Acute atmospheric PM 2.5 exposure in Montana: human health risk and analysis of related risk communication measures

Abstract

Particulate matter with a size of 2.5 microns or smaller (PM 2.5) is an atmospheric pollutant monitored by the Environmental Protection Agency (EPA) and the Montana Department of Environmental Quality. Once inhaled, PM 2.5 results in oxidative stress and inflammation that negatively impacts health, especially to respiratory and cardiovascular systems. Wildfires are a known source of PM 2.5 and since Montana is a state prone to wildfires, I assessed acute PM 2.5 exposure risk to Montanans using sensor data from 15 counties (8 western and 7 eastern) from 2017-2021. Statewide averages revealed acute PM 2.5 exposure risk, and a recurrence of exposure. The average 98th percentile PM 2.5 concentrations and percentage of days above acute thresholds were greater for western counties, and statewide this data positively correlated with wildfire acres burned in a year. Acute exposures typically occurred within fire season for eastern counties, but extended beyond fire season for many western counties, indicating exposure from sources other than wildfires. Using records from a Yellowstone County hospital for 2021, I grouped emergency admissions by PM 2.5 concentrations and found significantly higher admissions when concentrations were above acute thresholds, and a positive linear relationship between PM 2.5 and emergency admissions. I compared Montana with the top 10 states for wildfire in 2021, and found it ranked third in wildfire acres burned, but last in the ratio of PM 2.5 sensors per acres burned. I estimated 79% of Montanans live in a county with a PM 2.5 sensor, but that there are spatially fewer sensors in western Montana. I analyzed data from three Missoula County sensors and found greater differences in Air quality index (AQI) values with increasing distance between sensors and that AQI values differed more during the wildfire than other times of the year. Wildfires are predicted to increase with climate change and to properly communicate PM 2.5 exposure risk and retrospectively analyze health outcomes specific for Montanans, more PM 2.5 sensors should be placed throughout the state.