN={["1942-2466"]}, DOI={10.1029/2011ms000109}, abstractNote={Dust aerosol optical depth (AOD) and vertical distribution of aerosol extinction predicted by a global chemical transport model (GEOS‐Chem) are compared to space‐borne data from the Moderate‐resolution Imaging Spectroradiometer (MODIS), Multi‐Angle Imaging SpectroRadiometer (MISR), and Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) for March 2009 to February 2010. Model‐predicted and remotely‐sensed AOD/aerosol extinction profiles are compared over six regions where aerosol abundances are dominated by mineral dust. Calculations indicate that over the regions examined in this study (with the exception of Middle Eastern dust sources) GEOS‐Chem predicts higher AOD values compared to MODIS and MISR. The positive bias is particularly pronounced over the Saharan dust source regions, where model‐predicted AOD values are a factor of 2 to 3 higher. The comparison with CALIPSO‐derived dust aerosol extinction profiles revealed that the model overestimations of dust abundances over the study regions primarily occur below ∼4 km, suggesting excessive emissions of mineral dust and/or uncertainties in dust optical properties. The implementation of a new dust size distribution scheme into GEOS‐Chem reduced the yearly‐mean positive bias in model‐predicted AOD values over the study regions. The results were most noticeable over the Saharan dust source regions where the differences between model‐predicted and MODIS/MISR retrieved AOD values were reduced from 0.22 and 0.17 to 0.02 and −0.04, respectively. Our results suggest that positive/negative biases between satellite and model‐predicted aerosol extinction values at different altitudes can sometimes even out, giving a false impression for the agreement between remotely‐sensed and model‐predicted column‐integrated AOD data.}, journal={JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS}, author={Johnson, Matthew S. and Meskhidze, Nicholas and Kiliyanpilakkil, Velayudhan Praju}, year={2012}, month={Jul} }
 @article{gantt_xu_meskhidze_zhang_nenes_ghan_liu_easter_zaveri_2012, title={Global distribution and climate forcing of marine organic aerosol - Part 2: Effects on cloud properties and radiative forcing}, volume={12}, number={14}, journal={Atmospheric Chemistry and Physics}, author={Gantt, B. and Xu, J. and Meskhidze, N. and Zhang, Y. and Nenes, A. and Ghan, S. J. and Liu, X. and Easter, R. and Zaveri, R.}, year={2012}, pages={6555–6563} }
 @article{gantt_johnson_meskhidze_sciare_ovadnevaite_ceburnis_o'dowd_2012, title={Model evaluation of marine primary organic aerosol emission schemes}, volume={12}, ISSN={["1680-7316"]}, DOI={10.5194/acp-12-8553-2012}, abstractNote={Abstract. In this study, several marine primary organic aerosol (POA) emission schemes have been evaluated using the GEOS-Chem chemical transport model in order to provide guidance for their implementation in air quality and climate models. These emission schemes, based on varying dependencies of chlorophyll a concentration ([chl a]) and 10 m wind speed (U10), have large differences in their magnitude, spatial distribution, and seasonality. Model comparison with weekly and monthly mean values of the organic aerosol mass concentration at two coastal sites shows that the source function exclusively related to [chl a] does a better job replicating surface observations. Sensitivity simulations in which the negative U10 and positive [chl a] dependence of the organic mass fraction of sea spray aerosol are enhanced show improved prediction of the seasonality of the marine POA concentrations. A top-down estimate of submicron marine POA emissions based on the parameterization that compares best to the observed weekly and monthly mean values of marine organic aerosol surface concentrations has a global average emission rate of 6.3 Tg yr−1. Evaluation of existing marine POA source functions against a case study during which marine POA contributed the major fraction of submicron aerosol mass shows that none of the existing parameterizations are able to reproduce the hourly-averaged observations. Our calculations suggest that in order to capture episodic events and short-term variability in submicron marine POA concentration over the ocean, new source functions need to be developed that are grounded in the physical processes unique to the organic fraction of sea spray aerosol.
                    }, number={18}, journal={ATMOSPHERIC CHEMISTRY AND PHYSICS}, author={Gantt, B. and Johnson, M. S. and Meskhidze, N. and Sciare, J. and Ovadnevaite, J. and Ceburnis, D. and O'Dowd, C. D.}, year={2012}, pages={8553–8566} }
 @article{ghan_abdul-razzak_nenes_ming_liu_ovchinnikov_shipway_meskhidze_xu_shi_2011, title={Correction to “Droplet nucleation: Physically-based parameterizations and comparative evaluation”}, volume={3}, ISSN={1942-2466}, url={http://dx.doi.org/10.1029/2011MS000107}, DOI={10.1029/2011MS000107}, abstractNote={6 1. Atmospheric and Global Change Division, Pacific Northwest National 7 Laboratory, PO Box 999, Richland, Washington, 99352 8 9 2. Department of Mechanical Engineering, Texas A&M University-Kingsville, MSC 10 191, 700 University Blvd, Kingsville, Texas, 78363 11 12 3. Schools of Earth & Atmospheric Sciences and Chemical & Biomolecular 13 Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, Georgia, 14 30332-0340 15 16 4. Geophysical Fluid Dynamics Laboratory, P. O. Box 308, Princeton, New Jersey, 17 08542 18 19 5. United Kingdom Meteorology Office, Exeter, United Kingdom 20 21 6. Department of Marine, Earth, and Atmospheric Sciences, North Carolina State 22 University, 2800 Faucette Dr, Raleigh, North Carolina, 27695‐8208 23 24 7. Chinese Research Academy of Environment Sciences, No.8 Dayangfang, 25 Beiyuan, Chaoyang District, Beijing 100012, China 26 27 8. Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 10029, 28 China 29 30 31 Submitted to Journal of Advances in Modeling of Earth Systems, April 7, 2011 32}, number={4}, journal={Journal of Advances in Modeling Earth Systems}, publisher={American Geophysical Union (AGU)}, author={Ghan, Steven J. and Abdul-Razzak, Hayder and Nenes, Athanasios and Ming, Yi and Liu, Xiaohong and Ovchinnikov, Mikhail and Shipway, Ben and Meskhidze, Nicholas and Xu, Jun and Shi, Xiangjun}, year={2011}, month={Apr} }
 @article{kiliyanpilakkil_meskhidze_2011, title={Deriving the effect of wind speed on clean marine aerosol optical properties using the A-Train satellites}, volume={11}, ISSN={["1680-7324"]}, DOI={10.5194/acp-11-11401-2011}, abstractNote={Abstract. The relationship between "clean marine" aerosol optical properties and ocean surface wind speed is explored using remotely sensed data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the CALIPSO satellite and the Advanced Microwave Scanning Radiometer (AMSR-E) on board the AQUA satellite. Detailed data analyses are carried out over 15 regions selected to be representative of different areas of the global ocean for the time period from June 2006 to April 2011. Based on remotely sensed optical properties the CALIPSO algorithm is capable of discriminating "clean marine" aerosols from other types often present over the ocean (such as urban/industrial pollution, desert dust and biomass burning). The global mean optical depth of "clean marine" aerosol at 532 nm (AOD532) is found to be 0.052 ± 0.038 (mean plus or minus standard deviation). The mean layer integrated particulate depolarization ratio of marine aerosols is 0.02 ± 0.016. Integrated attenuated backscatter and color ratio of marine aerosols at 532 nm were found to be 0.003 ± 0.002 sr−1 and 0.530 ± 0.149, respectively. A logistic regression between AOD532 and 10-m surface wind speed (U10) revealed three distinct regimes. For U10 ≤ 4 m s−1 the mean CALIPSO-derived AOD532 is found to be 0.02 ± 0.003 with little dependency on the surface wind speed. For 4 < U10 ≤ 12 m s−1, representing the dominant fraction of all available data, marine aerosol optical depth is linearly correlated with the surface wind speed values, with a slope of 0.006 s m−1. In this intermediate wind speed region, the AOD532 vs. U10 regression slope derived here is comparable to previously reported values. At very high wind speed values (U10 > 18 m s−1), the AOD532-wind speed relationship showed a tendency toward leveling off, asymptotically approaching value of 0.15. The conclusions of this study regarding the aerosol extinction vs. wind speed relationship may have been influenced by the constant lidar ratio used for CALIPSO-derived AOD532. Nevertheless, active satellite sensor used in this study that allows separation of maritime wind induced component of AOD from the total AOD over the ocean could lead to improvements in optical properties of sea spray aerosols and their production mechanisms.}, number={22}, journal={ATMOSPHERIC CHEMISTRY AND PHYSICS}, author={Kiliyanpilakkil, V. P. and Meskhidze, N.}, year={2011}, pages={11401–11413} }
 @article{ghan_abdul-razzak_nenes_ming_liu_ovchinnikov_shipway_meskhidze_xu_shi_2011, title={Droplet nucleation: Physically-based parameterizations and comparative evaluation}, volume={3}, ISSN={1942-2466}, url={http://dx.doi.org/10.1029/2011MS000074}, DOI={10.1029/2011MS000074}, abstractNote={One of the greatest sources of uncertainty in simulations of climate and climate change is the influence of aerosols on the optical properties of clouds. The root of this influence is the droplet nucleation process, which involves the spontaneous growth of aerosol into cloud droplets at cloud edges, during the early stages of cloud formation, and in some cases within the interior of mature clouds. Numerical models of droplet nucleation represent much of the complexity of the process, but at a computational cost that limits their application to simulations of hours or days. Physically‐based parameterizations of droplet nucleation are designed to quickly estimate the number nucleated as a function of the primary controlling parameters: the aerosol number size distribution, hygroscopicity and cooling rate. Here we compare and contrast the key assumptions used in developing each of the most popular parameterizations and compare their performances under a variety of conditions. We find that the more complex parameterizations perform well under a wider variety of nucleation conditions, but all parameterizations perform well under the most common conditions. We then discuss the various applications of the parameterizations to cloud‐resolving, regional and global models to study aerosol effects on clouds at a wide range of spatial and temporal scales. We compare estimates of anthropogenic aerosol indirect effects using two different parameterizations applied to the same global climate model, and find that the estimates of indirect effects differ by only 10%. We conclude with a summary of the outstanding challenges remaining for further development and application.}, number={4}, journal={Journal of Advances in Modeling Earth Systems}, publisher={American Geophysical Union (AGU)}, author={Ghan, Steven J. and Abdul-Razzak, Hayder and Nenes, Athanasios and Ming, Yi and Liu, Xiaohong and Ovchinnikov, Mikhail and Shipway, Ben and Meskhidze, Nicholas and Xu, Jun and Shi, Xiangjun}, year={2011}, month={Apr} }
 @article{meskhidze_xu_gantt_zhang_nenes_ghan_liu_easter_zaveri_2011, title={Global distribution and climate forcing of marine organic aerosol: 1. Model improvements and evaluation}, volume={11}, number={22}, journal={Atmospheric Chemistry and Physics}, author={Meskhidze, N. and Xu, J. and Gantt, B. and Zhang, Y. and Nenes, A. and Ghan, S. J. and Liu, X. and Easter, R. and Zaveri, R.}, year={2011}, pages={11689–11705} }
 @article{johnson_meskhidze_kiliyanpilakkil_gasso_2011, title={Understanding the transport of Patagonian dust and its influence on marine biological activity in the South Atlantic Ocean}, volume={11}, ISSN={["1680-7324"]}, DOI={10.5194/acp-11-2487-2011}, abstractNote={Abstract. The supply of bioavailable iron to the high-nitrate low-chlorophyll (HNLC) waters of the Southern Ocean through atmospheric pathways could stimulate phytoplankton blooms and have major implications for the global carbon cycle. In this study, model results and remotely-sensed data are analyzed to examine the horizontal and vertical transport pathways of Patagonian dust and quantify the effect of iron-laden mineral dust deposition on marine biological productivity in the surface waters of the South Atlantic Ocean (SAO). Model simulations for the atmospheric transport and deposition of mineral dust and bioavailable iron are carried out for two large dust outbreaks originated at the source regions of northern Patagonia during the austral summer of 2009. Model-simulated horizontal and vertical transport pathways of Patagonian dust plumes are in reasonable agreement with remotely-sensed data. Simulations indicate that the synoptic meteorological patterns of high and low pressure systems are largely accountable for dust transport trajectories over the SAO. According to model results and retrievals from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), synoptic flows caused by opposing pressure systems (a high pressure system located to the east or north-east of a low pressure system) elevate the South American dust plumes well above the marine boundary layer. Under such conditions, the bulk concentration of mineral dust can quickly be transported around the low pressure system in a clockwise manner, follow the southeasterly advection pathway, and reach the HNLC waters of the SAO and Antarctica in ~3–4 days after emission from the source regions of northern Patagonia. Two different mechanisms for dust-iron mobilization into a bioavailable form are considered in this study. A global 3-D chemical transport model (GEOS-Chem), implemented with an iron dissolution scheme, is employed to estimate the atmospheric fluxes of soluble iron, while a dust/biota assessment tool (Boyd et al., 2010) is applied to evaluate the amount of bioavailable iron formed through the slow and sustained leaching of dust in the ocean mixed layer. The effect of iron-laden mineral dust supply on surface ocean biomass is investigated by comparing predicted surface chlorophyll-a concentration ([Chl-a]) to remotely-sensed data. As the dust transport episodes examined here represent large summertime outflows of mineral dust from South American continental sources, this study suggests that (1) atmospheric fluxes of mineral dust from Patagonia are not likely to be the major source of bioavailable iron to ocean regions characterized by high primary productivity; (2) even if Patagonian dust plumes may not cause visible algae blooms, they could still influence background [Chl-a] in the South Atlantic sector of the Southern Ocean.
                    }, number={6}, journal={ATMOSPHERIC CHEMISTRY AND PHYSICS}, author={Johnson, M. S. and Meskhidze, N. and Kiliyanpilakkil, V. P. and Gasso, S.}, year={2011}, pages={2487–2502} }
 @article{gantt_meskhidze_facchini_rinaldi_ceburnis_o'dowd_2011, title={Wind speed dependent size-resolved parameterization for the organic mass fraction of sea spray aerosol}, volume={11}, ISSN={["1680-7324"]}, DOI={10.5194/acp-11-8777-2011}, abstractNote={Abstract. For oceans to be a significant source of primary organic aerosol (POA), sea spray aerosol (SSA) must be highly enriched with organics relative to the bulk seawater. We propose that organic enrichment at the air-sea interface, chemical composition of seawater, and the aerosol size are three main parameters controlling the organic mass fraction of sea spray aerosol (OMSSA). To test this hypothesis, we developed a new marine POA emission function based on a conceptual relationship between the organic enrichment at the air-sea interface and surface wind speed. The resulting parameterization is explored using aerosol chemical composition and surface wind speed from Atlantic and Pacific coastal stations, and satellite-derived ocean concentrations of chlorophyll-a, dissolved organic carbon, and particulate organic carbon. Of all the parameters examined, a multi-variable logistic regression revealed that the combination of 10 m wind speed and surface chlorophyll-a concentration ([Chl-a]) are the most consistent predictors of OMSSA. This relationship, combined with the published aerosol size dependence of OMSSA, resulted in a new parameterization for the organic mass fraction of SSA. Global emissions of marine POA are investigated here by applying this newly-developed relationship to existing sea spray emission functions, satellite-derived [Chl-a], and modeled 10 m winds. Analysis of model simulations shows that global annual submicron marine organic emission associated with sea spray is estimated to be from 2.8 to 5.6 Tg C yr−1. This study provides additional evidence that marine primary organic aerosols are a globally significant source of organics in the atmosphere.
                    }, number={16}, journal={ATMOSPHERIC CHEMISTRY AND PHYSICS}, author={Gantt, B. and Meskhidze, N. and Facchini, M. C. and Rinaldi, M. and Ceburnis, D. and O'Dowd, C. D.}, year={2011}, pages={8777–8790} }
 @article{wang_jang_zhang_wang_zhang_streets_fu_lei_schreifels_he_et al._2010, title={Assessment of air quality benefits from national air pollution control policies in China. Part I: Background, emission scenarios and evaluation of meteorological predictions}, volume={44}, ISSN={["1873-2844"]}, DOI={10.1016/j.atmosenv.2010.05.051}, abstractNote={Under the 11th Five Year Plan (FYP, 2006–2010) for national environmental protection by the Chinese government, the overarching goal for sulfur dioxide (SO2) controls is to achieve a total national emissions level of SO2 in 2010 10% lower than the level in 2005. A similar nitrogen oxides (NOx) emissions control plan is currently under development and could be enforced during the 12th FYP (2011–2015). In this study, the U.S. Environmental Protection Agency (U.S.EPA)’s Community Multi-Scale Air Quality (Models-3/CMAQ) modeling system was applied to assess the air quality improvement that would result from the targeted SO2 and NOx emission controls in China. Four emission scenarios — the base year 2005, the 2010 Business-As-Usual (BAU) scenario, the 2010 SO2 control scenario, and the 2010 NOx control scenario—were constructed and simulated to assess the air quality change from the national control plan. The Fifth-Generation NCAR/Penn State Mesoscale Model (MM5) was applied to generate the meteorological fields for the CMAQ simulations. In this Part I paper, the model performance for the simulated meteorology was evaluated against observations for the base case in terms of temperature, wind speed, wind direction, and precipitation. It is shown that MM5 model gives an overall good performance for these meteorological variables. The generated meteorological fields are acceptable for using in the CMAQ modeling.}, number={28}, journal={ATMOSPHERIC ENVIRONMENT}, author={Wang, Litao and Jang, Carey and Zhang, Yang and Wang, Kai and Zhang, Qiang and Streets, David and Fu, Joshua and Lei, Yu and Schreifels, Jeremy and He, Kebin and et al.}, year={2010}, month={Sep}, pages={3442–3448} }
 @article{wang_jang_zhang_wang_zhang_streets_fu_lei_schreifels_he_et al._2010, title={Assessment of air quality benefits from national air pollution control policies in China. Part II: Evaluation of air quality predictions and air quality benefits assessment}, volume={44}, ISSN={["1873-2844"]}, DOI={10.1016/j.atmosenv.2010.05.058}, abstractNote={Following the meteorological evaluation in Part I, this Part II paper presents the statistical evaluation of air quality predictions by the U.S. Environmental Protection Agency (U.S. EPA)’s Community Multi-Scale Air Quality (Models-3/CMAQ) model for the four simulated months in the base year 2005. The surface predictions were evaluated using the Air Pollution Index (API) data published by the China Ministry of Environmental Protection (MEP) for 31 capital cities and daily fine particulate matter (PM2.5, particles with aerodiameter less than or equal to 2.5 μm) observations of an individual site in Tsinghua University (THU). To overcome the shortage in surface observations, satellite data are used to assess the column predictions including tropospheric nitrogen dioxide (NO2) column abundance and aerosol optical depth (AOD). The result shows that CMAQ gives reasonably good predictions for the air quality. The air quality improvement that would result from the targeted sulfur dioxide (SO2) and nitrogen oxides (NOx) emission controls in China were assessed for the objective year 2010. The results show that the emission controls can lead to significant air quality benefits. SO2 concentrations in highly polluted areas of East China in 2010 are estimated to be decreased by 30–60% compared to the levels in the 2010 Business-As-Usual (BAU) case. The annual PM2.5 can also decline by 3–15 μg m−3 (4–25%) due to the lower SO2 and sulfate concentrations. If similar controls are implemented for NOx emissions, NOx concentrations are estimated to decrease by 30–60% as compared with the 2010 BAU scenario. The annual mean PM2.5 concentrations will also decline by 2–14 μg m−3 (3–12%). In addition, the number of ozone (O3) non-attainment areas in the northern China is projected to be much lower, with the maximum 1-h average O3 concentrations in the summer reduced by 8–30 ppb.}, number={28}, journal={ATMOSPHERIC ENVIRONMENT}, author={Wang, Litao and Jang, Carey and Zhang, Yang and Wang, Kai and Zhang, Qiang and Streets, David and Fu, Joshua and Lei, Yu and Schreifels, Jeremy and He, Kebin and et al.}, year={2010}, month={Sep}, pages={3449–3457} }
 @article{johnson_meskhidze_solmon_gasso_chuang_gaiero_yantosca_wu_wang_carouge_2010, title={Modeling dust and soluble iron deposition to the South Atlantic Ocean}, volume={115}, ISSN={["2169-8996"]}, DOI={10.1029/2009jd013311}, abstractNote={The global chemical transport model GEOS‐Chem, implemented with a dust‐iron dissolution scheme, was used to analyze the magnitude and spatial distribution of mineral dust and soluble‐iron (sol‐Fe) deposition to the South Atlantic Ocean (SAO). The comparison of model results with remotely sensed data shows that GEOS‐Chem can capture dust source regions in Patagonia and characterize the temporal variability of dust outflow. For a year‐long model simulation, 22 Tg of mineral dust and 4 Gg of sol‐Fe were deposited to the surface waters of the entire SAO region, with roughly 30% of this dust and sol‐Fe predicted to be deposited to possible high nitrate low chlorophyll oceanic regions. Model‐predicted dissolved iron fraction of mineral dust over the SAO was small, on average only accounting for 0.57% of total iron. Simulations suggest that the primary reason for such a small fraction of sol‐Fe is the low ambient concentrations of acidic trace gases available for mixing with dust plumes. Overall, the amount of acid added to the deliquesced aerosol solution was not enough to overcome the alkalinity buffer of Patagonian dust and initiate considerable acid dissolution of mineral‐iron. Sensitivity studies show that the amount of sol‐Fe deposited to the SAO was largely controlled by the initial amount of sol‐Fe at the source region, with limited contribution from the spatial variability of Patagonian‐desert topsoil mineralogy and natural sources of acidic trace gases. Simulations suggest that Patagonian dust should have a minor effect on biological productivity in the SAO.}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, author={Johnson, Matthew S. and Meskhidze, Nicholas and Solmon, Fabien and Gasso, Santiago and Chuang, Patrick Y. and Gaiero, Diego M. and Yantosca, Robert M. and Wu, Shiliang and Wang, Yuxuan and Carouge, Claire}, year={2010}, month={Aug} }
 @article{gantt_meskhidze_carlton_2010, title={The contribution of marine organics to the air quality of the western United States}, volume={10}, ISSN={["1680-7324"]}, DOI={10.5194/acp-10-7415-2010}, abstractNote={Abstract. The contribution of marine organic emissions to the air quality in coastal areas of the western United States is studied using the latest version of the US Environmental Protection Agency (EPA) regional-scale Community Multiscale Air Quality (CMAQv4.7) modeling system. Emissions of marine isoprene, monoterpenes, and primary organic matter (POM) from the ocean are implemented into the model to provide a comprehensive view of the connection between ocean biology and atmospheric chemistry and air pollution. Model simulations show that marine organics can increase the concentration of PM2.5 by 0.1–0.3 μg m−3 (up to 5%) in some coastal cities such as San Francisco, CA. This increase in the PM2.5 concentration is primarily attributed to the POM emissions, with small contributions from the marine isoprene and monoterpenes. When marine organic emissions are included, organic carbon (OC) concentrations over the remote ocean are increased by up to 50% (25% in coastal areas), values consistent with recent observational findings. This study is the first to quantify the air quality impacts from marine POM and monoterpenes for the United States, and it highlights the need for inclusion of marine organic emissions in air quality models.
                    }, number={15}, journal={ATMOSPHERIC CHEMISTRY AND PHYSICS}, author={Gantt, B. and Meskhidze, N. and Carlton, A. G.}, year={2010}, pages={7415–7423} }
 @article{gantt_meskhidze_zhang_xu_2010, title={The effect of marine isoprene emissions on secondary organic aerosol and ozone formation in the coastal United States}, volume={44}, DOI={10.1016/j.atmosenv.2009.08.027}, abstractNote={The impact of marine isoprene emissions on summertime surface concentrations of isoprene, secondary organic aerosols (SOA), and ozone (O3) in the coastal areas of the continental United States is studied using the U.S. Environmental Protection Agency regional-scale Community Multiscale Air Quality (CMAQ) modeling system. Marine isoprene emission rates are based on the following five parameters: laboratory measurements of isoprene production from phytoplankton under a range of light conditions, remotely-sensed chlorophyll-a concentration ([Chl–a]), incoming solar radiation, surface wind speed, and sea-water optical properties. Model simulations show that marine isoprene emissions are sensitive to meteorology and ocean ecosystem productivity, with the highest rates simulated over the Gulf of Mexico. Simulated offshore surface layer marine isoprene concentration is less than 10 ppt and significantly dwarfed by terrestrial emissions over the continental United States. With the isoprene reactions included in this study, the average contribution of marine isoprene to SOA and O3 concentrations is predicted to be small, up to 0.004 μg m−3 for SOA and 0.2 ppb for O3 in coastal urban areas. The light-sensitivity of isoprene production from phytoplankton results in a midday maximum for marine isoprene emissions and a corresponding daytime increase in isoprene and O3 concentrations in coastal locations. The potential impact of the daily variability in [Chl-a] on O3 and SOA concentrations is simulated in a sensitivity study with [Chl-a] increased and decreased by a factor of five. Our results indicate that marine emissions of isoprene cause minor changes to coastal SOA and O3 concentrations. Comparison of model simulations with few available measurements shows that the model underestimates marine boundary layer isoprene concentration. This underestimation is likely due to the limitations in current treatment of marine isoprene emission and a coarse spatial resolution used in the model simulations.}, number={1}, journal={Atmospheric Environment}, author={Gantt, B. and Meskhidze, N. and Zhang, Y. and Xu, J.}, year={2010}, pages={115–121} }
 @article{gantt_meskhidze_kamykowski_2009, title={A new physically-based quantification of marine isoprene and primary organic aerosol emissions}, volume={9}, ISSN={["1680-7324"]}, DOI={10.5194/acp-9-4915-2009}, abstractNote={Abstract. The global marine sources of organic carbon (OC) are estimated here using a physically-based parameterization for the emission of marine isoprene and primary organic matter. The marine isoprene emission model incorporates new physical parameters such as light sensitivity of phytoplankton isoprene production and dynamic euphotic depth to simulate hourly marine isoprene emissions totaling 0.92 Tg C yr−1. Sensitivity studies using different schemes for the euphotic zone depth and ocean phytoplankton speciation produce the upper and the lower range of marine-isoprene emissions of 0.31 to 1.09 Tg C yr−1, respectively. Established relationships between sea spray fractionation of water-insoluble organic carbon (WIOC) and chlorophyll-a concentration are used to estimate the total primary sources of marine sub- and super-micron OC of 2.9 and 19.4 Tg C yr−1, respectively. The consistent spatial and temporal resolution of the two emission types allow us, for the first time, to explore the relative contributions of sub- and super-micron organic matter and marine isoprene-derived secondary organic aerosol (SOA) to the total OC fraction of marine aerosol. Using a fixed 3% mass yield for the conversion of isoprene to SOA, our emission simulations show minor (<0.2%) contribution of marine isoprene to the total marine source of OC on a global scale. However, our model calculations also indicate that over the tropical oceanic regions (30° S to 30° N), marine isoprene SOA may contribute over 30% of the total monthly-averaged sub-micron OC fraction of marine aerosol. The estimated contribution of marine isoprene SOA to hourly-averaged sub-micron marine OC emission is even higher, approaching 50% over the vast regions of the oceans during the midday hours when isoprene emissions are highest. As it is widely believed that sub-micron OC has the potential to influence the cloud droplet activation of marine aerosols, our findings suggest that marine isoprene SOA could play critical role in modulating properties of shallow marine clouds and influencing the climate.
                    }, number={14}, journal={ATMOSPHERIC CHEMISTRY AND PHYSICS}, author={Gantt, B. and Meskhidze, N. and Kamykowski, D.}, year={2009}, pages={4915–4927} }
 @article{solmon_chuang_meskhidze_chen_2009, title={Acidic processing of mineral dust iron by anthropogenic compounds over the north Pacific Ocean}, volume={114}, ISSN={["2169-8996"]}, DOI={10.1029/2008jd010417}, abstractNote={Atmospheric processing of mineral aerosol by anthropogenic pollutants may be an important process by which insoluble iron can be transformed into soluble forms and become available to oceanic biota. Observations of the soluble iron fraction in atmospheric aerosol exhibit large variability, which is poorly represented in models. In this study, we implemented a dust iron dissolution scheme in a global chemistry transport model (GEOS‐Chem). The model is applied over the North Pacific Ocean during April 2001, a period when concentrations of dust and pollution within the east Asia outflow were high. Simulated fields of many key chemical constituents compare reasonably well with available observations, although some discrepancies are identified and discussed. In our simulations, the production of soluble iron varies temporally and regionally depending on pollution‐to‐dust ratio, primarily due to strong buffering by calcite. Overall, we show that the chemical processing mechanism produces significant amounts of dissolved iron reaching and being deposited in remote regions of the Pacific basin, with some seasonal variability. Simulated enhancements in particulate soluble iron fraction range from 0.5% to 6%, which is consistent with the observations. According to our simulations, ∼30% to 70% of particulate soluble iron over the North Pacific Ocean basin can be attributed to atmospheric processing. On the basis of April 2001 monthly simulations, sensitivity tests suggest that doubling SO2 emissions can induce a significant increase (13% on average, up to 40% during specific events) in dissolved iron production and deposition to the remote Pacific. We roughly estimate that half of the primary productivity induced by iron deposition in a north Pacific high‐nutrient low‐chlorophyll region is due to soluble iron derived from anthropogenic chemical processing of Asian aerosol.}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, author={Solmon, F. and Chuang, P. Y. and Meskhidze, N. and Chen, Y.}, year={2009}, month={Jan} }
 @article{meskhidze_remer_platnick_juarez_lichtenberger_aiyyer_2009, title={Exploring the differences in cloud properties observed by the Terra and Aqua MODIS sensors}, volume={9}, DOI={10.5194/acp-9-3461-2009}, abstractNote={Abstract. The aerosol-cloud interaction in different parts of the globe is examined here using multi-year statistics of remotely sensed data from two MODIS sensors aboard NASA's Terra (morning) and Aqua (afternoon) satellites. Simultaneous retrievals of aerosol loadings and cloud properties by the MODIS sensor allowed us to explore morning-to-afternoon variation of liquid cloud fraction (CF) and optical thickness (COT) for clean, moderately polluted and heavily polluted clouds in different seasons. Data analysis for seven-years of MODIS retrievals revealed strong temporal and spatial patterns in morning-to-afternoon variation of cloud fraction and optical thickness over different parts of the global oceans and the land. For the vast areas of stratocumulus cloud regions, the data shows that the days with elevated aerosol abundance were also associated with enhanced afternoon reduction of CF and COT pointing to the possible reduction of the indirect climate forcing. A positive correlation between aerosol optical depth and morning-to-afternoon variation of trade wind cumulus cloud cover was also found over the northern Indian Ocean, though no clear relationship between the concentration of Indo-Asian haze and morning-to-afternoon variation of COT was established. Over the Amazon region during wet conditions, aerosols are associated with an enhanced convective process in which morning shallow warm clouds are organized into afternoon deep convection with greater ice cloud coverage. Analysis presented here demonstrates that the new technique for exploring morning-to-afternoon variability in cloud properties by using the differences in data products from the two daily MODIS overpasses is capable of capturing some of the major features of diurnal variations in cloud properties and can be used for better understanding of aerosol radiative effects.
                    }, number={10}, journal={Atmospheric Chemistry and Physics}, author={Meskhidze, N. and Remer, L. A. and Platnick, S. and Juarez, R. N. and Lichtenberger, A. M. and Aiyyer, A. R.}, year={2009}, pages={3461–3475} }
 @article{fountoukis_nenes_meskhidze_bahreini_conant_jonsson_murphy_sorooshian_varutbangkul_brechtel_et al._2007, title={Aerosol-cloud drop concentration closure for clouds sampled during the International Consortium for Atmospheric Research on Transport and Transformation 2004 campaign}, volume={112}, ISSN={0148-0227}, url={http://dx.doi.org/10.1029/2006JD007272}, DOI={10.1029/2006JD007272}, abstractNote={This study analyzes 27 cumuliform and stratiform clouds sampled aboard the CIRPAS Twin Otter during the 2004 International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) experiment. The data set was used to assess cloud droplet closure using (1) a detailed adiabatic cloud parcel model and (2) a state‐of‐the‐art cloud droplet activation parameterization. A unique feature of the data set is the sampling of highly polluted clouds within the vicinity of power plant plumes. Remarkable closure was achieved (much less than the 20% measurement uncertainty) for both parcel model and parameterization. The highly variable aerosol did not complicate the cloud droplet closure, since the clouds had low maximum supersaturation and were not sensitive to aerosol variations (which took place at small particle sizes). The error in predicted cloud droplet concentration was mostly sensitive to updraft velocity. Optimal closure is obtained if the water vapor uptake coefficient is equal to 0.06, but can range between 0.03 and 1.0. The sensitivity of cloud droplet prediction error to changes in the uptake coefficient, organic solubility and surface tension depression suggest that organics exhibit limited solubility. These findings can serve as much needed constraints in modeling of aerosol‐cloud interactions in the North America; future in situ studies will determine the robustness of our findings.}, number={D10}, journal={Journal of Geophysical Research: Atmospheres}, publisher={American Geophysical Union (AGU)}, author={Fountoukis, Christos and Nenes, Athanasios and Meskhidze, Nicholas and Bahreini, Roya and Conant, William C. and Jonsson, Haflidi and Murphy, Shane and Sorooshian, Armin and Varutbangkul, Varuntida and Brechtel, Fred and et al.}, year={2007}, month={Apr} }
 @article{meskhidze_nenes_chameides_luo_mahowald_2007, title={Atlantic Southern Ocean productivity: Fertilization from above or below?}, volume={21}, ISSN={["1944-9224"]}, DOI={10.1029/2006gb002711}, abstractNote={Primary productivity and the associated uptake of atmospheric carbon dioxide in the Southern Ocean (SO) is thought to be generally limited by bioavailable iron (Fe). Two sources of Fe for the surface waters of the SO have been proposed: (1) oceanic input of nutrient‐rich (i.e., Fe) waters from upwelling and lateral flows from continental margins; and (2) atmospheric input from the deposition of mineral dust emanating from the arid regions of South America and Australia. In this work, analysis of weekly remotely sensed sea surface temperature (SST), ocean chlorophyll a content [Chl a] and model‐derived atmospheric dust‐Fe fluxes are used to identify the predominant source of Fe during phytoplankton blooms in the surface waters of the south Atlantic Ocean between 40°S and 60°S. The results of our study suggest that oceanic source through upwelling of nutrient‐rich waters due to mesoscale frontal dynamics is the major source of bioavailable Fe controlling biological activity in this region. This result is consistent with the idea that acidification of aeolian dust prior to its deposition to the ocean may be required to solubilize the large fraction of mineral‐iron and make it bioavailable.}, number={2}, journal={GLOBAL BIOGEOCHEMICAL CYCLES}, author={Meskhidze, Nicholas and Nenes, Athanasios and Chameides, William L. and Luo, Chao and Mahowald, Natalie}, year={2007}, month={Apr} }
 @misc{meskhidze_nenes_2007, title={Isoprene, cloud droplets, and phytoplankton - Response}, volume={317}, number={5834}, journal={Science}, author={Meskhidze, N. and Nenes, A.}, year={2007}, pages={42–43} }
 @article{meskhidze_nenes_2006, title={Phytoplankton and cloudiness in the Southern Ocean}, volume={314}, ISSN={["1095-9203"]}, DOI={10.1126/science.1131779}, abstractNote={The effect of ocean biological productivity on marine clouds is explored over a large phytoplankton bloom in the Southern Ocean with the use of remotely sensed data. Cloud droplet number concentration over the bloom was twice what it was away from the bloom, and cloud effective radius was reduced by 30%. The resulting change in the short-wave radiative flux at the top of the atmosphere was –15 watts per square meter, comparable to the aerosol indirect effect over highly polluted regions. This observed impact of phytoplankton on clouds is attributed to changes in the size distribution and chemical composition of cloud condensation nuclei. We propose that secondary organic aerosol, formed from the oxidation of phytoplankton-produced isoprene, can affect chemical composition of marine cloud condensation nuclei and influence cloud droplet number. Model simulations support this hypothesis, indicating that 100% of the observed changes in cloud properties can be attributed to the isoprene secondary organic aerosol.}, number={5804}, journal={SCIENCE}, author={Meskhidze, Nicholas and Nenes, Athanasios}, year={2006}, month={Dec}, pages={1419–1423} }
 @article{meskhidze_2005, title={Dust and pollution: A recipe for enhanced ocean fertilization?}, volume={110}, ISSN={0148-0227}, url={http://dx.doi.org/10.1029/2004JD005082}, DOI={10.1029/2004JD005082}, abstractNote={[1] For Fe contained in aeolian dust to act as a micronutrient for oceanic phytoplankton, some fraction of it must first be transformed (mobilized) into a form soluble in ocean water. Fe solubilization in deliquesced mineral dust aerosols emanating from East Asia during the springtime outflow conditions is investigated here with a Lagrangian box model of the gas and aqueous-phase chemistry. The model simulates the scavenging of soluble and reactive gaseous species by mineral dust aerosols, chemical reactions of these species and mineral dust ions in deliquesced solution, and dissolution of Fe-III oxides that occurs as a result of the acid mobilization. The calculations indicate that mineral calcite (CaCO3) strongly buffers deliquesced dust aerosols with a pH that remains close to 8 until the amount of acid added to the aerosol solution exceeds CaCO3 alkalinity. SO2 pollutant emissions are a potential source of acidity to advecting dust from East Asia. The model is used to simulate the chemical evolution of dust plumes formed from two contrasting documented Gobi-desert storms that advected dust to Fe-limited regions of the North Pacific Ocean (NPO). These calculations indicate that only plumes with relatively high initial SO2-to-dust ratios are capable of delivering significant amounts of bioavailable Fe to the NPO. The estimated change in phytoplankton population inferred from the model-calculated inputs of bioavailable Fe for these two episodes is consistent with the satellite-measured chlorophyll a concentrations in the NPO. Model simulations indicate that (1) large dust advection episodes, that can export vast amounts of mineral dust to the open ocean, should have insignificant dissolved iron fraction (DIF) as the amount of SO2 required to acidify such dust plumes is about an order of magnitude higher than what can typically be entrained in the plume during its advection; (2) smaller dust plumes will generally have higher DIFs because they require lower amounts of SO2 and, even if such small plumes may not cause algae blooms, they could still be important sources of dissolved Fe to the NPO. The calculations suggest that future changes in SO2-pollutant emissions from East Asia, either up or down, may affect the productivity of the NPO.}, number={D3}, journal={Journal of Geophysical Research}, publisher={American Geophysical Union (AGU)}, author={Meskhidze, N.}, year={2005} }
 @article{luo_mahowald_meskhidze_chen_siefert_baker_johansen_2005, title={Estimation of iron solubility from observations and a global aerosol model}, volume={110}, ISSN={0148-0227}, url={http://dx.doi.org/10.1029/2005JD006059}, DOI={10.1029/2005JD006059}, abstractNote={Mineral aerosol deposition is the dominant source of iron to the open ocean. Soil iron is typically insoluble and understanding the atmospheric processes that convert insoluble iron to the more soluble forms observed over the oceans is crucial. In this paper, we model several proposed processes for the conversion of Fe(III) to Fe(II), and compare with cruise observations. The comparisons show that the model results in similar averaged magnitudes of iron solubility as measured during 8 cruises in 2001–2003. Comparisons show that results of cases including cloud, SO2 and hematite processing are better than the other approaches used using the reaction rates we assume in this paper; unfortunately the reaction rates are not well known, and this hampers our ability to conclusive show one process is more likely than another. The total soluble iron deposited to the global ocean is estimated by the model to range from 0.36 to 1.6 Tg y−1, with 0.88 Tg y−1 being the mean estimate; however there are large uncertainties in these estimates. Comparison shows that the regions with largest differences between the model simulations and observations of iron solubility are in the Southern Atlantic near South America coast and North Atlantic near Spain coast. More observations in these areas or in the South Pacific will help us identify the most important processes. Additionally, laboratory experiments that constrain the reaction rates of different compounds that will result in a net solubilization of iron in aerosols are required to better constrain iron processing in the atmosphere. Additionally, knowing what forms of iron are most bioavailable will assist atmospheric scientists in providing better budgets of iron deposited to the ocean surfaces.}, number={D23}, journal={Journal of Geophysical Research}, publisher={American Geophysical Union (AGU)}, author={Luo, Chao and Mahowald, N. M. and Meskhidze, N. and Chen, Y. and Siefert, R. L. and Baker, A. R. and Johansen, A. M.}, year={2005} }
 @article{meskhidze_2005, title={Evaluation of a new cloud droplet activation parameterization with in situ data from CRYSTAL-FACE and CSTRIPE}, volume={110}, ISSN={0148-0227}, url={http://dx.doi.org/10.1029/2004JD005703}, DOI={10.1029/2004JD005703}, abstractNote={[1] The accuracy of the 2003 prognostic, physically based aerosol activation parameterization of A. Nenes and J. H. Seinfeld (NS) with modifications introduced by C. Fountoukis and A. Nenes in 2005 (modified NS) is evaluated against extensive microphysical data sets collected on board the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft for cumuliform and stratiform clouds of marine and continental origin. The cumuliform cloud data were collected during NASA's Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL-FACE, Key West, Florida, July 2002), while the stratiform cloud data were gathered during Coastal Stratocumulus Imposed Perturbation Experiment (CSTRIPE, Monterey, California, July 2003). In situ data sets of aerosol size distribution, chemical composition, and updraft velocities are used as input for the NS parameterization, and the evaluation is carried out by comparing predicted cloud droplet number concentrations (CDNC) with observations. This is the first known study in which a prognostic cloud droplet activation parameterization has been evaluated against a wide range of observations. On average, predicted droplet concentration in adiabatic regions is within ∼20% of observations at the base of cumuliform clouds and ∼30% of observations at different altitudes throughout the stratiform clouds, all within experimental uncertainty. Furthermore, CDNC is well parameterized using either a single mean updraft velocity or by weighting droplet nucleation rates with a Gaussian probability density function of w. This study suggests that for nonprecipitating warm clouds of variable microphysics, aerosol composition, and size distribution the modified NS parameterization can accurately predict cloud droplet activation and can be successfully implemented for describing the aerosol activation process in global climate models.}, number={D16}, journal={Journal of Geophysical Research}, publisher={American Geophysical Union (AGU)}, author={Meskhidze, Nicholas}, year={2005} }