Long-range transport of Asian pollution to North America: mechanisms, chemistry and variability

Abstract

Long-range transport (LRT) of Asian pollutants affects the atmospheric composition over the North Pacific and has important implications in terms of air quality regulation in the United States. Through analysis of surface and aircraft observations with a global model of tropospheric chemistry, this dissertation investigates the mechanisms, chemistry, and variability of long-range transport of Asian pollution. This study has resulted in three papers, two of which have been published in the Journal of Geophysical Research - Atmospheres (Chapter 2 and 3), and one is in preparation for submission to the same journal (Chapter 4).Chapter 2 examines observations of carbon monoxide (CO, a tracer for anthropogenic emissions) in the North Pacific to understand the seasonality and transport of Asian pollution. The Asian influence on the North Pacific troposphere maximizes during spring and minimizes in summer, but LRT occurs throughout the year. We find that 80% of the export episodes over East Asia are mediated by mid-latitude cyclones and 3/4 of the events imported into the lower troposphere over the NE Pacific are by boundary layer transport.Chapter 3 focuses on the daily to interannual variability of transpacific transport. We relate the daily variability in Asian outflow to the passage of mid-latitude cyclones in East Asia, while transpacific transport is linked to the intensity of the Pacific High and the Aleutian low. On interannual timescales, we find that the variability in transpacific transport is favored by a strong Pacific High and a strong Aleutian Low.Chapter 4 focuses on observations of Asian pollution plumes in the free troposphere over North America during summer. The summertime Asian plumes are enhanced in many trace gases compared to background. When contrasted with previous springtime measurements, the summertime transport plumes show much higher levels of reactive nitrogen species and ozone as a result of active photochemistry.