Toxic volatile organic air pollutants across Canada: multi-year concentration trends, regional air quality modelling and source apportionment

Abstract

A Unified Regional Air-quality Modelling System, AURAMS, was expanded to predict six toxic volatile organic compounds (VOCs) within a continental domain and two nested domains covering eastern and western Canada. The model predictions were evaluated against Environment Canada's National Air Pollution Surveillance (NAPS) data set to assess the predictive capability of the model at daily and seasonal time scales. The predictions were also evaluated with satellite-derived column total maps for formaldehyde, carbon monoxide, and nitrogen dioxide. In general, the model showed fair to good predictive skill in terms of both correlation (R) and normalized mean bias (NMB) for benzene (R = 0.53 NMB = 26 %), formaldehyde (R = 0.73, NMB = −15 %) and acetaldehyde (R = 0.55, NMB = 29 %). For the other toxics VOCs, the model showed less predictive skill in the order 1,2,4-trimethylbenzene (R = 0.50, NMB = −41 %), 1,3-butadiene (R = 0.26, NMB = 40 %) and acrolein (R = 0.052, NMB = −51 %). The goal of this study was to apply an air quality model to assess the contribution of mobile sources to ambient levels of toxic VOCs at urban locations across Canada. The mobile source contribution varied in a complex manner for each species for different regions. For benzene and 1,2,4-trimethylbenzene, the mobile source contribution was in the range 40-65 % for major Canadian cities. The model predicted considerably lower

How much does traffic contribute to benzene and polycyclic aromatic hydrocarbon air pollution? Results from a high-resolution North American air quality model centred on Toronto, Canada

“…In the spring-summertime, domain-mean on-road vehicle contributions to ambient BENZ in the GTA were on the order of 14 %-37 %, consistent with, though slightly lower than, previously reported values (Stroud et al, 2016) due to the latter study including off-road mobile sources in their "mobile" category. PAH contributions in the GTA ranged from 5 % to 50 %, depending on species, season, and proximity to major highways.…”

“…The removal of on-road vehicle emissions would lead not only to reductions in ambient benzene and PAH concentrations (as well as in other pollutants), as demonstrated by our model results, but also to reductions in human exposure. Proximity to roadways and traffic has been linked to elevated exposure outdoors, and this has led to particular concerns for commuters (Miao et al, 2015;Yan et al, 2015;Tan et al, 2017;Lovett et al, 2018;Miri et al, 2018). Further inhalation exposure to traffic pollutants occurs in indoor environments, where infiltration of outdoor air can contribute a substantial proportion of benzene and PAH exposure (Naumova et al, 2002;Xu et al, 2016), adding to concerns about residences, schools, and workplaces that are situated near roadways.…”

“…National benzene emissions in Canada are compiled through the National Pollutant Release Inventory (NPRI) (NPRI, 2016) but only for major industrial, commercial, and institutional sources. Previous model-based estimates (Stroud et al, 2016) suggest that 40 %-54 % of benzene in the ambient air of major Canadian cities is due to mobile sources (e.g., cars, trains, ships), which are not included in the NPRI. In the US, the most recent National Emissions Inventory (NEI) (US EPA, 2018) includes benzene emissions estimates from a variety of natural and anthropogenic sources.…”

Diurnal, seasonal and long-term variations of global formaldehyde columns inferred from combined OMI and GOME-2 observations

“…Column inter-annual variabilities are mainly driven by fire events and temperature changes (Millet et al, 2008;Barkley et al, 2009;Stavrakou et al, 2014). However, over industrialised regions, changes in anthropogenic emissions have also been identified as drivers of observed H 2 CO column trends Zhu et al, 2014;Khokhar et al, 2015;Mahajan et al, 2015;Stroud et al, 2015).…”

Long-path measurements of pollutants and micrometeorology over Highway 401 in Toronto

“…The lifetime of HCHO in the atmosphere is on the scale of hours to days depending on the levels of ambient oxidants (Seinfeld and Pandis, 2006). Stroud et al (2016) reported on levels of HCHO in Toronto and Egbert, Ontario, and source apportionment. Primary mobile emissions were found to contribute ∼ 12 % of HCHO in Toronto.…”