Beyond Particulate Matter Mass: Heightened Levels of Lead and Other Pollutants Associated with Destructive Fire Events in California

Abstract

As the climate warms, wildfire activity is increasing, posing a risk to human health. Studies have reported on particulate matter (PM) in wildfire smoke, yet the chemicals associated with PM have received considerably less attention. Here, we analyzed 13 years (2006–2018) of PM2.5 chemical composition data from monitors in California on smoke-impacted days. Select chemicals (e.g., aluminum and sulfate) were statistically elevated on smoke-impacted days in over half of the years studied. Other chemicals, mostly trace metals harmful to human health (e.g., copper and lead), were elevated during particular fires only. For instance, in 2018, lead was more than 40 times higher on smoke days on average at the Point Reyes monitoring station, due mostly to the Camp Fire, burning approximately 200 km away. There was an association between these metals and the combustion of anthropogenic material (e.g., the burning of houses and vehicles). Although still currently rare, these infrastructure fires are likely becoming more common and can mobilize trace metals in smoke far downwind, at levels generally unseen except in the most polluted areas of the country. We hope a better understanding of the chemicals in wildfire smoke will assist in the communication and reduction of public health risks.

Quantifying fire-specific smoke severity

“…47 This work provides an approach to investigate these findings at a broader-scale and also enables further research into whether burning specific materials, such as man-made structures, results in more toxic air pollution. 48 As the climate continues to warm and wildfires increase across much of the Western US and beyond, 1,49 particulate matter air pollution from these events is trending upward and expected to worsen in the coming decades. [5][6][7]50 A growing literature finds that exposure to wildfire smoke results in a range of negative societal impacts, including impacts on respiratory-related morbidity and all-cause mortality, 44,51,52 interrupted learning, 10,53 and decreased labor productivity.…”

Wildfires in the western United States are mobilizing PM2.5-associated nutrients and may be contributing to downwind cyanobacteria blooms

“…Data from April 1–December 31 were analyzed to encompass the fire season, per previous work. 33 PM 2.5 measurements are taken once every 3–6 days, depending on the station. PM 2.5 samplers and operational requirements are described in EPA's Quality Assurance Guidance document.…”

“…Speciated PM 2.5 measurements were labeled as smoke-impacted if the monitor location fell within an HMS smoke plume on the day of measurement (Table S1†). 33 Concentration differences for each species (in μg m −3 and % above average) were calculated on smoke-impacted and non-smoke days for each station to account for station-specific differences. 33 In addition, a permutation test was used to determine if smoke and non-smoke day concentrations were significantly different for each species and each year, for data grouped by station and year.…”

“…33 Concentration differences for each species (in μg m −3 and % above average) were calculated on smoke-impacted and non-smoke days for each station to account for station-specific differences. 33 In addition, a permutation test was used to determine if smoke and non-smoke day concentrations were significantly different for each species and each year, for data grouped by station and year. 33,63 Data were excluded from the permutation test if fewer than 20 overall or 4 smoke-impacted measurements were observed at a station in a year.…”

Health effects of wildfires

“…55 In North America, where air quality monitoring is more comprehensive, evidence suggests that wildfires have played an increasingly important role in determining overall air quality levels over the last several decades. 56 While wildfires' impact on US air quality has historically been limited to the Pacific Northwest, 40,57 smoke's impact on surface average and extreme PM 2.5 concentrations is now observed throughout much of the Western US 42,58 and as far away as the East Coast. 59 In 2020 alone, an estimated more than 25 million people in the US were exposed to at least one day with wildfire PM 2.5 > 100 𝜇𝑔𝑚 −3 , 42 more than three times health-based daily air quality guidelines.…”