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

Abstract:

Highway traffic emissions are an important source of air pollution, especially in urban areas. Traffic-related pollution has been linked to a number of adverse health effects, such as respiratory problems, cancer, heart failure, and a general increase in mortality. Determining the pollutants involved and quantifying their emission rates is paramount in developing high resolution air quality models to predict future developments with some confidence.

Highway 401, as it passes through Toronto, is the world’s busiest highway with a typical traffic volume of over 450,000 vehicles per day. In July 2015, three weeks of measurements were conducted over the 401 with an open-path FTIR (Fourier Transform infra-red) spectrometer in parallel with a scintillometer, integrating a variety of gas concentrations as well as turbulence parameters over a 310m path length.

Relationships between traffic volume, micrometeorological conditions and the build-up and venting of pollutants on the highway are analyzed and quantified, demonstrating the role of stratification and turbulence in the accumulation and dispersal of traffic emissions. The feasibility of deriving emission rates by combining the micrometeorological data from the scintillometer with the gas concentrations from the FTIR using an inverse dispersion approach is investigated. The suitability of this novel approach for long-term monitoring of emissions is discussed. The findings will be compared with output from a high-resolution air quality model (GEM-MACH) to aid future improvements in the sub-grid parameterization of pollutant dispersion.