Asian dust storm influence on North American ambient PM levels: observational evidence and controlling factors

摘要

New observational evidence of the trans-Pacific transport of Asian dust andits contribution to the ambient particulate matter (PM) levels in NorthAmerica was revealed, based on the interannual variations between Asian duststorms and the ambient PM levels in western North America from year 2000 to2006. A high correlation was found between them with an R2 value of0.83. From analysis of the differences in the correlation between 2005 and2006, three factors explain the variation of trans-Pacific transport andinfluences of Asian dust storms on PM levels in western North America. Thesewere identified by modeling results and the re-analysis data. They were 1)Strength of frontal cyclones from Mongolia to north easternChina: The frontal cyclones in East Asia not only bring strong cold airoutbreaks, generating dust storms in East Asia, but also lift Asian dustinto westerly winds of the free troposphere for trans-Pacific transport; 2)Pattern of transport pathway over the North Pacific: Thecirculation patterns of westerlies over the North Pacific govern thetrans-Pacific transport pattern. Strong zonal airflow of the westerly jet inthe free troposphere over the North Pacific favor significant trans-Pacifictransport of Asian dust; 3) Variation of precipitation inthe North Pacific: The scavenging of Asian dust particles by precipitationis a major process of dust removal on the trans-Pacific transport pathway.Therefore, variation of precipitation in the North Pacific could affecttrans-Pacific transport of Asian dust.