MEASUREMENTS OF CO AND O-3 AT SHEMYA, ALASKA

In situ measurements of surface CO were conducted from June 1994 to Ma y 1995, and surface ozone was measured from February to May, 1995, at Shemya, Alaska (52o44'N, 174o06'E) using nondispersive infrared-gas fi lter correlation (GFC) and UV absorption spectroscopy, respectively. O ver the same period, air samples were collected in flasks for analysis of CO and other trace gases as part of the NOAA-CMDL cooperative air sampling network. We compared the continuous GFC measurements with the National Oceanic and Atmospheric Administration Climate Monitoring an d Diagnostics Laboratory (NOAA-CMDL) flask data. Over this 1-year peri od, CO mixing ratios varied between 60 and 250 parts per billion by vo lume (ppbv). Within this range, the comparison between the two measure ments is quite good, with an overall R-2 of 0.953 and an average diffe rence of 3.1%. A seasonal cycle is apparent in the CO data, with a spr ingtime maximum and a summer minimum. Synoptic influences on the data include transport from the lower-latitude Pacific, bringing air with v ery low CO mixing ratios to Shemya, and, occasionally, transport from industrial areas in east Asia, including northern China, Japan, and ea stern Russia. A scatterplot of CO versus O-3 using all the data shows essentially no relationship at this remote site. This result implies t hat the primary sources and sinks for these trace gases are different at this location, However, during a few 12- to 48-hour periods in fall and late spring, enhancements in CO or in both CO and O-3 were observ ed. During these periods, isentropic back trajectories indicate transp ort from the west and southwest. However, the trajectories are often d ifficult to interpret due to looping and are of short duration due to impact at the surface. These complexities are associated with the pres ence of cyclonic systems in the region. The local meteorological data suggest that the enhanced concentrations occurred around the time when these cyclonic systems passed near the sampling site. Synoptic surfac e pressure maps indicate that these cyclonic systems formed or crossed industrial regions in east Asia and passed near Shemya on their way t o the Bering Sea. This process suggests a role for transport of anthro pogenic pollutants by cyclonic systems moving northward along the west ern edge of the Pacific Ocean.