Rapid transpacific transport in autumn observed by the A‐train satellites

Abstract

Transpacific transport of dust and pollutants is well documented for spring but less so for other seasons. Here we investigate rapid transpacific transport in autumn utilizing the A‐train satellites. In three episodes studied as examples, SO2 plumes over East Asia were detected by the Ozone Monitoring Instrument aboard the Aura satellite and found to reach North America in 5–6 days. They were likely derived from anthropogenic sources, given that identical transport patterns of CO, a tracer for incomplete combustion, were simultaneously observed by the Aqua satellite. Trajectory analysis and meteorological data were employed to explore the meteorological circumstances surrounding these events: like many of their counterparts in spring, all three plumes were lifted to the free troposphere in warm conveyor belts associated with midlatitude wave cyclones, and their migration to the downwind region was regulated by the meteorology over the east Pacific. These cases provide further evidence that a fraction of SO2 could escape wet scavenging and be transported at much greater efficiency than could NOx (NO + NO2). An analysis of the SO2 and CO data from September to November during 2005–2008 found 16 SO2 long‐range transport episodes, out of 62 Asian outflow events. While the counts are sensitive to the choice of criteria, they suggest that the long‐range transport of Asian sulfur species occurs quite frequently and could exert strong impacts on large downstream areas. This study also highlights the importance of transpacific transport in autumn, which has thus far been rarely studied and deserves more attention from the community.