IMPACT OF ASIAN EMISSIONS ON THE REMOTE NORTH PACIFIC ATMOSPHERE: INTERPRETATION OF CO DATA FROM SHEMYA, GUAM, MIDWAY AND MAUNA LOA
by Daniel Jaffe1, Alexander Mahura1,2, John Atkins1, Paul C. Novelli3 and John Merrill4
Accepted by JGR-Atmospheres 8/96
1 Department of Chemistry and Geophysical Institute, University of Alaska Fairbanks
2Institute of Northern Ecological Problems,Kola Science Center, Russian Academy of Sciences
3Cooperative Institute for Research in Environmental Studies, University of Colorado; now at NOAA/CMDL Boulder, Colorado
4Center for Atmospheric Chemistry, Graduate School of Oceanography, University of Rhode Island
Industrial emissions from Asia are increasing and represent a growing portion of the global emissions for CO2, CO, NOx and SO2. In this study we look at the concentration of CO at four remote stations in the North Pacific to evaluate the impact of Asian industrial emissions on the remote atmosphere. Data is from the NOAA-CMDL cooperative air sampling network for Shemya, Guam, Mauna Loa and Midway
The weekly flask data clearly define a CO seasonal cycle [Novelli et al., 1994]. In the present analysis we use a locally weighted smoothing technique to identify individual data outliers from the smoothed seasonal cycle. Defining an event as a period when the CO observation is more than 5 ppb above the seasonal cycle, we have identified 22-92 outliers or "events" at each site for the 3-6 year data records. We hypothesize that these events represent periods when continental emissions directly influenced the atmospheric mixing ratios at these locations. Using isentropic back trajectories we try to identify a possible source region or pathway for each event and present a distribution of the trajectory types for the events.
For the events at Midway, Mauna Loa, Guam and Shemya, we are able to identify 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 events occur during spring and are usually associated with transport from Asia. These events bring the highest CO mixing ratios observed at any time during the year to these sites, with CO enhancements up to 46 ppb. For Mauna Loa, a small number of events during summer are due to transport from North and Central America. At Guam, easterly trade winds are the norm and bring with them clean air. However, occasionally synoptic events bring Asian emissions to the island, generally during late summer and fall, from either East Asia or Southeast Asia (e.g. Indonesia). These events bring with them the largest CO enhancements of any of the 4 sites considered in this paper, up to 58 ppb. At Shemya the picture is less clear. A relatively small fraction of the events can be explained by transport from the densely industrialized regions of East Asia. Some events appear to be associated with transport from Northeastern Russia and others possibly due to transport from the Arctic. However this interpretation is hampered somewhat by the trajectory model domain which ends at 70o N.
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 ppb above the seasonal cycle. Although these changes reduce the number of events identified at each site, it does not significantly change the fraction of events which can be attributed to a known source.