Chemistry of dimethyl sulfide in the equatorial Pacific atmosphere

A field study of the chemistry of dimethyl sulfide (DMS) was conducted on the island of Kiritimati (Christmas Island) during July and August, 1994. This island is located at 2 degrees N, 157 degrees W approximately 2000 km south of Hawaii. We obtained a very repeatable diurnal variation for both DMS and sulfur dioxide (SO2) during two 5-day and one 2-day experiments. Near sunrise DMS was about 200 pptv. It decreased to about 120 pptv by late afternoon. During the daytime SO2 increased from about 20 pptv to about 75 pptv. At night DMS increased and SO2 decreased almost linearly. About 62% of the DMS was converted to SO2. DMS was emitted from the ocean at an average flux of 3.7 x 10(13) molecules m(-2) s(-1). The average dry deposition velocity of SO2 was 6.8 mm sec(-1). Most of the SO2 appeared to be lost to the ocean although a comparable but not significantly larger nux to aerosol cannot be ruled out. Dimethyl sulfoxide was in the range 10 to 50 pptv with a mean of about 25 pptv. Dimethyl sulfone was in the range 0 to 15 pptv with a mean of about 3 pptv. There was no diurnal trend in either species. A much smaller fraction of the DMS was converted to dimethyl sulfone than dimethyl sulfoxide.