Open AccessSources of aerosol sulphate at Alert: Apportionment using stable isotopes
Author(s) -
Norman A. L.,
Barrie L. A.,
ToomSauntry D.,
Sirois A.,
Krouse H. R.,
Li S. M.,
Sharma S.
Publication year - 1999
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1999jd900078
Subject(s) - aerosol , sea salt , air mass (solar energy) , environmental science , arctic , atmospheric sciences , atmosphere (unit) , stable isotope ratio , haze , sulfate , environmental chemistry , oceanography , geology , chemistry , meteorology , geography , physics , boundary layer , quantum mechanics , thermodynamics , organic chemistry
From July 1993 to September 1994, seasonal variations in the sources of SO 4 2− aerosols in the Arctic lower atmosphere at Alert, Canada, (82°30′N, 62°20′W) were investigated using the sulphur isotope abundance of as little as 10 μg of sulphur analyzed by combustion‐flow isotope‐ratio mass spectrometry. In conjunction with air mass trajectories and in parallel with measurements of aerosol composition, the sulphur isotope composition was used to discern sources of aerosol SO 4 2− . Total SO 4 2− is composed of sea‐salt SO 4 2− , marine biogenic, and nonmarine SO 4 2− . From June through September the fraction of biogenic SO 4 2− in the non‐sea‐salt (nss) component ranged from 0.09 to 0.40 with an average of 0.31 ± 0.11. Summertime nonmarine SO 4 2− is likely anthropogenic in origin since it is isotopically indistinguishable from SO 4 2− in the polluted winter/spring period of arctic haze (δ 34 S = +5‰). In summer there was no significant difference in isotope composition of aerosol sulphate between air which recently traversed Eurasia and the Arctic Ocean and air arriving from North America. In contrast to summer and late winter/spring, δ 34 S values for nonmarine SO 4 2− in fall and early winter were often less than +5‰. These isotopically light samples were divisible into two groups: (1) those associated with air mass trajectories potentially affected by North American soils and/or smelters and (2) three weekly samples between October and December which could be attributed to fractionated sea‐salt aerosol formed on refrozen Arctic Ocean leads. For the latter the ratio of SO 4 2− /Na was estimated to be a factor of 3.6 lower than in bulk seawater. From November to May, nonmarine aerosol SO 4 2− was apportioned into 10 aerosol components using positive matrix factor analysis of 18 aerosol ions and trace elements [ Sirois and Barrie , this issue]. In turn, a multiple linear regression of δ 34 S values against the scores of the components was used to predict the isotope composition of six components. It was concluded that the main mass of anthropogenic SO 4 2− had a δ 34 S value near +5‰ and that biogenic SO 4 2− had a δ 34 S of +16 ± 3.9‰. Reasonable agreement between model results and sulphur isotope measurements at Alert show that SO 4 2− apportionment using positive matrix factor analysis is a reasonable approach which gives realistic results.