Biogenic and anthropogenic contributions to urban terpenoid fluxes

Abstract

Terpenoids influence atmospheric chemistry through rapid oxidation reactions which form secondary products including ozone and secondary organic aerosols (SOA). Source apportionment of terpenoids is complicated in urban environments because there are biogenic and anthropogenic sources. This study utilizes measured fluxes of isoprene, monoterpenes, and sesquiterpenes with MEGAN, a biogenic emissions model, and FIVE-VCP, an anthropogenic emissions inventory, to characterize urban terpenoid emissions. Volatile organic compound (VOC) mixing ratios were measured using a Vocus proton-transfer reaction mass spectrometer (PTR-MS) during the URBAN-EC (Urban Research on Biogenic and ANthropogenic Emissions of Carbon) study in Berkeley, California from May to November 2022. Fluxes were calculated using the eddy covariance technique. Median fluxes of isoprene, monoterpenes, and sesquiterpenes were 0.269, 0.182, and 0.013 nmol m-2 s-1 respectively. Terpenoids were 2 % of the measured molar flux, 26 % of OH reactivity flux, and 21 % of SOA formation potential. The MEGAN isoprene emission factor was 4.56 nmol (m2 leaf area)-1 s-1. MEGAN isoprene fluxes matched URBAN-EC distributions seasonally and diurnally, while MEGAN monoterpene and sesquiterpene fluxes had more pronounced seasonal trends and lower morning emissions relative to URBAN-EC. Weekday/weekend differences were used to determine if terpenoids had anthropogenic sources. Monoterpene and sesquiterpene fluxes were significantly higher on weekdays (p<0.05); these differences were not represented in MEGAN or FIVE-VCP. Monoterpenes and sesquiterpenes had lower-bound anthropogenic fractions of 23 % and 24 %. Personal care products were not an important contributor to monoterpene emissions. This study presents a detailed analysis of urban terpenoid fluxes and contributes to better understanding their sources.