A Deadly Mix: Wildfires and Urban Air Pollution Create Toxic Ozone

Wildfires have torn across the western United States over the last decade. Displacing thousands of people, destroying homes and businesses, and taking lives, wildfires have become a common extreme weather event. While wildfires themselves present a dangerous public health hazard, the lingering effects of atmospheric pollution are also linked to increases in urban ozone concentrations. Ozone is a harmful air pollutant made up of three oxygen atoms and is linked to respiratory illness. Typically seen as a “good” environmental actor, ozone is the chemical compound that makes up the protective ozone layer, shielding the Earth from harmful ultraviolet radiation. However, ground-level ozone, or ozone forming below the stratosphere, acts as an air pollutant and the main ingredient in urban smog.

Wildfire smoke is known to contribute to increased ozone levels in urban areas, but the exact chemistry was never well understood. A new study has determined that the complex chemical cocktail of wildfire smoke mixed with nitrous oxide can result in harmful levels of ozone. Nitrous oxide, a common transportation byproduct, is often found in urban regions due to the high prevalence of traffic congestion. A joint project between the National Aeronautic and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA) partnered with the Fire Influence on Regional to Global Environments and Air Quality flight campaign to create a flying laboratory. The research team collected air samples from this flying laboratory during times of wildfire to analyze the chemical components of the smoke plume. Using this data, lead researcher Dr. Xu and his team created an equation to calculate ozone production based on wildfire emissions.

As wildfire smoke drifts over cityscapes, the urban sources of nitrous oxide mix with the smoke to generate high volumes of dangerous ozone. Mixing could increase ozone concentrations by as much as 3 parts per billion (ppb), a figure well below the U.S. Environmental Protection Agency’s (EPA) health advisory of 70 ppb, but the increase may still result in increased respiratory distress, especially for those with pre-existing respiratory conditions. Climate change will only increase the frequency of wildfire events, leading to an increase in urban air pollution impacts. This poses a challenge for environmental regulatory agencies as wildfire smoke may undermine attempts to regulate ozone pollution.

Lu Xu is a research scientist in the tropospheric chemistry division of the National Oceanic and Atmospheric Administration. He holds a PhD in Chemical Engineering from the Georgia Institute of Technology and a Bachelors of Engineering in Chemical Engineering from Zhejiang University

Managing Correspondent: Samantha Tracy
Press Article: “Wildfire smoke may ramp up toxic ozone production in cities”
Journal Article: “Ozone chemistry in western U.S. wildfire plumes”
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