by Derek Neary
Northern News Services

NNSL (Apr 17/98) - Dust and sulphur-dioxide levels are falling in Yellowknife, a sign that air quality is improving.

The rates are documented in the 1996 Yellowknife Air Quality Data Report compiled by the NWT Environmental Protection Service. The report was released Tuesday.

At 55 micrograms per cubic metre, dust counts are below the annual standard and the lowest since 1992. The drop is attributed to increased paving of roads and heightened efforts by the city to remove grit and gravel from the streets.

Sulphur-dioxide levels have dropped for the fourth consecutive year, falling from an annual rate of 15 micrograms per cubic meter in 1994 to nine in 1997. However, there were two occasions when the amount of sulphur dioxide in the air eclipsed the levels at which exposure begins to affect human health.

Giant Mine produces the vast majority of sulphur dioxide in the Yellowknife area, approximately 30 tonnes per day, according to Emery Paquin, director of the EPS.

To the north of the city, the wind-blown sulphur dioxide has resulted in brown leaves and needles on trees, Paquin said.

Giant Mine is also responsible for the bulk of arsenic found in local air samples, according to the report. The average levels, at 0.008 micrograms per cubic meter annually, are easily considered acceptable compared with the Ontario standards of 0.3. Even a limited presence of arsenic trioxide has been linked to a small risk of cancer. Yellowknife's arsenic levels are higher than those of most Canadian cities, Paquin said.

Lead levels remain at a fraction of the maximum standard and the amount of acid rain is consistent with consistent with "non-polluted areas," said Paquin.

All in all, Paquin said there is nothing in the report that he finds troubling.

"In general, the air quality in Yellowknife is getting better," he said.