Seasonal and geographic variations of methanesulfonic acid in the arctic troposphere

• Published in: Atmospheric environment 1993-12, Vol.27 (17), p.3011-3024
• Main Authors: Li, S.-M, Barrie, L.A, Talbot, R.W, Harriss, R.C, Davidson, C.I, Jaffrezo, J.-L
• Format: Article
• Language: English
• Subjects: Aerosol; Arctic; biogeochemical cycle; Brackish; Freshwater; Greenland ice; Marine; methanesulfonic acid; organic sulfur
• ISSN: 0960-1686; 0004-6981
• DOI: 10.1016/0960-1686(93)90333-T

Measurements in the Arctic troposphere over several years show that MSA concentrations in the atmospheric boundary layer, 0.08-6.1 parts per trillion (ppt, molar mixing ration), are lower that those over mid-latitude oceans. The seasonal cycle of MSA at Alert, Canada (82.5°N, 62.3°W), has two peaks of 6 ppt in March–April and July–August and minima of 0.3 ppt for the rest of the year. At Dye 3 (65°N, 44°W) on the Greenland Ice Sheet, a similar seasonal MSA cycle is observed although the concentrations are much lower with a maximum of 1 ppt. Around Barrow, Alaska (71.3°N, 156.8°W), MSA is between 1.0 and 25 ppt in July, higher than 1.5 ± 1.0 ppt in March–April. The mid-tropospheric MSA level of 0.6-1 ppt in the summer Arctic is much lower than about 6 ppt in the boundary layer. At Alert, the ratio of MSA to non-sea-salt (nss) SO 4 2− ranges from 0.02 to 1.13 and is about 10 times higher in summer than in spring. The summer ratios are higher than found over mid-latitude regions and, when combined with reported sulfur isotope compositions from the Arctic, suggest that on average a significant fraction (about 16–23%) of Arctic summer boundary layer sulfur is marine biogenic. The measurements show that the summer Arctic boundary layer has a significantly higher MSA/nss-SO 4 2− ratio than aloft.