Evolving Perspectives on Urban Air Quality and Non-Traditional Sources of Reactive Gas-Phase Organic Compounds

Abstract: Understanding the broad range of anthropogenic sources contributing emissions of reactive gas-phase organic compounds, including volatile organic compounds (VOCs), is becoming increasingly important as non-traditional sources (e.g., volatile chemical products; VCPs) are now prominent contributors of reactive organic gases in urban areas with successful reductions in emissions from traditional sources (e.g., motor vehicles). These chemically-diverse sources affect both outdoor and indoor chemistry and air quality. They span a broad array of products and materials with three general emissions pathways—solvent evaporation, volatilization of lower-volatility product components, and off-gassing of compounds not present in declared formulations (e.g., degradation by-products)—emphasizing the importance of a lifecycle emissions perspective across a wide volatility and chemical functionality range. Laboratory and field observations include emissions of complex mixtures of gas-phase hydrocarbons and functionalized organic compounds in the volatile, intermediate-volatility, and semivolatile ranges, with experimental and modeled analysis of their chemical transformations under typical conditions and impacts on secondary organic aerosol (SOA) formation—a key component of ambient particulate matter (i.e., PM2.5). Examples include emissions from common products and materials in the built environment, some of which are sensitive to temperature and solar exposure, with substantial contributions to urban SOA precursors and limited representation in emissions inventories.