A43G-01 INVITED
Transport and Chemical Production of Ozone in the East Asian Pacific Rim Region: -Modeling Study Based on Observation-
Form satellite observational data, east-central China covering the North China Plain (NCP) and Yanzi Delta (YZD) has been identified as the most widely spread source area of air pollutants in the East Asian Pacific region. In order to quantify transport and chemical production of ozone in this region, both of observational and modeling studies in both of source and outflow region are necessary. In the present study, we investigated the budgets of ozone over East Asia by using regional chemical transport models (NAQPMS and CMAQ) based on observations at newly founded three mountain sites (Mt. Tai, Hua and Huang) in east-central China, and several sites from EANET and regional WMO/GAW. The observations show that a striking pattern of two sharp high ozone peaks in May-June and September-October at the three mountain sites. The budget analysis by the model confirms that maximum of net photochemical ozone production reaches 31.8, 15.1 and 11.4 ppb/day at Mt. Tai, Hua and Huang, respectively. The net chemical production dominates the formation of ozone maximum at Mt. Tai and Hua in June, and the importing transport also plays a comparable importance at Mt. Huang. In the outflow region at Oki, Japan, transport of ozone produced by East Asian emissions accounts up to 21 ppb in summer but less than 3 ppb in winter agreeing with the model analysis. The contribution of ozone due to East Asian emission is the largest (53.6%) in July-August, and somewhat smaller in May-June (34.0%) and September-October (30.7%) on the transect between Japan and the Asian continent.
A43G-02
Impact of East Asian Summer Monsoon on Seasonal Variations of Aerosols over Eastern China
Ground measurements show that seasonal variations of aerosols in Eastern China are different from those in the Eastern United States; while aerosol concentrations are the highest in winter over Eastern China, they are the highest in summer in the Eastern United States. We apply a global 3-D chemical transport model (GEOS-CHEM) driven by NASA/GEOS assimilated meteorological data to quantify the roles of East Asian summer monsoon and seasonal variations of emissions of aerosols/aerosol precursors in influencing seasonal variations of sulfate, nitrate, ammonium, black carbon, and organic carbon aerosols in Eastern China. Model results show that East Asian summer monsoon plays a major role in determining seasonal variations of aerosols in Eastern China. Rainfall associated with summer monsoon leads to large wet deposition of aerosols, and the cross-equatorial flows from the Southern Hemisphere bring clean and wet air to Eastern China, all contributing to the low concentrations of aerosols in summer. Sensitivity studies with no seasonal variations in emissions indicate that East Asian summer monsoon can reduce aerosol concentration averaged over the domain of 110-120E and 20- 45N by 60-70%, as the averaged surface-layer aerosol concentration in July is compared with that in January. We also examine the influence of East Asian monsoon on transport and distributions of aerosols in the free troposphere. Results have important implications for air quality and climate effects of aerosols in Eastern China.
A43G-03
An investigation into seasonal and regional aerosol characteristics in East Asia using model- predicted and satellite-/sunphotometer-derived aerosol properties
In this study, the spatial and seasonal distributions of EOS/Terra Moderate Resolution Imaging Spectroradiometer (MODIS)-derived aerosol optical depth (AOD) over East Asia are analyzed in conjunction with US EPA Models-3/CMAQ v4.3 modeling. First, AOD (τM-BAERMODIS) retrieved through a modified Bremen Aerosol Retrieval Algorithm (M-BAER algorithm) is compared with AOD (τCMAQ) calculated from the US EPA Models-3/CMAQ model simulations. For the four season episodes selected in this study, both τM-BAERMODIS and τCMAQ show high values around Chinese urban and industrial centers, such as Sichuan Basins, Bohai Bay area, and Yangtze Delta areas, as well as excessively high NH3 emission regions. The levels of τCMAQ are also comparable to those of τM-BAERMODIS throughout the domain. Since τM-BAERMODIS cannot provide information on the aerosol chemical composition in the atmosphere, different aerosol formation characteristics in different regions and different seasons in East Asia cannot be described or identified by τM-BAERMODIS itself. Therefore, the seasonally and regionally varying aerosol formation characteristics are investigated by the US EPA Models- 3/CMAQ v4.3 model simulations. The contribution of each particulate chemical species to τM- BAERMODIS and τCMAQ shows strong seasonal variations. For example, during the summer episode, τM-BAERMODIS and τCMAQ are both raised due to high concentrations of (NH4)2SO4 over the Chinese urban and industrial centers, whereas during the winter episode, τM- BAERMODIS and τCMAQ are raised largely due to active NH4NO3 formation over urban and industrial centers, as well as over Chinese agricultural and livestock farming areas. On the other hand, τM- BAERMODIS is strongly correlated with the AOD (τAERONET) from the AERONET sites in East Asia, with an average correlation coefficient of R=0.77, thereby indicating the promising potential in the application of the M-BAER algorithm to air quality studies and satellite-based monitoring studies in East Asia.
A43G-04
Regional pollution transport during the TexAQS field studies
Intra- and interstate transport of pollution is studied using observational data and transport models. Data from airborne platforms during the Texas Air Quality studies (TexAQS and TexAQS II) are presented to show pollution transport from Houston, from Dallas, and from Beaumont throughout eastern Texas and into neighboring States. Airborne data, surface observations, and trajectory and transport models from these studies are examined to illustrate the effects of metropolitan area and point source emissions on air quality downwind.
A43G-05
Contribution of Regional Transport to Ozone Exceedances in Houston and Dallas, Texas
During the TEXAQS and TEXAQS II field experiments, aircraft measured ozone concentrations upwind, across, and downwind of Houston and Dallas, and the transport contributions to Dallas area ozone were quantified using the CAMx photochemical grid model. The transport contribution to ozone exceedances in both urban areas was at least as large as the contribution from local emissions, on average. For example, analysis of a flight over Dallas on a day that had a significant exceedance showed that the background ozone transported into Dallas constituted about 73% of the total ozone concentration. The aircraft measurements show that these two major metropolitan areas can be brought close to exceeding the 8-hour National Ambient Air Quality Standard for ozone solely from the ozone contribution from regional transport and before any contribution from local sources. The CAMx Model-predicted ozone concentrations agreed with the measurements on the importance of regional transport of ozone relative to local ozone formation. These results emphasize the benefits of regional control strategies, suggesting that local controls may not be sufficient to ensure attainment of the 8-hour ozone standard in Houston and Dallas.
A43G-06
Regional Variations in Intercontinental Transport of Ozone to the United States
This study quantifies the contribution of emissions from Asia and Europe on surface ozone concentrations in nine regions of the U.S. using the MOZART global chemical transport model. In each region, we assess the magnitude of Asian and European influence on surface concentrations, and identify key processes controlling the transport of imported species from the free troposphere to the surface. We find that imported ozone exhibits a bimodal seasonal distribution in west coast regions (Pacific Northwest, Northern California, and Southern California), consistent with other analyses of seasonal patterns in long-range transport to Europe and Asia. However, this seasonal pattern is absent in eastern regions (New England, Mid-Atlantic, and Southeast). The relative contributions of Asian and European emissions vary by region, as does the magnitude of imported ozone, and the conditions under which maximum import occurs. These differences reflect regionally specific import processes and local emissions.
A43G-07
Tropospheric transport climate partitioned by surface origin and transit time
We perform the first analysis of tropospheric transport using the global boundary-propagator Green function, G, which partitions air at every point and time according to both the transit time since last surface contact and the location of that contact. We compute G for a 3-year period with the MATCH model driven by NCEP re-analyses. Last contact time is resolved in 3-day intervals, and last-contact location with a global tiling of 41 patches concentrated in the Northern Hemisphere. The transport climate is quantified for four midlatitude receptor regions in terms of the seasonal-mean surface-origin and transit-time partitioning of the column burden, the surface flux of newly arriving air, and the distribution of airmass in transit from source to receptor surface. At long transit times a nearly receptor independent pattern of last contact location is governed by where air is injected into the upper troposphere by deep convection and the high terrain of Tibet. The receptor origin composition of the column burden changes only slowly after ~40 days for winter and fall, while the composition of the flux onto the receptor continues to change at ~60 days. European and SE Asian air contribute comparably to the flux onto eastern N America, in spite of SE Asian air having the dominant burden. The flux of European air onto SE Asia in winter and fall is larger than the flux of SE Asian air onto Europe. The surface-to-surface transport mass distribution, ℛ, is used to identify transit-time dependent source- receptor teleconnections.