Articles | Volume 17, issue 17
Research article
12 Sep 2017
Research article |  | 12 Sep 2017

Changes in ozone and precursors during two aged wildfire smoke events in the Colorado Front Range in summer 2015

Jakob Lindaas, Delphine K. Farmer, Ilana B. Pollack, Andrew Abeleira, Frank Flocke, Rob Roscioli, Scott Herndon, and Emily V. Fischer

Abstract. The relative importance of wildfire smoke for air quality over the western US is expected to increase as the climate warms and anthropogenic emissions decline. We report on in situ measurements of ozone (O3), a suite of volatile organic compounds (VOCs), and reactive oxidized nitrogen species collected during summer 2015 at the Boulder Atmospheric Observatory (BAO) in Erie, CO. Aged wildfire smoke impacted BAO during two distinct time periods during summer 2015: 6–10 July and 16–30 August. The smoke was transported from the Pacific Northwest and Canada across much of the continental US. Carbon monoxide and particulate matter increased during the smoke-impacted periods, along with peroxyacyl nitrates and several VOCs that have atmospheric lifetimes longer than the transport timescale of the smoke. During the August smoke-impacted period, nitrogen dioxide was also elevated during the morning and evening compared to the smoke-free periods. There were nine empirically defined high-O3 days during our study period at BAO, and two of these days were smoke impacted. We examined the relationship between O3 and temperature at BAO and found that for a given temperature, O3 mixing ratios were greater (∼ 10 ppbv) during the smoke-impacted periods. Enhancements in O3 during the August smoke-impacted period were also observed at two long-term monitoring sites in Colorado: Rocky Mountain National Park and the Arapahoe National Wildlife Refuge near Walden, CO. Our data provide a new case study of how aged wildfire smoke can influence atmospheric composition at an urban site, and how smoke can contribute to increased O3 abundances across an urban–rural gradient.

Short summary
Wildfire smoke is becoming increasingly important for air quality in the US. We used measurements taken during the summer 2015 near Denver, CO, to provide a case study of how wildfire smoke can impact air quality, specifically ozone, which is harmful to humans. Wildfire smoke during this time period was associated with about 15 % more ozone than we would expect under normal conditions. This smoke came from fires in the Pacific Northwest and likely impacted much of the central and western US.
Final-revised paper