Ozone photochemistry in the northeastern Pacific troposphere and the impacts of trans-Pacific pollution transport.

摘要

This dissertation sets as its goals to quantify the ozone photochemical tendency, T(O3), in the springtime Northeastern Pacific troposphere, quantify the factors controlling T(O3), and determine the impacts of anthropogenic trace gases, transported from the Northwestern Pacific, on the chemical composition and chemistry of the Northeastern Pacific. Pursuant to these goals, a chemiluminescence instrument to measure atmospheric NO was prepared for airborne measurements, which involved quantifying and optimizing its response characteristics under conditions expected in the lower troposphere. In the spring of 1999 this instrument was installed on the University of Wyoming's King Air research aircraft as part of the Photochemical Ozone Budget of the Eastern North Pacific Atmosphere (PHOBEA) experiment. During 14 flights in late March and April, 1999, measurements of NO and other trace gases were made in vertical profiles over the Pacific Ocean off the coast of Washington State. Trajectory and chemical analyses indicated that the majority of all encountered air masses likely originated from the Northwestern Pacific and had characteristics of emissions from the East Asian continental region. Calculations of air mass age using two independent methods are consistent with transport from the Northwestern Pacific in 5--20 days. Further analyses provides evidence that anthropogenically influenced air masses from the Northwestern Pacific affect the overall chemical composition of the Northeastern Pacific troposphere. The aircraft measurements are also used to constrain a detailed photochemical box model, which is used to calculate T(O3) in this region. T(O3) in marine flow from the remote Pacific is found to be weakly ozone destroying from the surface up to 8 km. A general picture of T(O3) throughout the springtime North Pacific is presented. The model is further used to investigate the impacts of PAN decomposition on NOx and T(O3), both in the marine background and in a strongly subsiding air mass. Recent global modeling studies have estimated the impacts of doubling Asian emissions on the chemical composition of the Northeastern Pacific troposphere. These estimates are used in conjunction with the PHOBEA aircraft data to calculate T(O3) in the Northeastern Pacific under a scenario of doubled Asian emissions.