## 3 Results and Discussion
### Effect of 13 th FYP on Overall Air Quality in Haizhu in 2020  
Since the pollutant concentrations in October 2015 were very similar to those in the whole year, the simulated results in the four 2020 scenarios in October are used for evaluating the effect of the 13 th FYP on the air quality in Haizhu by comparing to the simulation for October 2015 (Figure 6). Figure 6 shows that simulated concentrations of five pollutant species (CO, NO\({}_{2}\), PM\({}_{2.5}\), PM\({}_{10}\), and SO\({}_{2}\)) in scenario 2020C are lower than pollutants concentrations simulated in 2015. For O\({}_{3}\), 2020 scenarios' simulation results are higher than 2015 result. CO, PM\({}_{2.5}\), PM\({}_{10}\), and SO\({}_{2}\) concentrations in 2020 scenarios A, B, D are higher than the pollutants concentration in 2015 simulation. NO\({}_{2}\) concentrations in the four 2020 scenarios are slightly lower than the concentration in 2015 simulation. Figure 5: Comparisons of simulated and observed CO, NO\({}_{2}\), PM\({}_{2.5}\), PM\({}_{10}\), SO\({}_{2}\), and O\({}_{3}\). (Daily statistical data in October 2015 in Haizhu district; O\({}_{3}\): daily 8-h maximum concentration; other pollutants: daily-averaged concentration). It is noticeable that O\({}_{3}\) concentrations in all of the four 2020 scenarios are higher than those in 2015 simulation, which means that ozone pollution will probably get worse by the end of 13 th FYP. Although scenario 2020A had the slightly less pollution than other scenarios had, the level of O\({}_{x}\) (O\({}_{3}\) + NO\({}_{2}\)) in scenario 2020A was higher than that of other scenarios (Figure 6), which means that atmospheric oxidation in scenario 2020A was more elevated [13, 85]. It would cause the more intensive formation of secondary aerosols, which would lead to regional pollution [86]. Meanwhile, the level of O\({}_{x}\) in scenario 2020C was the lowest. In Section 3.1, the observed concentrations of PM\({}_{2.5}\), PM\({}_{10}\), and NO\({}_{2}\) in 2015 exceeded the targets. Meanwhile, the WRF-Chem simulations suggested that from 2015 to 2020, the concentrations of PM\({}_{2.5}\) and PM\({}_{10}\) would increase in scenarios 2020A, 2020B, and 2020D. Therefore, the real concentrations of aerosols in 2020 could be higher than those in 2015 and further exceed the targets. The observed O\({}_{3}\)-8h concentration in 2015 did not exceed the target (Section 3.1), but with the increasing trend from 2015 to 2020 as simulated in all scenarios, the real O\({}_{3}\)-8h concentration in 2020 should be considered as a cause for concern. According to the simulations, by the end of 13 th FYP, if the emission control policy just follows 12 th FYP policy (scenario 2020A), the air pollution would increase and the control on all emission sectors in Haizhu (scenario 2020B) and control just on vehicle emissions in Haizhu (scenario 2020D) would have a similar impact on air quality, and could not improve air quality very much. The scenario 2020C (the comprehensive emission control measures taken in the whole Guangzhou city) would have the better effect on the emission control than other scenarios would do. Among the four 2020 scenarios, the scenario 2020C is the better scenario. According to Figure 6, pollutant concentrations between scenario 2020B and 2020D are similar. The effect of controlling every emission sectors in Haizhu district would be almost equal with the effect of only controlling the traffic emission in Haizhu district, suggesting that traffic source would be a key source in Haizhu district. [PERSON] et al. (2016) [13] used WRF-CMAQ model (a base case in 2010, two cases in 2020) and evaluated the impact of emission control measures on the air quality in the PRD region, and their results showed that reducing NO\({}_{x}\) emissions would cause rising PM\({}_{2.5}\) levels in certain areas, although it would benefit with reduction of regional PM\({}_{2.5}\). They also noted that O\({}_{3}\) formation in PRD was generally VOCs-limited and cutting VOCs emission could benefit the reduction of overall O\({}_{3}\).