Critical Roles of Fire and Soil Emissions in Trend Reversal of U.S. Air Quality and Mortality Burden

Since the enactment of the Clean Air Act in the 1970s, tremendous progress has been made in improving surface air quality in the U.S. through regulatory policies that reduced anthropogenic emissions from power plants, transportation, and other industrial sources. However, the steady nationwide improvement observed up to around 2010 has recently faced dual challenges from non-regulatory emissions, particularly those from wildfires and soils. By combining satellite data, atmospheric model outputs, and surface observations with a machine-learning framework, we show that wildfire-driven increases in surface aerosol and ozone concentrations—along with their associated mortality burden—have reversed decades of air quality gains in the western U.S. over the past 15 years. Long-range transport of fire emissions has also contributed to stagnant or worsening air quality in parts of the central U.S. While wildfire emissions are episodic and often treated as exceptional events for compliance purposes, soil emissions are persistent during the growing season and have become an increasingly important factor in meeting the latest, more stringent air quality standards. For example, in regions such as California, we found that soil-derived NOx emissions may now account for up to one-third of surface ozone concentrations. Looking ahead, we argue that further improvements in air quality and reductions in mortality burden will likely depend on preventive strategies, including enhanced satellite monitoring, improved neighborhood-scale model predictions, and both regulatory and community-level initiatives, before a viable pathway toward meeting more stringent national air quality standards can be fully established.

Prof. Jun Wang is a leading expert in satellite remote sensing and Earth system modeling, focusing on changes of air quality and atmospheric composition associated with wildfires, volcanic eruptions, and other natural and human activities. He directs the Atmospheric and Environmental Research Laboratory at the University of Iowa and has served in leadership roles for NASA satellite science teams, mission planning, and interdisciplinary projects in areas of precision agriculture, public health, and national security supported by NSF, USDA, NASA, NOAA, DoT, DoD, and industry partners. Prof. Wang is a Fellow of the American Meteorological Society and the American Geophysical Union, and a Senior Member of IEEE. He has published more than 230 peer-reviewed papers with an H-index of 71. In 2024, he was honored with the University of Iowa’s Scholar of the Year Award and Regents Award for Faculty Excellence, as well as the AGU Joanne Simpson Medal for “breakthroughs in remote sensing of fires and aerosols, seminal work in atmospheric composition studies, and outstanding service to the AGU community.”