Source and Budget of Sulfate in Precipitation From Central Alberta,Canada

Rain, hail, and snow samples collected in central Alberta have been analyzed for sulfate and chloride content using a conductometric titration method. The mean values of sulfate concentration in rain and hail collected in the region of sulfur extraction gas plants were 2.7 mg/l and 2.9 mg/l respectively. The mean value of the sulfate content of a large number of hail samples collected from one severe storm well removed from a major SO₂ source was only 0.6 mg/l. Several snow samples collected in Alberta and southern British Columbia had a mean sulfate content of less than 0.5 mg/l. These results are discussed in terms of the efficiency with which SO₂ is removed from the atmosphere by the different precipitation processes. The results strongly suggest that most of the sulfate found in central Alberta precipitation is of local industrial origin.

By comparing the sulfate deposition in precipitation around one isolated gas plant with the known SO₂ emission rate, a local atmospheric sulfur budget is derived. This budget indicates that the summertime convective storms are a very efficient mechanism for removing the SO₂ from the atmosphere, with between 32 and 46% of the sulfur emitted as SO₂ arriving at the ground as sulfate sulfur within a radius of 25 miles of the source. In contrast snow is a very inefficient removal mechanism, since in winter less than 2% of the sulfur emission is deposited in the snowfall near the source.