BIOGENIC SULFUR AEROSOL IN THE ARCTIC TROPOSPHERE .1. CONTRIBUTIONS TO TOTAL SULFATE

Long-term observations from 1980 to 1990 of aerosol methanesulfonate ( MSA), sulfate, sodium, and other related chemical species as well as a shorter time series of aerosol sulfur isotope composition (deltaS-34) at Alert, Northwest Territories, Canada, were used in two separate me thods to determine the contributions of sea salt, biogenic sources, an d pollution to aerosol SO4=. The first method, based on sulfur isotope composition, assumed a three-source model of anthropogenic, biogenic, and sea-salt sources for aerosol SO4=. Applying a Monte Carlo uncerta inty propagation technique to the three-source model, the MSA/biogenic SO4= mass ratio was estimated to be between 0.2 and 0.6 in summer and much lower in October to March (<0.08). The second method, based on a multivariate statistical analysis technique, apportioned aerosol SO4= into three major components attributable to the same three sources an d yielded an estimate of MSA/biogenic SO4= of 0.2 to 0.9 for the summe r months, in agreement with the isotopic estimate. Based on the isotop ic composition, aerosol SO4= in summer is 25 to 30% biogenic, 1 to 8% sea-salt, and the rest (62 to 74%) anthropogenic in origin. At other t imes of year it is < 14% biogenic, 1 to 8% sea salt, and the rest anth ropogenic in origin.