DMS photochemistry during the Asian dust-storm period in the Spring of 2001: model simulations vs. field observations

Abstract

This study examines the local/regional DMS oxidation chemistry on Jeju Island (33.17°N, 126.10°E) during the Asian dust-storm (ADS) period of April 2001. Three ADS events were observed during the periods of April 10–12, 13–14, and 25–26, respectively. For comparative purposes, a non-Asian-dust-storm (NADS) period was also considered in this study, which represents the entire measurement periods in April except the ADS events. The atmospheric concentrations of DMS and SO 2 were measured at a ground station on Jeju Island, Korea, as part of the ACE-Asia intensive operation. DMS (means of 34–52 pptv) and SO 2 (means of 0.96–1.14 ppbv) levels measured during the ADS period were higher than those (mean of 0.45 ppbv) during the NADS period. The enhanced DMS levels during the ADS period were likely due to the increase in DMS flux under reduced oxidant levels (OH and NO 3). SO 2 levels between the two contrasting periods were affected sensitively by some factors such as air mass origins. The diurnal variation patterns of DMS observed during the two periods were largely different from those seen in the background environment (e.g., the marine boundary layer (MBL)). In contrast to the MBL, the maximum DMS value during the ADS period was seen in the late afternoon at about sunset; this reversed pattern appears to be regulated by certain factors (e.g., enhanced NO 3 oxidation). The sea-to-air fluxes of DMS between the ADS and NADS periods were calculated based on the mass-balance photochemical-modeling approach; their results were clearly distinguished with the values of 4.4 and 2.4 μmole m −2 day −1, respectively. This study confirmed that the contribution of DMS oxidation to observed SO 2 levels on Jeju Island was not significant during our study period regardless of ADS or NADS periods.