The influence of long-range transport of pollution on the annual cycles of carbon monoxide and ozone
Abstract
During 2001-2002, carbon monoxide and ozone measurements were made at Cheeka Peak, Washington, a remote site on the northwestern tip of the contiguous U.S. These observations were combined with a global model, GEOS-CHEM, to yield information on the controlling factors of CO and ozone concentrations in different seasons. Previous CO-ozone measurement campaigns at Cheeka Peak (spring, 1997 and 1998) relied upon isentropic back trajectories to classify the data by source region. In this paper however, we show that GEOS-CHEM is a superior tool because it incorporates emission strengths, mixing/diffusion, and chemical processes, and gives a better agreement with the measurements. Two outputs from GEOS-CHEM were the most useful in classifying the data: the amount of CO from European+Asian pollution ("LRT" for long-range transport), and the amount of CO produced from the oxidation of CH4 and biogenic hydrocarbons ("Ox" for oxidation CO). LRT is the dominant source of CO from Jan. - Jun., whereas Ox dominates from Jul. to Oct. Peaks in LRT usually show a corresponding peak in measured CO. Ozone production and/or destruction during LRT events is dependent on a myriad of factors and is thus not well correlated with CO. Periods where Ox is enhanced generally show a decrease in CO and ozone concentrations compared to LRT-dominant times. When these Ox-events occur in the winter and spring, they are associated with transport from more southerly latitudes, which brings cleaner oceanic tropical air masses exposed to higher oxidation rates and a greater time since land contact (aged pollution). Hourly CO measurements from all seasons in 2001-2002, and the springs of 1997 and 1998, are well correlated (r=0.88) with the ratio LRT/Ox, indicating that these two parameters account for roughly 78% of the variability in CO. Ozone correlates to LRT/Ox less well: r=0.70, or 50% of the variability in ozone is accounted for by LRT/Ox.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFM.A31D0077W
- Keywords:
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- 0322 Constituent sources and sinks;
- 0368 Troposphere: constituent transport and chemistry