[Transition of Particulate Pollutant in the Parcel-based Catchment of Sponge City]

Most sponge city constructions in China are carried out in urban parcel-based catchments, and the quality and quantity of surface runoff can be controlled by several low impact development (LID) facilities. However, there are few reports on the generation and control of urban diffuse pollution. In this study, two areas with different hardening rates were compared to analyze the load conditions during the accumulation-wash-off-transport process of particulate pollutants. The results showed that the road surface in the catchment was the main underlying surface that the particulate pollutants contributed to. The road dust accumulation in the medium hardening rate (61.1%) and high hardening rate (73.6%) plots accounted for 88.4% (2.22-12.51 g ·m^-2) and 90.1% (4.99-33.43 g ·m^-2) of the catchment area unit, respectively. The contribution to the suspended solids (SS) load of runoff was 91.7% (0.97-7.34 g ·m^-2) and 90.5% (0.92-18.77 g ·m^-2), respectively. The SS load of road runoff accounted for approximately 95.2% and 83.1%, respectively. The pollution load (SS) after treatment by the LID facilities was approximately 24.0% and 40.2% of the surface runoff, respectively. The particle size distribution of road dust during the accumulation and wash-off processes was>150 μm, while that in surface and output runoff was <50 μm. With the increase in the impervious area, the distribution of finer particles (<105 μm) in the process of accumulation and wash-off increased (24.4%, 106.4%), while the distribution of particles <50 μm in road runoff decreased (12.4%). The particle size distribution of the accumulated, washed dust, and the rain runoff on the roof were roughly similar to those on the road. However, compared to the particle size distribution of road dust, in the accumulation and wash-off processes, the coarser particles (>1000 μm) of the medium hardening rate plot and the particles of size 250-450 μm and <45 μm of the high hardening rate plot increased significantly (>1000 μm: 58.1%, 108.5%; 250-450 μm: 72.9%, 41.8%; <45 μm: 59.2%, 64.8%). The results revealed the entire distribution process (accumulation-wash-off-transport) of particulate pollutants and the effect of LID facilities on the total SS pollution load of the catchment, which can provide an important reference for the scientific assessment of the project performance of LID installation in urban parcel-based catchments.