Summertime influence of Asian pollution in the middle and upper troposphere during INTEX-A
Abstract
We analyze aircraft observations obtained during INTEX-A (1 July - 14 August 2004) with the GEOS-CHEM global model of tropospheric chemistry to understand the influence of Asian pollution in the middle and upper troposphere over the United States (US) during summer. We apply Principal Component Analysis (PCA) to the observations and find 4 major types of airmasses: Asian, lower stratospheric, convection/lightning, and background. PCA identifies five major Asian pollution plumes during INTEX-A, consistent with results from the GEOS-CHEM model and back-trajectories. The geographic distributions of the Asian plumes span from the remote northeastern Pacific to the US east coast, where they join the local pollution outflow to the North Atlantic. The major trans-Pacific transport mechanisms were export in warm conveyor belts of mid-latitude cyclones as well as deep convection followed by advection in the middle and upper troposphere, with differing transport times (3-10 days), transport altitudes (5-11 km), and chemical compositions. On average, observed mixing ratios were significantly enhanced in Asian plumes compared to background airmasses in the middle and upper troposphere: CO (ΔCO = 19 ppbv relative to 94 ppbv for background aimasses), O3 (ΔO3 = 26 ppbv, background = 74 ppbv), PAN (ΔPAN = 270 pptv, background = 335 ppbv), HNO3 (ΔHNO3 = 125 pptv, background = 237 pptv), C2H6 (ΔC2H6 = 180 pptv, background = 744 pptv), C2H2 (ΔC2H2 = 93 pptv, background = 84 pptv), HCN (ΔHCN = 146 pptv, background = 271 pptv), and CH3OH (ΔCH3OH = 1006 pptv, background = 1364 pptv). Individual Asian plumes have very different ΔO3/ΔCO ratios, ranging from -0.27 to 1.11. Some of the very large O3 enhancements appear to be due to mixing of Asian airmasses with lower stratospheric air. Through detailed case studies, we will examine the influence of transport pathways, chemical evolution, wet deposition, and stratosphere-troposphere exchange on the composition of these Asian pollution plumes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFM.A41D..05L
- Keywords:
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- 0365 Troposphere: composition and chemistry;
- 0368 Troposphere: constituent transport and chemistry