Toward Linking Indoor Commercial Source Emissions to Outdoor Volatile Organic Compounds Using Mobile Measurements

Assessing the impact of indoor volatile organic compound (VOC) sources on outdoor concentrations remains challenging due to their variability, rapid dispersion, and chemical reactions in the atmosphere. Mobile monitoring can address these challenges by providing spatial and temporal resolution of localized emission sources. In this study, we developed a new approach to characterize the impact of indoor emissions on outdoor air quality using mobile measurements. We used geographic information to identify the locations of hundreds of individual source types in Bradford, England, including restaurants, beauty salons, and automobile repair shops. For each source type, we modeled the potential hourly contribution using an advanced Gaussian plume model─incorporating wind speed and direction─across 22 mobile measurement circuits (approximately 56 modeled hours). The outcome is a single source factor for each latitude-longitude coordinate at each hour of the measurement campaign, representing the influence level of each source type. We then applied K-means clustering to group source factors based on their spatial distributions and influence levels, and analyzed their relationship with the incremental concentrations of VOCs and NOx using bootstrap-validated generalized additive models (GAMs). Several previously identified key tracer compounds showed robust associations with specific source factors, including m/z 102 (tentatively assigned as butanone) with auto repair source factor, m/z 59 (acetone) with beauty salon source factor, and m/z 68 (isobaric compounds: isoprene and furan) with restaurant source factor. This method offers a new perspective on air quality monitoring by using source location information to inform the analysis of mobile measurements, providing a robust framework for identifying the outdoor signatures of commercial indoor activities.