Stephen D Steenrod | NASA Goddard Space Flight Center (original) (raw)
Papers by Stephen D Steenrod
Unexpected Repartitioning of Stratospheric Inorganic Chlorine After the 2020 Australian Wildfires
Geophysical Research Letters
Satellite-based retrievals of tropospheric NO 2 columns are widely used to infer NO x (≡ NO + NO ... more Satellite-based retrievals of tropospheric NO 2 columns are widely used to infer NO x (≡ NO + NO 2) emissions. These retrievals rely on model information for the vertical distribution of NO 2. The free tropospheric background above 2 km is particularly important because the sensitivity of the retrievals increases with altitude. Free tropospheric NO x also has a strong effect on tropospheric OH and ozone concentrations. Here we use observations from three aircraft campaigns (SEAC 4 RS, DC3, and ATom) and four atmospheric chemistry models (GEOS-Chem, GMI, TM5, and CAMS) to evaluate the model capabilities for simulating NO x in the free troposphere and attribute it to sources. NO 2 measurements during the Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC 4 RS) and Deep Convective Clouds and Chemistry (DC3) campaigns over the southeastern U.S. in summer show increasing concentrations in the upper troposphere above 10 km, which are not replicated by the GEOS-Chem, although the model is consistent with the NO measurements. Using concurrent NO, NO 2 , and ozone observations from a DC3 flight in a thunderstorm outflow, we show that the NO 2 measurements in the upper troposphere are biased high, plausibly due to interference from thermally labile NO 2 reservoirs such as peroxynitric acid (HNO 4) and methyl peroxy nitrate (MPN). We find that NO 2 concentrations calculated from the NO measurements and NO-NO 2 photochemical steady state (PSS) are more reliable to evaluate the vertical profiles of NO 2 in models. GEOS-Chem reproduces the shape of the PSS-inferred NO 2 profiles throughout the troposphere for SEAC 4 RS and DC3 but overestimates NO 2 concentrations by about a factor of 2. The model underestimates MPN and alkyl nitrate concentrations, suggesting missing organic NO x chemistry. On the other hand, the standard GEOS-Chem model underestimates NO observations from the Atmospheric Tomography Mission (ATom) campaigns over the Pacific and Atlantic oceans, indicating a missing NO x source over the oceans. We find that we can account for this missing source by including in the model the photolysis of particulate nitrate on sea salt aerosols at rates inferred from laboratory studies and field observations of nitrous acid (HONO) over the Atlantic. The median PSS-inferred tropospheric NO 2 column density for the ATom campaign is 1.7 ± 0.44 × 10 14 molec. cm −2 , and the NO 2 column density simulated by the four models is in the range of 1.4-2.4 × 10 14 molec. cm −2 , implying that the uncertainty from using modeled NO 2 tropospheric columns over clean areas in the retrievals for stratosphere-troposphere separation is about 1 × 10 14 molec. cm −2. We find from GEOS-Chem that lightning is the main primary NO x source in the free troposphere over the tropics and southern midlatitudes, but aircraft emissions dominate at northern midlatitudes in winter and in summer over the oceans. Particulate nitrate photolysis increases ozone concentrations by up to 5 ppbv (parts per billion by volume) in the free troposphere in the northern extratropics in the model, which would largely correct the low model bias relative to ozonesonde observations. Global tropospheric OH concentrations increase by 19 %. The contribution of the free tropospheric background to the tropospheric NO 2 columns observed by satellites over the contiguous U.S. increases from 25 ± 11 % in winter to 65 ± 9 % in summer, according to the GEOS-Chem vertical profiles. This needs to be accounted for when deriving NO x emissions from satellite NO 2 column measurements.
Aerosol-Chemistry Interactions: Biomass burning events in South East Asia
AGU Fall Meeting Abstracts, Dec 1, 2012
How Stratospheric Chemistry and Transport Drive Surface Variability of N 2 O
AGU Fall Meeting Abstracts, Dec 1, 2019
Unusually Low Chlorine in the 2011 Antarctic Vortex
AGU Fall Meeting Abstracts, Dec 1, 2013
Atmospheric Chemistry and Physics, 2021
The NASA Atmospheric Tomography (ATom) mission built a photochemical climatology of air parcels b... more The NASA Atmospheric Tomography (ATom) mission built a photochemical climatology of air parcels based on in situ measurements with the NASA DC-8 aircraft along objectively planned profiling transects through the middle of the Pacific and Atlantic oceans. In this paper we present and analyze a data set of 10 s (2 km) merged and gap-filled observations of the key reactive species driving the chemical budgets of O 3 and CH 4 (O 3 , CH 4 , CO, H 2 O, HCHO, H 2 O 2 , CH 3 OOH, C 2 H 6 , higher alkanes, alkenes, aromatics, NO x , HNO 3 , HNO 4 , peroxyacetyl nitrate, other organic nitrates), consisting of 146 494 distinct air parcels from ATom deployments 1 through 4. Six models calculated the O 3 and CH 4 photochemical tendencies from this modeling data stream for ATom 1. We find that 80 %-90 % of the total reactivity lies in the top 50 % of the parcels and 25 %-35 % in the top 10 %, supporting previous model-only studies that tropospheric chemistry is driven by a fraction of all the air. In other words, accurate simulation of the least reactive 50 % of the troposphere is unimportant for global budgets. Surprisingly, the probability densities of species and reactiv-Published by Copernicus Publications on behalf of the European Geosciences Union.
Chemical Reactivity in the Remote Troposphere: Patterns and Heterogeneity based on ATom measurements
Background ● The Global Modeling Initiative (GMI) supports the development of a state-of-the-art ... more Background ● The Global Modeling Initiative (GMI) supports the development of a state-of-the-art modular 3-D chemistry and transport model (CTM) ● The Atmospheric Tomography Mission (ATom) studies the impact of human-produced air pollution on chemically reactive gases in the atmosphere ● Airborne instruments onboard ATom campaign flights observe how atmospheric chemistry is transformed by air pollutants ● ATom air parcel measurements of key chemical species inform the CTM community about fine-scale atmospheric structures that matter to ozone (O3) and methane (CH4) budgets ● CTM communities to further determine how chemical species are affected by pollution
Chemical Patterns Controlling Tropospheric Ozone and Methane: The ATom Data Set
Bulletin of the American Meteorological Society, 2021
This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary... more This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary of selected scientific findings to date. ATom was an airborne measurements and modeling campaign aimed at characterizing the composition and chemistry of the troposphere over the most remote regions of the Pacific, Southern, Atlantic, and Arctic Oceans, and examining the impact of anthropogenic and natural emissions on a global scale. These remote regions dominate global chemical reactivity and are exceptionally important for global air quality and climate. ATom data provide the in situ measurements needed to understand the range of chemical species and their reactions, and to test satellite remote sensing observations and global models over large regions of the remote atmosphere. Lack of data in these regions, particularly over the oceans, has limited our understanding of how atmospheric composition is changing in response to shifting anthropogenic emissions and physical climate change...
Journal of Geophysical Research: Atmospheres, 2021
The mean time since air last contacted the midlatitude surface layer of the Northern Hemisphere (... more The mean time since air last contacted the midlatitude surface layer of the Northern Hemisphere (NH)-the mean age from the NH surface (Waugh et al., 2013)-is a fundamental measure of troposphere transport. Unlike more conventional global metrics, like the hemispherically integrated interhemispheric exchange time (e.g., Geller et al., 1997; Levin & Hesshaimer, 1996), the mean age provides a much richer (three-dimensional) description of interhemispheric transport (IHT).
Journal of Geophysical Research: Atmospheres, 2021
Nitrous oxide (N 2 O) is a long-lived greenhouse gas that directly affects climate and participat... more Nitrous oxide (N 2 O) is a long-lived greenhouse gas that directly affects climate and participates in stratospheric ozone depletion, further altering atmospheric composition and posing a threat to human health and society. Agricultural practices and fossil fuel combustion have played important roles in increasing the global burden of fixed nitrogen (Erisman et al., 2013), leading to a steady increase in atmospheric N 2 O abundance over the last 50 years (
Journal of the Atmospheric Sciences, 2016
The distribution of transit times from the Northern Hemisphere (NH) midlatitude surface is a fund... more The distribution of transit times from the Northern Hemisphere (NH) midlatitude surface is a fundamental property of tropospheric transport. Here, the authors present an analysis of the transit-time distribution (TTD) since air last contacted the NH midlatitude surface, as simulated by the NASA Global Modeling Initiative Chemistry Transport Model. Throughout the troposphere, the TTD is characterized by young modes and long tails. This results in mean transit times or “mean ages” Γ that are significantly larger than their corresponding modal transit times or “modal ages” τmode, especially in the NH, where Γ ≈ 0.5 yr, while τmode < 20 days. In addition, the shape of the TTD changes throughout the troposphere as the ratio of the spectral width Δ—the second temporal moment of the TTD—to the mean age decreases sharply in the NH from ~2.5 at NH high latitudes to ~0.7 in the Southern Hemisphere (SH). Decreases in Δ/Γ in the SH reflect a narrowing of the TTD relative to its mean and phys...
Journal of Geophysical Research: Atmospheres, 2014
This article has been accepted for publication and undergone full peer review but has not been th... more This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as
Ozone Trends from TOMS and SBUV data: Comparison to 3D Chemical-Transport Model Results
ABSTRACT
Atmospheric Chemistry and Physics, 2015
Using observations from aircraft, surface stations and a satellite instrument, we comprehensively... more Using observations from aircraft, surface stations and a satellite instrument, we comprehensively evaluate multi-model simulations of carbon monoxide (CO) and ozone (O 3) in the Arctic and over lower latitude emission regions, as part of the POLARCAT Model Intercomparison Project (POLMIP). Evaluation of 11-atmospheric models with chemistry shows that they generally underestimate CO throughout the Arctic troposphere, with the largest biases found during winter and spring. Negative CO biases are also found throughout the Northern Hemisphere, with multi-model mean gross errors (9-12 %) suggesting models perform similarly over Asia, North America and Europe. A multi-model annual mean tropospheric OH (10.8 ± 0.6 × 10 5 molec cm −3) is found to be slightly higher than previous estimates of OH constrained by methyl chloroform, suggesting negative CO biases in models may be improved through better constraints on OH. Models that have www.atmos-chem-phys.net/15/3575/2015/ Atmos. Chem.
Atmospheric Chemistry and Physics Discussions, 2014
Ozone (O 3) concentrations in the lower troposphere (LT) over Beijing have significantly increase... more Ozone (O 3) concentrations in the lower troposphere (LT) over Beijing have significantly increased over the past 2 decades as a result of rapid industrialization in China, with important implications for regional air quality and the photochemistry of the background troposphere. We characterize the vertical distribution of lower-tropospheric (0-6 km) O 3 over Beijing using observations from 16 ozonesonde soundings during a field campaign in April-May 2005 and MOZAIC (Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft) over 13 days in the same period. We focus on the origin of LT O 3 enhancements observed over Beijing, particularly in May. We use a global 3-D chemistry and transport model (GEOS-Chem CTM; GEOS-Goddard Earth Observing System) driven by assimilated meteorological fields to examine the transport pathways for O 3 pollution and to quantify the sources contributing to O 3 and its enhancements in the springtime LT over Beijing. Output from the Global Modeling Initiative (GMI) CTM is also used. High O 3 concentrations (up to 94.7 ppbv) were frequently observed at the altitude of ∼ 1.5-2 km. The CTMs captured the timing of the occurrences but significantly underestimated their magnitude. GEOS-Chem simulations and a case study showed that O 3 produced in the Asian troposphere (especially from Asian anthropogenic pollution) made major contributions to the observed O 3 enhancements. Contributions from anthropogenic pollution in the European and North American troposphere were reduced during these events, in contrast with days without O 3 enhancements when contributions from Europe and North America were substantial. The O 3 enhancements typically occurred under southerly wind and warmer conditions. It is suggested that an earlier onset of the Asian summer monsoon would cause more O 3 enhancement events in the LT over the North China Plain in late spring and early summer.
Atmospheric Chemistry and Physics, 2015
We have evaluated tropospheric ozone enhancement in air dominated by biomass burning emissions at... more We have evaluated tropospheric ozone enhancement in air dominated by biomass burning emissions at high latitudes ( > 50 • N) in July 2008, using 10 global chemical transport model simulations from the POLMIP multimodel comparison exercise. In model air masses dominated by fire emissions, O 3 / CO values ranged between 0.039 and 0.196 ppbv ppbv -1 (mean: 0.113 ppbv ppbv -1 ) in freshly fire-influenced air, and between 0.140 and 0.261 ppbv ppbv -1 (mean: 0.193 ppbv) in more aged fireinfluenced air. These values are in broad agreement with the range of observational estimates from the literature. Model PAN/ CO enhancement ratios show distinct groupings according to the meteorological data used to drive the models. ECMWF-forced models produce larger PAN/ CO values (4.47 to 7.00 pptv ppbv -1 ) than GEOS5-forced models (1.87 to 3.28 pptv ppbv -1 ), which we show is likely linked to differences in efficiency of vertical transport during poleward export from mid-latitude source regions. Simulations of a large plume of biomass burning and anthropogenic emissions exported from towards the Arctic using a Lagrangian chemical transport model show that 4-day net ozone change in the plume is sensitive to differences in plume chemical composition and plume vertical position among the POLMIP models. In particular, Arctic ozone evolution in the plume is highly sensitive to initial concentrations of PAN, as well as oxygenated VOCs (acetone, acetaldehyde), due to their role in producing the peroxyacetyl radical PAN precursor. Vertical displacement is also important due to its effects on the stability of PAN, and subsequent effect on NO x abundance. In plumes where net ozone production is limited, we find that the lifetime of ozone in the plume is sensitive to hydrogen peroxide loading, due to the production of HO x from peroxide photolysis, and the key role of HO 2 + O 3 in controlling ozone loss. Overall, our results suggest that emissions from biomass burning lead to large-scale photochemical enhancement in high-latitude tropospheric ozone during summer.
Global O3-CO Correlations in the Global Modeling Initiative Chemical Transport Model During July-August: Sensitivity to Emissions and Input Meteorological Data
Use of Tracers to Diagnose Ozone Interannual Variability in the Utls in the Global Modeling Initiative (gmi) Chemistry-Transport Model (ctm) Hindcast
Unexpected Repartitioning of Stratospheric Inorganic Chlorine After the 2020 Australian Wildfires
Geophysical Research Letters
Satellite-based retrievals of tropospheric NO 2 columns are widely used to infer NO x (≡ NO + NO ... more Satellite-based retrievals of tropospheric NO 2 columns are widely used to infer NO x (≡ NO + NO 2) emissions. These retrievals rely on model information for the vertical distribution of NO 2. The free tropospheric background above 2 km is particularly important because the sensitivity of the retrievals increases with altitude. Free tropospheric NO x also has a strong effect on tropospheric OH and ozone concentrations. Here we use observations from three aircraft campaigns (SEAC 4 RS, DC3, and ATom) and four atmospheric chemistry models (GEOS-Chem, GMI, TM5, and CAMS) to evaluate the model capabilities for simulating NO x in the free troposphere and attribute it to sources. NO 2 measurements during the Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys (SEAC 4 RS) and Deep Convective Clouds and Chemistry (DC3) campaigns over the southeastern U.S. in summer show increasing concentrations in the upper troposphere above 10 km, which are not replicated by the GEOS-Chem, although the model is consistent with the NO measurements. Using concurrent NO, NO 2 , and ozone observations from a DC3 flight in a thunderstorm outflow, we show that the NO 2 measurements in the upper troposphere are biased high, plausibly due to interference from thermally labile NO 2 reservoirs such as peroxynitric acid (HNO 4) and methyl peroxy nitrate (MPN). We find that NO 2 concentrations calculated from the NO measurements and NO-NO 2 photochemical steady state (PSS) are more reliable to evaluate the vertical profiles of NO 2 in models. GEOS-Chem reproduces the shape of the PSS-inferred NO 2 profiles throughout the troposphere for SEAC 4 RS and DC3 but overestimates NO 2 concentrations by about a factor of 2. The model underestimates MPN and alkyl nitrate concentrations, suggesting missing organic NO x chemistry. On the other hand, the standard GEOS-Chem model underestimates NO observations from the Atmospheric Tomography Mission (ATom) campaigns over the Pacific and Atlantic oceans, indicating a missing NO x source over the oceans. We find that we can account for this missing source by including in the model the photolysis of particulate nitrate on sea salt aerosols at rates inferred from laboratory studies and field observations of nitrous acid (HONO) over the Atlantic. The median PSS-inferred tropospheric NO 2 column density for the ATom campaign is 1.7 ± 0.44 × 10 14 molec. cm −2 , and the NO 2 column density simulated by the four models is in the range of 1.4-2.4 × 10 14 molec. cm −2 , implying that the uncertainty from using modeled NO 2 tropospheric columns over clean areas in the retrievals for stratosphere-troposphere separation is about 1 × 10 14 molec. cm −2. We find from GEOS-Chem that lightning is the main primary NO x source in the free troposphere over the tropics and southern midlatitudes, but aircraft emissions dominate at northern midlatitudes in winter and in summer over the oceans. Particulate nitrate photolysis increases ozone concentrations by up to 5 ppbv (parts per billion by volume) in the free troposphere in the northern extratropics in the model, which would largely correct the low model bias relative to ozonesonde observations. Global tropospheric OH concentrations increase by 19 %. The contribution of the free tropospheric background to the tropospheric NO 2 columns observed by satellites over the contiguous U.S. increases from 25 ± 11 % in winter to 65 ± 9 % in summer, according to the GEOS-Chem vertical profiles. This needs to be accounted for when deriving NO x emissions from satellite NO 2 column measurements.
Aerosol-Chemistry Interactions: Biomass burning events in South East Asia
AGU Fall Meeting Abstracts, Dec 1, 2012
How Stratospheric Chemistry and Transport Drive Surface Variability of N 2 O
AGU Fall Meeting Abstracts, Dec 1, 2019
Unusually Low Chlorine in the 2011 Antarctic Vortex
AGU Fall Meeting Abstracts, Dec 1, 2013
Atmospheric Chemistry and Physics, 2021
The NASA Atmospheric Tomography (ATom) mission built a photochemical climatology of air parcels b... more The NASA Atmospheric Tomography (ATom) mission built a photochemical climatology of air parcels based on in situ measurements with the NASA DC-8 aircraft along objectively planned profiling transects through the middle of the Pacific and Atlantic oceans. In this paper we present and analyze a data set of 10 s (2 km) merged and gap-filled observations of the key reactive species driving the chemical budgets of O 3 and CH 4 (O 3 , CH 4 , CO, H 2 O, HCHO, H 2 O 2 , CH 3 OOH, C 2 H 6 , higher alkanes, alkenes, aromatics, NO x , HNO 3 , HNO 4 , peroxyacetyl nitrate, other organic nitrates), consisting of 146 494 distinct air parcels from ATom deployments 1 through 4. Six models calculated the O 3 and CH 4 photochemical tendencies from this modeling data stream for ATom 1. We find that 80 %-90 % of the total reactivity lies in the top 50 % of the parcels and 25 %-35 % in the top 10 %, supporting previous model-only studies that tropospheric chemistry is driven by a fraction of all the air. In other words, accurate simulation of the least reactive 50 % of the troposphere is unimportant for global budgets. Surprisingly, the probability densities of species and reactiv-Published by Copernicus Publications on behalf of the European Geosciences Union.
Chemical Reactivity in the Remote Troposphere: Patterns and Heterogeneity based on ATom measurements
Background ● The Global Modeling Initiative (GMI) supports the development of a state-of-the-art ... more Background ● The Global Modeling Initiative (GMI) supports the development of a state-of-the-art modular 3-D chemistry and transport model (CTM) ● The Atmospheric Tomography Mission (ATom) studies the impact of human-produced air pollution on chemically reactive gases in the atmosphere ● Airborne instruments onboard ATom campaign flights observe how atmospheric chemistry is transformed by air pollutants ● ATom air parcel measurements of key chemical species inform the CTM community about fine-scale atmospheric structures that matter to ozone (O3) and methane (CH4) budgets ● CTM communities to further determine how chemical species are affected by pollution
Chemical Patterns Controlling Tropospheric Ozone and Methane: The ATom Data Set
Bulletin of the American Meteorological Society, 2021
This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary... more This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary of selected scientific findings to date. ATom was an airborne measurements and modeling campaign aimed at characterizing the composition and chemistry of the troposphere over the most remote regions of the Pacific, Southern, Atlantic, and Arctic Oceans, and examining the impact of anthropogenic and natural emissions on a global scale. These remote regions dominate global chemical reactivity and are exceptionally important for global air quality and climate. ATom data provide the in situ measurements needed to understand the range of chemical species and their reactions, and to test satellite remote sensing observations and global models over large regions of the remote atmosphere. Lack of data in these regions, particularly over the oceans, has limited our understanding of how atmospheric composition is changing in response to shifting anthropogenic emissions and physical climate change...
Journal of Geophysical Research: Atmospheres, 2021
The mean time since air last contacted the midlatitude surface layer of the Northern Hemisphere (... more The mean time since air last contacted the midlatitude surface layer of the Northern Hemisphere (NH)-the mean age from the NH surface (Waugh et al., 2013)-is a fundamental measure of troposphere transport. Unlike more conventional global metrics, like the hemispherically integrated interhemispheric exchange time (e.g., Geller et al., 1997; Levin & Hesshaimer, 1996), the mean age provides a much richer (three-dimensional) description of interhemispheric transport (IHT).
Journal of Geophysical Research: Atmospheres, 2021
Nitrous oxide (N 2 O) is a long-lived greenhouse gas that directly affects climate and participat... more Nitrous oxide (N 2 O) is a long-lived greenhouse gas that directly affects climate and participates in stratospheric ozone depletion, further altering atmospheric composition and posing a threat to human health and society. Agricultural practices and fossil fuel combustion have played important roles in increasing the global burden of fixed nitrogen (Erisman et al., 2013), leading to a steady increase in atmospheric N 2 O abundance over the last 50 years (
Journal of the Atmospheric Sciences, 2016
The distribution of transit times from the Northern Hemisphere (NH) midlatitude surface is a fund... more The distribution of transit times from the Northern Hemisphere (NH) midlatitude surface is a fundamental property of tropospheric transport. Here, the authors present an analysis of the transit-time distribution (TTD) since air last contacted the NH midlatitude surface, as simulated by the NASA Global Modeling Initiative Chemistry Transport Model. Throughout the troposphere, the TTD is characterized by young modes and long tails. This results in mean transit times or “mean ages” Γ that are significantly larger than their corresponding modal transit times or “modal ages” τmode, especially in the NH, where Γ ≈ 0.5 yr, while τmode < 20 days. In addition, the shape of the TTD changes throughout the troposphere as the ratio of the spectral width Δ—the second temporal moment of the TTD—to the mean age decreases sharply in the NH from ~2.5 at NH high latitudes to ~0.7 in the Southern Hemisphere (SH). Decreases in Δ/Γ in the SH reflect a narrowing of the TTD relative to its mean and phys...
Journal of Geophysical Research: Atmospheres, 2014
This article has been accepted for publication and undergone full peer review but has not been th... more This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as
Ozone Trends from TOMS and SBUV data: Comparison to 3D Chemical-Transport Model Results
ABSTRACT
Atmospheric Chemistry and Physics, 2015
Using observations from aircraft, surface stations and a satellite instrument, we comprehensively... more Using observations from aircraft, surface stations and a satellite instrument, we comprehensively evaluate multi-model simulations of carbon monoxide (CO) and ozone (O 3) in the Arctic and over lower latitude emission regions, as part of the POLARCAT Model Intercomparison Project (POLMIP). Evaluation of 11-atmospheric models with chemistry shows that they generally underestimate CO throughout the Arctic troposphere, with the largest biases found during winter and spring. Negative CO biases are also found throughout the Northern Hemisphere, with multi-model mean gross errors (9-12 %) suggesting models perform similarly over Asia, North America and Europe. A multi-model annual mean tropospheric OH (10.8 ± 0.6 × 10 5 molec cm −3) is found to be slightly higher than previous estimates of OH constrained by methyl chloroform, suggesting negative CO biases in models may be improved through better constraints on OH. Models that have www.atmos-chem-phys.net/15/3575/2015/ Atmos. Chem.
Atmospheric Chemistry and Physics Discussions, 2014
Ozone (O 3) concentrations in the lower troposphere (LT) over Beijing have significantly increase... more Ozone (O 3) concentrations in the lower troposphere (LT) over Beijing have significantly increased over the past 2 decades as a result of rapid industrialization in China, with important implications for regional air quality and the photochemistry of the background troposphere. We characterize the vertical distribution of lower-tropospheric (0-6 km) O 3 over Beijing using observations from 16 ozonesonde soundings during a field campaign in April-May 2005 and MOZAIC (Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft) over 13 days in the same period. We focus on the origin of LT O 3 enhancements observed over Beijing, particularly in May. We use a global 3-D chemistry and transport model (GEOS-Chem CTM; GEOS-Goddard Earth Observing System) driven by assimilated meteorological fields to examine the transport pathways for O 3 pollution and to quantify the sources contributing to O 3 and its enhancements in the springtime LT over Beijing. Output from the Global Modeling Initiative (GMI) CTM is also used. High O 3 concentrations (up to 94.7 ppbv) were frequently observed at the altitude of ∼ 1.5-2 km. The CTMs captured the timing of the occurrences but significantly underestimated their magnitude. GEOS-Chem simulations and a case study showed that O 3 produced in the Asian troposphere (especially from Asian anthropogenic pollution) made major contributions to the observed O 3 enhancements. Contributions from anthropogenic pollution in the European and North American troposphere were reduced during these events, in contrast with days without O 3 enhancements when contributions from Europe and North America were substantial. The O 3 enhancements typically occurred under southerly wind and warmer conditions. It is suggested that an earlier onset of the Asian summer monsoon would cause more O 3 enhancement events in the LT over the North China Plain in late spring and early summer.
Atmospheric Chemistry and Physics, 2015
We have evaluated tropospheric ozone enhancement in air dominated by biomass burning emissions at... more We have evaluated tropospheric ozone enhancement in air dominated by biomass burning emissions at high latitudes ( > 50 • N) in July 2008, using 10 global chemical transport model simulations from the POLMIP multimodel comparison exercise. In model air masses dominated by fire emissions, O 3 / CO values ranged between 0.039 and 0.196 ppbv ppbv -1 (mean: 0.113 ppbv ppbv -1 ) in freshly fire-influenced air, and between 0.140 and 0.261 ppbv ppbv -1 (mean: 0.193 ppbv) in more aged fireinfluenced air. These values are in broad agreement with the range of observational estimates from the literature. Model PAN/ CO enhancement ratios show distinct groupings according to the meteorological data used to drive the models. ECMWF-forced models produce larger PAN/ CO values (4.47 to 7.00 pptv ppbv -1 ) than GEOS5-forced models (1.87 to 3.28 pptv ppbv -1 ), which we show is likely linked to differences in efficiency of vertical transport during poleward export from mid-latitude source regions. Simulations of a large plume of biomass burning and anthropogenic emissions exported from towards the Arctic using a Lagrangian chemical transport model show that 4-day net ozone change in the plume is sensitive to differences in plume chemical composition and plume vertical position among the POLMIP models. In particular, Arctic ozone evolution in the plume is highly sensitive to initial concentrations of PAN, as well as oxygenated VOCs (acetone, acetaldehyde), due to their role in producing the peroxyacetyl radical PAN precursor. Vertical displacement is also important due to its effects on the stability of PAN, and subsequent effect on NO x abundance. In plumes where net ozone production is limited, we find that the lifetime of ozone in the plume is sensitive to hydrogen peroxide loading, due to the production of HO x from peroxide photolysis, and the key role of HO 2 + O 3 in controlling ozone loss. Overall, our results suggest that emissions from biomass burning lead to large-scale photochemical enhancement in high-latitude tropospheric ozone during summer.
Global O3-CO Correlations in the Global Modeling Initiative Chemical Transport Model During July-August: Sensitivity to Emissions and Input Meteorological Data
Use of Tracers to Diagnose Ozone Interannual Variability in the Utls in the Global Modeling Initiative (gmi) Chemistry-Transport Model (ctm) Hindcast