@article{del negro_gallardo-williams_2022, title={Labapalooza: What Happens When Students Return to In-Person Laboratories After Taking Laboratories Online for a Year?}, volume={6}, ISSN={["1938-1328"]}, DOI={10.1021/acs.jchemed.2c00141}, abstractNote={Due to the COVID-19 pandemic, in-person undergraduate chemistry laboratories at North Carolina State University were not available to students during the 2020-2021 academic year and were replaced with online laboratories. With the return to in-person laboratories in the fall semester of 2021, there was widespread concern among the faculty that chemistry majors might struggle with the application of concepts and techniques that they learned online in the in-person lab environment. An event to bring students back to campus for a day was designed by the faculty in charge of teaching organic and analytical chemistry laboratories with extensive input from students. Participants were asked to choose the lab techniques that they wanted to review, were given agency to choose the day and time of the gathering, and were encouraged to suggest a name for the event. In this paper we describe the outcomes regarding student choices, participation, and self-assessed efficacy before and after testing in person the lab techniques that had been learned online.}, journal={JOURNAL OF CHEMICAL EDUCATION}, author={Del Negro, Lori A. and Gallardo-Williams, Maria T.}, year={2022}, month={Jun} }
 @article{warneke_de gouw_del negro_brioude_mckeen_stark_kuster_goldan_trainer_fehsenfeld_et al._2010, title={Biogenic emission measurement and inventories determination of biogenic emissions in the eastern United States and Texas and comparison with biogenic emission inventories}, volume={115}, ISSN={0148-0227}, url={http://dx.doi.org/10.1029/2009JD012445}, DOI={10.1029/2009jd012445}, abstractNote={During the NOAA Southern Oxidant Study 1999 (SOS1999), Texas Air Quality Study 2000 (TexAQS2000), International Consortium for Atmospheric Research on Transport and Transformation (ICARTT2004), and Texas Air Quality Study 2006 (TexAQS2006) campaigns, airborne measurements of isoprene and monoterpenes were made in the eastern United States and in Texas, and the results are used to evaluate the biogenic emission inventories BEIS3.12, BEIS3.13, MEGAN2, and WM2001. Two methods are used for the evaluation. First, the emissions are directly estimated from the ambient isoprene and monoterpene measurements assuming a well‐mixed boundary layer and are compared with the emissions from the inventories extracted along the flight tracks. Second, BEIS3.12 is incorporated into the detailed transport model FLEXPART, which allows the isoprene and monoterpene mixing ratios to be calculated and compared to the measurements. The overall agreement for all inventories is within a factor of 2 and the two methods give consistent results. MEGAN2 is in most cases higher, and BEIS3.12 and BEIS3.13 lower than the emissions determined from the measurements. Regions with clear discrepancies are identified. For example, an isoprene hot spot to the northwest of Houston, Texas, was expected from BEIS3 but not observed in the measurements. Interannual differences in emissions of about a factor of 2 were observed in Texas between 2000 and 2006.}, journal={Journal of Geophysical Research}, publisher={American Geophysical Union (AGU)}, author={Warneke, C. and de Gouw, J. A. and Del Negro, L. and Brioude, J. and McKeen, S. and Stark, H. and Kuster, W. C. and Goldan, P. D. and Trainer, M. and Fehsenfeld, F. C. and et al.}, year={2010}, month={Mar} }
 @article{schwarz_gao_spackman_watts_thomson_fahey_ryerson_peischl_holloway_trainer_et al._2008, title={Measurement of the mixing state, mass, and optical size of individual black carbon particles in urban and biomass burning emissions}, volume={35}, ISSN={0094-8276}, url={http://dx.doi.org/10.1029/2008GL033968}, DOI={10.1029/2008gl033968}, abstractNote={In situ measurements of the mass, mixing state, and optical size of individual black‐carbon (BC) particles in the fine mode (90–600 nm) have been made in fresh emissions from urban and biomass burning sources with an airborne single‐particle soot photometer. Contrasts between the two sources are significant and consistent. Urban BC tends to smaller sizes, fewer coated particles, thinner coatings, and less absorption per unit mass than biomass‐burning BC. This suggests that urban BC may have a longer lifetime in the atmosphere and a different impact on BC radiative forcing in the first indirect effect than biomass‐burning BC. These measurements bound the likely variability in the microphysical state of BC emissions from typical continental processes, and provide direct measurements of the size distribution and coating state of fine‐mode BC for use in constraining climate and aerosol models. These results highlight the need for the integration of source‐specific information into such models.}, number={13}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Schwarz, J. P. and Gao, R. S. and Spackman, J. R. and Watts, L. A. and Thomson, D. S. and Fahey, D. W. and Ryerson, T. B. and Peischl, J. and Holloway, J. S. and Trainer, M. and et al.}, year={2008}, month={Jul} }
 @article{neuman_gao_fahey_holecek_ridley_walega_grahek_richard_mcelroy_thompson_et al._2001, title={In situ measurements of HNO3, NOy, NO, and O3 in the lower stratosphere and upper troposphere}, volume={35}, DOI={10.1016/s1352-2310(01)00354-5}, abstractNote={In situ measurements of nitric acid (HNO3), reactive nitrogen (NOy), nitric oxide (NO), and ozone (O3) made in the upper troposphere (UT) and lower stratosphere (LS) between 29° and 33°N latitudes during September 1999 are used to examine NOy partitioning and correlations between the measured species in these regions. The fast-response (1 s) HNO3 measurements are acquired with a new autonomous CIMS instrument. In the LS, HNO3 accounts for the majority of NOy, and the sum of HNO3 and NOx accounts for approximately 90% of NOy. In the UT, the sum of HNO3 and NOx varies between 40% and 100% of NOy. Both HNO3 and NOy are strongly positively correlated with O3, with larger correlation slopes in the UT than in the LS. In the UT at low values of the quantity (NOy–NOx–HNO3), it is uncorrelated with O3, while at higher values, a positive correlation with O3 is found. Of these two air mass types, those with higher (NOy–NOx–HNO3) mixing ratios are likely associated with the presence of peroxyacetyl nitrate (PAN) that is produced by NOx-hydrocarbon chemistry.}, number={33}, journal={Atmospheric Environment}, publisher={Elsevier BV}, author={Neuman, J.A. and Gao, R.S. and Fahey, D.W. and Holecek, J.C. and Ridley, B.A. and Walega, J.G. and Grahek, F.E. and Richard, E.C. and McElroy, C.T. and Thompson, T.L. and et al.}, year={2001}, month={Nov}, pages={5789–5797} }
 @article{gao_negro_swartz_salawitch_lloyd_proffitt_fahey_donnelly_neuman_stimpfle_et al._2001, title={JNO2at high solar zenith angles in the lower stratosphere}, volume={28}, DOI={10.1029/2000gl012615}, abstractNote={In situ measurements of NO, NO2, O3, HO2, ClO, pressure, and temperature have been made at high solar zenith angles (SZA, 70°–93°) in the lower stratosphere. These measurements are used to derive the photolysis rate of NO2, JNO2, using a time‐dependent method. The resultant JNO2 values and the results of a multiple‐scattering actinic flux model show a linear relationship throughout the SZA range. The difference of the two sets of JNO2 values of about 11% suggests that the model scattering calculation is very accurate at high SZA conditions near sunrise and sunset.}, number={12}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Gao, R. S. and Negro, L. A. Del and Swartz, W. H. and Salawitch, R. J. and Lloyd, S. A. and Proffitt, M. H. and Fahey, D. W. and Donnelly, S. G. and Neuman, J. A. and Stimpfle, R. M. and et al.}, year={2001}, month={Jun}, pages={2405–2408} }
 @article{perkins_hanisco_cohen_koch_stimpfle_voss_bonne_lanzendorf_anderson_wennberg_et al._2001, title={The NOx−HNO3System in the Lower Stratosphere:  Insights from In Situ Measurements and Implications of theJHNO3−[OH] Relationship}, volume={105}, DOI={10.1021/jp002519n}, abstractNote={During the 1997 Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) mission, simultaneous in situ observations of NO_x and HO_x radicals, their precursors, and the radiation field were obtained in the lower stratosphere. We use these observations to evaluate the primary mechanisms that control NO_x−HNO_3 exchange and to understand their control over the partitioning between NO_2 and HNO_3 in regions of continuous sunlight. We calculate NO_x production (P_(NO)_x) and loss (L_(NO)_x) in a manner directly constrained by the in situ measurements and current rate constant recommendations, using approaches for representing albedo, overhead O_3 and [OH] that reduce model uncertainty. We find a consistent discrepancy of 18% between modeled rates of NO_x production and loss (L_(NO)_x = 1.18P_(NO)_x) which is within the measurement uncertainty of ±27%. The partitioning between NO_x production processes is [HNO_3 + OH (41 ± 2)%; HNO+3 + hν (59 ± 2)%] and between NO_x loss processes is [NO_2 + OH, 90% to >97%; BrONO_2 + H_2O, 10% to <3%]. The steady-state description of NO_x−HNO_3 exchange reveals the significant influence of the tight correlation between the photolysis rate of HNO_3 and [OH] established by in situ measurements throughout the lower stratosphere. Parametrizing this relationship, we find (1) the steady-state value of [NO_2]_(24h-avg)/[HNO_3] in the continuously sunlit, lower stratosphere is a function only of temperature and number density, and (2) the partitioning of NO_x production between HNO_3 + OH and HNO_3 + hν is nearly constant throughout most of the lower stratosphere. We describe a methodology (functions of latitude, day, temperature, and pressure) for accurately predicting the steady-state value of [NO_2]_(24h-avg)/[HNO_3] and the partitioning of NO_x production within these regions. The results establish a metric to compare observations of [NO_2]_(24h-avg)/[HNO_3] within the continuously sunlit region and provide a simple diagnostic for evaluating the accuracy of models that attempt to describe the coupled NO_x−HO_x photochemistry in the lower stratosphere.}, number={9}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Perkins, K. K. and Hanisco, T. F. and Cohen, R. C. and Koch, L. C. and Stimpfle, R. M. and Voss, P. B. and Bonne, G. P. and Lanzendorf, E. J. and Anderson, J. G. and Wennberg, P. O. and et al.}, year={2001}, month={Mar}, pages={1521–1534} }
 @article{fahey_gao_negro_keim_kawa_salawitch_wennberg_hanisco_lanzendorf_perkins_et al._2000, title={Ozone destruction and production rates between spring and autumn in the Arctic stratosphere}, volume={27}, DOI={10.1029/2000gl011404}, abstractNote={In situ measurements of radical and long‐lived species were made in the lower Arctic stratosphere (18 to 20 km) between spring and early autumn in 1997. The measurements include O3, ClO, OH, HO2, NO, NO2, N2O, CO, and overhead O3. A photochemical box model constrained by these and other observations is used to compute the diurnally averaged destruction and production rates of O3 in this region. The rates show a strong dependence on solar exposure and ambient O3. Total destruction rates, which reach 19%/month in summer, reveal the predominant role of NOx and HOx catalytic cycles throughout the period. Production of O3 is significant only in midsummer air parcels. A comparison of observed O3 changes with destruction rates and transport effects indicates the predominant role of destruction in spring and an increased role of transport by early autumn.}, number={17}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Fahey, D. W. and Gao, R. S. and Negro, L. A. Del and Keim, E. R. and Kawa, S. R. and Salawitch, R. J. and Wennberg, P. O. and Hanisco, T. F. and Lanzendorf, E. J. and Perkins, K. K. and et al.}, year={2000}, month={Sep}, pages={2605–2608} }
 @article{cohen_perkins_koch_stimpfle_wennberg_hanisco_lanzendorf_bonne_voss_salawitch_et al._2000, title={Quantitative constraints on the atmospheric chemistry of nitrogen oxides: An analysis along chemical coordinates}, volume={105}, DOI={10.1029/2000jd900290}, abstractNote={In situ observations Of NO2, NO, NOy, ClONO2, OH, O3, aerosol surface area, spectrally resolved solar radiation, pressure and temperature obtained from the ER‐2 aircraft during the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) experiments are used to examine the factors controlling the fast photochemistry connecting NO and NO2 and the slower chemistry connecting NOx and HNO3. Our analysis uses “chemical coordinates” to examine gradients of the difference between a model and precisely calibrated measurements to provide a quantitative assessment of the accuracy of current photochemical models. The NO/NO2 analysis suggests that reducing the activation energy for the NO+O3 reaction by 1.7 kJ/mol will improve model representation of the temperature dependence of the NO/NO2 ratio in the range 215–235 K. The NOx/HNO3 analysis shows that systematic errors in the relative rate coefficients used to describe NOx loss by the reaction OH + NO2 → HNO3 and by the reaction set NO2 + O3 → NO3; NO2 + NO3 → N2O5; N2O5 + H2O → 2HNO3 are in error by +8.4% (+30/−45%) (OH+NO2 too fast) in models using the Jet Propulsion Laboratory 1997 recommendations [DeMore et al., 1997]. Models that use recommendations for OH+NO2 and OH+HNO3 based on reanalysis of recent and past laboratory measurements are in error by 1.2% (+30/−45%) (OH+NO2 too slow). The +30%/−45% error limit reflects systematic uncertainties, while the statistical uncertainty is 0.65%. This analysis also shows that the POLARIS observations only modestly constrain the relative rates of the major NOx production reactions HNO3 + OH → H2O + NO3 and HNO3 + hν → OH + NO2. Even under the assumption that all other aspects of the model are perfect, the POLARIS observations only constrain the rate coefficient for OH+HNO3 to a range of 65% around the currently recommended value.}, number={D19}, journal={Journal of Geophysical Research: Atmospheres}, publisher={American Geophysical Union (AGU)}, author={Cohen, R. C. and Perkins, K. K. and Koch, L. C. and Stimpfle, R. M. and Wennberg, P. O. and Hanisco, T. F. and Lanzendorf, E. J. and Bonne, G. P. and Voss, P. B. and Salawitch, R. J. and et al.}, year={2000}, month={Oct}, pages={24283–24304} }
 @article{gao_fahey_negro_donnelly_keim_neuman_teverovskaia_wennberg_hanisco_lanzendorf_et al._1999, title={A comparison of observations and model simulations of NOx/NOyin the lower stratosphere}, volume={26}, DOI={10.1029/1999gl900162}, abstractNote={Extensive airborne measurements of the reactive nitrogen reservoir (NOy) and its component nitric oxide (NO) have been made in the lower stratosphere. Box model simulations that are constrained by observations of radical and long‐lived species and which include heterogeneous chemistry systematically underpredict the NOx (= NO + NO2) to NOy ratio. The model agreement is substantially improved if newly measured rate coefficients for the OH + NO2 and OH + HNO3 reactions are used. When included in 2‐D models, the new rate coefficients significantly increase the calculated ozone loss due to NOx and modestly change the calculated ozone abundances in the lower stratosphere. Ozone changes associated with the emissions of a fleet of supersonic aircraft are also altered.}, number={8}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Gao, R. S. and Fahey, D. W. and Negro, L. A. Del and Donnelly, S. G. and Keim, E. R. and Neuman, J. A. and Teverovskaia, E. and Wennberg, P. O. and Hanisco, T. F. and Lanzendorf, E. J. and et al.}, year={1999}, month={Apr}, pages={1153–1156} }
 @article{toon_blavier_sen_margitan_webster_may_fahey_gao_negro_proffitt_et al._1999, title={Comparison of MkIV balloon and ER-2 aircraft measurements of atmospheric trace gases}, volume={104}, DOI={10.1029/1999jd900379}, abstractNote={On May 8, 1997, vertical profiles of over 30 different gases were measured remotely in solar occultation by the Jet Propulsion Laboratory MkIV Interferometer during a balloon flight launched from Fairbanks, Alaska. These gases included H2O, N2O, CH4, CO, NOx, NOy, HCl, ClNO3, CCl2F2, CCl3F, CCl4, CHClF2, CClF2CCl2F, SF6, CH3Cl, and C2H6, all of which were also measured in situ by instruments on board the NASA ER‐2 aircraft, which was making flights from Fairbanks during this same early May time period as part of the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) experiment. A comparison of the gas volume mixing ratios in the upper troposphere and lower stratosphere reveals agreement better than 5% for most gases. The three significant exceptions to this are SF6 and CCl4 for which the remote measurements exceed the in situ observations by 15–20% at all altitudes, and H2O for which the remote measurements are up to 30% smaller than the in situ observations near the hygropause.}, number={D21}, journal={Journal of Geophysical Research: Atmospheres}, publisher={American Geophysical Union (AGU)}, author={Toon, G. C. and Blavier, J.-F. and Sen, B. and Margitan, J. J. and Webster, C. R. and May, R. D. and Fahey, D. and Gao, R. and Negro, L. Del and Proffitt, M. and et al.}, year={1999}, month={Nov}, pages={26779–26790} }
 @article{negro_fahey_gao_donnelly_keim_neuman_cohen_perkins_koch_salawitch_et al._1999, title={Comparison of modeled and observed values of NO2and JNO2during the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) mission}, volume={104}, DOI={10.1029/1999jd900246}, abstractNote={Stratospheric measurements of NO, NO2, O3, ClO, and HO2 were made during spring, early summer, and late summer in the Arctic region during 1997 as part of the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) field campaign. In the sunlit atmosphere, NO2 and NO are in steady state through NO2 photolysis and reactions involving O3, ClO, BrO, and HO2. By combining observations of O3, ClO, and HO2, observed and modeled values of the NO2 photolysis rate coefficient (JNO2), and model estimates of BrO, several comparisons are made between steady state and measured values of both NO2 and JNO2. An apparent seasonal dependence in discrepancies between calculated and measured values was found; however, a source for this dependence could not be identified. Overall, the mean linear fits in the various comparisons show agreement within 19%, well within the combined uncertainties (±50 to 70%). These results suggest that photochemistry controlling the NO2/NO abundance ratio is well represented throughout much of the sunlit lower stratosphere. A reduction in the uncertainty of laboratory determinations of the rate coefficient of NO + O3 → NO2 + O2 would aid future analyses of these or similar atmospheric observations.}, number={D21}, journal={Journal of Geophysical Research: Atmospheres}, publisher={American Geophysical Union (AGU)}, author={Negro, L. A. Del and Fahey, D. W. and Gao, R. S. and Donnelly, S. G. and Keim, E. R. and Neuman, J. A. and Cohen, R. C. and Perkins, K. K. and Koch, L. C. and Salawitch, R. J. and et al.}, year={1999}, month={Nov}, pages={26687–26703} }
 @article{stimpfle_cohen_bonne_voss_perkins_koch_anderson_salawitch_lloyd_gao_et al._1999, title={The coupling of ClONO2, ClO, and NO2in the lower stratosphere from in situ observations using the NASA ER-2 aircraft}, volume={104}, DOI={10.1029/1999jd900288}, abstractNote={The first in situ measurements of ClONO2 in the lower stratosphere, acquired using the NASA ER‐2 aircraft during the Polar Ozone Loss in the Arctic Region in Summer (POLARIS) mission, are combined with simultaneous measurements of ClO, NO2, temperature, pressure, and the calculated photolysis rate coefficient (JClONO2) to examine the balance between production and loss of ClONO2. The observations demonstrate that the ClONO2 photochemical steady state approximation, [ClONO2]PSS = k × [ClO] × [NO2] / JClONO2, is in good agreement with the direct measurement, [ClONO2]MEAS. For the bulk of the data (80%), where T>220 K and latitudes >45°N, [ClONO2]PSS = 1.15±0.36 (1σ) × [ClONO2]MEAS, while for T<220 K and latitudes <45°N the result is somewhat less at 1.01±0.30. The cause of the temperature and/or latitude trend is unidentified. These results are independent of solar zenith angle and air density, thus there is no evidence in support of a pressure‐dependent quantum yield for photodissociation of ClONO2 at wavelengths >300 nm. These measurements confirm the mechanism by which active nitrogen (NOx = NO + NO2) controls the abundance of active chlorine (Clx = ClO + Cl) in the stratosphere.}, number={D21}, journal={Journal of Geophysical Research: Atmospheres}, publisher={American Geophysical Union (AGU)}, author={Stimpfle, R. M. and Cohen, R. C. and Bonne, G. P. and Voss, P. B. and Perkins, K. K. and Koch, L. C. and Anderson, J. G. and Salawitch, R. J. and Lloyd, S. A. and Gao, R. S. and et al.}, year={1999}, month={Nov}, pages={26705–26714} }
 @article{weinheimer_montzka_campos_walega_ridley_donnelly_keim_negro_proffitt_margitan_et al._1998, title={Comparison between DC-8 and ER-2 species measurements in the tropical middle troposphere: NO, NOy, O3, CO2, CH4, and N2O}, volume={103}, DOI={10.1029/98jd01421}, abstractNote={We compare measurements of six species taken aboard NASA DC‐8 and ER‐2 aircraft during two flight legs in the tropical middle troposphere near Hawaii. NO, NOy, O3, CH4, and N2O measurements agree to within the limits set by the known systematic errors. For CO2, which can be measured with better relative precision than the other five species, differences in measured values from the two platforms are slightly larger than expected if the air masses sampled by the two aircraft were indeed similar in CO2 composition to better than 0.08%.}, number={D17}, journal={Journal of Geophysical Research: Atmospheres}, publisher={American Geophysical Union (AGU)}, author={Weinheimer, A. J. and Montzka, D. D. and Campos, T. L. and Walega, J. G. and Ridley, B. A. and Donnelly, S. G. and Keim, E. R. and Negro, L. A. Del and Proffitt, M. H. and Margitan, J. J. and et al.}, year={1998}, month={Sep}, pages={22087–22096} }
 @article{wennberg_hanisco_jaegle_jacob_hintsa_lanzendorf_anderson_gao_keim_donnelly_et al._1998, title={Hydrogen radicals, nitrogen radicals, and the production of O3 in the upper troposphere}, volume={279}, DOI={10.1126/science.279.5347.49}, abstractNote={
            The concentrations of the hydrogen radicals OH and HO
            2
            in the middle and upper troposphere were measured simultaneously with those of NO, O
            3
            , CO, H
            2
            O, CH
            4
            , non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O
            3
            in this region of the atmosphere. Comparison of the measured concentrations of OH and HO
            2
            with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HO
            
              x
            
            required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O
            3
            is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO
            2
            and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O
            3
            than expected.
          }, number={5347}, journal={Science}, publisher={American Association for the Advancement of Science (AAAS)}, author={Wennberg, P.O. and Hanisco, T.F. and Jaegle, L. and Jacob, D.J. and Hintsa, E.J. and Lanzendorf, E.J. and Anderson, J.G. and Gao, R.-S. and Keim, E.R. and Donnelly, S.G. and et al.}, year={1998}, month={Jan}, pages={49–53} }
 @article{negro_fahey_donnelly_gao_keim_wamsley_woodbridge_dye_baumgardner_gandrud_et al._1997, title={Evaluating the role of NAT, NAD, and liquid H2SO4/H2O/HNO3solutions in Antarctic polar stratospheric cloud aerosol: Observations and implications}, volume={102}, DOI={10.1029/97jd00764}, abstractNote={Airborne measurements of total reactive nitrogen (NOy) and polar stratospheric cloud (PSC) aerosol particles were made in the Antarctic (68°S) as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAES A) campaign in late July 1994. As found in both polar regions during previous studies, substantial PSC aerosol volume containing NOy was observed at temperatures above the frost point, confirming the presence of particles other than water ice. The composition of the aerosol particles is evaluated using equilibrium expressions for nitric acid trihydrate (NAT), nitric acid dihydrate (NAD), and the supercooled ternary solution (STS) composed of nitric acid (HNO3), sulfuric acid (H2SO4), and water (H2O). The equilibrium abundance of condensed HNO3 is calculated for each phase and compared to estimates made using observations of aerosol volume and NOy. The best agreement is found for STS composition, using criteria related to the onset and abundance of aerosol volume along the flight track. Throughout the PSC region, a comparison of the number of particles between 0.4 and 4.0 μm diameter with the number of available nuclei indicates that a significant fraction of the background aerosol number participates in PSC growth. Modeled STS size distributions at temperatures below 191 K compare favorably with measured size distributions of PSC aerosol. Calculations of the heterogeneous loss of chlorine nitrate (ClONO2) show that the reactivity of the observed PSC surface area is 30 to 300% greater with STS than with NAT composition for temperatures less than 195 K. The total volume of STS PSCs is shown to be more sensitive than NAT to increases in H2O, HNO3, and H2SO4 from supersonic aircraft fleet emissions. Using the current observations and perturbations predicted by the current aircraft assessments, an increase of 50 to 260% in STS aerosol volume is expected at the lowest observed temperatures (190 to 192 K), along with an extension of significant PSC activity to regions ∼0.7 K higher in temperature. These results improve our understanding of PSC aerosol formation in polar regions while strengthening the requirement to include STS aerosols in studies of polar ozone loss and the effects of aircraft emissions.}, number={D11}, journal={Journal of Geophysical Research: Atmospheres}, publisher={American Geophysical Union (AGU)}, author={Negro, L. A. Del and Fahey, D. W. and Donnelly, S. G. and Gao, R. S. and Keim, E. R. and Wamsley, R. C. and Woodbridge, E. L. and Dye, J. E. and Baumgardner, D. and Gandrud, B. W. and et al.}, year={1997}, month={Jun}, pages={13255–13282} }
 @article{nevison_solomon_garcia_fahey_keim_loewenstein_podolske_gao_wamsley_donnelly_et al._1997, title={Influence of Antarctic denitrification on two-dimensional model NOy/N2O correlations in the lower stratosphere}, volume={102}, DOI={10.1029/96jd03250}, abstractNote={The mechanisms responsible for latitudinal and seasonal variations in the stratospheric NOy/N2O correlation, represented by the effective NOy yield from N2O loss, or FNOy, are explored using the Garcia‐Solomon two‐dimensional model. The model is run with and without Antarctic denitrification. Model results are compared to in situ NOy/N2O measurements taken onboard the NASA ER‐2 high‐altitude aircraft in the lower stratosphere during the 1994 Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft campaign, and to global‐scale measurements taken onboard the Upper Atmosphere Research Satellite (UARS) from 1992 to 1993. The southern hemisphere midlatitude seasonal cycle observed by the ER‐2 and the latitudinal gradients observed by UARS are consistent with the results of the denitrified model, although some aspects of the model results are sensitive to prescribed and/or calculated horizontal diffusion coefficients. The consistency with observations supports the model's prediction of a seasonal cycle in which FNOy, increases at southern midlatitudes during winter due to descent of FNOy‐enriched air from above and decreases in spring due to mixing with FNOy‐depleted air from the denitrified polar vortex. Antarctic denitrification appears to affect midlatitudes mainly by a one‐time dilution of the polar vortex following the final warming rather than by flow‐through vortex processing during the winter. Because of the high concentrations of NO3, at polar latitudes before denitrification a large fraction of total stratospheric NOy can be removed by a one‐time dilution of the denitrified polar vortex. The nondenitrified model results generally do not agree well with observations, suggesting that denitrification strongly influences latitudinal and seasonal variations in FNOy in the southern hemisphere.}, number={D11}, journal={Journal of Geophysical Research: Atmospheres}, publisher={American Geophysical Union (AGU)}, author={Nevison, C. D. and Solomon, S. and Garcia, R. R. and Fahey, D. W. and Keim, E. R. and Loewenstein, M. and Podolske, J. R. and Gao, R. S. and Wamsley, R. C. and Donnelly, S. G. and et al.}, year={1997}, month={Jun}, pages={13183–13192} }
 @article{keim_loewenstein_podolske_fahey_gao_woodbridge_wamsley_donnelly_negro_nevison_et al._1997, title={Measurements of the NOy-N2O correlation in the lower stratosphere: Latitudinal and seasonal changes and model comparisons}, volume={102}, DOI={10.1029/96jd03921}, abstractNote={The tracer species nitrous oxide, N2O, and the reactive nitrogen reservoir, NOy, were measured in situ using instrumentation carried aboard the NASA ER‐2 high altitude aircraft as part of the NASA Airborne Southern Hemisphere Ozone Expedition/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA) and Stratospheric Tracers of Atmospheric Transport (STRAT) missions. Measurements were made throughout the latitude range of 70°S to 60°N over the time period of March to October 1994 and October 1995 to January 1996, which includes the period when the Antarctic polar vortex is most intense. The correlation plots of NOy with N2O reveal compact, near‐linear curves throughout data obtained in the lower stratosphere (50 mbar to 200 mbar). The average slope of the correlation, ΔNOy/ΔN2O, in the southern hemisphere (SH) exhibited a much larger seasonal variation during this time period than was observed in the northern hemisphere (NH). Between March and October in the potential temperature range of 400 K to 525 K, the correlation slope in the SH midlatitudes increased by 28%. A smaller but still positive increase in the correlation slope was observed for higher‐latitude data obtained within or near the edge of the SH polar vortex. At NH midlatitudes the correlation slope did not significantly change between March and October, while between October and January the slope increased by +7%. The larger SH midlatitude increase is consistent with ongoing descent throughout the winter and spring and also suggests that denitrification, the irreversible loss of HNO3 through sedimentation of cloud particles, is not a significant term (<10–15%) in the budget of NOy at SH midlatitudes during the wintertime. A secular increase in the correlation slope is ruled out by comparison with SH data obtained during the 1987 Airborne Antarctic Ozone Expedition (AAOE) aircraft campaign. These results suggest that a seasonal cycle exists in the correlation slope for both hemispheres, with the SH correlation slope returning to the April value during the SH spring and summer. Changes in stratospheric circulation also probably play a role in both the SH and the NH correlation slope seasonal cycles. Comparisons with two‐dimensional model results suggest that the slope decreases when the denitrified Antarctic vortex is diluted into midlatitudes upon vortex breakup in the spring and that through the descent of stratospheric air, the slope recovers during the following fall/winter period.}, number={D11}, journal={Journal of Geophysical Research: Atmospheres}, publisher={American Geophysical Union (AGU)}, author={Keim, E. R. and Loewenstein, M. and Podolske, J. R. and Fahey, D. W. and Gao, R. S. and Woodbridge, E. L. and Wamsley, R. C. and Donnelly, S. G. and Negro, L. A. Del and Nevison, C. D. and et al.}, year={1997}, month={Jun}, pages={13193–13212} }
 @article{gao_fahey_salawitch_lloyd_anderson_demajistre_mcelroy_woodbridge_wamsley_donnelly_et al._1997, title={Partitioning of the reactive nitrogen reservoir in the lower stratosphere of the southern hemisphere: Observations and modeling}, volume={102}, DOI={10.1029/96jd01967}, abstractNote={Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO + NO2 + NO3 + HNO3 + ClONO2 + 2N2O5 + …) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitudes. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO2 photolysis rate used in the SS approximation are reasonably accurate for conditions in the lower stratosphere. However, NO2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self‐consistency in our understanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model also show good agreement with the NO and NO2 measurements, suggesting that the reactions affecting the partitioning of the NOy reservoir are well understood in the lower stratosphere.}, number={D3}, journal={Journal of Geophysical Research: Atmospheres}, publisher={American Geophysical Union (AGU)}, author={Gao, R. S. and Fahey, D. W. and Salawitch, R. J. and Lloyd, S. A. and Anderson, D. E. and DeMajistre, R. and McElroy, C. T. and Woodbridge, E. L. and Wamsley, R. C. and Donnelly, S. G. and et al.}, year={1997}, month={Feb}, pages={3935–3949} }
 @article{hanisco_wennberg_cohen_anderson_fahey_keim_gao_wamsley_donnelly_negro_et al._1997, title={The role of HOxin super- and subsonic aircraft exhaust plumes}, volume={24}, DOI={10.1029/96gl03724}, abstractNote={The generation of sulfuric acid aerosols in aircraft exhaust has emerged as a critical issue in determining the impact of supersonic aircraft on stratospheric ozone. It has long been held that the first step in the mechanism of aerosol formation is the oxidation of SO2 emitted from the engine by OH in the exhaust plume. We report in situ measurements of OH and HO2 in the exhaust plumes of a supersonic (Air France Concorde) and a subsonic (NASA ER‐2) aircraft in the lower stratosphere. These measurements imply that reactions with OH are responsible for oxidizing only a small fraction of SO2 (2%), and thus cannot explain the large number of particles observed in the exhaust wake of the Concorde.}, number={1}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Hanisco, T. F. and Wennberg, P. O. and Cohen, R. C. and Anderson, J. G. and Fahey, D. W. and Keim, E. R. and Gao, R. S. and Wamsley, R. C. and Donnelly, S. G. and Negro, L. A. Del and et al.}, year={1997}, month={Jan}, pages={65–68} }
 @article{fahey_donnelly_keim_gao_wamsley_del negro_woodbridge_proffitt_rosenlof_ko_et al._1996, title={In situobservations of NOy, O3, and the NOy/O3ratio in the lower stratosphere}, volume={23}, ISSN={0094-8276}, url={http://dx.doi.org/10.1029/96gl01476}, DOI={10.1029/96gl01476}, abstractNote={Extensive in situ measurements of reactive nitrogen (NOy) and ozone (O3) were made in the lower stratosphere over a broad latitude range (60°N–70°S) during two different seasons (March and October) in 1994. Both NOy and O3 mixing ratios show a strong latitude dependence, with values increasing toward the poles. The NOy/O3 ratio reveals a high‐gradient region near the tropics that is not well‐represented in standard 2‐D photochemical transport models. Improving the representation by changing the horizontal eddy‐diffusion coefficients near the tropics has important implications for the predicted impacts of aircraft emissions on stratospheric O3.}, number={13}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Fahey, D. W. and Donnelly, S. G. and Keim, E. R. and Gao, R. S. and Wamsley, R. C. and Del Negro, L. A. and Woodbridge, E. L. and Proffitt, M. H. and Rosenlof, K. H. and Ko, M. K. W. and et al.}, year={1996}, month={Jun}, pages={1653–1656} }
 @article{dye_baumgardner_gandrud_drdla_barr_fahey_delnegro_tabazadeh_jonsson_wilson_et al._1996, title={In-situ observations of an Antarctic polar stratospheric cloud: Similarities with Arctic observations}, volume={23}, DOI={10.1029/96gl01812}, abstractNote={Measured particle volumes in a type I polar stratospheric cloud near the Antarctic polar vortex during ASHOE/MAESA show that the onset of the cloud occurred near 193 K, 3 degrees colder than nitric acid trihydrate (NAT) saturation. The onset temperature, the smooth increase of volume with decreasing temperature, the inverse correlation of particle volume and enhanced NOy (HNO3 in the particles) with temperature, and comparisons of observations with an equilibrium model of ternary droplet growth all support the notion that much of this type I PSC was ternary solution droplets. This provides confirmation of previous findings in the northern hemisphere. However, the ternary model does not fit the observations in all regions. This may be due to the presence of some solid phase growth in agreement with impactor observations.}, number={15}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Dye, J. E. and Baumgardner, D. and Gandrud, B. W. and Drdla, K. and Barr, K. and Fahey, D. W. and Delnegro, L. A. and Tabazadeh, A. and Jonsson, H. H. and Wilson, J. C. and et al.}, year={1996}, month={Jul}, pages={1913–1916} }
 @article{keim_fahey_negro_woodbridge_gao_wennberg_cohen_stimpfle_kelly_hintsa_et al._1996, title={Observations of large reductions in the NO/NOyratio near the mid-latitude tropopause and the role of heterogeneous chemistry}, volume={23}, DOI={10.1029/96gl02593}, abstractNote={During the 1993 NASA Stratospheric Photochemistry, Aerosols and Dynamics Expedition (SPADE), anomalously low nitric oxide (NO) was found in a distinct sunlit layer located above the mid‐latitude tropopause. The presence of a significant amount of reactive nitrogen (NOy) in the layer implies the systematic removal of NO, which is without precedent in stratospheric in situ observations. Large increases in measured chlorine monoxide (ClO) and the hydroperoxyl radical (HO2) also were observed in the layer. Heterogeneous reaction rate constants of chlorine nitrate (ClONO2) with hydrogen chloride (HCl) and H2O to form nitric acid (HNO3) on sulfate aerosol are enhanced in the NO removal layer by local increases in H2O and aerosol surface area. The associated conversion of NOx (= NO + NO2) to HNO3 is the most likely cause of the observed low NO and NOx/NOy values and high ClO values.}, number={22}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Keim, E. R. and Fahey, D. W. and Negro, L. A. Del and Woodbridge, E. L. and Gao, R. S. and Wennberg, P. O. and Cohen, R. C. and Stimpfle, R. M. and Kelly, K. K. and Hintsa, E. J. and et al.}, year={1996}, month={Nov}, pages={3223–3226} }
 @article{fahey_keim_boering_brock_wilson_jonsson_anthony_hanisco_wennberg_miake-lye_et al._1995, title={Emission Measurements of the Concorde Supersonic Aircraft in the Lower Stratosphere}, volume={270}, DOI={10.1126/science.270.5233.70}, abstractNote={
            Emission indices of reactive gases and particles were determined from measurements in the exhaust plume of a Concorde aircraft cruising at supersonic speeds in the stratosphere. Values for NO
            x
            (sum of NO and NO
            2
            ) agree well with ground-based estimates. Measurements of NO
            x
            and HO
            x
            indicate a limited role for nitric acid in the plume. The large number of submicrometer particles measured implies efficient conversion of fuel sulfur to sulfuric acid in the engine or at emission. A new fleet of supersonic aircraft with similar particle emissions would significantly increase stratospheric aerosol surface areas and may increase ozone loss above that expected for NO
            x
            emissions alone.
          }, number={5233}, journal={Science}, publisher={American Association for the Advancement of Science (AAAS)}, author={Fahey, D. W. and Keim, E. R. and Boering, K. A. and Brock, C. A. and Wilson, J. C. and Jonsson, H. H. and Anthony, S. and Hanisco, T. F. and Wennberg, P. O. and Miake-Lye, R. C. and et al.}, year={1995}, month={Oct}, pages={70–74} }