Wildfires are stifling air-quality improvements in the western US

Thanks to regulations targeting power plants and motor vehicles, human-caused emissions of particulate matter have been declining in many areas of the US. These regulations usually target aerosols less than 2.5 µm in diameter, called PM_2.5, which can travel through the lungs and into the bloodstream, increasing the risk of respiratory and cardiovascular diseases. But in the western US, summer levels of PM_2.5 have been holding steady—and some years, they’ve increased. Researchers expected the national regulations to lead to improvements in all parts of the country, says Katelyn O’Dell, a graduate student in atmospheric chemistry at Colorado State University. Now she and her colleagues, including group leader Jeffrey Pierce, have tied the persistence of PM_2.5 to western wildfires (Environ. Sci. Technol. 2019, DOI: 10.1021/acs.est.8b05430). The scientists focused on the Pacific Northwest, where the PM_2.5 trend is particularly stark. The team used a combination of atmospheric modeling, air-quality data, and satellite observations of wildfire smoke to make the connection. Wildfire season has been getting longer and more intense in the West, a trend that could intensify due to climate change. O’Dell says researchers need to study the long-term public health effects of wildfire PM_2.5 and determine if they are similar to those caused by human-made PM_2.5.