Jim Hopkins

Abstract Urban volatile organic compounds (VOCs) are key precursors of tropospheric ozone and secondary organic aerosols (SOA), yet their long-term dynamics and health implications remain unclear across Europe. Here, we synthesize two decades of VOC observations (2002–2023) from 21 urban monitoring sites in six countries to assess emission trends, oxidation potentials, and human exposure risks.

1. Introduction The formation of tropospheric ozone from the reactions of volatile organic compounds (VOCs) and NOx in the presence of sunlight is very well-established science that dates back to atmospheric chemistry research in the 1950s (e.g. [1]).

Apocalypse. Armageddon. Plague. Judgment Day. Even in the San Francisco Bay Area, a region of the country noted for its low percentage of church attenders, religious language is being used by many to describe the recent fires, smoke-filled air and Wednesday’s surreal day-long darkness with the sky above glowing orange.