3-DIMENSIONAL DISTRIBUTION OF NONMENTHANE HYDROCARBONS AND HALOCARBONS OVER THE NORTHWESTERN PACIFIC DURING THE 1991 PACIFIC EXPLORATORY MISSION (PEM-WEST-A)

A total of 1667 whole air samples were collected onboard the NASA DC-8 aircraft during the Ci-week Pacific Exploratory Mission over the west ern Pacific (PEM-West A) in September and October 1991. The samples we re assayed for 15 C-2-C-7 hydrocarbons and six halocarbons. Latitudina l(0.5 degrees S to 59.5 degrees N) and longitudinal (114 degrees E to 122 degrees W) profiles were obtained from samples collected between g round level and 12.7 km. Thirteen of the 18 missions exhibited at leas t one vertical profile where the hydrocarbon mixing ratios increased w ith altitude. Longitude-latitude color patch plots at three altitude l evels and three-dimensional color latitude altitude and longitude-alti tude contour plots exhibit a significant number of middle-upper tropos pheric pollution events. These and several lower tropospheric pollutio n plumes were characterized by comparison with urban data from Tokyo a nd Hong Kong, as well as with natural gas and the products from incomp lete combustion. Elevated levels of nonmethane hydrocarbons (NMHC) and other trace gases in the upper-middle free troposphere were attribute d to deep convection over the Asian continent and to typhoon-driven co nvection near the western Pacific coast of Asia. In addition, NMHCs an d CH3CCl3 were found to be useful tracers with which to distinguish hy drocarbon and halocarbon augmented plumes emitted from coastal Asian c ities into the northwestern Pacific.