Asian dust storm influence on North American ambient PM levels: observational evidence and controlling factors T. L. Zhao1, S. L. Gong1,2, X. Y. Zhang2, and D. A. Jaffe3 1Air Quality Research Division, Science and Technology Branch, Environment Canada, 4905 Dufferin Street, Toronto, Ontario, M3H 5T4, Canada 2Centre for Atmosphere Watch and Services of CMA, Chinese Academy of Meteorological Sciences, Beijing 100081, China 3University of Washington-Bothell, 18115 Campus Way NE, Bothell, WA 98011-8246, USA
Abstract. New observational evidence of the trans-Pacific transport of Asian dust and
its contribution to the ambient particulate matter (PM) levels in North
America was revealed, based on the interannual variations between Asian dust
storms and the ambient PM levels in western North America from year 2000 to
2006. A high correlation was found between them with an R2 value of
0.83. From analysis of the differences in the correlation between 2005 and
2006, three factors explain the variation of trans-Pacific transport and
influences of Asian dust storms on PM levels in western North America. These
were identified by modeling results and the re-analysis data. They were 1)
Strength of frontal cyclones from Mongolia to north eastern
China: The frontal cyclones in East Asia not only bring strong cold air
outbreaks, generating dust storms in East Asia, but also lift Asian dust
into westerly winds of the free troposphere for trans-Pacific transport; 2)
Pattern of transport pathway over the North Pacific: The
circulation patterns of westerlies over the North Pacific govern the
trans-Pacific transport pattern. Strong zonal airflow of the westerly jet in
the free troposphere over the North Pacific favor significant trans-Pacific
transport of Asian dust; 3) Variation of precipitation in
the North Pacific: The scavenging of Asian dust particles by precipitation
is a major process of dust removal on the trans-Pacific transport pathway.
Therefore, variation of precipitation in the North Pacific could affect
trans-Pacific transport of Asian dust.
Citation: Zhao, T. L., Gong, S. L., Zhang, X. Y., and Jaffe, D. A.: Asian dust storm influence on North American ambient PM levels: observational evidence and controlling factors, Atmos. Chem. Phys., 8, 2717-2728, doi:10.5194/acp-8-2717-2008, 2008.