Increasing co-occurrence of fine particulate matter and ground-level ozone extremes in the western United States

Wildfires and meteorological conditions influence the co-occurrence of multiple harmful air pollutants including fine particulate matter (PM2.5) and ground-level ozone. We examine the spatiotemporal characteristics of PM2.5/ozone co-occurrences and associated population exposure in the western United States (US). The frequency, spatial extent, and temporal persistence of extreme PM2.5/ozone co-occurrences have increased significantly between 2001 and 2020, increasing annual population exposure to multiple harmful air pollutants by similar to 25 million person-days/year. Using a clustering methodology to characterize daily weather patterns, we identify significant increases in atmospheric ridging patterns conducive to widespread PM2.5/ozone co-occurrences and population exposure. We further link the spatial extent of co-occurrence to the extent of extreme heat and wildfires. Our results suggest an increasing potential for co-occurring air pollution episodes in the western US with continued climate change.

Automated summary

Wildfires and meteorological conditions have a significant impact on the co-occurrence of PM2.5 and ground-level ozone in the western US. The frequency and intensity of these co-occurrences have increased over the past two decades, leading to an increase in population exposure to harmful air pollutants. The extent of co-occurrence is linked to atmospheric ridging patterns and the extent of extreme heat and wildfires.