Temporal shifts in sources and composition of particulate metals in an environmental justice community: Impacts of continued emission reductions, COVID-19, and wildfires

Abstract

In this study, we evaluated trends in the composition and source contributions of ambient particulate metals, many of which are toxic air contaminants, in Paramount, California. Paramount is an environmental justice community disproportionately impacted by air pollution from multiple emission sources near sensitive receptors. Concentrations of ambient metals bound to total suspended particulates (TSP) were measured hourly using a Xact 625 ambient metal monitor between 2017 and 2020. The Positive Matrix Factorization (PMF) model identified traffic, industry, and soil dust as major contributors. Results showed that contributions of traffic and soil dust noticeably declined during the COVID-19 lockdown period (March–April 2020) due to reduced human activities but reverted to normal levels within a few months. Industry-related factors, however, dropped significantly during this period and remained low throughout the year. Contributions from industry-related sources in Paramount began declining even before 2020, despite no similar trend in regional levels, implying local emission reductions. These reductions resulted from tariffs, decreased demand, regulatory actions by the South Coast Air Quality Management District, and voluntary controls by local facilities. Consequently, Paramount is experiencing drastically lower levels of metals (up to 80%, depending on the metal and source) from metal-processing facilities and related sources. Moreover, we observed markedly elevated concentrations of several metals (e.g., Ba, Ca, Mn, K, etc.) during the unprecedented September 2020 wildfires that engulfed much of the western US, adding to the limited body of studies on this phenomenon and emphasizing the considerable impact of massive wildfires on ambient levels of particulate metals.