Multiyear characterization of volatile organic compounds in Zurich: evidence of urban volatile chemical products

Abstract Volatile organic compounds (VOCs) are important precursors of ozone and secondary organic aerosols. Here, we present a multiyear analysis of VOC composition and sources at an urban background site in Zurich in Switzerland, based on continuous hourly measurements of non-methane hydrocarbons (NMHCs) and oxygenated VOCs (OVOCs) in 2016, 2017 and 2024. Between 2016 and 2024 the total concentration of VOCs remained relatively stable, while their composition shifted towards a stronger dominance of OVOCs. Source apportionment using positive matrix factorization (PMF) identified six main factors: road transport, residential heating and wood burning, propane and butanes, volatile chemical products (VCPs), local emissions, and urban background and natural gas. The relative contributions of these sources remained stable between 2016–2017 and 2024. VCPs, mostly explained by OVOCs, contributed 11–20% of total VOCs, showing their importance as a persistent urban source. A comparison with previous studies conducted at the same site in 2005–2006 shows a strong long-term decrease in traditional anthropogenic sources such as traffic and solvent use, consistent with emission inventory trends, and a dominant fraction of ambient VOCs related to VCPs, confirming the need for OVOC measurements in air quality monitoring networks, in line with the new European AAQD (2024/2881).