Wildland Fire Smoke and Anthropogenic Urban VOC Profiles Downwind of Wildfires from 2023-2024

Air quality in the Las Vegas Valley (LVV) is generally affected by the combination of local emissions, upwind anthropogenic pollution (from, for example, southern California), terrain, meteorology, and wildfires. Given the increasing prevalence of wildfires in the western United States, ozone concentrations in the LVV have been significantly impacted, even in light of stricter emission controls on stationary and mobile nitrogen oxides (NO_x) emission sources. Transport of ozone precursors, such as volatile organic compounds (VOCs), can result in enhanced ozone production. While wildfire emissions typically enhance ozone production downwind, some cases show no enhancement or even depletion of ozone concentrations, meaning the effect of wildfire emissions downwind are not well characterized.

We used low-cost, automated active-sampling thermal desorption field samplers (EPA TO-17) and Summa Canisters (EPA TO-15) to collect anthropogenic and wildfire-specific VOC profiles in 2023 and 2024 from May through September to identify the impact of wildfire smoke on air quality in the LVV. Twelve wildfire-specific VOCs were selected to trace wildfire emissions in an urban area, including acetonitrile, furan, and furfural. Additionally, wildfire- and anthropogenic-emitted VOCs, including benzene and toluene, were selected for comparison with existing measurements. Samples were collected at three established monitoring sites (two urban and one background) in Las Vegas and compared with established pollutant monitoring methods (i.e., NCore and PAMS). With only two wildfire events affecting the LVV during the 2023 sampling period, this low-intensity wildfire year provides a large amount information useful for developing a background and anthropogenic VOC profile. VOC data from 2024, a year that exhibited increased wildfire activity in the region, will inform the wildfire and anthropogenic VOC profiles.

We perform statistical and positive matrix factorization analyses to determine wildfire-impacted profiles and a typical background profile of VOCs in the LVV. We use this two-year data set to characterize and quantify wildfire smoke in the LVV from 2023-2024. Expansion of this methodology will allow agencies to uniquely identify when wildfire emissions are affecting their area, quantify the impact of these emissions on ozone production, and meet regulatory objectives.