Air Pollutants Near Urban Roadways

Several studies have analyzed pollutant concentration near roads. Most experimental studies rely on short-term monitoring campaigns, where in some cases emissions are simulated using tracer gases. The actual concentrations of pollutants near roads and how that information can be used to design strategies addressed to mitigate the exposure to air pollutants of citizens living near roads remain unclear.

To address this need, we conducted a long-term (> 1 year) experimental study measuring the variables involved in the emissions of pollutant over the road (traffic) and their dispersion downwind the road (meteorology, atmospheric stability, and pollutant concentration). We selected a straight horizontal track, with negligible buildings on the surroundings, of a major road within the Monterrey Metropolitan Area, Mexico, and measured the upwind and downwind pollutant concentrations utilizing low-cost sensors in conjunction with instruments homologated by environmental authorities.

The main air pollutants were recorded, frequently exceeding the threshold values established by the local environmental authority. A moderate correlation between coarse and fine particle concentrations indicates the influence of multiple sources of PM. Furthermore, road emissions were found to increase concentrations relative to background concentrations, according to measurements performed with low-cost sensors. The low-cost sensors displayed high correlations between them proving they are effective for determining trends of particulate matter (PM) concentrations downwind the road. The concentration profile under neutral atmospheric conditions showed a decreasing exponential trend with distance from the road, strongly correlated with the profile observed under slightly stable conditions, which agrees with results from previous studies.