Abstract
Abstract. Frequent and widespread wildfires in the northwestern United States and Canada have become the “new normal” during the Northern Hemisphere summer months, which significantly degrades particulate matter air quality in the United States. Using the mid-visible Multi Angle Implementation of Atmospheric Correction (MAIAC) satellite-derived aerosol optical depth (AOD) with meteorological information from the European Centre for Medium-Range Weather Forecasts (ECMWF) and other ancillary data, we quantify the impact of these fires on fine particulate matter concentration (PM2.5) air quality in the United States. We use a geographically weighted regression (GWR) method to estimate surface PM2.5 in the United States between low (2011) and high (2018) fire activity years. Our results indicate an overall leave-one-out cross-validation (LOOCV) R2 value of 0.797 with root mean square error (RMSE) between 3 and 5 µg m−3. Our results indicate that smoke aerosols caused significant pollution changes over half of the United States. We estimate that nearly 29 states have increased PM2.5 during the fire-active year and that 15 of these states have PM2.5 concentrations more than 2 times that of the inactive year. Furthermore, these fires increased the daily mean surface PM2.5 concentrations in Washington and Oregon by 38 to 259 µg m−3, posing significant health risks especially to vulnerable populations. Our results also show that the GWR model can be successfully applied to PM2.5 estimations from wildfires, thereby providing useful information for various applications such as public health assessment.
Highlights
The United States (US) Clean Air Act (CAA) was passed in 1970 to reduce pollution levels and protect public health and has led to significant improvements in air quality (Hubbell et al, 2010; Samet, 2011)
We assess the spatial distribution of surface PM2.5 from the geographically weighted regression (GWR) method
To further demonstrate the impact of the NWUSC fires on PM2.5 air quality in the United States, we show the spatial distribution of the difference between August 2018 and August 2011 and quantify these results for 10 US Environmental Protection Agency (EPA) regions
Summary
The United States (US) Clean Air Act (CAA) was passed in 1970 to reduce pollution levels and protect public health and has led to significant improvements in air quality (Hubbell et al, 2010; Samet, 2011). The northern part of the US continues to experience an increase in surface PM2.5 due to fires in the northwestern United States and Canada (hereafter NWUSC), especially during the summer months, and these aerosols are a new source of “pollution” (Coogan et al, 2019; Dreessen et al, 2016). The smoke aerosols from these fires increase fine particulate matter (PM2.5) concentrations and degrade air quality in the United States (Miller et al, 2011). Wildfire pre-suppression and suppression costs have increased, the number of large fires and the burnt areas in many parts of western Canada and the United States have increased (Hanes et al, 2019; Tymstra et al, 2019). The accumulation of flammable materials like leaf litter can potentially trigger severe wildfire events, even in those forests that hardly experience wildfires (Calkin et al, 2015; Hessburg et al, 2015; Stephens, 2005)
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