Science Stories: Wildfires and air pollution: beyond deadly fires

Author: Alex Karambelas, Postdoctoral Research Scientist, Lamont-Doherty Earth Observatory of Columbia University.

Bio: Alex is an interdisciplinary air pollution scientist, working with air quality modelers, energy experts, epidemiologists, and environmental scientists to determine source contributions to health-damaging air pollution. In her work, she uses chemical transport computer models, designing various emissions scenarios to identify mitigation strategies to curb future air pollution and premature mortality. Her background is in atmospheric sciences, and she earned her Ph.D. in Environment and Resources at the University of Wisconsin—Madison.

Imagine a field filled with tall sunflowers, their yellow faces smiling in your direction. The sky is a bright, crisp blue, the minimal clouds are fluffy and pearly white. You take a look around you and breathe in one big deep breath, the air feeling cool and refreshing, even a bit rejuvenating.

Now imagine you’re stuck in traffic on a crowded highway. It’s a beautiful spring day, so your windows are down. Just as you’re about to take a big breath in, the semi-truck to the left of you belches thick black smoke from its exhaust pipe. The taste is sour and unpleasant, and you roll your windows back up to turn on your air conditioning.

The black smoke is an example of air pollution, or the gases and aerosols suspended in the air that are harmful for human health and the environment. Sometimes referred to as smog, air pollution includes surface level ozone (O3) [1]—formed from the reaction of pollutants directly emitted, for instance, from cars and power plants—and fine particulate matter (PM2.5) a fraction of the width of a single human hair—directly emitted (released) and formed from chemical reactions in the atmosphere. In New York City, we can sometimes see the summer haze when we look out over the city: a thin, discolored layer muting the skyline. Across the globe, millions of people die prematurely and millions more suffer disabilities each year due to breathing in O3 and PM2.5 air pollution for extended periods of time. In my own research, I seek to identify sources of air pollution that lead to the greatest health damages, designing future emissions scenarios to try to reduce the future health burden of air pollution.

Many different emissions sources lead to air pollution, and sources and pollutant concentrations vary from city to city and region to region. Most air pollution is man-made from the (incomplete) combustion of products like fossil fuels and woody biomass from which we meet our energy needs. Biomass burning can also be considered man-made, for instance agricultural biomass burning in India is considered man-made because farmers burn their crop waste. There are natural sources, too, like windblown dust, sea salt spray, and gases released from plants and trees during growing phases or when under stress such as from a drought (these are also called “biogenic sources”). Researchers like myself who study air pollution tend to consider seasonal sources like wildfires like the 2018 Camp Fire in California to be a “natural” source, even if the fire was started from a careless person with a lit match or hot car.

Wildfires are a unique source of air pollution because they are isolated events but can release considerable amounts of gases and aerosols, including that same black smoke. We don’t often think about wildfires as contributing to health-damaging air pollution, instead considering the direct catastrophic destruction they produce. Wildfires occur seasonally under hot, dry conditions in wooded areas all across the world, including in the western United States. They can be very strong in magnitude, burning or smoldering for days or weeks, and can cover a large area of “fuel,” i.e. dry woody biomass. In the western U.S. the wildfire season traditionally is late spring through summer, when brush is often dry and easy to ignite by a lightning strike or spark from semi-truck undercarriages. Around this time we tend to see dozens of news articles from local and national sources that cover the devastation caused by wildfires, often for weeks on end.

Wildfires can lead to dramatic increases in local and regional air pollution, releasing aerosol and gas-phase air pollutants that can chemically react to yield enhanced O3 and PM2.5 concentrations. Near-term health impacts such as increased incidences of hospital admissions due to asthma attacks or other respiratory ailments may be the first sign of elevated pollution due to a wildfire event. Pollution enhancements such as those from wildfires can exacerbate pre-existing health conditions, lead to an increase in hospital admissions, and impact economic productivity. People are susceptible to adverse effects from exposure to air pollution at different rates. Children and the elderly are much more likely to experience lung irritations at moderate exposure rates. Outdoor workers may have to limit their time outdoors, reducing productivity, or be harmed in the process of their workday. Besides structural and health damages from wildfires, other negative economic implications also occur. For instance, in Seattle during the 2018 wildfire season, local business owners faced an economic burden when they were required to cancel various outdoor tourist outings due to the nearby wildfires affecting visibility and human health exposure. Similarly, during the worst seasonal biomass burning events in northwestern India, Delhi will often ground flights due to reduced visibility, whether because of biomass burning in upwind regions or because the event was exacerbated by stagnant winds.

During a wildfire event, concentrations of O3 and PM2.5 in the atmosphere downwind of burn sites may exceed U.S. Environmental Protection Agency (EPA) air quality standards (exposure limits deemed unhealthy for humans). We can measure this enhancement with surface observations, noting changes hour by hour and comparing across air pollution monitor locations. Data from EPA monitor sites are accumulated into an Air Quality Index (AQI) warning system, visible on, which you can use to track all sorts of pollution episodes, even the O3 air pollution event during the recent heatwave in New York City. Surface monitors form a sort of constellation of air pollution measurements, to help us understand the changes in concentrations over time and space, however there is a lot of empty space between surface monitors where we have to make inferences about air pollution.

We can fill in this empty space and assess the amount of air pollution coming from wildfires—or other sources—using complex chemical transport computer models, made up of hundreds of chemical equations in four dimensions. Computer models are also how we get our daily and weekly weather forecasts, data from which is often used in forecasting air pollution. In my own research, I use such computer models to understand various energy sector contributions—such as biomass burning in India—to regional air pollution, and ways to reduce pollution and improve air quality into the future. We can test “What If?” scenarios where certain sources or pollutants are reduced or removed entirely from the system to understand emissions and chemistry contributions to air pollution. Models help researchers understand the space and time between observations, filling in gaps to help understand the sources and chemistry of air pollution, including helping us identify what might be missing when compared to observed values.

We can use models at a variety of scales from urban to globally. The bottom layer of this NASA image from the Earth Observatory blog shows light pollution, indicative of human population, observed from space, and it is overlaid with model data of different types of aerosols including sea salt, dust, and black carbon and their respective sources. In this image, you’ll notice that there are “plumes” of air pollution blown across continents and off coastlines. Air pollution is often localized to urban centers and downwind areas, but pollution, including from wildfires, can become lofted in the air and transported downwind, sometimes for very long distances. Even here on the east coast at Columbia University we can experience wildfire pollution plumes coming from Canada and even occasionally from the Pacific Northwest. Aside from using models, we can track the transport of air pollution including from wildfires using satellites. Long-range transport is nearly as important to air quality scientists as locally emitted pollution in understanding what sources contribute to ambient air pollution.

Wildfire air pollution is a small component of the total air pollution story, where there are many diverse sources across the globe, but the short-term air pollution and health implications from wildfire air pollution may be considerable. In Southeast Asia, modeled seasonal biomass burning events coupled with meteorology are estimated to contribute to more than 100,000 premature deaths due to air pollution across Indonesia, Malaysia, and Singapore (Koplitz et al., 2017). Similarly, fall agricultural waste burning in northwestern India contributes between 7 and 78% of Delhi’s air pollution, even though the burning occurs hundreds of kilometers away (Cusworth et al., 2018), leading to a near doubling of PM2.5 during waste burning episodes (Liu et al., 2018), and potentially contributing to thousands of deaths. In the western U.S., over 100 deaths occurred during California wine country wildfires in October 2017.

Is there a way to reduce the air pollution deaths associated with wildfires? Check for forecasts and tweet “#AirAirAir [place name]” on Twitter for current air pollution levels. Wear facemasks and stay indoors during events if you live in the direct downwind areas, and avoid travel to wildfire-active regions during and shortly after wildfire events will greatly reduce your air pollution exposure. Call family and friends in the vicinity of wildfire pollution exposure to suggest these steps is a good idea too. Save hiking trips in dry-prone regions for (slightly) wetter seasons if possible, and always make sure a campfire is fully extinguished.

You can also reduce air pollution and mitigate the impending enhancement of wildfires by reducing your carbon footprint, thereby reducing GHG emissions into the atmosphere. For instance, we can expand affordable public transportation with electric fleet vehicles to reduce the number of traditional gasoline passenger cars or affix pollution “scrubbers” to power plant stacks, removing PM2.5 precursors through adsorption processes. Exacerbation of drought and high temperatures due to climate change will likely lead to increased wildfire extent and strength in the coming decades, putting millions of people worldwide at risk of losing their homes or their lives. Many sources contribute to air pollution, some more manageable than others, but when it comes to wildfires, we can all take steps to reduce our impact and protect ourselves and our loved ones.


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[1] Although the same chemical compound as stratospheric ozone, surface-level ozone does not serve a positive purpose and is harmful to humans, animals, plants, and buildings.

Koplitz, Shannon N, Loretta J Mickley, Miriam E Marlier, Jonathan J Buonocore, Patrick S Kim, Tianjia Liu, Melissa P Sulprizio, et al. “Public Health Impacts of the Severe Haze in Equatorial Asia in September–October 2015: Demonstration of a New Framework for Informing Fire Management Strategies to Reduce Downwind Smoke Exposure.” Environmental Research Letters 11, no. 9 (2016): 094023.
Cusworth, Daniel H, Loretta J Mickley, Melissa P Sulprizio, Tianjia Liu, Miriam E Marlier, Ruth S DeFries, Sarath K Guttikunda, and Pawan Gupta. “Quantifying the Influence of Agricultural Fires in Northwest India on Urban Air Pollution in Delhi, India.” Environmental Research Letters 13, no. 4 (April 1, 2018): 044018.
Liu, Tianjia, Miriam E. Marlier, Ruth S. DeFries, Daniel M. Westervelt, Karen R. Xia, Arlene M. Fiore, Loretta J. Mickley, Daniel H. Cusworth, and George Milly. “Seasonal Impact of Regional Outdoor Biomass Burning on Air Pollution in Three Indian Cities: Delhi, Bengaluru, and Pune.” Atmospheric Environment 172, no. September 2017 (2018): 83–92.



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