When a wildfire breaks out public health recommendations are to stay indoors and close all windows, but is that the best advice? Toxicology researchers at Oregon State University are very interested in understanding the effect of wildfires on indoor and outdoor air quality. Dr. Kim Anderson and her team have been collecting samples before, during and after wildfires in the Pacific Northwest using community-engaged research for the last three years to help improve public health recommendations.


In 2017, wildfires results in over ten million acres burned across the United State. California, Oregon, Idaho and Washington were some of the largest sources of wildfires. In addition, fire seasons in Oregon and Washington were almost three weeks longer than ever recorded. The number of large wildfires (> 1,000 acres) has increased by a rate of seven fires per year, and since the mid-1980’s, total acreage burned and average wildfire size have risen drastically.

According to the National Interagency Fire Center, as of September 16th, 2020 106 large wildfires are burning across the western United States. Above normal fire activity is occurring in California, Oregon, Washington, Idaho, and other western states, with nearly 6.7 acres burned so far this year.

Dr. Anderson’s research team has been sampling indoor and outdoor air at thirteen different locations across four western states: Oregon, Washington, Idaho and California. Stars represent the locations where they are also measuring chemical movement between the air and the soil.

Wildfire smoke contains many chemicals that may impact health, but these exposures are largely unknown. Current public health messaging recommends individuals stay indoors and close all windows, but these recommendations are often based on risks to particulate matter and do not take into consideration chemicals in a gas form, referred to as the vapor phase. Additionally, little is understood about how long exposure to wildfire chemicals can last.

Particulate matter is a mixture of solid particles and liquid droplets found in the air. The particles are different shapes and sizes and can be made up of many different chemicals. Vapor phase chemicals exist freely in the air, and are not bound to particulates. Because they are not bound to particulates, vapor-phase chemicals have a higher chance of being absorbed by humans or animals.

During a wildfire, the heat begins to break down materials that are burning. As the materials break down, they produce and release different chemicals into the air. One chemical class of concern during wildfires is polycyclic aromatic hydrocarbons (PAHs). PAHs are found in fossil fuels such as oil and coal. When fossil fuels evaporate or are burned, PAHs enter the air. Burning wood, grasses, candles or tobacco will also release PAHs. Some PAHs are known air pollutants. Exposure to vapor-phase PAHs has been shown to account for up to 86% of the cancer-risk from inhalation exposure in studies.

Dr. Kim Anderson and her research team in the Food Safety and Environmental Stewardship Laboratory at Oregon State University are interested in better understanding the influence of wildfires on indoor and outdoor air quality, as well as the movement of chemicals produced by wildfires. While PAHs are commonly found both indoors and outdoors, researchers are looking specifically at the contribution of wildfires to PAH levels both inside and outside the home. The goal of the study is to look at how levels of PAHs change before, during and after a fire, as well as differences in PAH levels inside versus outside.

Air Samplers placed in a room inside the home and outside the home at all thirteen locations. At five locations, participants are also deploying soil air samplers to measure chemical movement.

Dr. Anderson’s lab uses passive samplers, which can sample thousands of chemicals in the environment. Chemicals are absorbed by passive samplers in a similar way to how they are absorbed by humans or animals. This similar absorption helps to inform researchers about potential exposures in the environment. Passive samplers are also easy to use, low cost and low maintenance in the field. These advantages make passive sapling an ideal approach for community-engaged research.

With the help of Dr. Diana Rohlman in the College of Public Health at Oregon State University, Dr. Anderson’s lab designed passive sampling kits that could be delivered to community members for deployment. Each participant receives a kit containing the passive samplers, passive sampling cages, an instruction packet, a survey and a prepaid return label. This is the first study by their lab to incorporate community-engaged research and environmental passive samplers without a face-to-face training.

With the help of interested community members, Dr. Anderson’s lab has been able to collect samples from 13 different locations in four western states: Washington, Idaho, Oregon and California. Starting in 2018, at each site volunteers have placed samplers in a room inside their home and outside their home during the wildfire season. This has allowed researchers to capture chemical concentrations before, during and after wildfires.

In addition to the passive sampling data, the lab is also collecting air quality index values published by the Environmental Protection Agency, satellite images of smoke coverage in sampling locations and wildfire smoke density values from the National Oceanic and Atmospheric Association. This data will be compared to PAH concentration values to more fully understand how wildfires impact air quality.

Once the passive samplers are returned to the lab, they are processed and analyzed on two methods. The first method looks for 63 individual PAHs. The second study looks at a specific class of PAHs, called alkylated PAHs, which can be useful in determining where PAHs come from. For example, the team can identify if PAHs in the samples are more associated with wood fires versus the burning of fossil fuels. Researchers can then use this data to make comparisons between indoor and outdoor air at each location and between each year.

Dr. Anderson’s lab is also using PAH results to determine how chemicals are moving in the environment. Chemicals are in a constant state of motion in the environment, which can affect how people are exposed to them. The type of movement they are measuring in this study is called diffusive flux. Diffusive flux describes the movement of chemicals from a very concentrated area to a lower concentrated area. If you have ever been in a room when someone walked in wearing too much perfume, you know that the scent travels. It is going from a high concentration (the person wearing the perfume) to a low concentration (the air in the room). We see this happen with chemicals. During a wildfire, the smoke in the air contains very high amounts of chemicals. As the soil has much lower levels by comparison, researchers believe PAHs deposit in the soil during wildfires. The chemicals may then move from the soil back into the air after wildfires, depending on their concentration.

Following the sampling period, individual data sets are returned to study participants. Reports include a comparison of different PAH concentrations for each location, overall study conclusions, common sources of PAHs and ways to reduce exposure. Returning data to participants increases understanding of environmental exposure and can empower individuals to take action to reduce exposure to wildfires and other PAH sources.

Over the past two years, Dr. Anderson’s research team has gathered data from before and after wildfires in the Pacific Northwest. In 2020, their goal was to gather environmental samples during an active wildfire. To do this, they sent kits to all participants in mid-April. Once a fire was detected in their area, Dr. Rohlman contacted the participant and asked them to set up the samplers. This allowed researchers to have a nearly immediate response, which is crucial given how quickly wildfires move. To date, all thirteen of the sampling locations have deployed their samplers due to smoke impact.

Preliminary results show that PAH air concentrations were generally higher indoors than outdoors after periods of moderate to unhealthy air quality from wildfires and during no wildfire activity. (For a description of air quality categories, review the Air Quality Index). PAH sourcing data also indicates that there is a difference in PAH exposure between indoor and outdoor air. Chemical movement after wildfire activity shows volatilization of PAHs from soils. Data collected during the 2020 wildfire season will be analyzed and compared to data from 2018 and 2019. 2020 has been the most active fire year on record for the West Coast. Many cities across Washington, Oregon and California saw historically poor air quality, ranging from unhealthy to hazardous, across multiple days. Heavy smoke impact covered most of the West Coast during the month of September, as poor weather conditions made wildfire containment difficult.

As 2020 Wildfires break out across the pacific Northwest, we are working with participants to deploy passive samplers. Here, OSU researchers, Rohlman (left), and Ghetu (right) place an outdoor sampler during historically poor air quality in the summer of 2020.

Dr. Anderson and her lab and Dr. Rohlman thank the study participants for their help in collecting this important data to better understand the impacts of wildfires! To learn more about this study, click here. Learn more about ways to improve your air quality and track fires in your area.

  1. Reducing exposure to air pollution [infographic]
  2. Indoor versus outdoor air quality during wildfires [scientific article]
  3. Study updates:
  4. Current wildfires:
  5. Historical wildfire information:
  6. EPA AirNow interactive maps: