Highly variable lead (Pb) air concentrations associated with fire events in California
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Lead (Pb) is one of the six primary criteria air pollutants regulated under the Clean Air Act by the United States Environmental Protection Agency (EPA). Exposure to lead has adverse impacts to human health, and terrestrial and aquatic ecosystems. From 1980 to 2014, the EPA successfully decreased levels of lead in the air by 98%. However, recent studies have shown the potential for remobilization of natural and historical lead by wildfires. In this study, we examine lead concentrations as measured by the EPA Air Quality System (AQS) monitors, specifically the PM2.5 speciation monitoring network. Our study focuses on lead measurements taken in California from 2008-2018 on non-fire vs. fire-impacted days. Fire-impacted days are identified using the National Oceanic and Atmospheric Administration’s Hazard Mapping System (HMS). Using this method, we observe high variability in lead concentrations across fire days and monitoring sites. Many fire-days do not exhibit elevated lead concentrations; instead, a few large fires are associated with some of the highest lead values. For instance, smoke from the Camp Fire caused the highest lead concentration (0.102 micrograms/cubic meter) recorded by any of the AQS monitors in California in 2018. This measurement, taken at Point Reyes on November 9th, 2018, is 77 times higher than the average lead value for that year. This variability in individual fires drove differences in lead concentration results between fire seasons, with some fire seasons showing no elevation in average lead concentrations on fire days. We are currently exploring potential mechanisms behind this variation, analyzing results by fuel type, fire severity, distance, and PM concentrations among others. The results of our research have implications for both human populations and ecosystems near these fires and suggest that wildfire will become an increasing contributor to lead air quality concentrations in the future, as fire seasons are predicted to become longer and more intense. Understanding why particular fires contribute more lead than others will be paramount in anticipating and potentially mitigating impacts.