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

Kalashnikov, Dmitri A; Schnell, Jordan L; Abatzoglou, John T; Swain, Daniel L; Singh, Deepti · Sci Adv · 2022

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Abstract

Wildfires and meteorological conditions influence the co-occurrence of multiple harmful air pollutants including fine particulate matter (PM<sub>2.5</sub>) and ground-level ozone. We examine the spatiotemporal characteristics of PM<sub>2.5</sub>/ozone co-occurrences and associated population exposure in the western United States (US). The frequency, spatial extent, and temporal persistence of extreme PM<sub>2.5</sub>/ozone co-occurrences have increased significantly between 2001 and 2020, increasing annual population exposure to multiple harmful air pollutants by ~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 PM<sub>2.5</sub>/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.