Quantifying ambient concentration and emission profile of D5-siloxane of a residential neighborhood in the Greater Houston area†

Abstract

Volatile chemical products (VCPs) in urban environments account for a significant portion of the volatile organic compounds (VOCs), enhancing the production of tropospheric ozone and secondary organic aerosols. Residential areas are an important source of VCPs in the urban environment, though few studies have examined the emission of VCPs in metropolitan areas from subtropical regions. To bridge the knowledge gap, this study aims to analyze the concentration and emission of D5-siloxane, a compound typically served as a tracer to characterize VCP emission from residential areas. The Texas A&M mobile laboratory, equipped with a Vocus 2R Chemical Ionization Mass Spectrometer (CIMS), and other gas and particle analyzers, continuously sampled the ambient gas phase concentration of D5-siloxane during a field deployment in a residential neighborhood near Houston, TX. A 0-D box model combining Planetary Boundary Layer Height (PBL) height, hourly D5-siloxane concentration, gas deposition velocities, and D5-siloxane reaction rate with hydroxyl radicals was constructed to represent emissions during our sampling period to derive the emission intensities of D5-siloxane. Monte Carlo statistical analysis was performed to gain insights into the emission profile of D5-siloxane, showing higher emission rates compared with other cities in North America but comparable to emissions of European cities. This study presents time-series concentrations and emissions of D5-siloxane in a subtropical residential area during the wintertime. The findings illustrate the temporal profile of D5-siloxane in a typical residential neighborhood in the Southeast United States and provide valuable data to enhance model parameterizations.