The intensification of wildfires in the United States is reversing decades of progress in reducing air pollution.
A study published in Science by the University of Iowa warns that these events have increased the presence of surface ozone, a pollutant that directly affects human health and air quality.
Difference between stratospheric and surface ozone
- Stratospheric ozone: located in the upper layers of the atmosphere, it protects the Earth from ultraviolet radiation.
- Surface ozone: forms at ground level by the reaction of VOCs (volatile organic compounds) and NOx (nitrogen oxides) under sunlight. It is harmful to the lungs, exacerbates respiratory diseases, and affects crops and vegetation.
- Setback in environmental policies
The Clean Air Act and other regulations had managed to reduce NOx levels in the eastern part of the country. However, since 2015 wildfires have changed the trend:
- Between 2003 and 2015: sustained decline in surface ozone.
- Between 2015 and 2024: significant increase, creating unhealthy air conditions in large areas.
Impact on public health
The study reveals a 46% increase in premature deaths related to ozone from fires after 2013.
- An estimated 318 additional deaths per year are linked to this phenomenon.
- In 2023, there were 7,974 premature deaths attributable to smog.
- Between 2022 and 2024, 43 million people were exposed to air that does not meet quality standards.
Transport of pollutants
Surface ozone not only affects areas near the fires: it can travel hundreds or thousands of kilometers, impacting distant regions.
This complicates emergency management, as states must demonstrate to the EPA that the pollution comes from distant fires, a procedure that is increasingly less effective.
Study methodology
Researchers used deep learning techniques to combine data from 1,000 ground stations and satellite records, creating a high-resolution map (1 km²) of daily ozone concentration between 2003 and 2024.
With this information, they calculated the incidence of premature deaths considering life expectancy, average exposure, and population density.
Comparison with other pollutants
The impact of surface ozone surpasses that of black carbon, another pollutant linked to respiratory and heart diseases.
According to Jun Wang, “the effect of surface ozone is always greater, although there are regional differences.”
Climate change and future risks
The intensification of fires, associated with climate change, could further exacerbate the situation. The 2023 fire season in Canada raised ozone levels above federal standards for 148 million Americans, equivalent to 44% of the population.
The study warns that emission reduction policies must adapt to the growing impact of wildfires.
Surface ozone pollution poses a serious risk to public health and agriculture, and requires strategies that address both local and remote sources of pollution.
