## 3 Results and Discussion  
### Air Quality in Haizhu in 2015  
#### 3.1.1 Overview  
The annually-averaged concentrations of PM\({}_{2.5}\), PM\({}_{10}\), SO\({}_{2}\), and NO\({}_{2}\) were 40 \(\upmu\)g/m\({}^{3}\), 61 \(\upmu\)g/m\({}^{3}\), 14 \(\upmu\)g/m\({}^{3}\), and 49 \(\upmu\)g/m\({}^{3}\), respectively, in Haizhu district in 2015, which were higher than those in the whole of Guangzhou city (39 \(\upmu\)g/m\({}^{3}\), 59 \(\upmu\)g/m\({}^{3}\), 13 \(\upmu\)g/m\({}^{3}\), and 47 \(\upmu\)g/m\({}^{3}\), respectively [64]). The 95 th percentile of the CO daily concentration was 0.9 mg/m\({}^{3}\), in Haizhu district in 2015, which was lower than that in the whole of Guangzhou city (1.5 mg/m\({}^{3}\), [64]), The routine pollutants (except for O\({}_{3}\)) peaked in January (winter), among which PM\({}_{2.5}\) and NO\({}_{2}\) were the major pollutants. The 90 th percentile of the daily 8 h maximum O\({}_{3}\) concentration (O\({}_{3}\)-8h) in 2015 was 139 \(\upmu\)g/m\({}^{3}\), slightly lower than that in Guangzhou (145 \(\upmu\)g/m\({}^{3}\); [64]). O\({}_{3}\)-8h peaked in September (summer to autumn, or hot season). O\({}_{3}\) was also the key pollutant in summer and autumn in Haizhu district [64]. These observational results suggested that air quality in Haizhu was still harmful to human health (the thresholds: PM\({}_{2.5}\leq 10\)\(\upmu\)g/m\({}^{3}\) annual mean, PM\({}_{10}\leq 20\)\(\upmu\)g/m\({}^{3}\) annual mean, NO\({}_{2}\leq 40\)\(\upmu\)g/m\({}^{3}\) annual mean, O\({}_{3}\)-8h \(\leq 100\)\(\upmu\)g/m\({}^{3}\) 8 h mean) [65] and it was worse than the Guangzhou average level in 2015, which highlights the necessity of district/town regulation in air quality control. Please note that this study does not intend to estimate the influence of air quality on human health which is sensitive to the exposure levels (the levels of air pollutants). The pollutant concentrations in October 2015 were very similar to those in the year of 2015 (a-SO\({}_{2}\), a-NO\({}_{2}\), a-PM\({}_{10}\), a-PM\({}_{2.5}\), a-O\({}_{3}\)-8h, a-CO, in Figure 3a).  
Figure 3: (**a**) Air pollutant monthly concentrations in 2015 averaged in four stations (Baogang, Chisha, Shayuan, and Haizhuhu) in Haizhu district, (**b**) comparison of air quality in 2015 in Haizhu district and the 13 th Five-Year targets. (In (a), a-SO\({}_{2}\), a-NO\({}_{2}\), a-PM\({}_{10}\), a-PM\({}_{2.5}\) means 2015 annual value for SO\({}_{2}\), NO\({}_{2}\), PM\({}_{10}\), PM\({}_{2.5}\), respectively; a-O\({}_{3}\)-8h means the 90 th percentile of O\({}_{3}\)-8h in 2015; a-CO means the 95 th percentile of the CO daily concentration in 2015; other pollutants: monthly-averaged concentrations. In (b), O\({}_{3}\): the 90 th percentile of O\({}_{3}\)-8h in a year; CO: the 95 th percentile of the CO daily concentration in a year; other pollutants: annually-averaged concentrations. These parameters were adopted according to the national standards in China [66].).  
Compared with the 13 th FYP targets in 2020 (PM\({}_{2.5}\)\(\leq\) 30 \(\mu\)g/m\({}^{3}\), PM\({}_{10}\)\(\leq\) 50 \(\mu\)g/m\({}^{3}\), SO\({}_{2}\)\(\leq\)15 \(\mu\)g/m\({}^{3}\), NO\({}_{2}\)\(\leq\) 40 \(\mu\)g/m\({}^{3}\), O\({}_{3}\)-8h \(\leq\) 160 \(\mu\)g/m\({}^{3}\), and CO \(\leq\) 2 mg/m\({}^{3}\)) in Guangzhou [49] (Figure 3b), PM\({}_{2.5}\), PM\({}_{10}\), and NO\({}_{2}\) concentrations in 2015 exceeded the targets, and the air pollutant emission could even rise in the coming years (Table 1). Haizhu district could face worsening air quality, and more emphasis should be placed on the control measures and effectiveness assessment for PM\({}_{2.5}\) and NO\({}_{2}\) during the 13 th FYP so that the measures can be duly adjusted to achieve the 13 th FYP targets.