Assessment of Prominent VOC Sources in the San Francisco Bay Area Using Proton Transfer Reaction Time of Flight Mass Spectrometry

The production of tropospheric ozone and secondary organic aerosol (SOA) is controlled by volatile organic compound (VOC) and NO + NO2 (NOx) emissions. It is presently of great importance to better understand the sources and fate of VOCs and NOx. For example, as vehicle emissions have declined over the last few decades, the relative importance of non-traditional VOC sources has grown, and broad, accurate adjustments to emissions inventories for atmospheric chemistry models is required to improve predictions of ozone and SOA.1 Intercomparison between field results and existing emissions inventories have revealed disparities,2 further highlighting the need for an updated understanding of the sources of VOCs and NOx.

In this study, we sought to identify and characterize VOC sources in the San Francisco Bay Area using a mobile laboratory equipped with a Vocus proton transfer reaction time of flight mass spectrometer (Vocus PTR-ToF-MS). Waste processing facilities such as trash transfer stations and an anaerobic dry digestion facility were specifically targeted for analysis, while other prominent VOC sources were identified by non-targeted analysis. Stationary sources like car washes, alcohol processing and distribution facilities, restaurants, and more were identified throughout the urban area. Waste processing facilities were a source of reactive VOCs like monoterpenes and isoprene and odorous VOCs like methanethiol. Ethanol and acetone both exhibited high concentration spikes above background throughout the study area and originated from numerous sources. Tracer species for volatile chemical products (VCPs) like parachlorobenzotrifluoride, D5 siloxane, and more exhibited variable spatial patterns. This analysis works towards understanding the chemical complexity and reactivity of stationary VOC sources across multiple neighborhood types (e.g., residential, industrial, etc.) in an urban area.

McDonald et al. (2018) Science

Karl et al. (2017) Scientific Reports