Evaluation of Traffic Density Parameters as an Indicator of Near-road Black Carbon Pollution: A Case Study with NEXUS Measurement Data

摘要

Near-road exposure to traffic-related air pollutants has become a focus of health risk studies. Some studies have shown effects of traffic density on the respiratory diseases. Traffic density is parameter integrating major road and traffic count. To better understand the correlation between the traffic density parameters and actual air pollutant concentrations we used measurement data from the US Environmental Protection Agency (US EPA)-sponsored Near-road Exposures and effects of Urban air pollutants Study (NEXUS) collected at about 30 locations across Detroit at various distances from major roadways with different traffic characteristics during two seasons (Fall 2010 and Spring 2011). For the correlation assessment we compared black carbon (BC) concentrations against different traffic density parameters. The average BC concentrations during a day showed variations consistent with the change in traffic volume which was classified into three categories of low, medium, and high for detailed studies. We found mean BC concentrations for the low, medium, and high traffic hours are 0.45, 0.64, and 0.94 μg/m3 respectively for the fall season and 0.35, 0.44, and 0.59 ug/m3 respectively for the spring season. Major-Road Density (MRD), All-Traffic Density (ATD) and Heavy-Traffic Density (HTD) gave an average correlation coefficient of 0.26, 0.18 and 0.48, respectively for the combined BC concentrations of all seasons and all distances from the major road. HTD, which includes only heavy duty diesel vehicles in the traffic count, gives statistically significant correlation coefficients for all near road distances (50, 100,150, 200, 250, and 300 m) analyzed. Generalized linear model (GLM) analyses show that season, traffic volume, HTD and distance from major roads are highly related to BC measurements. Our analyses indicate that traffic density parameters may be useful indicators of near-road BC concentrations for health risk studies.