Abstract
Abstract. An automated identification and integration method has been developed for in-use vehicle emissions under real-world conditions. This technique was applied to high-time-resolution air pollutant measurements of in-use vehicle emissions performed under real-world conditions at a near-road monitoring station in Toronto, Canada, during four seasons, through month-long campaigns in 2013–2014. Based on carbon dioxide measurements, over 100 000 vehicle-related plumes were automatically identified and fuel-based emission factors for nitrogen oxides; carbon monoxide; particle number; black carbon; benzene, toluene, ethylbenzene, and xylenes (BTEX); and methanol were determined for each plume. Thus the automated identification enabled the measurement of an unprecedented number of plumes and pollutants over an extended duration. Emission factors for volatile organic compounds were also measured roadside for the first time using a proton transfer reaction time-of-flight mass spectrometer; this instrument provided the time resolution required for the plume capture technique. Mean emission factors were characteristic of the light-duty gasoline-dominated vehicle fleet present at the measurement site, with mean black carbon and particle number emission factors of 35 mg kg fuel−1 and 7.5 × 1014 # kg fuel−1, respectively. The use of the plume-by-plume analysis enabled isolation of vehicle emissions, and the elucidation of co-emitted pollutants from similar vehicle types, variability of emissions across the fleet, and the relative contribution from heavy emitters. It was found that a small proportion of the fleet (< 25 %) contributed significantly to total fleet emissions: 100, 100, 81, and 77 % for black carbon, carbon monoxide, BTEX, and particle number, respectively. Emission factors of a single pollutant may help classify a vehicle as a high emitter; however, regulatory strategies to more efficiently target multi-pollutant mixtures may be better developed by considering the co-emitted pollutants as well.
Highlights
On-road motor vehicles are one of the largest contributors to air pollution in urban environments (Franco et al, 2013) and are one of the major sources underlying the estimated 3.7 million air-quality-related deaths in 2012 worldwide (WHO, 2014)
An important difference between the emission factors (EFs) calculated from measurements made in this quasi-street canyon compared to controlled laboratory conditions is the potential chemical or physical changes that occur for certain pollutants between emission at the tailpipe and measurement at the site (i.e., NO, NO2, volatile organic compounds (VOCs), UFPs)
Site and measurement validation was conducted by two methods: (1) coincident measurements at different distances to calculate EFs and (2) use of a test vehicle to drive by the measurement site multiple times
Summary
On-road motor vehicles are one of the largest contributors to air pollution in urban environments (Franco et al, 2013) and are one of the major sources underlying the estimated 3.7 million air-quality-related deaths in 2012 worldwide (WHO, 2014). Vehicle emissions contain a vast number of pollutants, some with toxicological relevance such as fine particulate matter (PM2.5), ultrafine particles (UFPs, < 100 nm diameter), carbon monoxide (CO), nitrogen oxides (NOx), and volatile organic compounds (VOCs) including their secondary transformation to tropospheric ozone and particulate matter (Seinfeld and Pandis, 2006; HEI, 2010). Other pollutants such as carbon dioxide (CO2) and black carbon (BC) have associated negative impacts on global climate (Sims et al, 2014). In order to better assess the impact of vehicle emissions on local and global air quality, emissions must be more consistently and representatively quantified and characterized
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