Comparison of Volatile Organic Compounds in Wildfire Smoke on a Dairy Farm and Nearby Cities

Wildfire seasons have become more prolonged and intense in the western US over recent decades due to climate change and other factors. Wildfire smoke contains volatile organic compounds (VOCs) and fine particulate matter (PM_2.5), which are associated with heart and lung diseases in humans and animals. The goal of this study was to assess VOCs and PM_2.5 in ambient air and smoke during wildfire events on an Idaho dairy farm compared to two other Idaho cities. From 2019 to 2022, weekly passive ground-based sampling using Tenax TA sorbent tubes was conducted in three select cities of Idaho: Moscow (dairy farm), Lewiston and Boise. Twenty-one VOCs including benzene (a human carcinogen), toluene, ethylbenzene and xylenes (BTEX) were quantified via thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). Similar increases of BTEX and PM2.5 (obtained from local monitors) were observed at the three sites during the summer months. Moscow background samples were significantly lower in most VOCs than the other sites. In early September 2020, PM_2.5 concentrations peaked at 313 μg/m³ and 282 μg/m³, accompanied by elevated levels of benzene at 1.81 ppb and 2.00 ppb in Lewiston and Moscow, respectively. These pollutants reflected large wildfire smoke exposures, which can impact both cattle and humans. The calculated human cancer risk due to benzene for chronic wildfire event exposure at the three sites were 4, 5 and 4 extra cancers per million people for Moscow, Lewiston and Boise, respectively. The non-carcinogenic VOCs were below the threshold reference concentrations, indicating low risk of noncancer health implications.