IMPACT OF ASIAN EMISSIONS ON THE REMOTE NORTH PACIFIC ATMOSPHERE - INTERPRETATION OF CO DATA FROM SHEMYA, GUAM, MIDWAY AND MAUNA-LOA

In this study we look at the concentration of CO at four remote statio ns in the North Pacific to evaluate the impact of Asian industrial emi ssions on the remote atmosphere. Using a locally weighted smoothing te chnique to identify individual data outliers from the seasonal cycle, we have identified 22-92 outliers or ''events'' (greater than 5 ppbv a bove the seasonal cycle) at each site for the 3-6 year data records. U sing isentropic back trajectories, we identify a possible source regio n for each event and present a distribution of the trajectory types. F or the events at Midway, Mauna Loa, Guam, and Shemya, we are able to i dentify a source region for the elevated CO in 82, 72, 65, and 50% of the events, respectively. At Mauna Loa and Midway a majority of the ev ents occur during spring and are usually associated with transport fro m Asia. These events bring the highest CO mixing ratios observed at an y time during the year to these sites, with CO enhancements up to 46 p pb. At Guam, easterly trade winds are the norm, but occasionally synop tic events bring Asian emissions to the island, generally during late summer and fall, from either East Asia or Southeast Asia (e.g., Indone sia). These events bring with them the largest CO enhancements of any of the four sites considered in this paper, up to 58 ppb. Finally, to examine the robustness of our conclusions, we redo our analysis using the more stringent definition that an event must be either 10 or 15 pp b above the seasonal cycle. Although this reduces the number of events identified at each site, it does not significantly change the fractio n of events which can be attributed to a known source.