Measurements of the mass concentration and chemical speciation of aerosols are important to inves... more Measurements of the mass concentration and chemical speciation of aerosols are important to investigate their chemical and physical processing from near emission sources to the most remote regions of the atmosphere. A common method to analyze aerosols is to collect them onto filters and to analyze filters off-line; however, biases in some chemical components are possible due to changes in the accumulated particles during the handling of the samples. Any biases would impact the measured chemical composition, which in turn affects our understanding of numerous physico-chemical processes and aerosol radiative properties. We show, using filters collected onboard the NASA DC-8 and NSF C-130 during six different aircraft campaigns, a consistent, substantial difference in ammonium mass concentration and ammonium-to-anion ratios, when comparing the aerosols collected on filters versus the Aerodyne Aerosol Mass Spectrometer (AMS). Another on-line measurement is consistent with the AMS in showing that the aerosol has lower ammonium-to-anion ratios than obtained by the filters. Using a gas uptake model with literature values for accommodation coefficients, we show that for ambient ammonia mixing ratios greater than 10 ppbv, the time scale for ammonia reacting with acidic aerosol on filter substrates is less than 30 s (typical filter handling time in the aircraft) for typical aerosol volume distributions. Measurements of gas-phase ammonia inside the cabin of the DC-8 show ammonia mixing ratios of 45±20 ppbv, consistent with mixing ratios observed in other indoor environments. This analysis enables guidelines for filter handling to reduce ammonia uptake. Finally, a more meaningful limit-of-detection for filters that either do not have an ammonia scrubber and/or are handled in the presence of human emissions is ~0.2 μg m -3 ammonium, which is substantially higher than the limit-of-detection of the ion chromatography.
Aerosol intercomparisons are inherently complex, as they convolve instrument-dependent detection ... more Aerosol intercomparisons are inherently complex, as they convolve instrument-dependent detection efficiencies vs. size (which often change with pressure, temperature, or humidity) and variations on the sampled aerosol population, in addition to differences in chemical detection principles (e.g., including inorganic-only nitrate vs. inorganic plus organic nitrate for two instruments). The NASA Atmospheric Tomography Mission (ATom) spanned four separate aircraft deployments, which sampled the remote marine troposphere from 86°S to 82°N over different seasons with a wide range of aerosol concentrations and compositions. Aerosols were quantified with a set of carefully characterized and calibrated instruments, some based on particle sizing and some on composition measurements. This study aims to provide a critical evaluation of the size-related factors impacting aerosol intercomparisons, and of aerosol quantification during ATom, with a focus on the Aerosol Mass Spectrometer (AMS). The volume determined from physical sizing instruments is compared in detail with that derived from the chemical measurements of the AMS and the Single Particle Soot Photometer (SP2). Special attention was paid to characterize the upper end of the AMS size-dependent transmission with in-field calibrations, which we show to be critical for accurate comparisons across instruments with inevitably different size cuts. Observed differences between campaigns emphasize the importance of characterizing AMS transmission for each instrument and field study for meaningful interpretation of instrument comparisons. Good agreement was found between the composition-based volume (including AMS-quantified sea salt) and that derived from the size spectrometers. The very clean conditions during most of ATom resulted in substantial statistical noise (i.e., precision error), which we show to be substantially reduced by averaging at several-minute time intervals. The AMS captured, on average, 95 ± 15% of the standard PM1 volume. These results support the absence of significant unknown biases and the appropriateness of the accuracy estimates for AMS total mass/volume for the mostly aged air masses encountered in ATom. The particle size ranges that contribute chemical composition information to the AMS and complementary composition instruments are investigated, to inform their use in future studies.
The cutoff sizes of selected submicron measurements Table : The cutoff sizes of AMS, URG PM1 cycl... more The cutoff sizes of selected submicron measurements Table : The cutoff sizes of AMS, URG PM1 cyclones, MOUDI 1 μm stage impactor, and SAGA MC at two dry aerosol densities: 1.7 g cm -3 of ATom-2 campaign average and 0.9 g cm -3 of typical oily particles . For AMS, the cut sizes in dva are native and the other two sizes are calculated with Eqs. 1-2 in the main text (here only the upper side is listed); for URG, MOUDI, and SAGA MC, the cut sizes in dta are native; for MOUDI, the cut sizes in dp are calculated using Eq. 5.28 in Hinds ( ): 𝑑 50 = √ 9𝜂𝐷 𝑗 (𝑆𝑡𝑘 50 ) 𝜌 𝑝 𝑈𝐶 𝑐 . For circular jets such as MOUDI, 50% collection efficiency corresponds to Stokes Number, Stk50, of 0.24. η is air viscosity, Dj is the nozzle size (0.78 mm) (Marple et al., 2014), U is air velocity (a nominal volumetric flow of 30 L m -3 gives 26.16 m s -1 with 40 nozzles at the size of 0.78 mm). The equation is also used to estimate the d50 for SAGA MC by dividing the formulas between two conditions, and the base case gives dta,sea,50 of 1 μm (van Donkelaar et al., 2008) (discussed below at Sect. 10). Since the conversion of dp or dva to dta is pressure dependent, dta at sea level, 6 km, and 12 km are calculated for AMS, MOUDI, and SAGA MC. The P at 6 km and 12 km are based on the U.S. standard atmosphere, 467 mbar and 185 mbar, respectively (NOAA, NASA, U. S. Air Force, 1976). Dry Aerosol density 1.7 [g cm -3 ] 0.9 [g cm -3 ] Diameter [nm] d p,50 d ta,sea,50 d ta,air,50 (6/12km) d va,50 d p,50 d ta,sea,50 d ta,air,50 (6/12km) d va,50
Journal of Geophysical Research: Atmospheres, 2022
Biomass burning (BB) events are occurring globally with increasing frequency, and their emissions... more Biomass burning (BB) events are occurring globally with increasing frequency, and their emissions are having more impacts on human health and climate. Large ash particles are recognized as a BB product with major influences on soil and water environments. However, fine‐ash particles, which have diameters smaller than several microns and characteristic morphologies and compositions (mainly Ca and Mg carbonates), have not yet been explicitly considered as a major BB aerosol component either in field observations or climate models. This study measured BB aerosol samples using transmission electron microscopy (TEM) and ion chromatography during the Fire Influence on Regional to Global Environments and Air Quality (FIREX‐AQ) campaign. We show that significant amounts of fine ash‐bearing particles are transported >100 km from their fire sources. Our environmental chamber experiments suggest that they can act as cloud condensation and ice nuclei. We also found considerable amounts of fi...
emissions inventory based on these documents - 2 GEOS-Chem species definitions are provided here:... more emissions inventory based on these documents - 2 GEOS-Chem species definitions are provided here: chem/index.php/Species_in_GEOS-Chem 3 Pers. Communication, Isobel Simpson 4 Conversion from SAPRC99 species carbon number to GEOS-Chem species carbon number
Geostationary satellite measurements of aerosol optical depth (AOD) over East Asia from the Geost... more Geostationary satellite measurements of aerosol optical depth (AOD) over East Asia from the Geostationary Ocean Color Imager (GOCI) and Advanced Himawari Imager (AHI) instruments can augment surface monitoring of fine particulate matter (PM 2.5 ) air quality, but this requires better understanding of the AOD-PM 2.5 relationship. Here we use the GEOS-Chem chemical transport model to analyze the critical variables determining the AOD-PM 2.5 relationship over East Asia by simulation of observations from satellite, aircraft, and ground-based datasets. This includes the detailed vertical aerosol profiling over South Korea from the KORUS-AQ aircraft campaign (May-June 2016) with concurrent ground-based PM 2.5 composition, PM 10 , and AERONET AOD measurements. The KORUS-AQ data show that 550 nm AOD is mainly contributed by sulfatenitrate-ammonium (SNA) and organic aerosols in the planetary boundary layer (PBL), despite large dust concentrations in the free troposphere, reflecting the optically effective size and high hygroscopicity of the PBL aerosols. We updated SNA and organic aerosol size distributions in GEOS-Chem to represent aerosol optical properties over East Asia by using in situ measurements of particle size distributions from KORUS-AQ. We find that SNA and organic aerosols over East Asia have larger size (number median radius of 0.11 µm with geometric standard deviation of 1.4) and 20 % larger mass extinction efficiency as compared to aerosols over North America (default setting in GEOS-Chem). Although GEOS-Chem is successful in reproducing the KORUS-AQ vertical profiles of aerosol mass, its ability to link AOD to PM 2.5 is limited by under-accounting of coarse PM and by a large overestimate of nighttime PM 2.5 nitrate. The GOCI-AHI AOD data over East Asia in different seasons show agreement with AERONET AODs and a spatial distribution consistent with surface PM 2.5 network data. The AOD observations over North China show a summer maximum and winter minimum, opposite in phase to surface PM 2.5 . This is due to low PBL depths compounded by high residential coal emissions in winter and high relative humidity (RH) in summer. Seasonality of AOD and PM 2.5 over South Korea is much weaker, reflecting weaker variation in PBL depth and lack of residential coal emissions.
Using a new approach that constrains thermodynamic modeling of aerosol composition with measured ... more Using a new approach that constrains thermodynamic modeling of aerosol composition with measured gas-to-particle partitioning of inorganic nitrate, we estimate the acidity levels for aerosol sampled in the South Korean planetary boundary layer during the NASA/NIER KORUS-AQ field campaign. The pH (mean ± 1σ = 2.43±0.68) and aerosol liquid water content determined were then used to determine the "chemical regime" of the inorganic fraction of particulate matter (PM) sensitivity to ammonia and nitrate availability. We found that the aerosol formation is always sensitive to HNO3 levels, especially in highly polluted regions, while it is only exclusively sensitive to NH3 in some rural/remote regions. Nitrate levels are further promoted because dry deposition velocity is low and allows its accumulation in the boundary layer. Because of this, HNO3 reductions achieved by NOx controls prove to be the most effective approach for all conditions examined, and that NH3 emissions can only partially affect PM reduction for the specific season and region. Despite the benefits of controlling PM formation to reduce ammoniumnitrate aerosol and PM mass, changes in the acidity domain can significantly affect other processes and sources of aerosol toxicity (such as e.g., solubilization of Fe, Cu and other metals) as well as the deposition patterns of these trace species and reactive nitrate.
Atmospheric Chemistry and Physics Discussions, 2016
Formation of ozone and organic aerosol in continental atmospheres depends on whether isoprene emi... more Formation of ozone and organic aerosol in continental atmospheres depends on whether isoprene emitted by vegetation is oxidized by the high-NO x pathway (where peroxy radicals react with NO) or by low-NO x pathways (where peroxy radicals react by alternate channels, mostly with HO 2 ). We used mixed layer observations from the SEAC 4 RS aircraft campaign over the Southeast US to test the ability of the GEOS-Chem chemical transport model at different grid resolutions to simulate this chemistry under high-isoprene, variable-NO x conditions. Observations of isoprene and NO x over the Southeast US show a negative correlation, reflecting in part the spatial segregation of emissions; this negative correlation is captured in the model at 0.25 • × 0.3125 • resolution but not at coarser resolutions. As a result, less isoprene oxidation takes place by the high-NO x pathway in the model at 0.25 • × 0.3125 • resolution (54%) than at coarser resolution (59%). The cumulative probability distribution functions (CDFs) of NO x , isoprene, and ozone concentrations show little difference across model resolutions and good agreement with observations, while formaldehyde is overestimated at coarse resolution because excessive isoprene oxidation takes place by the high-NO x pathway (which has high formaldehyde yield). Correlations of simulated vs. observed concentrations do not improve with grid resolution because finer modes of variability are intrinsically more difficult to capture. Higher model resolution leads to decreased conversion of NO x to organic nitrates and increased conversion to nitric acid, with total reactive nitrogen oxides (NO y ) changing little across model resolutions. In the lower free troposphere, model output is similarly insensitive to grid resolution, indicating that the effect on export of ozone 1
Aerosol sulfate is a major component of submicron particulate matter (PM 1 ). Sulfate can be pres... more Aerosol sulfate is a major component of submicron particulate matter (PM 1 ). Sulfate can be present as inorganic (mainly ammonium sulfate, AS) or organic sulfate (OS). Although OS are thought to be a smaller fraction of total sulfate in most cases, recent literature argues that this may not be the case in more polluted environments. Aerodyne Aerosol Mass Spectrometers (AMS) measure total submicron sulfate, but it has been difficult to apportion AS vs. OS as the detected ion fragments are similar. Recently, two new methods have been proposed to quantify OS separately from AS with AMS data. We use observations collected during several airborne field campaigns covering a wide range of sources and airmass ages (spanning the continental US, marine remote troposphere, and Korea) and targeted laboratory experiments to investigate the performance and validity of the proposed OS methods. Four chemical regimes are defined to categorize the factors impacting sulfate fragmentation (Fig. shown in abstract). In polluted areas with high ammonium nitrate concentrations and in remote areas with high aerosol acidity, the decomposition and fragmentation of sulfate in the AMS is influenced by multiple complex effects, and estimation of OS does not seem possible with current methods . In regions with lower acidity (pH>0) and ammonium nitrate (fraction<0.3), the proposed OS methods might be more reliable, although application of these methods often produced nonsensical results. However, the fragmentation of ambient neutralized sulfate varies somewhat within studies, adding uncertainty, possibly due to variations in the effect of organics. Under highly acidic conditions, sulfate fragment ratios show a clear relationship with acidity (pH and ammonium balance). The measured ammonium balance (and to a lesser extent, the H y SO x + /SO x + AMS ratio) is a promising indicator for rapid estimation of aerosol pH < 0, including when gas-phase NH 3 and HNO 3 are not available. These results allow an improved understanding of important intensive properties of ambient aerosols.
The UNH investigation during TRACE-P provided measurements of selected acidic gases and aerosol s... more The UNH investigation during TRACE-P provided measurements of selected acidic gases and aerosol species aboard the NASA DC-8 research aircraft. Our investigation fwused on measuring "03, S02, and fine (<2 pm) aerosol SO,'with two minute time resolution in near-real-time. We also quantified mixing ratios of aerosol ionic species, and aerosol 21@Pb and 7Be collected onto bulk filters at better than 10 minute resolution. This suite of measurements contributed extensively to achieving the principal objectives of TRACE-P. In the context of the full data set collected by experimental teams on the DC-8, our observations provide a solid basis for assessing decadal changes in the chemical composition and source strength of Asian continental outflow. This iegon ofthe Pacific should be k p i c t & pidotindly by Asian emissions at this time with significant degradation of air quality over the next few decades. Atmospheric measurements in the western Pacific region will provide a valuable time series to help quantify the impact of Asian anthropogenic activities. Our data also provide important insight into the chemical and physical processes transforming Asian outflow during transport over the Pacific, particularly uptake and reactions of soluble gases on aerosol particles. In addition, the TRACE-P data set provide strong constraints for assessing and improving the chemical fields simulated by chemical transport models.
The SASS Ozone and Nitrogen Oxides Experiment (SONEX) over the North Atlantic during October/Nove... more The SASS Ozone and Nitrogen Oxides Experiment (SONEX) over the North Atlantic during October/November 1997 offered an excellent opportunity to examine the budget of total reactive nitrogen (NOy) inthe upper troposphere (8 -12 km altitude). The median measured NOy mixing ratio was 425 parts per trillion by volume (pptv). Two different methods were used to measure HNO3: (1) the mist chamber technique and, (2) chemical ionization mass spectrometry. Two merged data sets using these HNO3 measurements were used to calculate NO r by summing the reactive nitrogen species (a combination of measured plus modeled results) and comparing the resultant values to measured NOy (gold catalytic reduction method). Both comparisons showed good agreement in the two quantities (slope > 0.9 and r2 > 0.9). Thus, the total reactive nitrogen budget in the upper troposphere over the North Atlantic can be explained in a general manner as a simple mixture of NOx (NO + NOz), HNO3, and PAN. Median values of NO_/NOy were _0.25, HNO3/NOy =0.35 and PAN/NOy _0.17. Particulate NO 3" and alk-yl nitrates together composed <10% of NOy, while mode/ estimated HNO, averaged 12%.
Accurate representation of aerosol optical properties is essential for the modeling and remote se... more Accurate representation of aerosol optical properties is essential for the modeling and remote sensing of atmospheric aerosols. Although aerosol optical properties are strongly dependent upon the aerosol size distribution, the use of detailed aerosol microphysics schemes in global atmospheric models is inhibited by associated computational demands. Computationally efficient parameterizations for aerosol size are needed. In this study, airborne measurements over the United States (DISCOVER-AQ) and South Korea (KORUS-AQ) are interpreted with a global chemical transport model (GEOS-Chem) to investigate the variation in aerosol size when organic matter (OM) and sulfate-nitrate-ammonium (SNA) are the dominant aerosol components. The airborne measurements exhibit a strong correlation (r = 0.83) between dry aerosol size and the sum of OM and SNA mass concentration (M SNAOM ). A global microphysical simulation (GEOS-Chem-TOMAS) indicates that M SNAOM and the ratio between the two components (OM/SNA) are the major indicators for SNA and OM dry aerosol size. A parameterization of the dry effective radius (R eff ) for SNA and OM aerosol is designed to represent the airborne measurements (R 2 = 0.74; slope = 1.00) and the GEOS-Chem-TOMAS simulation (R 2 = 0.72; slope = 0.81). When applied in the GEOS-Chem high-performance model, this parameterization improves the agreement between the simulated aerosol optical depth (AOD) and the ground-measured AOD from the Aerosol Robotic Network (AERONET; R 2 from 0.68 to 0.73 and slope from 0.75 to 0.96). Thus, this parameterization offers a computationally efficient method to represent aerosol size dynamically.
Improvements in air quality and Earth's climate predictions require improvements of the aerosol s... more Improvements in air quality and Earth's climate predictions require improvements of the aerosol speciation in chemical transport models, using observational constraints. Aerosol speciation (e.g., organic aerosols, black carbon, sulfate, nitrate, ammonium, dust or sea salt) is typically determined using in situ instrumentation. Continuous, routine aerosol composition measurements from ground-based networks are not uniformly widespread over the globe. Satellites, on the other hand, can provide a maximum coverage of the horizontal and vertical atmosphere but observe aerosol optical properties (and not aerosol speciation) based on remote sensing instrumentation. Combinations of satellite-derived aerosol optical properties can inform on air mass aerosol types (AMTs). However, these AMTs are subjectively defined, might often be misclassified and are hard to relate to the critical parameters that need to be refined in models. In this paper, we derive AMTs that are more directly related to sources and hence to speciation. They are defined, characterized and derived using simultaneous in situ gas-phase, chemical and optical instruments on the same aircraft during the Study of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC 4 RS, an airborne field campaign carried out over the US during the summer of 2013). We find distinct optical signatures for AMTs such as biomass burning (from agricultural or wildfires), biogenic and polluted dust. We find that all four AMTs, studied when prescribed using mostly airborne in situ gas measurements, can be successfully extracted from a few combinations of airborne in situ aerosol optical properties (e.g., extinction Ångström exponent, absorption Ångström exponent and real refractive index). However, we Published by Copernicus Publications on behalf of the European Geosciences Union. 3714 M. S. F. Kacenelenbogen et al.: Bridging aerosol chemistry and physics find that the optically based classifications for biomass burning from agricultural fires and polluted dust include a large percentage of misclassifications that limit the usefulness of results related to those classes. The technique and results presented in this study are suitable to develop a representative, robust and diverse source-based AMT database. This database could then be used for widespread retrievals of AMTs using existing and future remote sensing suborbital instruments/networks. Ultimately, it has the potential to provide a much broader observational aerosol dataset to evaluate chemical transport and air quality models than is currently available by direct in situ measurements. This study illustrates how essential it is to explore existing airborne datasets to bridge chemical and optical signatures of different AMTs, before the implementation of future spaceborne missions (e.g., the next generation of Earth Observing System (EOS) satellites addressing Aerosols, Cloud, Convection and Precipitation (ACCP) designated observables).
The Greenland Summit Halogen-HO x (GSHOX) Campaign was performed in spring 2007 and summer 2008 t... more The Greenland Summit Halogen-HO x (GSHOX) Campaign was performed in spring 2007 and summer 2008 to investigate the impact of halogens on HO x (= OH + HO 2 ) cycling above the Greenland Ice Sheet. Chemical species including hydroxyl and peroxy radicals (OH and HO 2 + RO 2 ), ozone (O 3 ), nitrogen oxide (NO), nitric acid (HNO 3 ), nitrous acid (HONO), reactive gaseous mercury (RGM), and bromine oxide (BrO) were measured during the campaign. The median midday values of HO 2 + RO 2 and OH concentrations observed by chemical ionization mass spectrometry (CIMS) were 2.7 × 10 8 molec cm -3 and 3.0 × 10 6 molec cm -3 in spring 2007, and 4.2 × 10 8 molec cm -3 and 4.1 × 10 6 molec cm -3 in summer 2008. A basic photochemical 0-D box model highly constrained by observations of H 2 O, O 3 , CO, CH 4 , NO, and J values predicted HO 2 + RO 2 (R = 0.90, slope = 0.87 in 2007; R = 0.79, slope = 0.96 in 2008) reasonably well and under predicted OH (R = 0.83, slope = 0.72 in 2007; R = 0.76, slope = 0.54 in 2008). Constraining the model to HONO observations did not significantly improve the ratio of OH to HO 2 + RO 2 and the correlation between predictions and observations. Including bromine chemistry in the model constrained by observations of BrO improved the correlation between observed and predicted HO 2 + RO 2 and OH, and brought the average hourly OH and HO 2 + RO 2
The inorganic fraction of fine particles affects numerous physicochemical processes in the atmosp... more The inorganic fraction of fine particles affects numerous physicochemical processes in the atmosphere. However, there is large uncertainty in its burden and composition due to limited global measurements. Here, we present observations from eleven different aircraft campaigns from around the globe and investigate how aerosol pH and ammonium balance change from polluted to remote regions, such as over the oceans. Both parameters show increasing acidity with remoteness, at all altitudes, with pH decreasing from about 3 to about −1 and ammonium balance decreasing from almost 1 to nearly 0. We compare these observations against nine widely used chemical transport models and find that the simulations show more scatter (generally R 2 < 0.50) and typically predict less acidic aerosol in the most remote regions. These differences in observations and predictions are likely to result in underestimating the model-predicted direct radiative cooling effect for sulfate, nitrate, and ammonium aerosol by 15-39%.
Particulate matter was measured during August and September of 2006 in Houston as part of the Tex... more Particulate matter was measured during August and September of 2006 in Houston as part of the Texas Air Quality Study II Radical and Aerosol Measurement Project. Aerosol size and composition were determined using an Aerodyne quadrupole aerosol mass spectrometer. Aerosol was dominated by sulfate (4.1 AE 2.6 mg m À3) and organic material (5.5 AE 4.0 mg m À3), with contributions of organic material from both primary (w32%) and secondary (w68%) sources. Secondary organic aerosol appears to be formed locally. In addition, 29 aerosol filter samples were analyzed using proton nuclear magnetic resonance (1 H NMR) spectroscopy to determine relative concentrations of organic functional groups. Houston aerosols are less oxidized than those observed elsewhere, with smaller relative contributions of carbon-oxygen double bonds. These particles do not fit 1 H NMR source apportionment fingerprints for identification of secondary, marine, and biomass burning organic aerosol, suggesting that a new fingerprint for highly urbanized and industrially influenced locations be established.
Journal Of Geophysical Research: Atmospheres, Sep 6, 2018
Although urban NO x lifetimes have been examined extensively during summertime conditions, winter... more Although urban NO x lifetimes have been examined extensively during summertime conditions, wintertime NO x chemistry has been comparatively less studied. We use measurements of NO x and its oxidation products from the aircraft-based WINTER (Wintertime INvestigation of Transport, Emissions, and Reactivity) experiment over the northeastern United States during February-March 2015 to describe the NO x lifetime during conditions when days are shorter, actinic flux is reduced, and temperatures are colder. By analyzing regional outflow from the East Coast, we show that NO x is long lived during the winter, with a longer daytime lifetime (29 hr) than nighttime lifetime (6.3 hr). We demonstrate that wintertime NO x emissions have an overall lifetime controlled by the nighttime conversion of NO x to nitric acid (HNO 3) via N 2 O 5 heterogeneous chemistry, and we discuss constraints on the rates of NO x conversion to HNO 3. Additionally, analysis of the nighttime O x budget suggests that approximately 15% of O 3 is lost overnight through N 2 O 5 production and subsequent reaction with aerosol to form HNO 3. Plain Language Summary The atmospheric lifetime (how long something persists in the atmosphere) and fate of nitrogen oxides in urban areas during the summer has been studied extensively, but relatively few studies have looked at the lifetime of nitrogen oxides in the atmosphere during winter. We use aircraft data from the East Coast of the United States during February-March 2015 to characterize the wintertime lifetime of nitrogen oxides when days are shorter, sunlight is reduced, and temperatures are colder. We are able to measure the wintertime lifetime of nitrogen oxides and assess the relative roles of mixing, deposition, and chemistry on their fate. We determine that nitrogen oxide loss during winter is dominated by nighttime rather than daytime chemistry and that this nighttime chemistry effectively removes ozone from the atmosphere. NO x is emitted to the atmosphere as NO both anthropogenically, through fossil fuel combustion, agriculture, and biomass burning (e.g.
EGU General Assembly Conference Abstracts, Apr 1, 2012
Sunlit snow is increasingly recognized as a chemical reactor that plays an active role in uptake,... more Sunlit snow is increasingly recognized as a chemical reactor that plays an active role in uptake, transformation, and release of atmospheric trace gases. Snow is known to influence boundary layer air on a local scale, and given the large global surface coverage of snow may also be significant on regional and global scales. We present a new detailed one-dimensional snow chemistry module that has been coupled to the 1-D atmospheric boundary layer model MISTRA. The new 1-D snow module, which is dynamically coupled to the overlaying atmospheric model, includes heat transport in the snowpack, molecular diffusion, and wind pumping of gases in the interstitial air. The model includes gas phase chemical reactions both in the interstitial air and the atmosphere. Heterogeneous and multiphase chemistry on atmospheric aerosol is considered explicitly. The chemical interaction of interstitial air with snow grains is simulated assuming chemistry in a liquid-like layer (LLL) on the grain surface. The coupled model, referred to as MISTRA-SNOW, was used to investigate snow as the source of nitrogen oxides (NO x) and gas phase reactive bromine in the atmospheric boundary layer in the remote snow covered Arctic (over the Greenland ice sheet) as well as to investigate the link between halogen cycling and ozone depletion that has been observed in interstitial air. The model is validated using data taken 10 June
Uploads
Papers by Jack Dibb