Development of a Static Model to Identify Best Management Practices for Trace Metals from Non-Exhaust Traffic Emissions

Risk through exposure to non-exhaust traffic emissions continues to increase as both the number of vehicles and traveling distances continue to increase with global urbanization. To better understand their impacts on the urban environment, a contaminant pathway was developed to describe important release mechanisms, transitory environmental media, and exposure media. Sources of contaminants were identified and characterized using published literature values. Concentrations of non-exhaust sources were used in conjunction with mean emission factors to estimate contaminant loads from individual vehicles (μg/km/veh). Published daily vehicle distances traveled were used to estimate total annual emissions (kg/yr) for the United States and Houston metropolitan area. This equates to approximately 5.1 million kg of Cu, 12.8 million kg of Zn, 4.9 million kg of Pb, and 2400 kg of Cd being released each year in the United States. Tires are responsible for 92% of total Zn emissions, with heavy-duty vehicles responsible for 77% of these emissions. Tires are also responsible for 86% of total Cd emissions. Brake dust contributes to 99.9% of Cu emissions. Wheel weights contribute approximately 94% of total Pb emissions. Identified best management practices include: 1. installation of grass buffer zones (e.g., rain gardens, vegetated swales) immediately adjacent to road surfaces, and 2. permeable pavements and green roofs near major highways. There are several limitations, assumptions and uncertainties associated with the study due to its static nature. However, evidence is substantial for the need to create new policies that address the pollution created by non-exhaust traffic emissions.