Wildfire Air Pollution and Immune Health: How To Stay Healthy During Fire Season

By Bing Bing Guo

Wildfire records now seem to be broken every year. According to the National Interagency Fire Center (NIFC), 48,331 fires have burned over 6 million acres across the United States, with 46 active wildfires continuing to burn as of September 1, 2022.  The McKinney Fire in northern California claimed four lives and burned more than 55,000 acres — an area more than one and a half times the size of San Francisco — making it the largest wildfire in California so far this year. Additionally, the European Union is currently on track for a record wildfire season. According to the European Forest Fire Information System, wildfires in the European Union have consumed 660,249 hectares (1,631,511 acres) of land as of August 13, 2022.

Wildfires Are Intensifying 

While wildfires are nothing new, increasingly severe wildfire events have been occurring on a global scale. In 2021, two of the largest active wildfires in the U.S., the Dixie Fire in California and the Bootleg Fire in Oregon (the nation’s largest active wildfire to-date), burned land nearly the size of New York City, Los Angeles and Chicago combined. That same year, Turkey also experienced its worst wildfires in decades and wildfires raged across other parts of the world including Spain, Italy, Greece and Russia. In 2019-2020, Australia recorded its worst bushfire season on record, burning at rates never seen before. 

Though many factors contribute to wildfires, climate change is a key driver that cannot be ignored. Higher temperatures, earlier snow melt, increased droughts and unusual rain patterns due to the changing climate all combine together to form the perfect conditions for fires of unprecedented scale and intensity. 

One of the many alarming consequences of the increasing wildfires is far-spreading and long-lasting smoke pollution. On July 20, 2021 the smoke from the Western Wildfires traveled across the continent and contributed to the worst air quality New York City has seen in 15 years, blanketing the city in a red haze. During the West Coast Wildfires in 2020, warnings of “hazardous” or “very unhealthy” air quality were in place from California to Washington State, with the air quality in many parts of Oregon ranking among the worst in the world. While the wildfires themselves have been concentrated on the West Coast, the resultant smoke traveled to the U.S. East Coast and even Europe. 

While it is important to learn about the health consequences that occur due to wildfire smoke exposure and take steps to mitigate these risks, we must first understand what exactly fire season is and when it occurs. 

What Is Wildfire Season? 

A wildfire refers to any unplanned or accidental fire that occurs in a natural area such as a forest, grassland or prairie. Fire season typically refers to the period of time between the season's first large wildfire to the season’s last wildfire. 

Caused by a myriad of factors ranging from short-term weather (such as lightning) to longer-term climate change, the risk of wildfires increases in extremely hot and dry conditions and high winds. Certain areas are thus more prone to wildfires than others, depending on temperature, weather conditions and other factors such as human activity. 

When Is Wildfire Season? 

While there is no official start date for wildfire season, historically, wildfires are more likely to occur between May and October. However, as evident in recent years, wildfire season has become longer, with wildfires occurring year-round for much of the U.S. In fact, the term “fire season” has now begun to shift to “fire year” as typical wildfire seasons now last around six to eight months. 

How Does Wildfire Smoke Impact Our Health? 

Wildfire smoke contains a mixture of carbon monoxide (CO), particulate matter (PM) and volatile chemicals. These components differ based on the components feeding the fire. For example, fires that burn through cities tend to release more toxic compounds due to burning plastics, paint and consumer products that contain more chemicals compared to forest fires or rural fires which are more limited to burning organic matter such as vegetation and wood. 

PM Is the Pollutant of Greatest Concern 

Currently, the U.S. Air Quality Index (AQI) used to report daily air quality levels and associated health risks measures five major pollutants: CO, PM, ground-level ozone, sulfur dioxide and nitrogen dioxide. It is divided into 6 color-coded categories in which each category corresponds to a different level of health concern. 

However, 90% of total particle mass emitted from wildfires comprises fine particulate matter, or particles 2.5 microns or smaller in size (PM2.5), which poses the biggest threat to our health. Due to their small size, PM2.5 can penetrate deep into the lungs, with smaller particles passing through the lungs and into the bloodstream, ultimately settling into and impacting various body tissues. Once the particles penetrate this deeply, the body is unable to filter it out, which creates long-lasting inflammation within the body. 

Short-Term Effects of Wildfire Smoke 

Short-term effects of PM2.5 may include:

• Irritation of the eyes, nose, throat and lungs
• Coughing
• Shortness of breath
• Worsening of pre-existing respiratory or cardiovascular diseases.

One study found that exposure to PM2.5 during wildfire events was associated with increased ambulatory dispatches after just one hour of exposure. 

Long-Term Effects of Wildfire Smoke 

While the long-term health effects of wildfire smoke are currently unknown, a recent study followed community residents living in Seeley Lake during the 2017 summer fires that lasted for 49 days, 39 of which exposed residents to EPA-designated “very unhealthy” and “hazardous” levels of PM2.5. Researchers found that after one year of post-wildfire exposure, lung function significantly decreased among the study participants, with more than double reporting lung function below normal thresholds. Lung function remained low even two years after the wildfires had occurred. 

Despite limited research on long-term PM2.5 exposure from wildfire air pollution, the long-term health effects due to ambient PM2.5 has been well established and are associated with:

• Cardiovascular disease
• Respiratory illnesses such as asthma and lung cancer
• Diabetes
• Premature death among individuals with heart or lung disease, as well as premature births and low birthweight babies

Certain People Are at Greater Risk  

Given that wildfire smoke can spread thousands of miles away, the effects of smoke exposure are far-reaching and can greatly impact us all. However, certain people may be at higher risk than others. 

For example, people living close to areas that are prone to wildfires may be exposed to significantly higher levels and longer periods of air pollutants from fires. Furthermore, certain groups of people are at higher risk of the adverse effects of wildfire smoke, including people with chronic health conditions, older adults, pregnant women and children.  

Covid-19 and Wildfire Smoke Pollution 

As the pandemic continues, wildfire events will continue to overlap and potentially make Covid-19 more dangerous. PM exposure may result in weakened pulmonary immunity and thus compromise the ability of our bodies to respond to respiratory viruses such as the influenza virus or SARS-CoV-2 (which causes Covid-19). One study found that the effects of smoke on the immune system may last for months, as exposure to higher levels of PM2.5 during the wildfire seasons has been associated with a more severe flu season the following winter. Thus, wildfire smoke exposure may also increase the risk of contracting Covid-19 and/or increase the severity of disease among those already infected.  

This effect can also be seen in reverse. People who currently have or are recovering from Covid-19 may be at higher risk of health effects from wildfire smoke exposure due to compromised heart and lung function resulting from Covid-19. It is also important to note that other at-risk groups for wildfire smoke largely overlap with those who are at-risk for Covid-19, such as adults 65 or older, pregnant women, those with chronic health conditions (e.g., asthma, diabetes, heart and lung disease), immuno-compromised individuals and those who are of a lower socio-economic status. 

What Can We Do To Limit Exposure to Wildfire Air Pollution? 

While it is not possible, nor ecologically appropriate, to eradicate all wildfires – there are measures that we can take to mitigate our smoke exposure, as well as help reduce climate change and/or human behavior-driven wildfire events.  

Take Precautions During Wildfire Events  

• Check the AQI in your area to see whether you need to limit your time outdoors on a given day. 
• Listen to advisories: if you are told to stay indoors or if the air looks smokey outside, stay indoors whenever possible. 
• If you are in a car, keep your windows and vents closed. If you are using the air conditioner, change the setting to “recirculate” mode. 
• While cloth masks help to prevent the spread of Covid-19, they do not protect against smoke exposure. For individuals who must spend time outdoors, consider wearing a fit-tested and approved N95 or P100 respirator to help reduce your exposure (however, note that these respirators may be in shorter supply due to the pandemic). Avoid N95 respirators with exhalation valves, as they may promote the transmission of Covid-19. 

Improve Indoor Air Quality (IAQ) at Home 

• If the outdoor air quality is poor, keep windows and doors closed. When using the AC, keep the fresh air intake closed to prevent infiltration of outdoor smoke. If you are not able to turn off the fresh air intake, make sure the filter on the fresh air intake is clean.  
• Use an air filter and/or portable air cleaner capable of high particle removal efficiency to protect lung health.
• Integrate air purifying plants to naturally improve air quality indoors. The presence of plants may also help reduce stress during these times. 
• Reduce indoor air pollution by limiting combustion activities such as lighting candles and fireplaces, smoking, or using gas stoves without functioning kitchen hoods. Particles may be resuspended by daily activities such as walking or vacuuming. If possible, use a vacuum with a High Efficiency Particulate Air (HEPA) filter or wear a mask when using a traditional vacuum. 

Help Combat Climate Change  

• Switch to eco-friendly modes of transportation. Vehicles are one of the main sources of PM pollution. Use public transportation or bike when possible. If you rely on your own vehicle, consider switching to a hybrid or electric car to reduce PM emissions.   
• Plant more trees. Trees help to remove carbon dioxide from the air and help to combat climate change. 
• Lower your own environmental impact. There are many small changes you can incorporate into your life to help reduce your carbon footprint and live a more sustainable life. Simple examples include bringing your own bags to the grocery store and using reusable water bottles. 
• Prevent human-caused wildfires. Did you know that, on average, 89% of wildfires are caused by humans? If you live near or are visiting a wildfire-prone area (e.g., national parks or forests), follow these tips to avoid starting a wildfire. 

Cleaner Air Indoors and Out  

While it is crucial to ensure that you have good IAQ during wildfire events, clean indoor air is important all year round for immune health. Delos is committed to transforming indoor environments into vehicles for health, well-being, performance and resilience. To explore our air purifiers, check out the Delos Shop and contact us to learn more about how our air purification solutions can help you to breathe easier.

About the Author 

Bing Bing Guo
Senior Associate, Delos Labs
Bing Bing Guo, MPH, is an Senior Associate at Delos Labs specializing in content creation and research on the relationship between health and the built environment. She draws upon her background in epidemiology to investigate the impact of environmental and behavioral factors on occupant health, well-being and productivity.

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