Atmospheric chemistry of biogenic sulfur in the Southern Hemisphere

Abstract

Measurements of atmospheric dimethylsulfide (DMS), as well as methanesulfonic acid (MSA) and non sea salt sulfate (NSSS) concentrations in atmospheric aerosol, rain water and Antarctic snow and ice core samples carried out between December 1990 and January 1993. Major ions in rain water, aerosol and snow samples were also determined. Samples were collected in the marine troposphere at two coastal North Island sites (Leigh and Baring Head) in New Zealand, and at coastal (McDonald Beach) and remote (East Antarctic Plateau) sites on the Antarctic continent. The air masses sampled were predominately of a marine origin and allowed the comparison between DMS and sulfur aerosol concentrations over a wide range of environmental conditions and with respect to latitude. Atmospheric DMS, MSA and NSSS concentrations in rain water and aerosol samples were observed to vary seasonally and latitudinally. At the New Zealand, sites, seasonal atmospheric DMS concentrations ranged from the detection limit (0.25 nmol m-3) to 14.9 nmol m-3 (median 3.15 nmol m-3) with a spring maximum. An atmospheric DMS diurnal variation factor of approximately 1.7 was observed. Marine aerosol MSA concentrations ranged seasonally from 0.02 to 1.40 nmol m-3 (combined site median 0.30 nmol m-3) also with a spring maximum. The marine MSA/NSSS molar ratios ranged from 2.38 to 22.3% (median 6.40 %) for rain water and from 0.82 to 21.4% (median 3.27%) for aerosol samples. At McDonald Beach, in Antarctica, atmospheric DMS concentrations ranged from 2.98 to 19.2 nmol m-3 (median 6.27 nmol m-3) during the austral summer. Aerosol concentrations ranged from 0.60 to 3.46 nmol m-3 (median 1.68 nmol m-3) for MSA and from 3.05 to ll.6 nmol m-3 (median 6.77 nmol m-3) for NSSS. A remote site on the East Antarctic Plateau also showed elevated aerosol MSA concentrations (0.09 to 0.43 nmol m-3, median 0.14 nmol m-3). The aerosol MSA/NSSS molar ratios ranged from 6.54 to 40.4% (combined median 24%) for these sites. Ice core, snow pit and surface snow samples from the East Antarctic Plateau site showed concentrations ranging from 0.01 to 0.31 µeq L-1 (median 0.04 µeq L-1) for MSA and from 0.54 to 29.5 µeq L-l (median 2.95 µeq L-1) for NSSS. Some generalizations as to the importance of DMS and the wet and dry sulfur deposition of MSA and NSSS at these sites are made. The atmospheric DMS concentrations at coastal New Zealand and Antarctic sites are comparable to other remote Southern Hemisphere sites suggesting some uniformity over the South West Pacific troposphere. However, between the Antarctic and New Zealand sites there are large variations in the MSA and NSSS depositional rates, the aerosol MSA size distribution and the ratio of MSA/NSSS.