Gas-to-particle conversion of tropospheric sulfur as estimated from observations in the western North Pacific during PEM-West B

Abstract

Aircraft observations during the Pacific Exploratory Mission in the western Pacific Ocean, phase B (PEM-West B), taken in February-March 1994, have been used to constrain a numerical model that calculates local concentrations of gaseous H2S04, rates of homogeneous nucleation, and concentrations of newly formed, nanometer-sized particles. The data was selected from 13 flights over the western Pacific Ocean that covered an altitude range from the boundary layer (BL) to the upper troposphere (UT) and latitudes from 10°S to 60°N. The largest nucleation rates were calculated for the data from the flights over the temperate latitudes (λ>30°N). Within these latitudes, homogeneous nucleation rates averaged about 1-100 particles cm-3 s-1. Significantly smaller nucleation rates were calculated for the tropical (λ<20°N) and subtropical (20°N