Evaluating the Impact of Traffic Congestion on Mid-block Fine Particulate Matter Concentrations on an Urban Arterial

The primary objective of this paper is to evaluate the impact of traffic congestion on mid-block fine particulate matter (PM_2.5) concentrations on an urban arterial. Data of mid-block and background PM_2.5 concentrations were collected second by second during peak and non-peak hours on an urban arterial. Then micro traffic conditions were extracted from videos at ten seconds intervals, including traffic volume, traffic flow speed and high-duty vehicle fraction. Results showed that traffic volume had significant influence on mid-block PM_2.5 concentrations. Mid-block PM_2.5 concentrations were not correlated with traffic level of service. Furthermore, a modified passenger car equivalent was calculated from the aspect of contribution on PM_2.5 concentrations using multiple linear regressions model. Then a comprehensive model was established to model the impact of micro traffic conditions on PM_2.5 concentrations. Results of the comprehensive model showed that PM_2.5 concentrations increased with the increase of total volume or heavy-duty vehicle fraction. Besides, low traffic flow speed resulted in high PM_2.5 emission factor, leading to the increase of PM_2.5 concentrations. The findings of this study can help better understand traffic congestion and micro traffic conditions on PM_2.5 concentrations.