13B.5 Urban Air Quality during Smoke Events in the Western U.S.

Thursday, 10 January 2019: 4:30 PM
North 126A (Phoenix Convention Center - West and North Buildings)
Claire Buysse, Univ. of Washington Bothell, Bothell, WA; and D. Jaffe, A. Kaulfus, and U. Nair

Biomass burning events emit particulate matter (PM), carbon monoxide, and a wide range of volatile organic compounds, including many ozone (O3) precursors. When smoke from these events is transported to urban areas, the impact on O3 is highly variable. Under projections of increasing wildfire frequency and severity in the western U.S., many cities, which are already prone to poor air quality, are poised to experience greater O3 impacts from smoke events. While urban smoke impacts on O3 have been observed, they are not well-understood and vary by season, region, and city.

In this study, we investigate O3 impacts from smoke from July-September, 2013-2017, in 18 cities in the western U.S. We use satellite-based Hazard Mapping System (HMS) fire and smoke product to identify overhead smoke, classifying days as nonsmoke, adjacent to smoke (immediately preceding or following a smoke event), first smoke (first day of smoke event), and consecutive smoke (any smoke days following the first day of the event). We identify four key findings:

  1. Elevated O3, PM2.5, and NO2 occur under smoke influence, with the greatest mean enhancement of all three pollutants occurring on consecutive smoke days.
  2. The rate of morning O3 production (dO3/dt) is higher under smoke influence, indicating the importance of transported O3 precursors, rather than O3 itself.
  3. Absolute enhancements in PM2.5 and NO2 under smoke influence are not well-correlated with O3 enhancements across sites or smoke classifications. This may result, in part, from differences in chemical regime (e.g., NOx sensitivity) among cities and/or non-linearity in the O3 relationship with PM2.5 (see next point).
  4. We show that O3 enhancements in smoke generally increase with 24-h PM2.5 up to ~30 ug/m3 (smoke). Above this level, O3 enhancements appear to decline.

We note that the HMS product is a useful tool for smoke identification, but elevated O3 and PM2.5 on days before and after smoke events suggests that some smoke events are not detected (e.g., low smoke levels, cloud cover), but still impact air quality.

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