135 degrees W): A comparison of field data and model results .1. Dimethylsulfide Atmospheric sulfur cycling in the tropical Pacific marine boundary layer (12 degrees S

Shipboard measurements of atmospheric and seawater DMS were made at 12S, 135W for 6 days during March 1992. The mean seawater DMS concentration during this period was 4.1 0.45 nM (1, n = 260) and the mean atmospheric DMS mole fraction was 453 93 pmol mol1 (1, n = 843). Consistent atmospheric diel cycles were observed, with a nighttime maximum and daytime minimum and an amplitude of approximately 85 pmol mol1. Photochemical box model calculations were made to test the sensitivity of atmospheric DMS concentrations to the following parameters: 1) seatoair flux, 2) boundary layer height, 3) oxidation rate, and 4) vertical entrainment velocities. The observed relationship between the mean oceanic and atmospheric DMS levels require the use of an airsea exchange coefficient which is at the upper limit end of the range of commonly used parameterizations. The amplitude of the diel cycle in atmospheric DMS is significantly larger than that predicted by a photochemical model. This suggests that the seatoair DMS flux is higher than was previously thought, and the rate of daytime oxidation of DMS is substantially underestimated by current photochemical models of DMS oxidation.

Atmospheric sulfur cycling in the tropical Pacific marine boundary layer (12 degrees S,135 degrees W): A comparison of field data and model results .1. Dimethylsulfide