Investigating the Emission Sources of Air Pollutants Using an Atmospheric Chemical Transport Model and Its Adjoint

• Main Author: Lee, Hyung-Min
• Format: Text
• Language: unknown
• Published: CU Scholar 2016
• Subjects: adjoint modeling; air pollution; Antarctica; atmospheric chemical transport model; nitrogen deposition; PM2.5; Environmental Chemistry; Environmental Sciences; Antarctic; Austral; Antarc*
• Online Access: https://scholar.colorado.edu/cven_gradetds/44; https://scholar.colorado.edu/cgi/viewcontent.cgi?article=1049&context=cven_gradetds

Quantifying the origin of air pollutants that have detrimental impacts on human health and ecosystems is a necessary but challenging aspect of studying and mitigating our impact on the environment. Using a 3-dimensional atmospheric chemical transport model, GEOS-Chem, and its adjoint we investigate emission sources and transport mechanisms of air pollutants. Adjoint-based source attribution enables quantification of the percent contribution of each emission source and gas-phase chemical reaction to the air pollutants of interest. This thesis is a collection of three studies conducted at different regional and temporal scales: 1) monthly average surface level nitrate in Antarctica, 2) seasonality of nitrogen deposition in federal Class I areas in the US, and 3) daily PM2.5 concentrations in Seoul metropolitan area, Korea. The results of these studies highlight the various roles of gas and aerosol emissions in impacting different aspects of the environment. Our results suggest that background levels of total nitrate at the surface level in Antarctic in austral winter are sensitive to NOx emissions from mid-latitudes, which is transported to Antarctica as total nitrate formed above continental source regions in the free troposphere. In other seasons, more NOx is transported as a reservoir species (e.g., peroxyacetyl nitrate, PAN) through the free troposphere, transforming into total nitrate within a cone of influence that extends to 35 degrees S and above 4 km altitude. From the second project, we find that while it is effective to control emissions in the western US to reduce the area of regions in critical loads (CL) exceedance, it can be more effective to control emissions in the eastern US to reduce the magnitude of Nr deposition above the CL. In our final project, we find that average contributions to the high PM2.5 episodes occurred in Seoul in May from 2009 to 2013 simulated by the model are 39% from the Shandong region, 16% from the Shanghai region, 14% from the Beijing region, and 15% from South Korea. Anthropogenic SO2 emissions from South Korea are negligible with 90% of the total contribution originating from China. Findings from this study may guide 1) interpretation of nitrate records from Antarctic ice cores, 2) setting protection plans for Class I areas, and 3) strategizing to meet PM2.5 air quality standards for the Seoul metropolitan area.