scholarly journals Unraveling pathways of elevated ozone induced by the 2020 lockdown in Europe by an observationally constrained regional model using TROPOMI

2021 ◽  
Vol 21 (24) ◽  
pp. 18227-18245
Author(s):  
Amir H. Souri ◽  
Kelly Chance ◽  
Juseon Bak ◽  
Caroline R. Nowlan ◽  
Gonzalo González Abad ◽  
...  
Keyword(s):  
Transport Model ◽  
Atmospheric Transport ◽  
Model Simulation ◽  
Surface Ozone ◽  
Ozone Production ◽  
Anthropogenic Emissions ◽  
Nox Emissions ◽  
Chemical Transport Model ◽  
Voc Emissions ◽  
Constrained Model

Abstract. Questions about how emissions are changing during the COVID-19 lockdown periods cannot be answered by observations of atmospheric trace gas concentrations alone, in part due to simultaneous changes in atmospheric transport, emissions, dynamics, photochemistry, and chemical feedback. A chemical transport model simulation benefiting from a multi-species inversion framework using well-characterized observations should differentiate those influences enabling to closely examine changes in emissions. Accordingly, we jointly constrain NOx and VOC emissions using well-characterized TROPOspheric Monitoring Instrument (TROPOMI) HCHO and NO2 columns during the months of March, April, and May 2020 (lockdown) and 2019 (baseline). We observe a noticeable decline in the magnitude of NOx emissions in March 2020 (14 %–31 %) in several major cities including Paris, London, Madrid, and Milan, expanding further to Rome, Brussels, Frankfurt, Warsaw, Belgrade, Kyiv, and Moscow (34 %–51 %) in April. However, NOx emissions remain at somewhat similar values or even higher in some portions of the UK, Poland, and Moscow in March 2020 compared to the baseline, possibly due to the timeline of restrictions. Comparisons against surface monitoring stations indicate that the constrained model underrepresents the reduction in surface NO2. This underrepresentation correlates with the TROPOMI frequency impacted by cloudiness. During the month of April, when ample TROPOMI samples are present, the surface NO2 reductions occurring in polluted areas are described fairly well by the model (model: −21 ± 17 %, observation: −29 ± 21 %). The observational constraint on VOC emissions is found to be generally weak except for lower latitudes. Results support an increase in surface ozone during the lockdown. In April, the constrained model features a reasonable agreement with maximum daily 8 h average (MDA8) ozone changes observed at the surface (r=0.43), specifically over central Europe where ozone enhancements prevail (model: +3.73 ± 3.94 %, +1.79 ppbv, observation: +7.35 ± 11.27 %, +3.76 ppbv). The model suggests that physical processes (dry deposition, advection, and diffusion) decrease MDA8 surface ozone in the same month on average by −4.83 ppbv, while ozone production rates dampened by largely negative JNO2[NO2]-kNO+O3[NO][O3] become less negative, leading ozone to increase by +5.89 ppbv. Experiments involving fixed anthropogenic emissions suggest that meteorology contributes to 42 % enhancement in MDA8 surface ozone over the same region with the remaining part (58 %) coming from changes in anthropogenic emissions. Results illustrate the capability of satellite data of major ozone precursors to help atmospheric models capture ozone changes induced by abrupt emission anomalies.

scholarly journals Unraveling Pathways of Elevated Ozone Induced by the 2020 Lockdown in Europe by an Observationally Constrained Regional Model: Non-Linear Joint Inversion of NO<sub>x</sub> and VOC Emissions using TROPOMI

2021 ◽  
Author(s):  
Amir H. Souri ◽  
Kelly Chance ◽  
Juseon Bak ◽  
Caroline R. Nowlan ◽  
Gonzalo González Abad ◽  
...  
Keyword(s):  
Central Europe ◽  
Joint Inversion ◽  
Surface Ozone ◽  
Ozone Production ◽  
Anthropogenic Emissions ◽  
Nox Emissions ◽  
Physical Processes ◽  
Model Estimate ◽  
Large Variability ◽  
Voc Emissions

Abstract. Questions about how emissions are changing during the COVID-19 lockdown periods cannot be answered by observations of atmospheric trace gas concentrations alone, in part due to simultaneous changes in atmospheric transport, emissions, dynamics, photochemistry, and chemical feedback. A chemical transport model simulation benefiting from a multi-species inversion framework using well-characterized observations should differentiate those influences enabling to closely examine changes in emissions. This approach has another advantage in that we can, to a certain extent, disentangle the chemical and physical processes involved in the formation of ozone. Accordingly, we jointly constrain NOx and VOC emissions using well-characterized TROPOMI HCHO and NO2 columns during the months of March, April, and May 2020 (lockdown) and 2019 (baseline). We observe a noticeable decline in the magnitude of NOx emissions in March 2020 (14–31 %) in several major cities including Paris, London, Madrid, and Milan expanding further to Rome, Brussels, Frankfurt, Warsaw, Belgrade, Kyiv, and Moscow (34–51 %) in April. The large variability of changes in NOx emissions is indicative of different dates and the degree of restrictions enacted to prevent the spread of the virus. For instance, NOx emissions remain at somewhat similar values or even higher in northern Germany and Moscow in March 2020 compared to the baseline. Comparisons against surface monitoring stations indicate that the model estimate of the NO2 reduction is underestimated, a picture that correlates with the TROPOMI frequency impacted by cloudiness. During the month of April, when ample TROPOMI samples are present, the surface NO2 reductions occurring in polluted areas are described fairly well by the model (model: −21 ± 17 %, observation: −29 ± 21 %). Changes in VOC emissions are dominated by eastern European biomass burning activities and biogenic isoprene emissions. In March, however, TROPOMI HCHO sets an upper limit for HCHO changes such that the chemical feedback of NOx on HCHO constrained by TROPOMI NO2 reveals a non-negligible decline in anthropogenic VOC emissions in Paris (−9 %), Milan (−29 %), London (−5 %), and Rome (−5 %). Results support an increase in surface ozone during the lockdown. In April, the constrained model features a reasonable agreement with maximum daily 8 h average (MDA8) ozone changes observed at the surface (r = 0.43), specifically over central Europe where ozone enhancements prevail (model: +3.73 ± 3.94 %, +1.79 ppbv, observation: +7.35 ± 11.27 %, +3.76 ppbv). Results of integrated process rates of MDA8 surface ozone over central Europe in the same month suggest that physical processes (dry deposition, advection and diffusion) decrease ozone on average by −4.83 ppbv, while ozone production rates dampened by largely negative JNO2[NO2]-kNO+O3[NO][O3] become less negative, leading ozone to increase by +5.89 ppbv. Experiments involving fixed anthropogenic emissions suggest that meteorology (mainly as air temperature and photolysis) contributes to 42 % enhancement in MDA8 surface ozone over the same region with the remaining part (58 %) coming from changes in anthropogenic emissions. Results illustrate the capability of satellite data of major ozone precursors to help atmospheric models capture the essential character of ozone changes induced by abrupt emission anomalies.

scholarly journals Regional and intercontinental pollution signatures on modeled and measured PAN at northern mid-latitude mountain sites

2018 ◽  
Author(s):  
Arlene M. Fiore ◽  
Emily V. Fischer ◽  
Shubha Pandey Deolal ◽  
Oliver Wild ◽  
Dan Jaffe ◽  
...  
Keyword(s):  
Transport Model ◽  
Ozone Production ◽  
Anthropogenic Emissions ◽  
Chemical Transport Model ◽  
Reservoir Species ◽  
Remote Troposphere ◽  
Global Chemical Transport Model ◽  
Peroxy Acetyl Nitrate ◽  
Source Receptor Relationships

Abstract. Peroxy acetyl nitrate (PAN) is the most important reservoir species for nitrogen oxides (NOx) in the remote troposphere. Upon decomposition in remote regions, PAN promotes efficient ozone production. We evaluate monthly mean PAN abundances from global chemical transport model simulations (HTAP1) for 2001 with measurements from five northern mid-latitude mountain sites (four European and one North American). The multi-model mean generally captures the observed monthly mean PAN but individual models simulate a factor of ~ 4–8 range in monthly abundances. We quantify PAN source-receptor relationships at the measurement sites with sensitivity simulations that decrease regional anthropogenic emissions of PAN (and ozone) precursors by 20 % from North America (NA), Europe (EU), and East Asia (EA). The HTAP1 models attribute more of the observed PAN at Jungfraujoch (Switzerland) to emissions in NA and EA, and less to EU, than a prior trajectory-based estimate. The trajectory-based and modeling approaches agree that EU emissions play a role in the observed springtime PAN maximum at Jungfraujoch. The signal from anthropogenic emissions on PAN is strongest at Jungfraujoch and Mount Bachelor (Oregon, U.S.A.) during April. In this month, PAN source-receptor relationships correlate both with model differences in regional anthropogenic volatile organic compound (AVOC) emissions and with ozone source-receptor relationships. PAN observations at mountaintop sites can thus provide key information for evaluating models, including links between PAN and ozone production and source-receptor relationships. Establishing routine, long-term, mountaintop measurements is essential given the large observed interannual variability in PAN.

scholarly journals Impact of regional climate change and future emission scenarios on surface O<sub>3</sub> and PM<sub>2.5</sub> over India

2018 ◽  
Vol 18 (1) ◽  
pp. 103-127 ◽  
Author(s):  
Matthieu Pommier ◽  
Hilde Fagerli ◽  
Michael Gauss ◽  
David Simpson ◽  
Sumit Sharma ◽  
...  
Keyword(s):  
Climate Change ◽  
Transport Model ◽  
Surface Ozone ◽  
Deposition Velocity ◽  
Public Health Issue ◽  
Anthropogenic Emissions ◽  
Reference Scenario ◽  
Chemical Transport Model ◽  
Data Set ◽  
Gangetic Plain

Abstract. Eleven of the world's 20 most polluted cities are located in India and poor air quality is already a major public health issue. However, anthropogenic emissions are predicted to increase substantially in the short-term (2030) and medium-term (2050) futures in India, especially if no further policy efforts are made. In this study, the EMEP/MSC-W chemical transport model has been used to predict changes in surface ozone (O3) and fine particulate matter (PM2.5) for India in a world of changing emissions and climate. The reference scenario (for present-day) is evaluated against surface-based measurements, mainly at urban stations. The evaluation has also been extended to other data sets which are publicly available on the web but without quality assurance. The evaluation shows high temporal correlation for O3 (r =  0.9) and high spatial correlation for PM2.5 (r =  0.5 and r =  0.8 depending on the data set) between the model results and observations. While the overall bias in PM2.5 is small (lower than 6 %), the model overestimates O3 by 35 %. The underestimation in NOx titration is probably the main reason for the O3 overestimation in the model. However, the level of agreement can be considered satisfactory in this case of a regional model being evaluated against mainly urban measurements, and given the inevitable uncertainties in much of the input data.For the 2050s, the model predicts that climate change will have distinct effects in India in terms of O3 pollution, with a region in the north characterized by a statistically significant increase by up to 4 % (2 ppb) and one in the south by a decrease up to −3 % (−1.4 ppb). This variation in O3 is assumed to be partly related to changes in O3 deposition velocity caused by changes in soil moisture and, over a few areas, partly also by changes in biogenic non-methane volatile organic compounds.Our calculations suggest that PM2.5 will increase by up to 6.5 % over the Indo-Gangetic Plain by the 2050s. The increase over India is driven by increases in dust, particulate organic matter (OM) and secondary inorganic aerosols (SIAs), which are mainly affected by the change in precipitation, biogenic emissions and wind speed.The large increase in anthropogenic emissions has a larger impact than climate change, causing O3 and PM2.5 levels to increase by 13 and 67 % on average in the 2050s over the main part of India, respectively. By the 2030s, secondary inorganic aerosol is predicted to become the second largest contributor to PM2.5 in India, and the largest in the 2050s, exceeding OM and dust.

scholarly journals Seasonal and spatial variability of surface ozone over China: contributions from background and domestic pollution

2011 ◽  
Vol 11 (7) ◽  
pp. 3511-3525 ◽  
Author(s):  
Y. Wang ◽  
Y. Zhang ◽  
J. Hao ◽  
M. Luo
Keyword(s):  
Yangtze River ◽  
Transport Model ◽  
Surface Ozone ◽  
Eastern China ◽  
Long Range Transport ◽  
Anthropogenic Emissions ◽  
Spatial Gradient ◽  
Chemical Transport Model ◽  
Background Ozone ◽  
Range Transport

Abstract. Both observations and a 3-D chemical transport model suggest that surface ozone over populated eastern China features a summertime trough and that the month when surface ozone peaks differs by latitude and region. Source-receptor analysis is used to quantify the contributions of background ozone and Chinese anthropogenic emissions on this variability. Annual mean background ozone over China shows a spatial gradient from 55 ppbv in the northwest to 20 ppbv in the southeast, corresponding with changes in topography and ozone lifetime. Pollution background ozone (annual mean of 12.6 ppbv) shows a minimum in the summer and maximum in the spring. On the monthly-mean basis, Chinese pollution ozone (CPO) has a peak of 20–25 ppbv in June north of the Yangtze River and in October south of it, which explains the peaks of surface ozone in these months. The summertime trough in surface ozone over eastern China can be explained by the decrease of background ozone from spring to summer (by −15 ppbv regionally averaged over eastern China). Tagged simulations suggest that long-range transport of ozone from northern mid-latitude continents (including Europe and North America) reaches a minimum in the summer, whereas ozone from Southeast Asia exhibits a maximum in the summer over eastern China. This contrast in seasonality provides clear evidence that the seasonal switch in monsoonal wind patterns plays a significant role in determining the seasonality of background ozone over China.

scholarly journals Seasonal and spatial variability of surface ozone over China: contributions from background and domestic pollution

2010 ◽  
Vol 10 (11) ◽  
pp. 27853-27891 ◽  
Author(s):  
Y. Wang ◽  
Y. Zhang ◽  
J. Hao ◽  
M. Luo
Keyword(s):  
Yangtze River ◽  
Transport Model ◽  
Surface Ozone ◽  
Eastern China ◽  
Chemical Transport ◽  
Anthropogenic Emissions ◽  
Spatial Gradient ◽  
Chemical Transport Model ◽  
Significant Drop ◽  
Background Ozone

Abstract. Both observations and a 3-D chemical transport model suggest that surface ozone over populated eastern China features a significant drop in mid-summer and that the peak month differs by latitude and region. Source-receptor analysis is used to quantify the contributions of background ozone and Chinese anthropogenic emissions on this variability. Annual mean background ozone over China shows a spatial gradient from 55 ppbv in the northwest to 20 ppbv in the southeast, corresponding with changes in topography and ozone lifetime. Anthropogenic background (annual mean of 12.6 ppbv) shows distinct troughs in the summer and peaks in the spring. On the monthly-mean basis, Chinese pollution ozone (CPO) has a peak of 20–25 ppbv in June north of the Yangtze River and in October south of it, which explains the peaks of surface ozone in these months. The mid-summer drop in ozone over eastern China is driven by the decrease of background ozone (−15 ppbv). Tagged simulations suggest that this decrease is driven by reduced transport from Europe and North America, whereas ozone from Southeast Asia and Pacific Ocean exhibits a maximum in the summer over eastern China. This contrast in seasonality provides clear evidence that the seasonal switch in monsoonal wind patterns plays a significant role in determining the seasonality of background ozone over China.

scholarly journals Effect of changing NO<sub><i>x</i></sub> lifetime on the seasonality and long-term trends of satellite-observed tropospheric NO<sub>2</sub> columns over China

2019 ◽  
Author(s):  
Viral Shah ◽  
Daniel J. Jacob ◽  
Ke Li ◽  
Rachel F. Silvern ◽  
Shixian Zhai ◽  
...  
Keyword(s):  
Transport Model ◽  
Eastern China ◽  
Anthropogenic Emissions ◽  
Organic Nitrates ◽  
Nox Emissions ◽  
Chemical Transport Model ◽  
Volatile Organic ◽  
Tropospheric No2 ◽  
Long Term Trends

Abstract. Satellite observations of tropospheric NO2 columns are extensively used to infer trends in anthropogenic emissions of nitrogen oxides (NOx ≡ NO + NO2), but this may be complicated by trends in NOx lifetime. Here we use 2004–2018 observations from the OMI satellite-based instrument (QA4ECV and POMINO v2 retrievals) to examine the seasonality and trends of tropospheric NO2 columns over central-eastern China, and we interpret the results with the GEOS-Chem chemical transport model. The observations show a factor of 3 increase in NO2 columns from summer to winter, which we explain in GEOS-Chem as reflecting a longer NOx lifetime in winter than in summer (21 h versus 5.9 h in 2017). The 2005–2018 summer trends of OMI NO2 closely follow the trends in the Multi-resolution Emission Inventory for China (MEIC), with a rise over the 2005–2011 period and a 25 % decrease since. We find in GEOS-Chem no significant trend of the NOx lifetime in summer, supporting the emission trend reported by MEIC. The winter trend of OMI NO2 is steeper than in summer over the entire period, which we attribute to a decrease in NOx lifetime at lower NOx emissions. Half of the NOx sink in winter is from N2O5 hydrolysis, which counterintuitively becomes more efficient as NOx emissions decrease due to less titration of ozone at night. Formation of organic nitrates also becomes an increasing sink of NOx as NOx emissions decrease but emissions of volatile organic compounds (VOCs) do not.

scholarly journals Low modeled ozone production suggests underestimation of precursor emissions (especially NO<sub><i>x</i></sub>) in Europe

2018 ◽  
Vol 18 (3) ◽  
pp. 2175-2198 ◽  
Author(s):  
Emmanouil Oikonomakis ◽  
Sebnem Aksoyoglu ◽  
Giancarlo Ciarelli ◽  
Urs Baltensperger ◽  
André Stephan Henry Prévôt
Keyword(s):  
Air Quality ◽  
Surface Ozone ◽  
Model Performance ◽  
Ozone Production ◽  
Nox Emissions ◽  
Air Quality Model ◽  
Quality Model ◽  
Voc Emissions ◽  
Mixing Ratios ◽  
The Impact

Abstract. High surface ozone concentrations, which usually occur when photochemical ozone production takes place, pose a great risk to human health and vegetation. Air quality models are often used by policy makers as tools for the development of ozone mitigation strategies. However, the modeled ozone production is often not or not enough evaluated in many ozone modeling studies. The focus of this work is to evaluate the modeled ozone production in Europe indirectly, with the use of the ozone–temperature correlation for the summer of 2010 and to analyze its sensitivity to precursor emissions and meteorology by using the regional air quality model, the Comprehensive Air Quality Model with Extensions (CAMx). The results show that the model significantly underestimates the observed high afternoon surface ozone mixing ratios (≥ 60 ppb) by 10–20 ppb and overestimates the lower ones (< 40 ppb) by 5–15 ppb, resulting in a misleading good agreement with the observations for average ozone. The model also underestimates the ozone–temperature regression slope by about a factor of 2 for most of the measurement stations. To investigate the impact of emissions, four scenarios were tested: (i) increased volatile organic compound (VOC) emissions by a factor of 1.5 and 2 for the anthropogenic and biogenic VOC emissions, respectively, (ii) increased nitrogen oxide (NOx) emissions by a factor of 2, (iii) a combination of the first two scenarios and (iv) increased traffic-only NOx emissions by a factor of 4. For southern, eastern, and central (except the Benelux area) Europe, doubling NOx emissions seems to be the most efficient scenario to reduce the underestimation of the observed high ozone mixing ratios without significant degradation of the model performance for the lower ozone mixing ratios. The model performance for ozone–temperature correlation is also better when NOx emissions are doubled. In the Benelux area, however, the third scenario (where both NOx and VOC emissions are increased) leads to a better model performance. Although increasing only the traffic NOx emissions by a factor of 4 gave very similar results to the doubling of all NOx emissions, the first scenario is more consistent with the uncertainties reported by other studies than the latter, suggesting that high uncertainties in NOx emissions might originate mainly from the road-transport sector rather than from other sectors. The impact of meteorology was examined with three sensitivity tests: (i) increased surface temperature by 4 ∘C, (ii) reduced wind speed by 50 % and (iii) doubled wind speed. The first two scenarios led to a consistent increase in all surface ozone mixing ratios, thus improving the model performance for the high ozone values but significantly degrading it for the low ozone values, while the third scenario had exactly the opposite effects. Overall, the modeled ozone is predicted to be more sensitive to its precursor emissions (especially traffic NOx) and therefore their uncertainties, which seem to be responsible for the model underestimation of the observed high ozone mixing ratios and ozone production.

scholarly journals Impact of regional climate change and future emission scenarios on surface O<sub>3</sub> and PM<sub>2.5</sub> over India

2017 ◽  
Author(s):  
Matthieu Pommier ◽  
Hilde Fagerli ◽  
Michael Gauss ◽  
David Simpson ◽  
Sumit Sharma ◽  
...  
Keyword(s):  
Climate Change ◽  
Transport Model ◽  
Surface Ozone ◽  
Deposition Velocity ◽  
Temporal Correlation ◽  
Public Health Issue ◽  
Anthropogenic Emissions ◽  
Reference Scenario ◽  
Chemical Transport Model ◽  
Data Set

Abstract. Eleven of the world’s 20 most polluted cities are located in India and poor air quality is already a major public health issue. However, anthropogenic emissions are predicted to increase substantially in the short-term (2030) and medium-term (2050) futures in India, especially if no more policy efforts are made. In this study, the EMEP/MSC-W chemical transport model has been used to calculate changes in surface ozone (O3) and fine particulate matter (PM2.5) for India in a world of changing emissions and climate. The reference scenario (for present-day) is evaluated against surface-based measurements, mainly at urban stations. The evaluation has also been extended to other data sets which are publicly available on the web but without quality assurance. The evaluation shows high temporal correlation for O3 (r=0.9) and high spatial correlations for PM2.5 (r=0.5 and r=0.8 depending on the data set) between the model results and observations. While the overall bias in PM2.5 is small (lower than 6%), the model overestimates O3 by 35%. The underestimation in NOx titration is probably the main reason for the O3 overestimation in the model. However, the level of agreement can be considered satisfactory in this case of a regional model being evaluated against mainly urban measurements, and given inevitable uncertainties in much of the input data For the 2050s, the model predicts that climate change will have distinct effects in India in terms of O3 pollution, with a region in the North characterized by a statistically significant increase by up to 4% (2 ppb) and one in the South by a decrease up to -3% (-1.4 ppb). This variation in O3 is found to be partly related to changes in O3 deposition velocity caused by changes in soil moisture and, over a few areas, partly also by changes in biogenic NMVOCs. Our calculations suggest that PM2.5 will increase by up to 6.5% in the 2050s, driven by increases in dust, particulate organic matter (OM) and secondary inorganic aerosols (SIA), which are mainly affected by the change in precipitation, biogenic emissions and wind speed. The large increase in anthropogenic emissions has a larger impact than climate change, causing O3 and PM2.5 levels to increase by 13% and 67% in average in 2050s, respectively. By the 2030s, secondary inorganic aerosol is predicted to become the second largest contributor to PM2.5 in India, and the largest in 2050s, exceeding OM and dust.

scholarly journals Anthropogenic drivers of 2013–2017 trends in summer surface ozone in China

2018 ◽  
Vol 116 (2) ◽  
pp. 422-427 ◽  
Author(s):  
Ke Li ◽  
Daniel J. Jacob ◽  
Hong Liao ◽  
Lu Shen ◽  
Qiang Zhang ◽  
...  
Keyword(s):  
Transport Model ◽  
Southern China ◽  
Surface Ozone ◽  
Fine Particulate Matter ◽  
Eastern China ◽  
Multiple Linear Regression Model ◽  
Urban China ◽  
Ozone Production ◽  
Chemical Transport Model ◽  
Ozone Trends

Observations of surface ozone available from ∼1,000 sites across China for the past 5 years (2013–2017) show severe summertime pollution and regionally variable trends. We resolve the effect of meteorological variability on the ozone trends by using a multiple linear regression model. The residual of this regression shows increasing ozone trends of 1–3 ppbv a−1 in megacity clusters of eastern China that we attribute to changes in anthropogenic emissions. By contrast, ozone decreased in some areas of southern China. Anthropogenic NOx emissions in China are estimated to have decreased by 21% during 2013–2017, whereas volatile organic compounds (VOCs) emissions changed little. Decreasing NOx would increase ozone under the VOC-limited conditions thought to prevail in urban China while decreasing ozone under rural NOx-limited conditions. However, simulations with the Goddard Earth Observing System Chemical Transport Model (GEOS-Chem) indicate that a more important factor for ozone trends in the North China Plain is the ∼40% decrease of fine particulate matter (PM2.5) over the 2013–2017 period, slowing down the aerosol sink of hydroperoxy (HO2) radicals and thus stimulating ozone production.

scholarly journals Trans-Pacific transport of reactive nitrogen and ozone to Canada during spring

2010 ◽  
Vol 10 (17) ◽  
pp. 8353-8372 ◽  
Author(s):  
T. W. Walker ◽  
R. V. Martin ◽  
A. van Donkelaar ◽  
W. R. Leaitch ◽  
A. M. MacDonald ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Production Efficiency ◽  
Transport Model ◽  
North Pacific Ocean ◽  
Chemical Transport ◽  
Eastern Pacific ◽  
Chemical Mechanism ◽  
Ozone Production ◽  
Anthropogenic Emissions ◽  
Nox Emissions

Abstract. We interpret observations from the Intercontinental Chemical Transport Experiment, Phase B (INTEX-B) in spring 2006 using a global chemical transport model (GEOS-Chem) to evaluate sensitivities of the free troposphere above the North Pacific Ocean and North America to Asian anthropogenic emissions. We develop a method to use satellite observations of tropospheric NO2 columns to provide timely estimates of trends in NOx emissions. NOx emissions increased by 33% for China and 29% for East Asia from 2003 to 2006. We examine measurements from three aircraft platforms from the INTEX-B campaign, including a Canadian Cessna taking vertical profiles of ozone near Whistler Peak. The contribution to the mean simulated ozone profiles over Whistler below 5.5 km is at least 7.2 ppbv for Asian anthropogenic emissions and at least 3.5 ppbv for global lightning NOx emissions. Tropospheric ozone columns from OMI exhibit a broad Asian outflow plume across the Pacific, which is reproduced by simulation. Mean modelled sensitivities of Pacific (30° N–60° N) tropospheric ozone columns are at least 4.6 DU for Asian anthropogenic emissions and at least 3.3 DU for lightning, as determined by simulations excluding either source. Enhancements of ozone over Canada from Asian anthropogenic emissions reflect a combination of trans-Pacific transport of ozone produced over Asia, and ozone produced in the eastern Pacific through decomposition of peroxyacetyl nitrates (PANs). A sensitivity study decoupling PANs globally from the model's chemical mechanism establishes that PANs increase ozone production by removing NOx from regions of low ozone production efficiency (OPE) and injecting it into regions with higher OPE, resulting in a global increase in ozone production by 2% in spring 2006. PANs contribute up to 4 ppbv to surface springtime ozone concentrations in western Canada. Ozone production due to PAN transport is greatest in the eastern Pacific; commonly occurring transport patterns advect this ozone northeastward into Canada. Transport events observed by the aircraft confirm that polluted airmasses were advected in this way.

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