Sources of Atmospheric Volatile Organic Compounds During the Salt Lake Regional Smoke, Ozone and Aerosol Study (SAMOZA) 2022

Abstract

We present measurements of volatile organic compounds (VOCs) and other trace gases taken in Salt Lake City, Utah in August and September 2022. As part of the Salt Lake regional Smoke, Ozone and Aerosol Study (SAMOZA), 35 VOCs were measured with two methods: a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) and 2,4-dinitrophenylhydrazine (DNPH) cartridges analyzed by high-performance liquid chromatography (HPLC). Over two months, the total measured VOCs averaged 32 ± 24 ppb (mean ± standard deviation) with the hourly maximum at 141 ppb, and the total calculated OH reactivity averaged 3.7 ± 3.0 s⁻¹ (maximum at 20.7 s⁻¹). Among them, methanol and ethanol were the most abundant VOCs, making up 42% of the ambient mixing ratio. Isoprene and monoterpenes contributed 25% of the OH reactivity from VOCs, while formaldehyde and acetaldehyde made up another 30%. The positive matrix factorization analysis showed 5 major sources of VOCs, with 32% of abundance being attributed to secondary production/biogenic sources, 44% from the combination of traffic and personal care products, 15% from industrial solvent use, and the rest from biomass burning (10%). Moderate smoke-impacted days elevated various hazardous air pollutants (HAPs) on average by 45%–217% compared to smoke-free days. The ratio of OH reactivity from NO_x to that from VOCs showed that ozone production was mostly VOC-limited throughout the campaign, consistent with our modeling study. VOCs and NO_x both showed increased OH reactivity due to smoke influence. NO_x featured increased reactivity on weekdays compared to weekends, an effect not shown for VOC reactivity during SAMOZA.