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EMCs of each component in 25 rainfall events were calculated in terms of Equation (1). The VWMs of the components in the roof runoff were calculated based on the EMCs and runoff data of 25 rainfall events during 2011–2012. In the roof runoff, TOC has a VWM of 5.42 mg/L, which is the second highest among the measured components; Ca2+, K+ and Na+ have VWMs of 10.01 mg/L, 1.64 mg/L and 1.24 mg/L, respectively, which are much higher than the other cations; NO3, SO42– and Cl have VWMs of 2.81 mg/L, 4.41 mg/L and 1.09 mg/L, respectively, which are much higher than the other inorganic anions; and formic acid and acetic acid have VWMs of 0.128 mg/L and 0.095 mg/L, respectively, which are higher than the other organic acids. In addition, the VWM pH in the roof runoff is 7.78, showing the alkalinity of roof runoff in the study area. VWM of NH4+ in the study is much lower than that in Beijing and a little lower than that in France and Greece; while VWM of NO3 in the study area is higher than that in the cities listed in Table 4. EMCs of the 25 rainfall events are shown in a box-whisker plot, which indicates that the EMCs are highly variable, dependent upon different rainfall events (Figure 2(b)).

Table 4

Mean pH and EMCs in roof runoff in Shenzhen and other cities (mg/L)

AreaTimepHNa+NH4+K+Mg2+Ca2+PO43–ClNO3SO42–Reference
This study 2011 7.78 1.237 0.185 1.644 0.145 10.05 0.01 1.094 2.813 4.413  
Beijing 2000 6.82  3.47     2.78 1.98 55.24 Che et al. (2001)  
Southwest France 2009 6.5 1.1 0.58 1.2 0.27 4.4 0.17 1.9 2.8 1.9 Vialle et al. (2011)  
Xanthi 2002–2004 7.77  0.47 5.74 1.20 24.06   1.48 0.06 Melidis et al. (2007)  
AreaTimepHNa+NH4+K+Mg2+Ca2+PO43–ClNO3SO42–Reference
This study 2011 7.78 1.237 0.185 1.644 0.145 10.05 0.01 1.094 2.813 4.413  
Beijing 2000 6.82  3.47     2.78 1.98 55.24 Che et al. (2001)  
Southwest France 2009 6.5 1.1 0.58 1.2 0.27 4.4 0.17 1.9 2.8 1.9 Vialle et al. (2011)  
Xanthi 2002–2004 7.77  0.47 5.74 1.20 24.06   1.48 0.06 Melidis et al. (2007)  

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