Estimation of winter PM2.5 concentrations in East Asia associated with climate variability

2020 ◽  
Author(s):  
Jaein Jeong ◽  
Rokjin Park ◽  
Sang-Wook Yeh ◽  
Joon-Woo Roh
Keyword(s):  
Climate Variability ◽  
East Asia ◽  
Transport Model ◽  
Climate Index ◽  
Anthropogenic Emissions ◽  
Climate Indices ◽  
Linear Regression Models ◽  
Chemical Transport Model ◽  
High Position ◽  
The Relationship

<p>Interannual variability in large circulations associated with climate connections, such as monsoon and El Niño, have a significant impact on winter PM<sub>2.5</sub> concentrations in East Asia. In this study, we use the global 3D chemical transport model (GEOS-Chem) over the last 35 years to investigate the relationship between major climate variability and winter PM<sub>2.5</sub> concentrations in East Asia. First, the model is evaluated by comparing the simulated and observed aerosol concentrations with the ground and satellite-based aerosol concentrations. The results indicate that this model well reproduces the variability and magnitude of aerosol concentrations observed in East Asia. Sensitivity simulations are then used with fixed anthropogenic emissions to investigate the effects of meteorological variability on changes in aerosol concentrations in East Asia. The variability of winter PM<sub>2.5</sub> concentrations in northern East Asia was found to be closely correlated with ENSO and Siberian high position. To predict PM<sub>2.5</sub> concentrations using key climate indices, we develop multiple linear regression models. As a result, the predicted winter PM<sub>2.5</sub> concentrations using the key climate index are well reproduced in the simulated PM<sub>2.5</sub> concentrations, especially in northern East Asia.</p>

scholarly journals Evaluation of anthropogenic emissions of carbon monoxide in East Asia derived from observations of atmospheric radon-222 over the Western North Pacific

2012 ◽  
Vol 12 (6) ◽  
pp. 15337-15372
Author(s):  
A. Wada ◽  
H. Matsueda ◽  
S. Murayama ◽  
S. Taguchi ◽  
A. Kamada ◽  
...  
Keyword(s):  
East Asia ◽  
North Pacific ◽  
Western North Pacific ◽  
Transport Model ◽  
Three Dimensional ◽  
Anthropogenic Emissions ◽  
Chemical Transport Model ◽  
Air Masses ◽  
Range Transport ◽  
The Difference

Abstract. We used the observed CO/222Rn ratio in Asian outflows at Minamitorishima (MNM), Yonagunijima (YON), and Ryori (RYO) over the Western North Pacific from 2007 to 2011, together with a three-dimensional chemical transport model (STAG), in order to estimate anthropogenic emissions of CO in East Asia. The measurements captured high-frequency synoptic variations of enhanced 222Rn (ERN) events associated with long-range transport of continental air masses. 222Rn and CO showed high correlation during the ERN events observed at MNM and YON in the winter and spring, but not at RYO. The STAG transport model reproduced well the concentration of observed 222Rn when forced with constant and uniform flux density of 1.0 atom cm−2 s−1, but underestimated the associated enhancement of synoptically variable CO caused by the underestimated flux values in the EDGAR ver. 4.1 emission database used in the model for East Asia. Better estimates for the East Asian emission were derived using a radon tracer method based on the difference in the enhancement ratio of CO/222Rn between observation and model. The anthropogenic emission of CO for China, Japan, and Korea was estimated to be 203 Tg CO yr−1, 93% of which originated in China. When compared with other estimated emissions of CO, our estimated result showed consistency with those of the inverse method, whereas the emission database of EDGAR was about 45% smaller than our anthropogenic estimation for China.

scholarly journals Evaluation of anthropogenic emissions of carbon monoxide in East Asia derived from the observations of atmospheric radon-222 over the western North Pacific

2012 ◽  
Vol 12 (24) ◽  
pp. 12119-12132 ◽  
Author(s):  
A. Wada ◽  
H. Matsueda ◽  
S. Murayama ◽  
S. Taguchi ◽  
A. Kamada ◽  
...  
Keyword(s):  
East Asia ◽  
North Pacific ◽  
Western North Pacific ◽  
Transport Model ◽  
Three Dimensional ◽  
Anthropogenic Emissions ◽  
Chemical Transport Model ◽  
Air Masses ◽  
Range Transport ◽  
The Difference

Abstract. We used the observed CO/222Rn ratio in the Asian outflows at Minamitorishima (MNM), Yonagunijima (YON), and Ryori (RYO) in the western North Pacific from 2007 to 2011, together with a three-dimensional chemical transport model (STAG), in order to estimate anthropogenic emissions of CO in East Asia. The measurements captured high-frequency synoptic variations of enhanced 222Rn (ERN) events associated with the long-range transport of continental air masses. 222Rn and CO showed high correlation during the ERN events observed at MNM and YON in the winter and spring, but not at RYO. The STAG transport model reproduced well the concentrations of observed 222Rn when forced with a constant and uniform flux density of 1.0 atom cm−2 s−1, but underestimated the associated enhancement of synoptically variable CO caused by the underestimated flux values in the EDGAR ver. 4.1 emission database used in the model for East Asia. Better estimates for the East Asian emission were derived using a radon tracer method based on the difference in the enhancement ratio of CO/222Rn between the observation and the model. The anthropogenic emissions of CO for China, Japan, and Korea were estimated to be 203 Tg CO yr−1, 91% of which originated in China. When compared with other estimated emissions of CO, our estimated result showed consistency with those of the inverse method, whereas the emission database of EDGAR was about 45% smaller than our anthropogenic estimation for China.

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 Source attribution of Arctic black carbon constrained by aircraft and surface measurements

2017 ◽  
Vol 17 (19) ◽  
pp. 11971-11989 ◽  
Author(s):  
Jun-Wei Xu ◽  
Randall V. Martin ◽  
Andrew Morrow ◽  
Sangeeta Sharma ◽  
Lin Huang ◽  
...  
Keyword(s):  
North America ◽  
Biomass Burning ◽  
Western Siberia ◽  
Transport Model ◽  
Chemical Transport ◽  
The Arctic ◽  
Anthropogenic Emissions ◽  
Chemical Transport Model ◽  
Northern Asia ◽  
Airborne Measurements

Abstract. Black carbon (BC) contributes to Arctic warming, yet sources of Arctic BC and their geographic contributions remain uncertain. We interpret a series of recent airborne (NETCARE 2015; PAMARCMiP 2009 and 2011 campaigns) and ground-based measurements (at Alert, Barrow and Ny-Ålesund) from multiple methods (thermal, laser incandescence and light absorption) with the GEOS-Chem global chemical transport model and its adjoint to attribute the sources of Arctic BC. This is the first comparison with a chemical transport model of refractory BC (rBC) measurements at Alert. The springtime airborne measurements performed by the NETCARE campaign in 2015 and the PAMARCMiP campaigns in 2009 and 2011 offer BC vertical profiles extending to above 6 km across the Arctic and include profiles above Arctic ground monitoring stations. Our simulations with the addition of seasonally varying domestic heating and of gas flaring emissions are consistent with ground-based measurements of BC concentrations at Alert and Barrow in winter and spring (rRMSE  < 13 %) and with airborne measurements of the BC vertical profile across the Arctic (rRMSE  = 17 %) except for an underestimation in the middle troposphere (500–700 hPa).Sensitivity simulations suggest that anthropogenic emissions in eastern and southern Asia have the largest effect on the Arctic BC column burden both in spring (56 %) and annually (37 %), with the largest contribution in the middle troposphere (400–700 hPa). Anthropogenic emissions from northern Asia contribute considerable BC (27 % in spring and 43 % annually) to the lower troposphere (below 900 hPa). Biomass burning contributes 20 % to the Arctic BC column annually.At the Arctic surface, anthropogenic emissions from northern Asia (40–45 %) and eastern and southern Asia (20–40 %) are the largest BC contributors in winter and spring, followed by Europe (16–36 %). Biomass burning from North America is the most important contributor to all stations in summer, especially at Barrow.Our adjoint simulations indicate pronounced spatial heterogeneity in the contribution of emissions to the Arctic BC column concentrations, with noteworthy contributions from emissions in eastern China (15 %) and western Siberia (6.5 %). Although uncertain, gas flaring emissions from oilfields in western Siberia could have a striking impact (13 %) on Arctic BC loadings in January, comparable to the total influence of continental Europe and North America (6.5 % each in January). Emissions from as far as the Indo-Gangetic Plain could have a substantial influence (6.3 % annually) on Arctic BC as well.

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 Nitrate transboundary heavy pollution over East Asia in winter

2017 ◽  
Vol 17 (6) ◽  
pp. 3823-3843 ◽  
Author(s):  
Syuichi Itahashi ◽  
Itsushi Uno ◽  
Kazuo Osada ◽  
Yusuke Kamiguchi ◽  
Shigekazu Yamamoto ◽  
...  
Keyword(s):  
Air Pollution ◽  
East Asia ◽  
Transport Model ◽  
Chemical Transport ◽  
First Episode ◽  
Chemical Transport Model ◽  
High Concentration ◽  
Air Mass ◽  
Transboundary Air Pollution ◽  
Western Japan

Abstract. High PM2. 5 concentrations of around 100 µg m−3 were observed twice during an intensive observation campaign in January 2015 at Fukuoka (33.52° N, 130.47° E) in western Japan. These events were analyzed comprehensively with a regional chemical transport model and synergetic ground-based observations with state-of-the-art measurement systems, which can capture the behavior of secondary inorganic aerosols (SO42−, NO3−, and NH4+). The first episode of high PM2. 5 concentration was dominated by NO3− (type N) and the second episode by SO42− (type S). The concentration of NH4+ (the counterion for SO42− and NO3−) was high for both types. A sensitivity simulation in the chemical transport model showed that the dominant contribution was from transboundary air pollution for both types. To investigate the differences between these types further, the chemical transport model results were examined, and a backward trajectory analysis was used to provide additional information. During both types of episodes, high concentrations of NO3− were found above China, and an air mass that originated from northeast China reached Fukuoka. The travel time from the coastline of China to Fukuoka differed between types: it was 18 h for type N and 24 h for type S. The conversion ratio of SO2 to SO42− (Fs) was less than 0.1 for type N, but reached 0.3 for type S as the air mass approached Fukuoka. The higher Fs for type S was related to the higher relative humidity and the concentration of HO2, which produces H2O2, the most effective oxidant for the aqueous-phase production of SO42−. Analyzing the gas ratio as an indicator of the sensitivity of NO3− to changes in SO42− and NH4+ showed that the air mass over China was NH3-rich for type N, but almost NH3-neutral for type S. Thus, although the high concentration of NO3− above China gradually decreased during transport from China to Fukuoka, higher NO3− concentrations were maintained during transport owing to the lower SO42− for type N. In contrast, for type S, the production of SO42− led to the decomposition of NH4NO3, and more SO42− was transported. Notably, the type N transport pattern was limited to western Japan, especially the island of Kyushu. Transboundary air pollution dominated by SO42− (type S) has been recognized as a major pattern of pollution over East Asia. However, our study confirms the importance of transboundary air pollution dominated by NO3−, which will help refine our understanding of transboundary heavy PM2. 5 pollution in winter over East Asia.

scholarly journals Changes in dissolved iron deposition to the oceans driven by human activity: a 3-D global modelling study

2015 ◽  
Vol 12 (5) ◽  
pp. 3943-3990
Author(s):  
S. Myriokefalitakis ◽  
N. Daskalakis ◽  
N. Mihalopoulos ◽  
A. R. Baker ◽  
A. Nenes ◽  
...  
Keyword(s):  
Air Quality ◽  
Transport Model ◽  
Organic Ligand ◽  
Photochemical Reactions ◽  
Anthropogenic Emissions ◽  
Spatial And Temporal Variability ◽  
Deposition Flux ◽  
Chemical Transport Model ◽  
The Future ◽  
The Impact

Abstract. The global atmospheric iron (Fe) cycle is parameterized in the global 3-D chemical transport model TM4-ECPL to simulate the proton- and the organic ligand-promoted mineral Fe dissolution as well as the aqueous-phase photochemical reactions between the oxidative states of Fe(III/II). Primary emissions of total (TFe) and dissolved (DFe) Fe associated with dust and combustion processes are also taken into account. TFe emissions are calculated to amount to ~35 Tg Fe yr−1. The model reasonably simulates the available Fe observations, supporting the reliability of the results of this study. Accounting for proton- and organic ligand-promoted Fe-dissolution in present-day TM4-ECPL simulations, the total Fe-dissolution is calculated to be ~0.163 Tg Fe yr−1 that accounts for up to ~50% of the calculated total DFe emissions. The atmospheric burden of DFe is calculated to be ~0.012 Tg Fe. DFe deposition presents strong spatial and temporal variability with an annual deposition flux ~0.489 Tg Fe yr−1 from which about 25% (~0.124 Tg Fe yr−1) are deposited over the ocean. The impact of air-quality on Fe deposition is studied by performing sensitivity simulations using preindustrial (year 1850), present (year 2008) and future (year 2100) emission scenarios. These simulations indicate that an increase (~2 times) in Fe-dissolution may have occurred in the past 150 years due to increasing anthropogenic emissions and thus atmospheric acidity. On the opposite, a decrease (~2 times) of Fe-dissolution is projected for near future, since atmospheric acidity is expected to be lower than present-day due to air-quality regulations of anthropogenic emissions. The organic ligand contribution to Fe dissolution shows inverse relationship to the atmospheric acidity thus its importance has decreased since the preindustrial period but is projected to increase in the future. The calculated changes also show that the atmospheric DFe supply to High-Nutrient-Low-Chlorophyll oceanic areas (HNLC) characterized by Fe scarcity, has increased (~50%) since the preindustrial period. However, the DFe deposition flux is expected to decrease (~30%) to almost preindustrial levels over the Northern Hemisphere HNLC oceanic regions in the future. Significant reductions of ~20% over the Southern Ocean and the remote tropical Pacific Ocean are also projected which can further limit the primary productivity over HNLC waters.

scholarly journals Composite study of aerosol export events from East Asia and North America

2012 ◽  
Vol 12 (8) ◽  
pp. 21977-22022 ◽  
Author(s):  
Y. Luan ◽  
L. Jaeglé
Keyword(s):  
Boundary Layer ◽  
North America ◽  
East Asia ◽  
Transport Model ◽  
Lower Troposphere ◽  
Temporal Variations ◽  
The Arctic ◽  
Chemical Transport Model ◽  
Mean Values ◽  
Warm Conveyor Belts

Abstract. We use satellite observations of aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectrometer (MODIS) together with the GEOS-Chem global chemical transport model to contrast export of aerosols from East Asia and North America during 2004–2010. The GEOS-Chem model reproduces the spatial distribution and temporal variations of Asian aerosol outflow generally well, although a low bias (−30%) is found in the model fine mode AOD. We use the model to identify 244 aerosol pollution export events from E. Asia and 251 export events from N. America over our 7-yr study period. When these events are composited by season, we find that the AOD in the outflow is enhanced by 50–100% relative to seasonal mean values. The composite Asian plume splits into one branch going poleward towards the Arctic, with the other crossing the Pacific in 6–8 days. A fraction of the aerosols is trapped in the subtropical Pacific High. The N. American plume travels to the northeast Atlantic, reaching Europe after 4–5 days. Part of the composite plume turns anticyclonically in the Azores High, where it slowly decays. Both the Asian and N. American export events are favored by a dipole structure in sea-level pressure anomalies, associated with mid-latitude cyclone activity over the respective source regions. The observed AOD in the E. Asian outflow exhibits stronger seasonality, with a spring maximum, than the N. American outflow, with a weak summer maximum. The large spring AOD in the Asian outflow is the result of enhanced sulfate and dust aerosol concentrations, but is also due to a larger export efficiency of sulfate and SO2 from the Asian boundary layer relative to the N. American boundary layer. While the N. American sulfate outflow is mostly found in the lower troposphere (1–3 km altitude), the Asian sulfate outflow occurs at higher altitudes (2–6 km). In the Asian outflow 42–59% of the sulfate column is present above 2 km altitude, with only 24–35% in the N. American outflow. We link this to the factor of 2–5 lower precipitation in the warm conveyor belts (WCB) of midlatitude cyclones over E. Asia compared to N. America. This relative lack of precipitation makes Asian WCB very efficient for injecting aerosols in the middle troposphere.

scholarly journals Diagnosing recent CO emissions and springtime O<sub>3</sub> evolution in East Asia using coordinated ground-based observations of O<sub>3</sub> and CO during the East Asian Regional Experiment (EAREX) 2005 campaign

2008 ◽  
Vol 8 (1) ◽  
pp. 3525-3561
Author(s):  
H. Tanimoto ◽  
Y. Sawa ◽  
S. Yonemura ◽  
K. Yumimoto ◽  
H. Matsueda ◽  
...  
Keyword(s):  
East Asia ◽  
Transport Model ◽  
East Asian ◽  
Source Region ◽  
Measurement Techniques ◽  
High Time Resolution ◽  
Monitoring Networks ◽  
Chemical Transport Model ◽  
Individual Calibration ◽  
Ambient Measurements

Abstract. Simultaneous ground-based measurements of ozone (O3) and carbon monoxide (CO) were conducted in March 2005 as part of the East Asian Regional Experiment (EAREX) 2005 under the umbrella of the Atmospheric Brown Clouds (ABC) project. Multiple air quality monitoring networks were integrated by performing intercomparison of individual calibration standards and measurement techniques to ensure comparability of ambient measurements, along with providing consistently high time-resolution measurements of O3 and CO at the surface sites in East Asia. Ambient data collected from eight surface stations were compared with simulation results obtained by a regional chemical transport model to infer recent changes in CO emissions from East Asia. Our inverse estimates of the CO emissions from China up to 2005 suggested an increase of 16% since 2001, in good agreement with the recent MOPITT satellite observations and the bottom-up estimates up to 2006. The O3 enhancement relative to CO in continental pollution plumes traversed in the boundary layer were examined as a function of transport time from the Asian continent to the western Pacific Ocean. Comparison of the observed δO3/Δ CO ratios and their modeled spatial distributions suggests an increase in the Δ O3/Δ CO ratio due likely to en-route photochemical O3 formation during eastward transport, confirming that East Asia is an important O3 source region during spring.

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