A study of DMS oxidation in the tropics:: Comparison of christmas island field observations of DMS, SO2, and DMSO with model simulations

This study reports comparisons between model simulations, based on current sulfur mechanisms, with the DMS, SO2 and DMSO observational data reported by Bandy et al. (1996) in their 1994 Christmas Island field study. For both DMS and SO2, the model results were found to be in excellent agreement with the observations when the observations were filtered so as to establish a common meteorological environment. This filtered DMS and SO2 data encompassed approximately half of the total sampled days. Based on these composite profiles, it was shown that oxidation of DMS via OH was the dominant pathway with no more than 5 to 15% proceeding through Cl atoms and less than 3% through NO3. This analysis was based on an estimated DMS sea-to-air flux of 3.4 x 10(9) molecs cm(-2) s(-1). The dominant source of BL SO2 was oxidation of DMS, the overall conversion efficiency being evaluated at 0.65 +/- 0.15. The major loss of SO2 was deposition to the ocean's surface and scavenging by aerosol. The resulting combined first order k value was estimated at 1.6 x 10(-5) s(-1). In contrast to the DMS and SO2 simulations, the model under-predicted the observed DMSO levels by nearly a factor of 50. Although DMSO instrument measurement problems can not be totally ruled out, the possibility of DMSO sources other than gas phase oxidation of DMS must be seriously considered and should be explored in future studies.