Characterizing urban VOC emissions and their sources using flux observations

 

Volatile organic compounds (VOCs) are key precursors of secondary air pollutants such as ozone and secondary organic aerosols, which have widespread health and environmental impacts. In urban settings, the diversity of emission sources (both anthropogenic and biogenic) and the complexity of emission characteristics lead to substantial uncertainty in urban VOC emissions and their source attribution. Here, we present comprehensive eddy covariance measurements of VOC fluxes in a Chinese megacity. The measurements capture a wide range of VOC species spanning multiple functional groups and chemical reactivities, with low-carbon-number compounds contributing substantially to the total emission flux. Seasonally resolved observations reveal pronounced variability in VOC fluxes, driven by both environmental conditions (e.g., temperature) and changes in anthropogenic activities. Using these flux measurements, we compare positive matrix factorization (PMF) analyses based on flux and concentration datasets, demonstrating the advantages of flux-based source apportionment in resolving urban emission sources. Our findings highlight that flux measurements provide new insights into the sources and emission characteristics of urban atmospheric composition.