Quantifying the Spatial and Temporal Distributions of Volatile Chemical Products (VCPs) in the Greater Houston Area

Volatile chemical products (VCPs), including organic species emitted from pesticides, coatings, cleaning products, and personal care products, account for more than half of the urban VOC emissions in major North American and European cities. However, VCP emissions, spatial and temporal distributions, and impacts vary widely. Despite being the fourth largest U.S. city, Houston, Texas, lacks measured VCP concentration and emission data. This study presents the first spatial and temporal measurements of selected VCP tracers in Houston, Texas, using a Vocus 2R Chemical Ionization Mass Spectrometer on a mobile platform. Ambient measurements of five major VCP tracers, including D5-siloxane, monoterpenes, para-dichlorobenzene, para-chlorobenzotrifluoride (PCBTF), and 2,2,4-trimethyl-1,3-pentanediol isobutyrate (Texanol), were collected in winter and summer 2023. Several compounds exhibited significantly higher averaged concentrations, with pronounced spatial and seasonal variability, distinguishing Houston from urban areas in the temperate and cooler climate zone. A customized box model was employed to estimate seasonal emissions for the Greater Houston Area, showing that emissions of most VCPs were significantly higher during the summer. This study provides critical insights into the distribution and emission of VCPs in a subtropical metropolitan area, advancing methods for assessing VCP emissions and concentrations across cities and improving understandings of their impacts on air quality, climate, and public health.