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IMPACTS OF BIOMASS BURNING AND LARGE-SCALE TRANSPORT ON THE SOUTHEAST ASIAN HAZE

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Title
IMPACTS OF BIOMASS BURNING AND LARGE-SCALE TRANSPORT ON THE SOUTHEAST ASIAN HAZE
Author
Son Truong Cong Hoang
Advisor
Lee, Myong-In
Issue Date
2016-08
Publisher
Graduate School of UNIST
Abstract
Biomass burning has significant impacts on regional air quality and climate in Southeast Asia. This study examines the impacts of biomass burning on the large-scale transport of aerosols and haze events using observational analysis and numerical model simulations. The spatiotemporal variation of observed aerosols shows significant correlations, positively with the emission induced by fire and negatively with the removal by precipitation both in seasonal and inter-annual timescale. Particularly, the variation of aerosol optical depth (AOD) retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) is primarily affected by El Niño Southern Oscillation (ENSO), leading to a substantial year-to-year variation. The aerosol reanalysis data from the Modern-Era Retrospective analysis for Research and Applications 2 (MERRA-2) reveals that the aerosols emitted from combustion such as organic carbon and sulfate are the main contributors to the total AOD variation in this region. Organic carbon accounts for over 60 % of total AOD amounts, being highly correlated with the biomass burning, while sulfate also serves as a significant source for the background aerosol concentration. The impacts of aerosols on meteorology and the local air quality have been further investigated using the Weather Research and Forecasting/Chemistry (WRF-Chem) model simulations for June 2013 and September 2015. Overall, the model simulation can capture the most of observed spatial and temporal variations of aerosol appeared in MODIS and MERRA-2, although it tends to underestimate AOD for the both tested cases. The model sensitivity experiments show that both aerosol direct and indirect effects have significant impacts on meteorology and local air quality. The direct impact of aerosols tends to reduce the incoming shortwave radiation at the surface, thereby decreasing surface temperature and the planetary boundary layer (PBL) height. Because of decreasing the PBL height and stabilizing lower atmosphere, the aerosol direct effect tends to increase near-surface concentration of atmospheric trace gases such as NOx, CO and O3. The indirect impact of aerosols also contributes to decrease the shortwave radiation through enhanced activation of cloud condensation nuclei particularly over the ocean. The near-surface concentration of trace gases tends to increase also by the aerosol indirect impact near the emission source except O3, which actually decreases. In case of AOD and PM2.5, both aerosol effects have significant impacts in which the direct effect increases AOD and PM2.5 whereas aerosol indirect effect decreases AOD and PM2.5. Although the direct and indirect feedbacks on aerosol mass concentrations are subject to uncertainties, this work demonstrates the significance role of aerosol feedback for real-time air quality forecasting under haze conditions.
Description
Department of Urban and Environmental Engineering (Environmental Science and Engineering)
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