New insights into urban ethanol and oxygenated volatile organic compound sources from combined flux tower and mobile measurements

Abstract. Oxygenated volatile organic compounds (OVOCs) including ethanol, methanol, acetone, and acetaldehyde are important components of urban VOC emissions, yet their sources and emissions magnitudes remain highly uncertain. In this study, we leveraged data from a Vocus proton-transfer reaction mass spectrometer deployed during a long-term tower-based eddy covariance flux study and a mobile monitoring campaign to characterize the emissions and sources of urban OVOCs. Ethanol accounted for about half of the measured molar flux and a fifth of the calculated OH reactivity flux. A tracer-based source apportionment approach revealed that cooking is the predominant source of ethanol in the flux footprint (71 % of the ethanol flux), followed by volatile chemical products (VCPs, 20 %), and motor vehicles (9 %). This result supports the recent inclusion of cooking in VOC emissions inventories and further supports indoor environments as important contributors to urban atmospheric chemistry. Cooking was also a major source of acetaldehyde, while VCPs were the main sources of acetone and methanol in the flux footprint. Mobile monitoring within the flux footprint and beyond informed the representativeness of the tower-based measurements and identified additional OVOC sources. In the broader urban region, fossil fuel combustion was a key source of acetaldehyde, and industrial zones and waste treatment facilities missed by the flux tower were hotspots for ethanol, methanol, and acetone. Together, these results provide new constraints on the sources, seasonality, and magnitude of OVOC fluxes in urban environments through a unique synthesis of tower-based and mobile measurements.