Volatile Chemical Products Have a Major Impact on Air Quality in U.S. cities

Abstract:

With traffic emissions of volatile organic compounds (VOCs) decreasing rapidly over the last decades, the contributions of the emissions from other source categories, such as volatile chemical products (VCPs), have become more apparent in urban air. In this work, in-situ measurements of various VOCs are reported for New York City (NYC), Pittsburgh, Chicago, and Denver and the importance of VCP emissions in those cities is demonstrated in three different ways.

(1) The enhancement ratios of several VCP compounds to benzene correlate well with population density (R²~0.6–0.8). Some human activity should correlate better with the population density than transportation emissions, due to the lower per capita rate of driving in denser cities. Using these data, we identify tracer compounds for different VCP categories: D5-siloxane for personal care products, monoterpenes for fragrances, p-dichlorobenzene for insecticides, D4-siloxane for adhesives, parachlorobenzotrifluoride (PCBTF) for solvent-based coatings, and Texanol for water-based coatings.

(2) Positive matrix factorization was used to attribute hundreds of compounds to mobile and VCP sources. VCP emissions contributed to 42% and 78% of anthropogenic VOC emissions for Boulder and NYC, respectively, while mobile source emissions contributed 58% and 22%.

(3) Using box and 3D modeling during an extreme heat event, VCPs were responsible for more than 30% of the ozone produced downwind of NYC from anthropogenic sources. Ethanol and fragrances account for over 25% of the VCP-associated ozone. Ozone production was VOC-sensitive within 40 km of NYC, and reductions in anthropogenic VOC emissions would significantly reduce local ozone exceedances.