Summer and Winter Nonmethane Hydrocarbon Emissions from On-Road Motor Vehicles in the Midwestern United States

Abstract

On-road vehicle emission rates of nonmethane hydrocarbons (NMHCs) were measured in two tunnels in Milwaukee Milwaukee area with tunnel emissions showed the impact of seasonal differences in fuels and emissions on the urban atmosphere. Composition of fuel samples collected from area gas stations in both seasons was correlated with vehicle emissions; the predominant difference was increased winter emissions of lighter hydrocarbons present in winter gasoline. A chemical mass balance model was used to determine the contributions of whole gasoline and gasoline headspace vapors to vehicle emissions in the tunnel and cold-start tests, which were found to vary with season. Results of the mass balance model also indicate that partially combusted components of gasoline are a major contributor to emissions of aromatic compounds and air toxic compounds, including benzene, toluene, xylenes, napthalene, and 1,3-butadiene, whereas air toxics hexane and 2,2,4-trimethylpentane are largely attributed to gasoline and headspace vapors.

Multi-year (2004–2008) record of nonmethane hydrocarbons and halocarbons in New England: seasonal variations and regional sources

“…Additionally, the slope of the correlation between i-pentane and n-pentane (range for each season each year=1.5-2.6) (Fig. 7c) was within the range of reported emission ratios for vehicle exhaust and tunnel studies (∼2.2-3.8), liquid gasoline (1.5-3), and fuel evaporation (1.8-4.6) (Conner et al, 1995;Harley et al, 2001;Watson et al, 2001;Jobson et al, 2004;McCaughey et al, 2004;Lough et al, 2005;Velasco et al, 2007). Overall, these results suggest that a uniform mix of emissions from numerous alkane sources is observed at TF.…”

Long-term study of VOCs measured with PTR-MS at a rural site in New Hampshire with urban influences

“…Daily can measurements (usually obtained at mid-day) showed that unlike other anthropogenic hydrocarbons, toluene was elevated in summer and fall as well as winter (85±5, 88±5 and 95±3 pptv, respectively), with a spring minima (56±4 pptv). White et al (2008b) examined the summer enhancement of toluene in detail, attributing it to primarily a combination of enhanced fuel evaporation of reformulated gasoline with its higher toluene content (Lough et al, 2005) and to vegetative emissions, with a minor contribution from local industrial emissions. The vegetative emissions of toluene observed by White et al (2008b) from a loblolly pine at Duke Forest were well correlated with monoterpenes.…”

“…Recently, Schnitzhofer et al (2008) have suggested that the toluene:benzene ratio in winter should be lower than that in summer due to reduced evaporation of toluene. However, Lough et al (2005) conducted tunnel studies in Milwaukee, WI (latitude 43.11 • N, the same as TF) that show emissions of toluene are nearly constant throughout the year with mean emissions of 357±143 mg L −1 fuel in summer (largely due to evaporation) and 363±232 mg L −1 fuel in winter (largely due to incomplete combustion). Benzene emissions from mobile sources were observed to be 167±59 mg L −1 fuel in summer and 95±26 mg L −1 fuel in winter (Lough et al, 2005).…”

“…However, Lough et al (2005) conducted tunnel studies in Milwaukee, WI (latitude 43.11 • N, the same as TF) that show emissions of toluene are nearly constant throughout the year with mean emissions of 357±143 mg L −1 fuel in summer (largely due to evaporation) and 363±232 mg L −1 fuel in winter (largely due to incomplete combustion). Benzene emissions from mobile sources were observed to be 167±59 mg L −1 fuel in summer and 95±26 mg L −1 fuel in winter (Lough et al, 2005). Their results from two winter tunnel studies and a study of cold starts in a parking ramp suggest that even in winter mobile emissions of toluene and benzene should lead to a ratio in the range from ∼2-5 (Lough et al, 2005).…”

“…Benzene emissions from mobile sources were observed to be 167±59 mg L −1 fuel in summer and 95±26 mg L −1 fuel in winter (Lough et al, 2005). Their results from two winter tunnel studies and a study of cold starts in a parking ramp suggest that even in winter mobile emissions of toluene and benzene should lead to a ratio in the range from ∼2-5 (Lough et al, 2005). So at TF, it would be expected that the toluene:benzene ratio would exhibit a diurnal cycle where the ratio increases at night to reflect recent mobile emissions, but it does not.…”