Removal of SO2 from the marine boundary layer over the Atlantic Ocean - A case study on the kinetics of the heterogeneous S(IV) oxidation on marine aerosols

Measurements of SO2 and NSS-SO4(2-) were made over the Atlantic Ocean on board the RV Polarstern from October 9 to November 2, 1996, as part of the ALBATROSS campaign. The measurements were performed between 66.7 deg N and 37.8 deg S with a mean longitude of approximately 30 deg W. The most frequent background values for SO2 were found to be 13 parts per trillion by volume (pptv) (0.54 nmol/cu m at standard ambient temperature and pressure (SATP)) in the Southern Hemisphere, and 15 pptv (0.62 nmol/cu m SATP) in the Northern Hemisphere. The mean values for total NSS-SO4(2-) in particles with a d greater than 0.2 micron were (5.99 +/- 2.93) nmol/cu m (SATP) in the Southern Hemisphere, and (8.93 +/- 5.29) nmol/cu m (SATP) in the Northern Hemisphere. An analysis of the size-fractionated aerosol samples (d greater than 1 micron and d in the range of 0.2-1 micron) of NSS-SO4(2-) shows that (34 +/- 13) percent of the total NSS-SO4(2-) exists in coarse mode particles with d greater than 1 micron. The main fraction of this NSS-SO4(2-) is most likely produced by the oxidation of dissolved SO2 via heterogeneous reactions occurring in the aqueous phase of coarse-mode marine aerosols. (Author)