Wood smoke, forest fires, and PM2.5 in British Columbia

Exposure to air pollutants is an important public health problem in British Columbia. Conservative estimates place the premature death toll from air pollution in BC at approximately 140 to 400 deaths per year, with 700 to 2000 hospital admissions and 900 to 2700 emergency rooms visits caused annually by air pollution.[1]

From a human health perspective, particulate matter is the air pollutant with greatest cause for concern in BC. Particles that are 2.5 micrometers or less in diameter (PM_2.5), are able to penetrate deep into the lungs. Exposure to PM_2.5 has been linked to many adverse health effects including premature death, exacerbation of asthma, acute respiratory symptoms, chronic bronchitis, and decreased lung function.[2]

Contrary to what many British Columbians may believe, the highest levels of PM_2.5 are not found in the Lower Fraser Valley air shed. The highest ambient air concentrations occur in the northern and interior regions of the province, where wood smoke forms a major component of air pollution (see the Figure [not availible online]). Environment Canada recently reported that wood smoke from forest fires, residential wood-burning, and prescribed burning may contribute more than 50% of total PM_2.5 emissions in certain regions of BC. Although wood smoke is generally emitted outdoors, substantial indoor infiltration may occur, leading to the degradation of indoor air quality.

The human health consequences of wood smoke exposure need to be taken seriously. A study by a respirologist, Dr Sverre Vedal, reported that children experience significantly decreased lung function following exposure to high concentrations of wood smoke.[3] Wood smoke exposure from poorly maintained wood stoves has also been linked to an increased risk of asthma in adults.[4]

Forest fires provide the opportunity to study health impacts of exposure to high episodic levels of PM_2.5. The Central Okanagan region had high levels of PM_2.5 between mid-August and mid-September, 2003, due to forest fires. To see whether the forest fires had any detectable effect on the health of Kelowna residents, billings for physician services submitted to the Medical Services Plan (MSP) were reviewed. Patient use of physician services for the period 1 June 2003 to 12 October 2003 was compared with average levels for the same periods from 1993 to 2002. While no increase in billings was seen for circulatory conditions, a significant increase for respiratory conditions was found. One week following the peak in PM_2.5 caused by forest fires, there was a 46% increase in patient visits for respiratory conditions compared with the mean rate from the same week in the previous 10 years. Four weeks following the peak in PM_2.5, a 78% increase was evident.

Although forest fires present the potential for elevated exposure to PM_2.5, they are relatively infrequent events compared to residential wood-burning during winter months. Exposure to lower levels of wood smoke may also increase the incidence of respiratory conditions. No clear threshold has been shown for the effects of PM_2.5. There is evidence from large-scale epidemiological studies that levels as low as 15 µg/m3, averaged over a 24-hour period, may be associated with an increase in health risks.

Education on the importance of a correctly designed and well-maintained wood stove should be encouraged in all regions where residential wood combustion is a large contributor to PM_2.5. From a respiratory health perspective, it should also be emphasized that the largest reduction to indoor PM_2.5 exposure comes from the elimination of indoor smoking.

—Patti Dods, MET
—Ray Copes, MD
British Columbia Centre for Disease Control

References

1. British Columbia. Provincial Health Officer. Every breath you take: Provincial Health Officer’s Annual Report 2003. Air quality in British Columbia, a public health perspective. Victoria: BC Ministry of Health Services; 2004.
2. Environmental Protection Agency. Health and environmental effects of particulate matter; 1997. www.epa.gov/ttn/oarpg/naaqsfin/pmhealth.html (accessed 22 February 2005).
3. Vedal S. Health Effects of Wood Smoke: A Report to the Provincial Health Officer of British Columbia.
4. Bates DV, Koenig J, Brauer M. Health and air quality 2002-phase 1. Methods for estimating and applying relationships between air pollution and health effects. RWDI Project: W02-304. British Columbia: British Columbia Lung Association;