Articles | Volume 17, issue 22
Research article
28 Nov 2017
Research article |  | 28 Nov 2017

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

Yuan You, Ralf M. Staebler, Samar G. Moussa, Yushan Su, Tony Munoz, Craig Stroud, Junhua Zhang, and Michael D. Moran

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.

Short summary
A novel approach for traffic emission measurements is shown to have the capacity to provide high-time-resolution accurate concentrations of key air pollutants. A top-down method for quantifying real-world emission rates produced vehicular emission factor estimates for carbon monoxide that agreed well with bottom-up values. Significant ammonia and hydrogen cyanide emissions were observed. The main factors modulating the concentrations were turbulent mixing and traffic density.
Final-revised paper