CHEMICAL CHARACTERISTICS OF CONTINENTAL OUTFLOW FROM ASIA TO THE TROPOSPHERE OVER THE WESTERN PACIFIC-OCEAN DURING FEBRUARY-MARCH 1994 - RESULTS FROM PEM-WEST-B

We present here the chemical composition of outflow from the Asian con tinent to the atmosphere over the western Pacific basin during the Pac ific Exploratory Mission - West (PEM-West B) in February-March 1994. C omprehensive measurements of important tropospheric trace gases and ae rosol particulate matter were performed from the NASA DC-8 airborne la boratory. Backward 5 day isentropic trajectories were used to partitio n the outflow from two major source regions: continental north (>20 de grees N) and continental south (<20 degrees N). Air parcels that had n ot passed over continental areas for the previous 5 days were classifi ed as originating from an aged marine source. The trajectories and the chemistry together indicated that there was extensive rapid outflow o f air parcels at altitudes below 5 km, while aged marine air was rarel y encountered and only at <20 degrees N latitude. The outflow at low a ltitudes had enhancements in common industrial solvent vapors such as C2Cl4, CH3CCl3, and C6H6, intermixed with the combustion emission prod ucts C2H2, C2H6, CO, and NO. The mixing ratios of all species were up to tenfold greater in outflow from the continental north compared to t he continental south source region, with Pb-210 concentrations reachin g 38 fCi (10(-15) curies) per standard cubic meter. In the upper tropo sphere we again observed significant enhancements in combustion-derive d species in the 8-10 km altitude range, but water-soluble trace gases and aerosol species were depleted. These observations suggest that gr ound level emissions were lofted to the upper troposphere by wet conve ctive systems which stripped water-soluble components from these air p arcels. There were good correlations between C2H2 and CO and C2H6 (r(2 ) = 0.70 - 0.97) in these air parcels and much weaker ones between C2H 2 and H2O2 or CH3OOH (r(2) approximate to 0.50). These correlations we re the strongest in the continental north outflow where combustion inp uts appeared to be recent (I - 2 days old). Ozone and PAN showed gener al correlation in these same air parcels but not with the combustion p roducts. It thus appears that several source inputs were intermixed in these upper tropospheric air masses, with possible contributions from European or Middle Eastern source regions. In aged marine air mixing ratios of O-3 (approximate to 20 parts per billion by volume) and PAN (less than or equal to 10 parts per trillion by volume) were nearly id entical at <2 km and 10 - 12 km altitudes due to extensive convective uplifting of marine boundary layer air over the equatorial Pacific eve n in wintertime. Comparison of the Pacific Exploratory Mission-West A and PEM-West B data sets shows significantly larger mixing ratios of S O2 and H2O2 during PEM-West A. Emissions from eruption of Mount Pinatu bo are a likely cause for the former, while suppressed photochemical a ctivity in winter was probably responsible for the latter. This compar ison also highlighted the twofold enhancement in C2H2, C2H6, and C3H8 in the continental north outflow during PEM-West B. Although this coul d be due to reduced OH oxidation rates of these species in wintertime, we argue that increased source emissions are primarily responsible.