New Directions: Toward a community emissions approach

Tropospheric ozone (O3) negatively impacts human health and ecosystems, and is a greenhouse gas. Wildfires are a source of tropospheric O3, and studies show that wildfires are increasing in North America. In this study, we present a critical review of O3 production from wildfires focusing on three key topics: the influence of wildfire emissions on O3 production; the influence of photochemistry on wildfire O3 production; and regulatory issues associated with wildfire O3 production in the United States. Observations of ΔO3/ΔCO range from approximately −0.1 to 0.9, and are caused by the interplay of numerous factors including fire emissions, efficiency of combustion, chemical and photochemical reactions, aerosol effects on chemistry and radiation, and local and downwind meteorological patterns. Using average ΔO3/ΔCO ratios for major biomes, we estimate global wildfires produce approximately 170 Tg of O3 per year, which is 3.5% of all global tropospheric O3 production. Areas of uncertainty in wildfire O3 production include the net effect of aerosols on chemical and photochemical reactions within a fire plume, the impact of oxygenated volatile organic compounds and nitrous acid on O3 production, and the interplay of variables that lead to extreme ΔO3/ΔCO values. Because wildfire frequencies are likely increasing and have been shown to contribute to elevated O3 at air quality monitoring sites, it is important to better understand the emissions, photochemistry and impacts of these fires.