Wildfire smoke covering the Pacific Northwest and British Columbia on September 6, 2017, from MODIS true color reflectance image. Red dots represent fire locations. Source: https://worldview.earthdata.nasa.gov.
New research by James Laing and Dan Jaffe shows how increases in wildfire smoke have impacted air quality in the western US. Their recent paper, published in the June 2019 issue of EM—The Magazine for Environmental Managers, describes the changing air quality picture for western states. Even though air quality in most of the US has improved in the last four decades, due in large part to the US Clean Air Act regulations, it is not improving in much of the western US. The reason for the decrease in air quality in western states is wildfire smoke.
In 2017 and 2018, wildfires caused the largest daily mean concentrations of fine particulate matter (PM2.5; particles with diameter less than 2.5 μm) ever measured at monitoring sites in the US. Some of the extreme PM2.5 events of 2017–2018 include the following:
- Seeley Lake, Montana, September 6, 2017—Highest daily PM2.5 on record (642 μg/m3). In August-September 2017, there were 35 days with PM2.5 > 150 μg/m3 and 18 with PM2.5 > 250 μg/m3.
- Ventura, California, December 6, 2017—PM2.5 of 557 μg/m3, with a two-week average concentration of 165 μg/m3.
- Seattle, Washington, August 21, 2018—Highest daily PM2.5 ever recorded in Seattle (110 μg/m3).
- Medford, Oregon, September 6, 2017—Highest daily PM2.5 ever recorded in Medford (268 μg/m3), and eight days over 100 μg/m3 in 2017.
To put these measurements in context, the US Environmental Protection Agency (EPA) has set the daily PM2.5 standard at 35 μg/m3 (98th percentile < 35 μg/m3, averaged over 3 years). The EPA has also defined PM2.5 > 150 μg/m3 as very unhealthy and PM2.5 > 250 μg/m3 as hazardous. PM2.5 is such a health hazard because it can travel deep into the respiratory system due to its small size. Despite the gains in air quality in the US, about 30 million people live where the PM2.5 standard is not being met.
The estimated increase in the number and size of wildfires in the future raises issues for public officials and environmental managers. Complying with air quality standards and reducing human exposure to PM2.5 are causes for concern in the western US now and going forward.
Read the full paper here
In a new paper published in Elementa, Dan Jaffe and his coauthors look at background ozone in the US and how it influences whether states can meet air quality standards. Background ozone (O3) includes “contributions from natural and foreign sources of O3 that cannot be controlled by precursor emissions reductions solely within the US.” Understanding background O3 is necessary for air quality management overall and for states and municipalities to meet national air quality standards.
They examined over 100 published studies in order to assess what is the current knowledge about the distribution, trends, and sources of background ozone in the continental US. They found that “noncontrollable O3 sources, such as stratospheric intrusions or precursors from wildfires, can make significant contributions to O3 on some days, but it is challenging to quantify accurately these contributions.” In order to address this shortcoming, they recommend a more coordinated and focused approach to understanding background ozone in the US: improvements in the monitoring network, large-scale field experiments, more accurate and consistent chemical transport models, and more detailed observations of wildfires.
Read the paper here
A new paper authored by Crystal McClure and Dan Jaffe describes the increasing particulate matter (PM2.5) pollution over the last few decades in the Northwest. This research, published Monday in Proceedings of the National Academy of Sciences, analyzed PM2.5 data from rural monitoring (IMPROVE) sites across the contiguous US for 1988–2016. They found a decreasing trend in PM2.5, and cleaner air, around the country except for in the Northwest, where there is a positive trend in PM2.5. This positive trend is associated with total carbon, a marker for wildfires.
The figure below shows trends in PM2.5 for 1988–2016 for the 98th quantile, that is, the seven highest days. In most of the Northwest (red and orange areas), these days are getting worse, while most of the country has improving air quality trends (purple, blue, and green areas).
The 98th Quantile Regression of PM2.5 trends. Observed PM trends for 1988–2016 (calculated using QR methods) from IMPROVE sites are shown by black dots with corresponding values in µg·m−3·y−1. Krige-interpolated values (calculated from observed data) are shown by the color ramp. Solid black lines with arrows (indicating direction) show the boundary where the Krige-interpolated PM2.5 trends within have a 90% probability of being positive or negative. Of the 157 sites, 92 show statistical significance (8 positive/84 negative).
Read the abstract on the PNAS website
This new research has been garnering a lot of press since its publication:
The Jaffe Group has kicked off 2018 with 3 new publications.
- Xi Gong, et al., Ozone in China: Spatial distribution and leading meteorological factors controlling O3 in 16 Chinese cities. Gong and her coauthors examined ozone (O3) concentrations in 16 Chinese cities and developed a statistical model to estimate the maximum daily 8-hour (MDA8) O3 during 2014–2016. They found that the Generalized Additive Model (GAM) captured 43-90% of daily O3 variations. They also identified the leading meteorological factors that affect O3 for each city. Read the full paper here.
Average maximum daily 8-hour (MDA8, ug/m3) ozone concentrations for 16 Chinese cities, 2014-2016.
- Pao Baylon, et al., Impact of biomass burning plumes on photolysis rates and ozone formation at the Mount Bachelor Observatory. Baylon and his coauthors examined biomass burning (BB) events at Mt. Bachelor Observatory (MBO) during the summer of 2015. Biomass burning can emit large amounts of aerosols and gases into the atmosphere. These plumes contain compounds that react with sunlight to produce ozone, a health hazard to sensitive individuals. The photochemistry in BB plumes is poorly understand. Baylon and his coauthors addressed this knowledge gap by using MBO data to calculate ozone production rates and comparing these values with modeled values. Read the full paper here.
- Lei Zhang, et al., A quantification method for peroxyacetyl nitrate (PAN) using gas chromatography (GC) with a non-radioactive pulsed discharge detector (PDD). Zhang and his coauthors developed a method for continuous peroxyacetyl nitrate (PAN) measurements using gas chromatography with a non-radioactive detector. PAN is a known precursor of ozone. Their method has high accuracy and is more readily deployable in field campaigns than the traditional gas chromatography method that utilizes a radioactive detector. Read the full paper here.
Two Jaffe Group members have published peer-reviewed papers in October. Well done to Xi Gong and Pao Baylon for their outstanding work!
Xi Gong and her coauthors used a statistical approach, the Generalized Additive Model, to quantify ozone impacts from wildfires on 8 US cities. They showed that this approach can provide quantitative support for situations when large contributions from noncontrollable sources, such as wildfires, caused an exceedance of the EPA’s daily ozone standard.
Read the full paper here.
Pao Baylon and his coauthors looked at a Siberian biomass burning event in Spring 2015 that was observed at Mt. Bachelor Observatory and by satellite instruments, and also intercepted by a research aircraft. When the plume was in the eastern Pacific, it split into two plumes, one moving eastward toward MBO and the other moving northeast to Alaska and then south to the US Midwest. The second plume was observed by the aircraft in the Midwest. Baylon et al. found that the ozone production observed at MBO was higher than that of the aircraft plume. This was due to the plume at MBO being warmer and the aircraft plume being colder.
Read the full paper here.