Vehicle emissions, home
and commercial heating
The Whitehorse area has been occupied by humans for centuries. There is evidence of old settlements upstream of Miles Canyon and downstream of Whitehorse Rapids. Kwanlin Dun, the name of one of the Whitehorse First Nations, is Southern Tutchone for "water running through canyon".
During the Gold Rush, tent cities were established at Canyon City and on the east bank of the Yukon River where Riverdale is now located. The new settlement of Whitehorse later expanded to the present downtown area. The population of Whitehorse remained at about 1,000 from 1901 to the 1940s when construction of the Alaska Highway precipitated considerable growth throughout the Yukon. The pioneering days in Whitehorse are past and the city now is the largest population centre in the territory. Not surprisingly some of the environmental issues facing the city are ones associated with southern cities - air and water quality problems.
Although the air over downtown Whitehorse is usually very clean, Whitehorse is subject to episodes of poor air quality. Vehicle use and wood burning are contributing factors. During the winter, when the weather is calm and cold, warmer air above the city can trap the colder air at ground level for hours or days. These temperature inversions lead to a temporary build-up of gaseous pollutants and fine particles in the air.
Air quality data are collected downtown and in Riverdale, a neighbourhood that is particularly susceptible to temperature inversions. The Wood Smoke By-law was enacted in 1986 authorizing the city to enforce no-burn periods for wood stoves in Riverdale during temperature inversions.
In this section we review information from the downtown Whitehorse air quality station for total suspended particulates (TSP) and for two gaseous pollutants - carbon monoxide (CO) and nitrogen dioxide (NO2). The downtown Whitehorse air quality station is part of a national network that monitors urban air quality. Gaseous pollutants are measured from late fall to early spring only (from 1985 on); particulates are measured year-round. The Whitehorse air quality station was shut down in 1992-93. Data collected since the station restarted have not yet been analysed.
This question is best answered by comparing Whitehorse air quality
data with national air quality objectives. These objectives were
developed by the Canadian government and are based largely on
considerations of human health. The health risks are determined
by the type of pollutant, the pollutant concentration and the
length of exposure. Thus, for each pollutant there are several
objectives corresponding to "good" (no effects), "fair",
"poor" and "very poor" air quality ranges.
Whitehorse air is usually in the "good" range for all
pollutants measured. However, periods of "fair" or "poor"
air quality occur as a result of episodes of high levels of CO,
NO2 or TSP.
Carbon Monoxide or CO: is a common air pollutant and is usually present in the atmosphere at low concentration. At higher levels, this colourless, odourless gas can represent an acute health risk.
Vehicle emissions, home
and commercial heating
The data from the downtown
monitoring station show that Whitehorse frequently has periods
during winter when CO levels do not meet the objective for "good"
air quality. It is important to recognize that, even when CO gas
concentrations are at their highest levels in downtown Whitehorse,
the air is still of "fair" quality, and there should
be no detectable human health effects.
Downtown Vancouver, consistently one of the worst locations for carbon monoxide levels in Canada, has improved dramatically since 1985. The trend is less clear for Whitehorse. Of the 54 Canadian stations measuring CO, Whitehorse ranked 7th to 15th worst each year in terms of high CO events. High CO events are 8-hour periods when CO levels put air quality into the 'fair' range (Whitehorse) or 'fair' or 'poor' range (Vancouver).
Nitrogen dioxide or NO2: is a reddish-brown gas that people can smell. At elevated concentrations, NO2 can adversely affect human health, vegetation, materials and visibility. Children and people with respiratory diseases can be particularly sensitive to NO2 gas.
Vehicle
emissions, home and commercial heating
Whitehorse is one of the
few monitoring stations in Canada where nitrogen dioxide concentrations
sometimes reach unhealthy levels. This is indicated by the occurrence
of episodes when concentrations for 24-hour periods result in
"poor" air quality. These events seem to be infrequent
and they are difficult to explain. They may be related to year
to year changes in weather or vehicle use, and instrument error
has not been discounted.
Total suspended particulates or TSP: is a measure of all sizes of suspended particles, including fine particles of smoke and exhaust, and windblown dust. Particles in air reduce visibility, cause soiling, and, at higher levels, affect people with respiratory problems.
Vehicle emissions, wood
smoke, dust in spring
The annual mean TSP level
has declined steadily since the 1970s and is generally in the
"good" range. However, Whitehorse continues to experience
occasional 24-hour periods when the TSP level places air quality
in the "poor" range. Although occasional high levels
in the winter may be related to wood smoke and vehicle exhaust,
the highest average TSP levels in Whitehorse occur each year in
the early spring when dust is blown through the city streets just
after the snow has melted.
The main year round water source for Whitehorse is Schwatka Lake,
a hydro electric impoundment on the Yukon River. In the winter,
warmer ground water is mixed with lake water to decrease the reliance
on water heaters at the pumping stations; in summer ground water
is used to reduce sediment content. Water quality is monitored
for faecal and total coliform bacteria. The recommended guideline
for raw drinking water is no more than 10 organisms per 100 millilitres
of water for total coliform and no occurrence of faecal coliform
bacteria. Levels of bacteria in the water intake sometimes exceed
this guideline, especially in the spring. The frequency of high
coliform bacteria levels in samples has increased in recent years.
Growing residential, recreational and industrial development upstream
from the city may contribute to high bacteria counts, along with
natural sources, such as birds.
Although the city has conducted water conservation projects, there is little incentive to save water as resident users pay a flat fee for water. To reduce water consumption, the city enacted a by-law requiring that all new construction and retrofitting include low flush toilets. The city's aging water delivery infrastructure is being upgraded to reduce leakage, and bleeders are not allowed in new home construction.
Sewage Disposal
Whitehorse has three sewage treatment systems: the Whitehorse and Porter Creek lagoons, which discharge continuously into the Yukon River, and the Crestview system which discharges to the ground. The Whitehorse system is being upgraded and is expected to result in improved water quality downstream of Whitehorse.
