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The volume-weighted mean concentrations (VWMs) of components in the rainwater were calculated based on the rainfall amount and rainwater quality data of 25 rainfall events during 2011–2012. TOC has a VWM of 3.98 mg/L, which is the highest among all the measured components; Ca²⁺ and NH₄⁺ have VWMs of 0.86 mg/L and 0.47 mg/L, respectively, which are much higher than the other cations; NO₃^– and SO₄^2– have VWMs of 1.74 mg/L and 1.71 mg/L, respectively, which are much higher than the other inorganic anions; and formic acid and acetic acid have VWMs of 0.26 mg/L and 0.12 mg/L, respectively, which are higher than the other organic acids. Furthermore, the VWMs of PO₄^3–, glutaric acid, succinic acid, malonic acid, methanesulfonic acid in the samples are lower than 0.1 mg/L, and some of them are lower than detective limits. In addition, the VWM pH in the rainwater is 4.99, showing the acidity of rainfall in the study area. The concentrations of components in rainwater in the study area are lower than those in Guangzhou, Beijing, Shanghai, Nanjing, Ankara and Galicia; while they are similar to those in other cities listed in Table 3. Water quality of rainwater in rainfall events is shown in a box-whisker plot, which indicates that the concentrations of components in the rainwater are highly variable, dependent upon different rainfall events (Figure 2(a)).

Table 3

The volume-weighted mean pH and component concentrations in rainwater in Shenzhen and other cities (mg/L)

Area	Time	pH	Na⁺	NH₄⁺	K⁺	Mg²⁺	Ca²⁺	Cl^–	NO₃^–	SO₄^2–	Reference
This study	2011	4.99	0.235	0.473	0.180	0.042	0.857	0.554	1.743	1.712
Guangzhou	2006	4.56	1.265	1.271	1.283	0.204	2.072	3.077	3.311	7.838	Cao et al. (2009)
Shanghai	2005	4.49	1.152	1.453	0.581	0.355	4.08	2.067	3.088	9.581	Huang et al. (2008)
Beijing	2003	6.18	1.346	6.768	1.564	1.92	7.94	2.935	10.788	25.008	Hu et al. (2005)
Jinhua	2004	4.54	0.173	1.746	0.207	0.053	1.122	0.365	2.294	5.611	Zhang et al. (2007)
Nanjing	1992–2003	5.15	0.529	3.478	0.472	0.38	5.908	5.055	2.455	11.606	Tu et al. (2005)
Mexico	2001–2002	5.08	0.161	1.663	0.086	0.03	0.528	0.34	2.641	2.971	Báez et al. (2007)
Ankara	1994–1996	6.3	0.359	1.555	0.382	0.112	1.428	0.723	1.81	2.304	Topçu et al. (2002)
Singapore	1999–2000	4.2	0.754	0.344	0.281	0.078	0.322	1.212	1.383	4.008	Hu et al. (2003)
Tokyo	1990–2002	4.52	0.851	0.727	0.113	0.138	0.498	1.957	1.891	2.41	Okuda et al. (2005)
Seoul	1996–1998	4.7	0.242	1.195	0.137	0.083	0.698	0.645	1.854	3.403	Lee et al. (2000)
Galicia	1999	6.55	3.358	4.536	1.599	0.528	1.7	6.097	1.55	4.752	Vázquez et al. (2003)
Newark	2006–2007	4.6	0.251	0.439	0.051	0.04	0.12	0.379	0.893	1.829	Song & Gao (2009)

Area	Time	pH	Na⁺	NH₄⁺	K⁺	Mg²⁺	Ca²⁺	Cl^–	NO₃^–	SO₄^2–	Reference
This study	2011	4.99	0.235	0.473	0.180	0.042	0.857	0.554	1.743	1.712
Guangzhou	2006	4.56	1.265	1.271	1.283	0.204	2.072	3.077	3.311	7.838	Cao et al. (2009)
Shanghai	2005	4.49	1.152	1.453	0.581	0.355	4.08	2.067	3.088	9.581	Huang et al. (2008)
Beijing	2003	6.18	1.346	6.768	1.564	1.92	7.94	2.935	10.788	25.008	Hu et al. (2005)
Jinhua	2004	4.54	0.173	1.746	0.207	0.053	1.122	0.365	2.294	5.611	Zhang et al. (2007)
Nanjing	1992–2003	5.15	0.529	3.478	0.472	0.38	5.908	5.055	2.455	11.606	Tu et al. (2005)
Mexico	2001–2002	5.08	0.161	1.663	0.086	0.03	0.528	0.34	2.641	2.971	Báez et al. (2007)
Ankara	1994–1996	6.3	0.359	1.555	0.382	0.112	1.428	0.723	1.81	2.304	Topçu et al. (2002)
Singapore	1999–2000	4.2	0.754	0.344	0.281	0.078	0.322	1.212	1.383	4.008	Hu et al. (2003)
Tokyo	1990–2002	4.52	0.851	0.727	0.113	0.138	0.498	1.957	1.891	2.41	Okuda et al. (2005)
Seoul	1996–1998	4.7	0.242	1.195	0.137	0.083	0.698	0.645	1.854	3.403	Lee et al. (2000)
Galicia	1999	6.55	3.358	4.536	1.599	0.528	1.7	6.097	1.55	4.752	Vázquez et al. (2003)
Newark	2006–2007	4.6	0.251	0.439	0.051	0.04	0.12	0.379	0.893	1.829	Song & Gao (2009)

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Figure 2

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Water quality of rainwater and roof runoff in rainfall events.

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