SO2 in the Fall in the Arctic: Source Identification Using Sulfur Isotopes

The Arctic atmosphere, although far from industrial sources, has a large anthropogenic SO₂ load. Sulfur dioxide can have other sources including from dimethylsulphide (DMS) oxidation. One way to distinguish between these two types of SO₂ is through sulfur isotope apportionment. During the Fall seasons of 2007 and 2008 aerosol sulfate and SO₂ were measured at two sites in the Arctic. One site was on board the Canadian Coast Guard Ship, The Amundsen, as it traveled throughout the Arctic and the other site was at Alert, Nunavut, Canada. Sulfur dioxide concentrations at Alert varied between 0.02 and 18 nmol/m³ throughout the study with a median of 0.4 nmol/m³. δ³⁴S values ranged between 0 and +11%. Concentrations and δ³⁴S values aboard the Amundsen were much more diverse with concentrations ranging between 0.09 and 134 nmol/m³ (2007 median = 9.4 nmol/m³; 2008 median = 2.0 nmol/m³) and δ³⁴S values ranging between -15 and +18%. High concentrations of SO₂ on board the Amundsen were not directly from the Amundsen itself as there was no correlation with peaks in coincident CO₂ measurements. Low concentrations of SO₂ may, in a few instances, be associated with DMS oxidation. Negative δ³⁴S values were present for samples collected near the Amundsen Gulf and are consistent with a third source of SO₂ in the Arctic. This is likely the local source of SO₂ from the Smoking Hills in the North West Territories. Distinguishing between these sources of SO₂ in the Arctic and the importance of local verses regional sources will be discussed.