A pair of researchers with the University of Washington has found that an increase in wildfire size and duration over the past 28 years has led to worsening bad air days in the U.S. Northwest. In their paper published in Proceedings of the National Academy of Sciences, Crystal McClure and Daniel Jaffe describe their study and what their results mean for people living in affected areas.

They obtained data from 100 rural air quality monitoring sites from across the country and sifted through the data, collecting information only on particles that were smaller than 2.5 micrometers. They entered the data into a mapping application that displayed levels of such particulates across the continental U.S. Next, they set filters to show changes in levels of the fine particulates over the years 1988 to 2016 for only the worst air quality days. Doing so showed that the northwest part of the country has experienced more bad days over the past 28 years, and those bad days have been worsening. In sharp contrast, they found that the rest of the United States experienced better  over the same time period. The researchers note that even people who are not normally at risk from  particulates can be harmed if they are exposed to them on a regular basis. And sometimes, levels can be extreme, such as when a fire burns for a long time near a community.

 Explore further: Smoke from wildfires can tip air quality to unhealthy levels

More information: Crystal D. McClure et al. US particulate matter air quality improves except in wildfire-prone areas, Proceedings of the National Academy of Sciences (2018). DOI: 10.1073/pnas.1804353115

Abstract

Using data from rural monitoring sites across the contiguous United States, we evaluated fine particulate matter (PM2.5) trends for 1988–2016. We calculate trends in the policy-relevant 98th quantile of PM2.5 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 PM2.5 at sites within the Northwest United States (average 0.21 ± 0.12 µg·m−3·y−1; ±95% confidence interval). This was in contrast with sites throughout the rest of country, which showed a negative trend in 98th quantile PM2.5, likely due to reductions in anthropogenic emissions (average −0.66 ± 0.10 µg·m−3·y−1). The positive trend in 98th quantile PM2.5 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) PM2.5 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 PM2.5 over most of the country but a positive trend in the 98th quantile PM2.5 across the Northwest due to wildfires.

Read more at: https://phys.org/news/2018-07-wildfires-bad-air-days-northwest.html#jCp