An investigation into seasonal and regional aerosol characteristics in East Asia using model-predicted and remotely-sensed aerosol properties
In this study, the spatio-temporal and seasonal distributions of EOS/Terra Moderate Resolution Imaging Spectroradiometer (MODIS)-derived aerosol optical depth (AOD) over East Asia were analyzed in conjunction with US EPA Models-3/CMAQ v4.3 modeling. In this study, two MODIS AOD products (&ta...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2008-11-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/8/6627/2008/acp-8-6627-2008.pdf |
| Summary: | In this study, the spatio-temporal and seasonal distributions of EOS/Terra Moderate Resolution Imaging Spectroradiometer (MODIS)-derived aerosol optical depth (AOD) over East Asia were analyzed in conjunction with US EPA Models-3/CMAQ v4.3 modeling. In this study, two MODIS AOD products (&tau;<sub>MODIS</sub>: &tau;<sub>M-BAER</sub> and &tau;<sub>NASA</sub>) retrieved through a modified Bremen Aerosol Retrieval (M-BAER) algorithm and NASA collection 5 (C005) algorithm were compared with the AOD (&tau;<sub>CMAQ</sub>) that was calculated from the US EPA Models-3/CMAQ model simulations. In general, the CMAQ-predicted AOD values captured the spatial and temporal variations of the two MODIS AOD products over East Asia reasonably well. Since &tau;<sub>MODIS</sub> 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 &tau;<sub>MODIS</sub> itself. Therefore, the seasonally and regionally varying aerosol formation and distribution characteristics were investigated by the US EPA Models-3/CMAQ v4.3 model simulations. The contribution of each particulate chemical species to &tau;<sub>MODIS</sub> and &tau;<sub>CMAQ</sub> showed strong spatial, temporal and seasonal variations. For example, during the summer episode, &tau;<sub>MODIS</sub> and &tau;<sub>CMAQ</sub> were mainly raised due to high concentrations of (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> over Chinese urban and industrial centers and secondary organic aerosols (SOAs) over the southern parts of China, whereas during the late fall and winter episodes, &tau;<sub>MODIS</sub> and &tau;<sub>CMAQ</sub> were higher due largely to high levels of NH<sub>4</sub>NO<sub>3</sub> formed over the urban and industrial centers, as well as in areas with high NH<sub>3</sub> emissions. &tau;<sub>CMAQ</sub> was in general larger than &tau;<sub>MODIS</sub> during the year, except for spring. The high biases (&tau;<sub>CMAQ</sub>&gt;&tau;<sub>MODIS</sub>) may be due to the excessive formation of both (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> (summer episode) and NH<sub>4</sub>NO<sub>3</sub> (fall and winter episodes) over China, possibly from the use of overestimated values for NH<sub>3</sub> emissions in the CMAQ modeling. According to CMAQ modeling, particulate NH<sub>4</sub>NO<sub>3</sub> made a 14% (summer) to 54% (winter) contribution to &sigma;<sub>ext</sub> and &tau;<sub>CMAQ</sub>. Therefore, the importance of NH<sub>4</sub>NO<sub>3</sub> in estimating τ should not be ignored, particularly in studies of the East Asian air quality. In addition, the accuracy of &tau;<sub>M-BAER</sub> and &tau;<sub>NASA</sub> was evaluated by a comparison with the AOD (&tau;<sub>AERONET</sub>) from the AERONET sites in East Asia. Both &tau;<sub>M-BAER</sub> and &tau;<sub>NASA</sub> showed a strong correlation with &tau;<sub>AERONET</sub> around the 1:1 line (<I>R</I>=0.79), indicating promising potential for the application of both the M-BAER and NASA aerosol retrieval algorithms to satellite-based air quality monitoring studies in East Asia. |
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| ISSN: | 1680-7316 1680-7324 |