Wildfire Smoke: How Much of a Concern?

Wildfire Smoke: How Much of a Concern?

With the continued dry weather and forest fires that southern BC has been experiencing, the smoke has not only blanketed the cities but also the mountains and forests. With intense heat, the smoke rises high in the air until it cools then it begins to descend and wind plays a role in spreading the smoke and diluting it out until it reaches ground level. Outdoor enthusiasts need to know how the smoke will affect their health when partaking in physical exercise.

Composition of Smoke

Smoke is composed of gases, small particles and water vapor with the latter comprising the majority of smoke.1 The gases of smoke is a mixture of carbon dioxide (CO2), carbon monoxide (CO), volatile organic compounds (VOCs) and nitrogen oxide (NOx) that varies depending on the type of wood and vegetation burning, fire temperature, moisture content and wind conditions.2  A flaming combustion occurs when a mixture of tars and gases from the organic composition ignites and most of the gases released are CO2, NOx and sulfur dioxide whereas a smoldering fire produces more CO and methane.3 Smoldering fires can last weeks and release more toxic compounds than flaming combustion. These compounds include volatile organic compounds (VOCs)  which comprise hydrocarbons, aromatic hydrocarbons and oxygenated organics and some VOCs (eg. venzene,  toluene,  ethylbenzene,  xylenes, and phenols) are irritants and have the potential to cause cancer.4 This is more of a concern to firefighters who are in close proximity to wildfires.5

Nitrogen Oxide

Nitrogen Oxide (NOx) contains a mix of nitrogen dioxide (NO2) and nitric oxide (NO) with the latter being more toxic since it is a soluble gas which enters the body through the lining of the nose and this makes it more dangerous as it easily permeates the nasal mucous membrane during breathing and depending on the concentration this gas can cause cough, shortness of breath and inflammation of the airways.6  When NOx from forest fires is combined with those from emissions such as transportation from automobiles, diesel engines and other mobile sources7 children and those with respiratory disease are at risk for respiratory illness from short-term exposure ranging from 30 minutes to 24 hours.8


Since wildfires emit large amounts of VOCs and NOx, these two compounds in the presence of sunlight are converted into ozone (O3)9 which can be transported over long distances and can increase ground level ozone concentrations in cities.10

Short-term ozone exposure is not expected to have adverse effects but long term exposure can result in a decrease in lung function, lung inflammation and fatigue even among young and healthy individuals.11

Carbon Monoxide

Carbon Monoxide (CO) is a toxic and odorless gas which causes an oxygen deficiency by reducing oxygen to tissues when it binds with hemoglobin in red blood cells to form carboxyhaemoglobin (COHb) however it does not pose a significant hazard unless you have heart disease.3 In contrast, smokers are exposed to more CO than non-smokers and the concentration increases with the amount of cigarettes smoked so they are more at risk for CO poisoning.12

Particulate Matter

The most hazardous components of smoke are particulate matter (PM) since it occurs in larger concentrations than gasses13 and they can remain suspended in the air for long duration and travel long distances. Particulate matter from smoke are tiny solid particles suspended in air and measures 2.5 micrometers (PM2.5) or smaller which can easily be inhaled into the deep parts of the lung.14 For reference, the diameter of human hair is 60 micrometers (μm) and any particles less than 10 μm will easily reach the lower areas of the respiratory tract. Chronic exposure to PM2.5 can induce inflammation, deplete levels of antioxidants in cells and generate excess free radicals that damage the lungs15 and result in a reduction in lung function, increased risk for lung cancer and decreased life expectancy.16

Short-term exposure to PM2.5 and PM10 is of concern to those with chronic obstructive pulmonary  disease (COPD) and asthma which can lead to hospital admissions17 as a result of increased respiratory symptoms and inflammatory reactions in the lungs. Short-term exposure to PM2.5 has been reported in one study to increase blood pressure18 through its free-radical damaging effect. The intake of dietary antioxidants (in food) may slightly reduce the effect of PM2.5 on blood pressure19 but there is not enough evidence for an overall beneficial effect and studies are limited.

Public Awareness

In a study by Semenza JC et.al. (2008), only 10 to 15% of those aware of public alerts for hot weather and urban air pollution episodes actually changed their behavior and rather than a public advisory, it was their personal perception of bad air quality or heat that change their behavior.20  It is not known how effective public warnings about poor air quality is in getting the message across to the public.


One must keep in mind that there is no safe level of air pollution at which adverse effects are absent and not every pollutant will affect every individual in the same manner but consider that people live, work and exercise in urban environments and then head outdoors at a time when air quality is poor so there is a greater risk for adverse health outcomes. In general, those with chronic cardiovascular or respiratory disease, children and older folks are thought to be more sensitive to air pollutants and short-term exposure increases vulnerability in diabetics, asthmatics, COPD individuals and those with atherosclerosis.21 There is a growing body of evidence which suggests that maternal exposure to particulate matter pollutants may affect the development of the fetus.22 Those aforementioned individuals should keep track of air pollution in their area by using the Air Quality Health Index at http://www.env.gov.bc.ca/epd/bcairquality/readings/aqhi-table.xml 23

Exercising at moderate intensity has been shown to result in 4.5 times greater deposition of ultra-fine particles into the lungs compared to resting24 and breathing through the nose filters out more particles and limits gases and vapors from reaching the lungs compared to mouth breathing.

No studies have been done to compare the benefits of exercising indoors vs outdoors during high levels of pollution but a European risk assessment showed that the cardiovascular disease benefits of exercise outweigh the cardiovascular disease risks when cyclists were exposed to air pollution when commuting in an urban environment.25 So, one can extend this to outdoor activities and imply that the risks associated with hiking in a smoky environment is reduced due to  the cardiovascular benefits but only if exercise is done on a regular basis rather than just once a week.

Ron (solo75) has enjoyed the outdoors for the past 42 years; most of those years are solo trips where he likes to observe nature and take photographs. He spends his free time researching on sports nutrition and living a vegetation lifestyle.

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