Transport pathways of fire generated tracers to the upper troposphere as determined by A-Train satellite measurements
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Convective and long-range transport of air mass controls the global distributions and impacts of the pollutants generated in limited source regions. However, an observational characterization of such transport based on long-term satellite data has been difficult in part because adequate satellite measurements were not available until recent years and lack of an automated method for identifying the transport pathways. My dissertation addresses this problem through three steps: First, I developed a method to automate the identification of two pathways that are responsible for the transport of biomass burning generated tracers from the surface to the upper troposphere (UT). I focused on carbon monoxide (CO) because it has a relatively long lifetime in the atmosphere, and thus it is commonly used as a tracer of convective and long-range mass transport. Next, I applied this method to investigate the relative importance of the two pathways in determining the seasonal pattern of UT CO distribution. Results show that the seasonality of CO concentrations in the tropical UT mainly reflects the seasonality of the “local convection” pathway, because the “local convection” pathway typically transports significantly more CO to the UT than the “advection within the lower troposphere followed by convective transport” pathway. Then, I investigated the impacts of transport pathways on the interannual variation of tropical UT CO concentration. Results show that the interannual variation of CO in the tropical UT is dominated by UT CO anomaly over Southeast Asia related to the El Niño-Southern Oscillation, and the average mass of CO transported per event of “local convection” is the factor that accounts for the UT CO difference between two El Niño periods. After that, I began to address the transport of more complex pollutants such as aerosols. First, the seasonal and diurnal variations of the vertical distributions of aerosol properties were characterized through a statistical analysis of aerosol profile data. Then, the transport pathways associated with the aerosol layer at the tropopause level over Asian area during boreal summer were investigated through back-trajectory model analyses. Three major pathways were found and the occurrence frequency of each pathway was analyzed and discussed.