Wildfire impacts on O3 and particulate matter in urban areas of the western US

Ozone (O3) precursors are emitted from wildfires, yet ozone production is highly variable and difficult to predict. Particulate matter (PM) is directly emitted from wildfires but may also be produced or lost during transport. This project focuses on understanding several key questions that link wildfire emissions to O3 and PM at urban monitoring sites in the Western US:

1. How do wildfires influence O3 mixing ratios in urban areas of the Western US?

2. What combination of observed and modeled parameters can be used to understand O3 and PM production in urban areas of the Western US?

3. Are UV-based O3 measurements accurate in wildfire plumes?

As part of this project, we will develop a new, simplified method to measure acetonitrile (CH3CN or ACN), a highly specific tracer of wildfires. This method will be deployed at 3 urban monitoring sites in the Western US (Salt Lake City, Boise, Reno). Each site is an existing National Core (NCore) multipollutant monitoring station and has ongoing measurements of O3, carbon monoxide (CO) and PM2.5. We will add measurements of Peroxyacetyl Nitrate (PAN) and NOx (NO + NO2) at the Salt Lake City site for two summer campaigns during the Fire Influence on Regional and Global Environments Experiment (FIREX). These data will help us improve our understanding of wildfire impacts and will be used to develop statistical and photochemical models of O3 in urban areas. The data will also be used by local air quality agencies to better understand wildfire impacts and may be useful to support exceptional event designations. We will use the urban observations of CO, ACN and PM during wildfire events to examine consistency with primary emissions, which can lead to insights into the importance of secondary aerosol formation. We will examine potential biases in the standard UV O3 method, which is used extensively at air monitoring sites. For this, we will compare a well-calibrated UV O3 monitor with a method based on NO chemiluminescence in a region known to get enhanced O3 due to wildfires.

These data and analyses will provide substantial new understanding on the impact of wildfires on O3 and PM in urban areas. Data from this project will also help document interannual variations in wildfire impacts in urban areas of the Western US and will be useful to the FIREX modeling groups. Our work has strong collaborations with state agencies in Utah, Nevada and Idaho, other scientists and with the NOAA FIREX science team. These collaborations are documented through letters of support.

Our project is directly relevant to key FIREX science questions, specifically:

�?� What are the formation mechanisms for secondary species (ozone, SOA and sulfate)?

�?� What environmental or chemical conditions control their relative importance?

�?� What is the local air quality and visibility impact of North American fires?

Finally, our project is directly relevant to NOAA�??s long-term climate goals by contributing to improvements in the prediction of air quality from wildfires.