On a cold winter's day in Yukon communities, you can see smoke and other pollutants in the air. On the coldest days, they float in a thick, white haze just above the chimneys or sink into the streets as ice fog.

But how can you identify and measure the pollutants? Air isn't as easy to collect as water or soil.

A couple of different air sampling methods have been used in the Yukon, says Vic Enns, Head of Environment Canada's Pollution Abatement Division in Whitehorse.

For many years, Whitehorse has had a National Air Pollution Surveillance (NAPS) station, a joint federal/Yukon government initiative. It used to be located on the roof of the old federal building, but now it sits on top of the Yukon Government's Law Building in downtown Whitehorse.

The NAPS station monitors nitrogen dioxide and carbon monoxide on a continuous basis, as well as sampling the air once every six days for suspended particles, says Enns.

To measure suspended particles in the air, a big vacuum motor sucks a constant volume of air through a filter for 24 hours. At the end of the 24-hour period, the filter is removed and sent to a lab in Ottawa, where the total suspended particulates are determined by weight.

The lab also measures the amount of lead trapped in the filter. Since lead was removed from automobile fuel several years ago, the amount of the lead in the air has dropped dramatically, says Enns.

In most Yukon communities, woodsmoke is easy to see and smell in the air on cold days in winter. Sometimes it is thick enough to raise health concerns.

For several years, a woodsmoke station has operated in Riverdale, a part of Whitehorse where woodsmoke tends to build up in cold weather. Readings from the station's instruments were used to determine when residents should be told to stop burning wood and switch to other forms of heat.

The Riverdale station is a 25-metre tower draped with instruments. Temperature can be measured at three elevations above the ground and wind speed at two different elevations. The level of particles in the air is tracked by a nephelometer located near ground level.

The nephelometer doesn't measure the particles themselves, says Enns.

"What it actually measures is the way light is scattered as it passes through a stream of air," he says. "The outdoor air is pumped through the unit, past a light source and mirrors. There's a good correlation between the light measurements and the amount of fine particulate material in the air."

Fine particulate material is the component of woodsmoke that causes most concern, says Enns. Particles less than 10 micrometres in diameter, too small to be seen individually by the naked eye, can penetrate deep into the lungs and have been linked with respiratory problems.

In order to make sure the Riverdale woodsmoke station was tracking the fine particulate matter accurately, Environment Canada's Yukon office imported, this winter, an instrument designed specifically to sample those tiny particles. Unfortunately, says Enns, the City of Whitehorse isn't using the woodsmoke station this year so the instrument, called a PM10 sampler, is sitting idle.

However, another Yukon community is measuring woodsmoke. In the past, Watson Lake residents have expressed some concern about the level of woodsmoke in their community. Data collected this winter should tell them whether their concern was justified.

The Watson Lake data is being collected by a High Volume Sampler that will run for 24 hours straight during problem woodsmoke periods, Enns says.

"They'll try to hit as many pollution events as possible over about a six-week period," he says. "It's a sort of short-term snapshot."

The snapshots should give Watson Lake residents an indication of whether woodsmoke is potentially a problem in the community and whether they need to do further monitoring.

For more information, contact Environment Canada in Whitehorse.