However, affected by rainfall distribution and catchments types, EMC of urban runoff is significantly variable in each event or in each catchment [22]. Then, average EMC (AEMC) was put forward to predict the overall runoff quality accurately by data from more than check FAQ one rainfall event [23]. Based on statistical analysis for a total of 645 samples during 12 rainfall events, the AEMC values of runoff pollutants in different phases were shown in Table 3. Table 3AEMC values and proportion of runoff pollutants in different phases.In general, the AEMC values of runoff pollutants in different phases from urban roads (RD1 and RD2) were higher than the ones from urban roofs (RF1, RF2, and RF3). It was suggested that road runoff is more polluted than roof runoff.

Compared with RD2, runoff pollution of RD1 was more serious because of heavier traffic. Pollution rank of roof runoff was in the following order: RF1 > RF2 > RF3. It might be caused that the cover material of RF1 is asphalt, which was easy to age and chip after a long time use under the outdoor environment. And low AEMC of RF3 was attributed to using tile as cover material to a certain extent, because the production of some pollutants would be reduced by the good erosion-corrosion resistance of tile roof during the runoff process. Furthermore, distributions of runoff pollutants for all the catchments were similar except for DCOD. The proportions of TDS, DTN, and DTP in total ones were 26.19%�C30.91%, 83.29%�C90.51%, and 61.54%�C68.09%, respectively. It could be observed that solids exist as particulate phase in urban runoff.

Conversely, dissolved matters are the mainly existing phase of nutrients which is usually expressed as nitrogen and phosphorus [24]. Based on the monitoring data, distribution of organic pollutants was closely related to the cover material of urban catchments. For asphalt road and roof (RD1, RD2, and RF1), the proportions of DCOD in TCOD were in the range from 71.76% to 86.23%. But because about half TCOD exist as dissolved phase, the distribution of organic pollutants was equally represented in rainfall runoff from the catchments used inorganic cover material, such as concrete and tile.3.2. Characterizing Runoff Pollutants in Different Phases during Typical Rainfall EventDuring a rainfall event, pollutants transport in different phases is affected by several factors, such as rainfall distribution, catchments type, and pollutant component. Taking a rainfall event of July 20, 2011 (22.2mm) for example, the rainfall distribution was showed in Figure 1. Figure 1Distribution Anacetrapib of typical rainfall (July 20, 2011).