The Impact of Wildfires on Air Pollution and Human Health

Climate change has many consequences. Some of the most well-known consequences include rising sea levels and increasing temperatures. However, one of the less studied consequences of climate change is the increasing frequency and intensity of wildfires that are occurring due to a drier and warmer climate.8 Therefore, vegetation in those climates lose more water and the amount of dry fuel in the environment will increase. Wildfires that occur due to climate change can also spread faster as climate change has an impact on winds which are often the drivers of the fire.

A hot and dry climate with strong winds is the ideal environment for wildfires. This is a common climate in the western United States, which is why wildfires are so prevalent in that region. Fires are either started by humans or lightning. Due to climate change, the number of fires that are started by lightning has increased. It has been estimated that for every Celsius of warming, the number of fires started by lightning strikes will increase by 12 percent. As climate change is creating a more favorable environment for wildfire ignition, the particles emitted from wildfire smoke will have a greater impact on the climate and human health. However, there are strategies that can be adopted to mitigate wildfires. In the future, the education and cooperation of homeowners with state and federal governments along with the implementation of a specific wildfire risk management framework will be necessary for wildfire mitigation.

Since 1970, the number of wildfires has doubled each year. Depending on the rate of climate change, the frequency of wildfires that occur in the western area of the United States can increase by 6-fold. Higher spring temperatures with decreasing snowpack is increasing the annual fire season by 2 months. The intergovernmental panel on climate change, a body that is part of the United Nations focused on informing the world on the political and economic impacts of climate change, find that climate change will increase the time period for wildfire risk in the summer by 10-30 percent. This is significant not only because of the increased risk of fire damage but also because wildfires release lots of carbon dioxide, brown carbon, black carbon, and ozone precursors into the atmosphere which will also increase the effects of climate change. The carbon emissions from wildfires may create a feedback loop that will further increase the progress of climate change.

While both black and brown carbon can scatter and absorb the sunlight, studies have indicated that brown carbon emitted from wildfires travels much higher in the atmosphere than black carbon and therefore has a greater impact on climate. Brown carbon is emitted from the smoldering of biological matter. Black carbon is formed from the high-temperature combustion of biofuels or fossil fuels. According to a study that looked at air samples gathered by NASA, brown carbon was found in the upper levels of the troposphere. While most brown carbon that is emitted stays in the lower atmosphere, there is a small proportion of brown carbon that travels to the upper atmosphere where it can have a great impact on the radiation of the planet. The brown carbon in the upper levels of the atmosphere can either cool or warm the air. Brown carbon reaches the upper troposphere by first traveling upward with the wildfire smoke where it then mixes with the clouds. The upward convective flow in the clouds then carries the brown carbon into the upper atmosphere. The higher the molecules travel in the atmosphere, the greater influence the molecule will have on climate.

Aside from containing brown and black carbon, wildfire smoke also contains PM2. Research has started to associate adverse health consequences to the increasing concentration of PM2. and PM10 that is released into the ambient air. PM2. is a mixture of particles that are smaller than 2.5 micrometers in diameter. PM is a mixture of particles that are smaller than 10 micrometers in diameter. Studies looking at the effect wildfires have on human health have looked at the concentration of PM10 and/or PM2. in the ambient air. In general, the smaller the molecule, the deeper into the respiratory system the particle can travel and therefore the greater the impact it has on health. In the United States, the EPA national ambient air quality standards have been successful in decreasing the amount of PM2. in the air. However, according to a study released by the Proceedings of the National Academy of Sciences, the increasing amount of wildfires due to climate change can undo the air pollution gains made after enacting the Clean Air Act. In fact, the regions of the United States that have the most frequent wildfires have seen an increase in the concentration of PM2.5 in the ambient air. PM2. can often travel long distances and stay in the atmosphere for a long period of time because of its small size. Other than wildfires, PM2. is often emitted by motor vehicles, furnaces and power plants. PM2. can be directly emitted or it can come from reactions by precursor gases in the atmosphere. Research has shown that both short-term and long-term ambient concentrations of PM2. in urban areas can lead to premature deaths from heart or lung disease. PM2. has also been shown to decrease lung function and make the symptoms of those afflicted with asthma worse. PM2. levels increase in the summer due to the occurrence of wildfires during that season. However, the levels of fine particles and air pollution can also increase in the winter due to temperature inversion.

In a review that looked at 61 epidemiology studies investigating the association between wildfires and human health, it was found that in most of the studies, the daily pollution level during and after a wildfire was much higher than the requirements regulated by the EPA.5 In terms of health effects, it was found that the respiratory morbidity had a strong association with wildfire smoke.

In a 7-month study that was conducted in Darwin Australia, it was found that the number of people who went to the hospital for symptoms relating to asthma more than doubled when the concentration of PM10 in the atmosphere was greater than 40 g/m3. The 40 g/m3 threshold of PM10 might be an anomaly as other epidemiology studies looking at the threshold for particles emitted from wildfires found different results. However, there were several advantages to the Darwin study. First was the place of the study. Darwin Australia was an ideal place to conduct a study looking at the effect of ambient air pollution from wildfires on human health because it was a place that had no other sources of air pollution other than those emitted by the wildfires. Not only that, but wildfires occur in Darwin every dry season. Also, during the dry seasons, there is a consistent inversion and not a lot of convective mixing so the measurements of the levels of air pollution in this region is fairly reliable.4 The study also had the advantage of looking at the changes that occurred over time due to air pollution as the occupants of Darwin had a continuous exposure over a 7-month period.

Children, the elderly and those already afflicted with related respiratory diseases are some of the parts of the population that is most vulnerable to wildfire smoke. It was found that when exposed to wildfire smoke, women may be more vulnerable to symptoms related to asthma and they also had more visits to the doctor due to wildfire smoke than men. Not only that but counties that have lower socioeconomic status have a greater number of people who are at risk for congestive heart failure and asthma due to wildfire smoke.

The increasing prevalence of wildfires in the world has caused significant economic consequences. From 2002 to 2011, wildfires in the United States have caused insurance companies 6.2 to 7.9 billion dollars.6 Due to this and the increased risk of disease and premature deaths associated with exposure to wildfire smoke discussed above, methods in combating wildfires are very important. Unfortunately, successful long-term prevention methods are complicated and difficult to develop due in no small part to the wildfire paradox. The buildup of plant biomass due to wildfire suppression methods can actually lead to a faster and more intense wildfire.

One method that can help prevent wildfire disasters is to implement a wildfire risk management framework. When creating a wildfire risk management framework, it is important to take into account the relationship between climate and wildfires, wildfires and home ignition and also migration opportunities. As wildfires are caused by either humans or lightning, looking at ways to reduce fuel load and reduce the risk of home ignition is also critical. One common way to prevent wildfires is to reduce the fuel load on public lands. Fuel loads are often dry or dead grass, leaves, and bushes. By reducing the amount of flammable material, the intensity and severity of the fires can also be reduced. Reducing the risk of home ignition is also crucial. Some ways to reduce the risks of home ignition is to clean roofs, gutters and exterior attic vents of debris. Making sure flammable materials such as juniper and firewood piles are away from the walls of the house is also very important. If there is land that is also attached to the house, actions such as mowing the lawn, creating fuel breaks, removing vegetation under trees, spacing trees with at least 18 feet between them and grouping trees and shrubs into small clumps are recommended. The type of community the house is located in must also be considered. Places, where there are a lot of suburban communities, can be susceptible to fires through home to home ignition.

However, while employing methods near the house, on private and public land to reduce the risk for wildfires is very important, wildland ecosystems must also be taken into account. If the wildland ecosystems are damaged due to the methods employed to reduce wildfire risk, the repair of the wildland ecosystems is often much more complicated, difficult, expensive and time-consuming than the restoration of a home or community.6 Wildfire prevention is a tricky, complicated and expensive process. There must be a fine balance between reducing the risk for wildfires during wildfire season, respecting the environment and all its ecosystems and making sure the wildfire prevention methods are not creating a potential risk for a bigger, more intense wildfire in the future. An effective wildfire risk management approach must be detailed, specific and take in multiple perspectives. Weather conditions, the type of house, the type of material in and around the house, the proximity to other houses, the effects of climate change and the geographic landscape are all things that must be taken in consideration when creating a wildfire risk management plan. Mitigating the risk of wildfires is a responsibility that must be shared by both the government, the community, and the individual homeowner.

Although wildfires may not have previously been thought of as a significant contributor to air pollution, they are becoming a severe problem because of the increasingly favorable environment for ignition due to climate change. The adverse health effects of PM2. and PM10, in particular, have a large effect on the respiratory health of the children and the elderly. Vulnerable populations such as minorities and those with lower socioeconomic status may be more at risk to the adverse health effects from wildfire smoke. Therefore, it is essential that the federal government, state government, communities, and individual homeowners all work together to try and decrease the risk of wildfires. Research and education are vital for wildfire prevention. Although wildfire mitigation is a complex and difficult task, successful mitigation is possible if there is adequate research, cooperation, education, resources, and preparation.

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