Characterization of Atmospheric Nitrogen Chemistry and the Formation/ Evolution of Particulate Matter in Houston, TX
Leong, Yu Jun
Doctor of Philosophy
This thesis covers laboratory experiments to study the homogeneous reduction of nitric acid (HNO₃) to nitrous acid (HONO) in the presence of volatile organic compounds that are surrogates for those emitted by motor vehicles. The results presented in this study focus on the impact of environmental variables on the rate of formation of HONO in this process. The homogeneous conversion of HNO₃ to HONO has significant atmospheric implications due to the “renoxification” of less reactive HNO₃ into more reactive HONO. Consecutively, this thesis describes particulate matter (PM) data collected from a month-long (September 2013) field project in Houston, TX. A mobile laboratory containing state-of-the-art PM instrumentation and auxiliary measurements was deployed. The main focus for the thesis work was to utilize this dataset to better characterize PM pollution in the city of Houston. This was achieved by several analysis approaches including cluster analysis, back-trajectory analysis, and principal component analysis to describe spatial and temporal variations in submicron PM in the Houston region. Finally, this work describes the use of a statistical source apportionment technique, positive matrix factorization, on the field dataset to apportion important constituents of atmospheric aerosols in Houston. This technique allowed the apportionment of four organic aerosol factors, two of which were associated with organic nitrates from biogenic sources. Submicron PM plume events from on-road, industrial, and biomass burning sources in Houston also were chemically characterized. Because sources of PM pollution are still poorly understood, particularly in the highly industrial and urban city of Houston, the results from this thesis will advance PM modeling capabilities and allow improved PM control strategies in polluted urban areas similar to Houston.