Using observations from the Cheeka Peak Observatory in northwestern Washington State during March-April, 1997, we show that Asian anthropogenic emissions significantly impact the concentrations of a large number of atmospheric species in the air arriving to North America during spring. Isentropic backtrajectories can be used to identify possible times when this impact will be felt, however trajectories alone are not sufficient to β’ndicate the presence of Asian pollutants. Detailed chemical and meteorological data from one of these periods (March 29th, 1997) indicates that the surface emissions were lifted into the free troposphere over Asia and then transported to North America in --6 days. 1997; VanArdeen et al., 1998]. From the mid-1970s to the 1990's the emissions of both NOx and SO2 from the East Asian region increased at an average rate of -4%/year. Transport of these pollutants into the central North Pacific atmosphere, especially during spring, has been well established [Prospero and Savoie, 1989; Talbot et al., 1997; Jaffe et al., 1997]. Transport of Asian desert dust to the North Pacific region during spring has also been observed [e.g. Merrill et al., 1989; Xiao et al., 1997]. However, impacts on North America from Asian pollution have not been previously reported.
In this report, we use isentropic back trajectories to identify times when the air sampled at a coastal site in Washington state had recently (within 10 days) been over East Asia. Detection of Asian pollution in these samples is complicated by three factors: 1) the trajectories may be in error or vertical uplift over the source region may be insufficient to raise surface pollutants into the free troposphere; 2) wet or dry deposition, chemical removal or dilution of the pollutants may occur enroute; and, 3) high global background levels or local sources of pollutants may obscure a smaller contribution from distant sources.