US particulate matter air quality improves except in wildfire-prone areas

Abstract

Using data from rural monitoring sites across the contiguous United States, we evaluated fine particulate matter (PM) trends for 1988-2016. We calculate trends in the policy-relevant 98th quantile of PM using Quantile Regression. We use Kriging and Gaussian Geostatistical Simulations to interpolate trends between observed data points. Overall, we found positive trends in 98th quantile PM at sites within the Northwest United States (average 0.21 ± 0.12 µg·m·y; ±95% confidence interval). This was in contrast with sites throughout the rest of country, which showed a negative trend in 98th quantile PM, likely due to reductions in anthropogenic emissions (average -0.66 ± 0.10 µg·m·y). The positive trend in 98th quantile PM is due to wildfire activity and was supported by positive trends in total carbon and no trend in sulfate across the Northwest. We also evaluated daily moderate resolution imaging spectroradiometer (MODIS) aerosol optical depth (AOD) for 2002-2017 throughout the United States to compare with ground-based trends. For both Interagency Monitoring of Protected Visual Environments (IMPROVE) PM and MODIS AOD datasets, we found positive 98th quantile trends in the Northwest (1.77 ± 0.68% and 2.12 ± 0.81% per year, respectively) through 2016. The trend in Northwest AOD is even greater if data for the high-fire year of 2017 are included. These results indicate a decrease in PM over most of the country but a positive trend in the 98th quantile PM across the Northwest due to wildfires.

Global Emergence of Anthropogenic Climate Change in Fire Weather Indices

“…Emergence for FWI is delayed and exhibits more geographic variability relative to the emergence of temperature-based measures (e.g., King et al, 2015) given the complementary (e.g., Mediterranean) and competing (e.g., boreal) roles of changes in precipitation during the fire season on FWI. Likewise, the regional emergence in fire weather metrics is reasoned to have notable impacts on regional to continental air quality and human health (McClure & Jaffe, 2018;Spracklen et al, 2009). Emergence at regional scales occurs earlier than at local scales as noted in previous ToE and attribution studies (Fischer & Knutti, 2014;King et al, 2015).…”

Scientific assessment of background ozone over the U.S.: Implications for air quality management

“…In the western U.S., forest management and climatic factors (e.g., drought and pine bark beetle infestations) have resulted in extensive tree mortality (Raffa et al, 2008), a significant increase in wildfire activity (Dennison et al, 2014), and deteriorating air quality in some areas (McClure and Jaffe, 2018). Agricultural burning is commonplace in the central and eastern U.S.…”

Santa Ana Winds of Southern California Impact PM2.5With and Without Smoke From Wildfires

“…Secondary aerosols can account for more than 50% of the total PM 2.5 mass, though it varies greatly among regions and seasons (Finn et al, ). PM 2.5 from anthropogenic sources in the United States, including Southern California (SoCal), has decreased in the past decades due to policy implementation (Lurmann et al, ; McClure & Jaffe, ).…”

“…PM 2.5 also results from biomass burning and is the main component of wildfire smoke with the biggest impact on public health related to short‐term exposure (Gan et al, ; Gupta et al, ; Liu et al, ; McClure & Jaffe, ). In the United States, McClure and Jaffe () observed a downward trend in PM 2.5 during the last three decades, except in regions that were prone to wildfires.…”