Abstract
Abstract. Traffic emissions contribute significantly to urban air pollution. Measurements were conducted over Highway 401 in Toronto, Canada, with a long-path Fourier transform infrared (FTIR) spectrometer combined with a suite of micrometeorological instruments to identify and quantify a range of air pollutants. Results were compared with simultaneous in situ observations at a roadside monitoring station, and with output from a special version of the operational Canadian air quality forecast model (GEM-MACH). Elevated mixing ratios of ammonia (0–23 ppb) were observed, of which 76 % were associated with traffic emissions. Hydrogen cyanide was identified at mixing ratios between 0 and 4 ppb. Using a simple dispersion model, an integrated emission factor of on average 2.6 g km−1 carbon monoxide was calculated for this defined section of Highway 401, which agreed well with estimates based on vehicular emission factors and observed traffic volumes. Based on the same dispersion calculations, vehicular average emission factors of 0.04, 0.36, and 0.15 g km−1 were calculated for ammonia, nitrogen oxide, and methanol, respectively.
Highlights
In 1996, 45.2 % of the population of Toronto, Canada’s largest city, lived within 500 m of a highway or within 100 m of a major road (HEI, 2010)
Pollutants that have been previously reported from motor vehicles include nitrogen oxides (NOx), carbon monoxide (CO), ultrafine particles, PM2.5, black carbon, volatile organic compounds (VOCs), semi- and low-volatile organic compounds, aromatics, polycyclic aromatic hydrocarbons (PAHs), and greenhouse gases (Brugge et al, 2007; Zhou and Levy, 2007; Karner et al, 2010, Gentner et al, 2012, 2017; Popa et al, 2014)
The objectives to be addressed with this analysis are (1) to evaluate the capabilities of the long-path Fourier transform infrared (FTIR) spectroscopy for quantifying the mixing ratios of gaseous pollutants in a heavily polluted open urban traffic environment for a length of time sufficient to cover a range of environmental conditions (16 days); (2) to quantify gaseous-pollutant mixing ratios as a function of traffic volume and micrometeorological conditions; (3) to compare mixing ratios from these direct measurements to GEM-MACH model results; and (4) to evaluate the feasibility of deriving emission rate estimates from these measurements using an inverse dispersion model
Summary
In 1996, 45.2 % of the population of Toronto, Canada’s largest city, lived within 500 m of a highway or within 100 m of a major road (HEI, 2010). Durant et al (2010) presented 1-day measurements of pollutant mixing ratios, wind speed, and ambient temperature, along with traffic density They observed an increase of pollutant levels before sunrise and a sharp decrease after sunrise. The objectives to be addressed with this analysis are (1) to evaluate the capabilities of the long-path FTIR spectroscopy for quantifying the mixing ratios of gaseous pollutants in a heavily polluted open urban traffic environment for a length of time sufficient to cover a range of environmental conditions (16 days); (2) to quantify gaseous-pollutant mixing ratios as a function of traffic volume and micrometeorological conditions; (3) to compare mixing ratios from these direct measurements to GEM-MACH model results; and (4) to evaluate the feasibility of deriving emission rate estimates from these measurements using an inverse dispersion model
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