@article{cornwell_mccluskey_hill_levin_rothfuss_tai_petters_demott_kreidenweis_prather_et al._2023, title={Bioaerosols are the dominant source of warm-temperature immersion-mode INPs and drive uncertainties in INP predictability}, volume={9}, ISSN={["2375-2548"]}, DOI={10.1126/sciadv.adg3715}, abstractNote={Ice-nucleating particles (INPs) are rare atmospheric aerosols that initiate primary ice formation, but accurately simulating their concentrations and variability in large-scale climate models remains a challenge. Doing so requires both simulating major particle sources and parameterizing their ice nucleation (IN) efficiency. Validating and improving model predictions of INP concentrations requires measuring their concentrations delineated by particle type. We present a method to speciate INP concentrations into contributions from dust, sea spray aerosol (SSA), and bioaerosol. Field campaign data from Bodega Bay, California, showed that bioaerosols were the primary source of INPs between -12° and -20°C, while dust was a minor source and SSA had little impact. We found that recent parameterizations for dust and SSA accurately predicted ambient INP concentrations. However, the model did not skillfully simulate bioaerosol INPs, suggesting a need for further research to identify major factors controlling their emissions and INP efficiency for improved representation in models.}, number={37}, journal={SCIENCE ADVANCES}, author={Cornwell, Gavin C. and McCluskey, Christina S. and Hill, Thomas C. J. and Levin, Ezra T. and Rothfuss, Nicholas E. and Tai, Sheng-Lun and Petters, Markus D. and DeMott, Paul J. and Kreidenweis, Sonia and Prather, Kimberly A. and et al.}, year={2023}, month={Sep} }
 @article{cornwell_sultana_petters_al-mashat_rothfuss_mohler_demott_martin_prather_2022, title={Discrimination between individual dust and bioparticles using aerosol time-of-flight mass spectrometry}, ISSN={["1521-7388"]}, DOI={10.1080/02786826.2022.2055994}, abstractNote={Ice nucleating particles (INPs) impact cloud properties and precipitation processes through their ability to trigger cloud glaciation. Dust and bioparticles are two important sources of INPs that have markedly different atmospheric loadings and ice nucleating efficiencies. In-situ identification of the sources of INPs in clouds has been accomplished using single particle mass spectrometry (SPMS). However, external mixtures of dust and bioparticles present a unique challenge as they have overlapping mass spectral ion signatures, complicating their unambiguous identification. This study presents a detailed discussion of dust and bioparticle SPMS signatures, uniting data from a broad array of studies. As emphasized, the ion signals from both dust and bioparticles are highly sensitive to ionization conditions. To understand the observed variations, we characterize the mass spectral dependence of distinct dust and bioparticle samples using total positive ion intensity (TPII) as an indicator of the laser pulse energy each particle encountered. Through this analysis, a broad range of characteristic biogenic low intensity ion peaks that may be useful to distinguish bioparticles from dust became apparent and are highlighted. Insights informed by this analysis were utilized to identify bioparticles in ambient SPMS data. Ambient particles exhibiting both dust and characteristic biogenic spectral fingerprints were excluded from the bioparticle classification. Although bioparticles only made up 0.2% of all sampled particles, their abundance was moderately correlated with INP concentrations measured at −15 °C.Copyright © 2022 American Association for Aerosol Research}, journal={AEROSOL SCIENCE AND TECHNOLOGY}, author={Cornwell, G. C. and Sultana, C. M. and Petters, M. D. and Al-Mashat, H. and Rothfuss, N. E. and Mohler, O. and DeMott, P. J. and Martin, A. C. and Prather, K. A.}, year={2022}, month={Mar} }
 @article{rothfuss_petters_champion_grieshop_petters_2019, title={Characterization of a dimer preparation method for nanoscale organic aerosol}, volume={53}, ISSN={["1521-7388"]}, url={https://doi.org/10.1080/02786826.2019.1623379}, DOI={10.1080/02786826.2019.1623379}, abstractNote={Nanoscale dimers have application in studies of aerosol physicochemical properties such as aerosol viscosity. These particle dimers can be synthesized using the dual tandem differential mobility analyzer (DTDMA) technique, wherein oppositely charged particle streams coagulate to form dimers that can be isolated using electrostatic filtration. Although some characterization of the technique has been published, a detailed thesis on the modes and theory of operation has remained outside the scope of prior work. Here, we present new experimental data characterizing the output DTDMA size distribution and the physical processes underlying its apparent modes. Key experimental limitations for both general applications and for viscosity measurements are identified and quantified in six distinct types of DTDMA experiments. The primary consideration is the production of an adequate number of dimers, which typically requires high mobility-selected number concentration in the range 25,000–100,000 cm−3. The requisite concentration threshold depends upon the rate of spontaneous monomer decharging, which arises predominately from interactions of the aerosol with ionizing radiation within the coagulation chamber and is instrument location dependent. Lead shielding of the coagulation chamber reduced the first-order decharging constant from ∼2.0 × 10−5 s−1 to ∼0.8 × 10−5 s−1 in our laboratory. Dimer production at monomer diameters less than 40 nm is hindered by low bipolar charging efficiency. Results from the characterization experiments shed light on design considerations for general applications and for characterization of viscous aerosol phase transitions.Copyright © 2019 American Association for Aerosol Research}, number={9}, journal={AEROSOL SCIENCE AND TECHNOLOGY}, publisher={Informa UK Limited}, author={Rothfuss, Nicholas E. and Petters, Sarah S. and Champion, Wyatt M. and Grieshop, Andrew P. and Petters, Markus D.}, year={2019}, month={Sep}, pages={998–1011} }
 @article{tandon_rothfuss_petters_2019, title={The effect of hydrophobic glassy organic material on the cloud condensation nuclei activity of particles with different morphologies}, volume={19}, ISSN={["1680-7324"]}, DOI={10.5194/acp-19-3325-2019}, abstractNote={Abstract. Particles composed of organic and inorganic components can assume core-shell morphologies. The kinetic limitation of water uptake due to the presence of a hydrophobic viscous outer shell may increase the critical supersaturation required to activate such particles into cloud droplets. Here we test this hypothesis through laboratory experiments. Results show that the viscosity of polyethylene particles is 5×106 Pa s at 60 ∘C. Extrapolation of temperature dependent viscosity measurements suggests that the particles are glassy at room temperature. Cloud condensation nuclei (CCN) activity measurements demonstrate that pure polyethylene particles are CCN inactive at diameters less than 741 nm and 2.5 % water supersaturation. Thus, polyethylene is used as proxy for hydrophobic glassy organic material. Ammonium sulfate is used as proxy for hygroscopic CCN active inorganic material. Mixed particles were generated using coagulation of oppositely charged particles; charge-neutral polyethylene–ammonium sulfate dimer particles were then isolated for online observation. Morphology of these dimer particles was varied by heating, such that liquefied polyethylene partially or completely engulfed the ammonium sulfate. Critical supersaturation was measured as a function of dry particle volume, particle morphology, and organic volume fraction. The data show that kinetic limitations do not change the critical supersaturation of 50 nm ammonium sulfate cores coated with polyethylene and polyethylene volume fractions up to 97 %. Based on these results, and a synthesis of literature data, it is suggested that mass transfer limitations by glassy organic shells are unlikely to affect cloud droplet activation near laboratory temperatures.}, number={5}, journal={ATMOSPHERIC CHEMISTRY AND PHYSICS}, author={Tandon, Ankit and Rothfuss, Nicholas E. and Petters, Markus D.}, year={2019}, month={Mar}, pages={3325–3339} }
 @article{champion_rothfuss_petters_grieshop_2019, title={Volatility and Viscosity Are Correlated in Terpene Secondary Organic Aerosol Formed in a Flow Reactor}, volume={6}, ISSN={["2328-8930"]}, url={https://doi.org/10.1021/acs.estlett.9b00412}, DOI={10.1021/acs.estlett.9b00412}, abstractNote={Secondary organic aerosol (SOA) is a complex mixture of largely unspeciated compounds. The volatility and viscosity of the bulk organic aerosol influence new particle formation, processing, and lifetime in the atmosphere. Relationships between these properties are well-defined for pure compounds but currently unavailable for bulk organic aerosol. In this survey study, we characterized SOA formed from a range of biogenic precursors and conditions in an oxidation flow reactor for volatility (thermodenuder), viscosity (dimer coagulation, isolation, and coalescence), and oxidation state (aerosol chemical speciation monitor). We find linear trends in log–linear and log–log plots of single-parameter representations of volatility and viscosity, with higher condensed-phase fractions of extremely low and low volatility material associated with an increased viscosity (R = 0.69). Per this relationship, an increase in the contribution of these fractions (i.e., lower volatility) by 0.1 results in an increase in viscosity of approximately 200%. The viscosity (at 30 °C) of SOA fell between 6.2 × 105 and 8.0 × 108 Pa s and thus in the semisolid range. The SOA oxidation state ranged from −1.0 and 0.1 and was weakly anticorrelated with volatility (but not viscosity). We found larger SOA mass loadings generally associated with increased volatility and decreased viscosity. The results of this preliminary study are consistent with “molecular corridor”-style frameworks employing molecular mass and volatility to estimate the viscosity of bulk real-world SOA.}, number={9}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS}, publisher={American Chemical Society (ACS)}, author={Champion, Wyatt M. and Rothfuss, Nicholas E. and Petters, Markus D. and Grieshop, Andrew P.}, year={2019}, month={Sep}, pages={513–519} }
 @article{rothfuss_marsh_rovelli_petters_reid_2018, title={Condensation Kinetics of Water on Amorphous Aerosol Particles}, volume={9}, ISSN={["1948-7185"]}, DOI={10.1021/acs.jpclett.8b01365}, abstractNote={Responding to changes in the surrounding environment, aerosol particles can grow by water condensation changing rapidly in composition and changing dramatically in viscosity. The timescale for growth is important to establish for particles undergoing hydration processes in the atmosphere or during inhalation. Using an electrodynamic balance, we report direct measurements at −7.5, 0, and 20 °C of timescales for hygroscopic condensational growth on a range of model hygroscopic aerosol systems. These extend from viscous aerosol particles containing a single saccharide solute (sucrose, glucose, raffinose, or trehalose) and a starting viscosity equivalent to a glass of ∼1012 Pa·s, to nonviscous (∼10–2 Pa·s) tetraethylene glycol particles. The condensation timescales observed in this work indicate that water condensation occurs rapidly at all temperatures examined (<10 s) and for particles of all initial viscosities spanning 10–2 to 1012 Pa·s. Only a marginal delay (<1 order of magnitude) is observed for particles starting as a glass.}, number={13}, journal={JOURNAL OF PHYSICAL CHEMISTRY LETTERS}, author={Rothfuss, Nicholas E. and Marsh, Aleksandra and Rovelli, Grazia and Petters, Markus D. and Reid, Jonathan P.}, year={2018}, month={Jul}, pages={3708–3713} }
 @article{rothfuss_petters_2017, title={Characterization of the temperature and humidity-dependent phase diagram of amorphous nanoscale organic aerosols}, volume={19}, ISSN={["1463-9084"]}, DOI={10.1039/c6cp08593h}, abstractNote={The amorphous phase state diagram for sucrose aerosol is obtained from a mix of measurements and model calculations.}, number={9}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Rothfuss, Nicholas E. and Petters, Markus D.}, year={2017}, month={Mar}, pages={6532–6545} }
 @article{demott_hill_petters_bertram_tobo_mason_suski_mccluskey_levin_schill_et al._2017, title={Comparative measurements of ambient atmospheric concentrations of ice nucleating particles using multiple immersion freezing methods and a continuous flow diffusion chamber}, volume={17}, number={18}, journal={Atmospheric Chemistry and Physics}, author={DeMott, P. J. and Hill, T. C. J. and Petters, M. D. and Bertram, A. K. and Tobo, Y. and Mason, R. H. and Suski, K. J. and McCluskey, C. S. and Levin, E. J. T. and Schill, G. P. and et al.}, year={2017}, pages={11227–11245} }
 @article{rothfuss_petters_2017, title={Influence of Functional Groups on the Viscosity of Organic Aerosol}, volume={51}, ISSN={["1520-5851"]}, DOI={10.1021/acs.est.6b04478}, abstractNote={Organic aerosols can exist in highly viscous or glassy phase states. A viscosity database for organic compounds with atmospherically relevant functional groups is compiled and analyzed to quantify the influence of number and location of functional groups on viscosity. For weakly functionalized compounds the trend in viscosity sensitivity to functional group addition is carboxylic acid (COOH) ≈ hydroxyl (OH) > nitrate (ONO2) > carbonyl (CO) ≈ ester (COO) > methylene (CH2). Sensitivities to group addition increase with greater levels of prior functionalization and decreasing temperature. For carboxylic acids a sharp increase in sensitivity is likely present already at the second addition at room temperature. Ring structures increase viscosity relative to linear structures. Sensitivities are correlated with analogously derived sensitivities of vapor pressure reduction. This may be exploited in the future to predict viscosity in numerical models by piggybacking on schemes that track the evolution of organic aerosol volatility with age.}, number={1}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Rothfuss, Nicholas E. and Petters, Markus D.}, year={2017}, month={Jan}, pages={271–279} }
 @article{martin_cornwell_atwood_moore_rothfuss_taylor_demott_kreidenweis_petters_prather_2017, title={Transport of pollution to a remote coastal site during gap flow from California's interior: impacts on aerosol composition, clouds, and radiative balance}, volume={17}, number={2}, journal={Atmospheric Chemistry and Physics}, author={Martin, A. C. and Cornwell, G. C. and Atwood, S. A. and Moore, K. A. and Rothfuss, N. E. and Taylor, H. and DeMott, P. J. and Kreidenweis, S. M. and Petters, M. D. and Prather, K. A.}, year={2017}, pages={1491–1509} }