Waste treatment facility emissions of volatile organic compounds in urban environments

Volatile organic compounds (VOCs) provide the fuel for criteria air pollutants like ozone and particulate matter to form in the atmosphere in the presence of NOx and sunlight. As motor vehicle VOC emissions have declined in the U.S., non-traditional sources of VOCs such as volatile chemical products (VCPs) and others have gained relative importance in urban areas. Here, we describe VOC emissions from waste treatment facilities (waste transfer stations, wastewater treatment plants, compositing facilities, landfills) in the San Francisco Bay Area, California. VOC measurements were conducted using a new proton transfer reaction time of flight mass spectrometer, the Vocus PTR-ToF-MS, on a mobile sampling platform in April 2021. Hundreds of VOCs were detected and quantified downwind of each site, with backgrounds determined nearby. All waste treatment facilities visited were a source of ethanol and acetone. Trash transfer stations and composting sites were sources of VOCs associated with VCPs (e.g., D5-siloxane) and highly reactive species like isoprene and monoterpenes, presumably from biomass. Wastewater treatment plants were a source of methane thiol and other odorous compounds. The concentration gradient of these odorous species was quantified in downwind residential neighborhoods. We also present the reactivity weighted VOC concentrations for each waste treatment facility and analyze the potential implications for urban air quality. This work demonstrates the complexity and importance of non-traditional urban VOC sources and highlights the potentially important waste treatment facility sources of reactive VOCs to urban environments.