Ozone from Wildfires: Peering through the Smog

Abstract:

In the western US, many areas are near the current air quality standard for O3. Yet there is substantial inter-annual variability (IAV) in the number of days that exceed the O3 air quality threshold (currently 75 ppbv for an 8-hour average). We propose that wildfires are the dominant cause for this IAV. However there are large uncertainties around O3 production from wildfires due to numerous complicating factors. Ozone formation in wildfire plumes differs substantially from urban O3 production in several ways: substantial variations in the emissions, much larger aerosol loadings, a much greater variety of reactive and oxygenated VOCs, rapid and substantial formation of PAN and very different sources of HOx in the plume. These factors make it challenging to model wildfire impacts on photochemistry in the usual way.

In this presentation we will show examples of three common situations based on data from the Mt. Bachelor Observatory:

1. Rapid O3 formation (within one day) in a wildfire plume.
2. Slow, but substantial, O3 formation (over days to a week) in a wildfire plume.
3. No detectable O3 formation in a wildfire plume.

We will interpret these results with respect to the observed NOy mixing ratios, the photochemical environment, the combustion efficiency, the plume transport and other factors and suggest some key experiments and modeling studies that can help further our understanding of wildfire O3 production.