Antecedent dry weather period (ADP) is commonly recognized as one of the most important influencing variables controlling the pollutants’ build-up process. In a conceptual rainfall-runoff model, the stormwater pollution in the wash-off process is dependent on the build-up process, runoff rate and other influencing variables. In this context, the wash-off process of trace metals during the rainfall event would affect the potential deterioration level of runoff water quality. Among the pollutants found in surface runoff, trace metals are of great concern due to their toxicity, persistence, and abiotic degradation in the environment and bioaccumulation in the food webs. The rainfall-induced surface runoff would wash the anthropogenic pollutants of trace metals, polycyclic aromatic hydrocarbons (PAHs), and other toxics off the impervious surface and eventually discharge into the nearby water bodies through storm sewers or combined sewer overflows (CSOs). It has gained increasing attention and the deteriorated stormwater runoff has been regarded as a leading source of pollutants causing water quality impairment related to human activities in the natural hydrological system, , ]. Urban stormwater runoff affects water quality, water quantity, habitat and biological resources, public health, and the aesthetic appearance of urban waterways. Therefore, to accurately model the pollutant migration in the surface runoff requires an improving method considering different surfaces and antecedent environment conditions. The sensitivity analysis based on the Bayesian network indicates that the wash-off concentrations of metals were mainly dependent on the antecedent environmental conditions or the surface properties while the sampling methods had a minor influence. The wash-off concentrations of Cd, Cu, and Zn on the road surface 45–780% higher than those on the facade surfaces. The result shows that the wash-off concentrations of trace metals were found in the order of Cd (2.28 ± 2.08 μg/l) 38% and >79% of metals and TS concentrations in the facade surface and road surface runoff respectively. Wet-vacuuming sweeping (WVS) and surface washing (SW) methods, representing the maximum pollution potential and common rainfall-induced wash-off condition respectively, were used to collect the particulate matters. Cd, Pb, Cu, Zn and total solids (TS) washed off two different surfaces (low-elevated facade and road surfaces) under two kinds of antecedent environmental conditions (dry and snow-melting) were determined in this study. Particulate-associated trace metals have been regarded as an important pollution source for urban surface runoff.
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