Pollution release from urban asphalt surfaces
A novel method was developed to collect samples of surface sediment that had accumulated upon a road surface with high traffic loading over a period of 17 months. The method was designed to remove the smallest size fraction of sediment from a set area on the road surface by washing with water and collecting the effluent. The sediment collected was analysed for total mass and particle size distribution, ‘total’ sediment attached metal concentration of Zn, Cu, Pb and Cd (2 - 500 mm), dissolved pollutants consisting of the ionic species F-, C1-, SO42-, NO3- PO43-, NH4+, total carbon (TC), total organic carbon (TOC) and pH. Road run-off was also measured, both continuously and discretely. Continuous measurement parameters (temperature, conductivity, pH, turbidity, depth) were correlated with climate and rainfall characteristics but no consistent relationship was found. Levels of pollutant in run-off (Zn, Cu, Pb, Cd, F-, C1-, SO42-, NO3-, PO43-, NH4+ TC, TOC, pH) were related to levels of the same pollutants collected on the surface. Levels of sediment and dissolved pollutants collected on the surface showed distinctive seasonal and spatial variation, and were elevated due to the application of road de-icing salts during periods of cold weather. Concentrations of heavy metals tended to increase with decreasing particle size and a seasonal variation was observed with higher concentrations found during the summer months. Little evidence was found to indicate that rainfall patterns were influencing concentrations of pollutants deposited, although a slight correlation (r = 0.55, p = 0.04) was observed between certain parameters and antecedent dry weather period during the summer.