Summer PM_2.5 Pollution Extremes Caused by Wildfires Over the Western United States During 2017–2018

Abstract

Using observations and model simulations (ESM4.1) during 1988–2018, we show large year‐to‐year variability in western U.S. PM2.5 pollution caused by regional and distant fires. Widespread wildfires, combined with stagnation, caused summer PM2.5 pollution in 2017 and 2018 to exceed 2 standard deviations over long‐term averages. ESM4.1 with a fire emission inventory constrained by satellite‐derived fire radiative energy and aerosol optical depth captures the observed surface PM2.5 means and extremes above the 35 μg/m3 U.S. air quality standard. However, aerosol emissions from the widely used Global Fire Emissions Database (GFED) must be increased by 5 times for ESM4.1 to match observations. On days when observed PM2.5 reached 35–175 μg/m3, wildfire emissions can explain 90% of total PM2.5, with smoke transported from Canada contributing 25–50% in northern states, according to model sensitivity simulations. Fire emission uncertainties pose challenges to accurately assessing the impacts of fire smoke on air quality, radiation, and climate.

Assessing the Risk of Respiratory-Related Healthcare Visits Associated with Wildfire Smoke Exposure in Children 0–18 Years Old: A Systematic Review

“…Systemic impacts are also observed, including effects on pregnancy outcomes such as preterm birth [10]. Wildfire smoke significantly increases PM 2.5 levels in the air, spreading long distances from the source and remaining elevated for weeks [11,12]. Regardless of the source, increased levels of PM 2.5 in the air have adverse health effects such as increased cardiorespiratory morbidity and mortality and public health burdens [13,14], including cost and increased numbers of healthcare visits.…”

High Temporal Resolution Satellite Observations of Fire Radiative Power Reveal Link Between Fire Behavior and Aerosol and Gas Emissions

“…Quantitative comparisons between different fire emissions inventories remain scarce due to the variable transport models used in each study and the spatial/temporal averaging used for comparison to observations (Liu et al, 2020). However, a few recent studies have shown significant variability in aerosol emissions from fire emissions inventories and large discrepencies between observations and fire emissions inventory driven predictions of surface aerosol concentrations (Pan et al, 2020; Xie et al, 2020).…”

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

“…During widespread co-occurrence days in recent seasons (2015, 2017, 2018, and 2020), PM 2.5 concentrations averaged across all constituent grid cells experiencing PM 2.5 /ozone co-occurrence exceeded the Environmental Protection Agency (EPA) regulatory limit of 35 μg/m 3 on 13 individual days ( Fig. 2D , orange markers), peaking at 47.7 μg/m 3 on 3 September 2017 during a period of widespread fire activity and smoke conditions in the western US ( 25 ). Ozone concentrations averaged across the same grid cells on these days ( n = 13) ranged from 57 to 63 parts per billion (ppb) ( Fig.…”

“…1D ). The largest spatial extents of co-occurrence were observed in 2015, 2017, 2018, and 2020—coincident with hot, dry summers and widespread fire activity, including the largest burned areas across the western US wildland-urban interface ( 20 , 24 , 25 , 29 , 36 , 47 ). Increases in the frequency and spatial extent of co-occurrences are associated with an increasing trend in July to September population exposure of ~24.9 million person-days/year ( P < 0.001) in the western US during 2001 to 2020 ( Fig.…”