Comparison between Spatially Resolved Airborne Flux Measurements and Emission Inventories of Volatile Organic Compounds in Los Angeles

Los Angeles is a major hotspot for ozone and particulate matter air pollution in the United States. Ozone and PM_(2.5) in this region have not improved substantially for the past decade, despite a reduction in vehicular emissions of their precursors, NOₓ and volatile organic compounds (VOCs). This reduction in "traditional" sources has made the current emission mixture of air pollutant precursors more uncertain. To map and quantify emissions of a wide range of VOCs in this urban area, we performed airborne eddy covariance measurements with wavelet analysis. VOC fluxes measured include tracers for source categories, such as traffic, vegetation, and volatile chemical products (VCPs). Mass fluxes were dominated by oxygenated VOCs, with ethanol contributing ∼29% of the total. In terms of OH reactivity and aerosol formation potential, terpenoids contributed more than half. Observed fluxes were compared with two commonly used emission inventories: the California Air Resources Board inventory and the combination of the Biogenic Emission Inventory System with the Fuel-based Inventory of Vehicle Emissions combined with Volatile Chemical Products (FIVE-VCP). The comparison shows mismatches regarding the amount, spatial distribution, and weekend effects of observed VOC emissions with the inventories. The agreement was best for typical transportation related VOCs, while discrepancies were larger for biogenic and VCP-related VOCs. ; © 2022 The Authors. Published by American Chemical Society. This publication is licensed under CC-BY 4.0. ; The authors thank Dennis Baldocchi, Glenn Wolfe, Erin Delaria, and Tianxin Wang for insightful discussions about vertical flux divergence, Matthew Coggon, Chelsea Stockwell, and Carsten Warneke for valuable discussions on PTR-ToF-MS VOC corrections, the Regional Chemical Modeling Group of NOAA CSL for help with weather forecasting, and the Modeling and Meteorology Branch at CARB for providing their inventory. We gratefully acknowledge Greg Cooper for excellent mission support, the pilots ...