Near-road multipollutant profiles: Associations between volatile organic compounds and a tracer gas surrogate near a busy highway

Abstract

This research characterizes associations between multiple pollutants in the near-road environment attributed to a roadway line source. It also examines the use of a tracer gas as a surrogate of mobile source pollutants. Air samples were collected in summa canisters along a 300 m transect normal to a highway in Raleigh, North Carolina for five sampling periods spanning four days. Samples were subsequently measured for volatile organic compounds (VOCs) using an electron capture gas chromatograph. Sulfur hexafluoride (SF6) was released from a finite line source adjacent to the roadway for two of the sampling periods, collected in the canisters and measured with the VOCs. Associations between each VOC, and between VOCs and the tracer, were quantified with Pearson correlation coefficients to assess the consistency of the multi-pollutant dispersion profiles, and assess the tracer as a potential surrogate for mobile source pollutants. As expected, benzene, toluene, ethylbenzene, and m,p- and o-xylenes (collectively, BTEX) show strong correlations between each other; further, BTEX shows a strong correlation to SF6. Between 26 VOCs, correlation coefficients were greater than 0.8, and 14 VOCs had coefficients greater than 0.6 with the tracer gas. Even under non-downwind conditions, chemical concentrations had significant correlations with distance. Results indicate that certain VOCs are representative of a larger multi-pollutant mixture, and many VOCs are well-correlated with the tracer gas. Implications: This research characterizes associations between volatile organic compounds in a near-road environment to evaluate the consistency of the composition of the multipollutant mixture. It demonstrates the potential use of a tracer gas as an indicator of pollutant dispersion. Near-roadway exposures have been associated with a myriad of health effects; however, associations with individual pollutant components have yet to be well established. This work characterizes a multipollutant profile for a moderately traveled highway with typical rush hour characteristics. Insights on the composition of the complex mixture emitted from mobile sources will improve exposure, health, and epidemiological assessments. Supplemental Materials: Supplemental materials are available for this article. Go to the publisher's online edition of the Journal of the Air & Waste Management Association to view statistical results for the full set of pollutants.