*3.3. Comparative Analysis of Beijing's Air Quality before, during, and after the IECERM for the Military Parade*

Table 2 and Figure 7 show the changes in various pollutants in the monitoring station of the Olympic Sports Center and the comparison of various pollutants before, during, and after the traffic restriction in 2013, 2014, and 2015, respectively. It can be seen that during the IECERM of the 2015 Military Parade, the concentration of PM2.5, PM10, and NO2, significantly decreased, among which the concentration of PM10 decreased the most, from 109 μg·m−<sup>3</sup> to 34 μg·m<sup>−</sup>3, and the concentration of PM2.5 decreased by 72.73%. Combined with the changes before and after the implementation, it could be seen that the concentration of PM10 and PM2.5 increased after the implementation of the emission-reduction measures, indicating that enhanced control and emission-reduction measures greatly contribute to the emission reduction in particulate matter. The concentration of NO2 decreased by 40.82% according to the comparison of during and before the implementation; however, the concentration increased by 51.67% compared to after implementation. For PM2.5 and PM10, after the implementation changed to greater than before the implementation, which may be related to a large amount pollutants' exhaust after the implementation. The concentration of O3 had been decreasing at any implementation moment, which may be related to the current season in Beijing. In addition, the concentration of SO2 changed little before, during, and after the implementation of the measures and remained at a low concentration level. Compared with the concentration of various pollutants in the same period of 2013 and 2014, it was found that the concentration of various pollutants in the early period of 2015 had not changed a lot, among which PM2.5 and PM10 increased, while NO2 decreased slightly. During and after the implementation of measures, except for O3, PM2.5, PM10, and NO2 concentrations were lower than those in 2013 and 2014, indicating that IECREM had improved Beijing's air quality to some extent.

**Table 2.** Changes in pollutants in the Olympic Sports Center monitoring station.


**Figure 7.** The change trend of pollutants over the same period when before, during, and after the IECERM from 2013 to 2015. Notes: The unit on the *y*-axis is μg·m−3.

#### *3.4. Evolution Analysis of Air Quality during the Same Period of Military Parade from 2013 to 2015*

Figure 8 shows the evolution chart of the daily mean PM2.5 concentration in the monitoring station of the Beijing Olympic Sports Center from 2013 to 2015. It could be seen that the number of days with an average daily concentration below 150 μg·m−<sup>3</sup> in 2015 was less than that in 2014 and 2013. Although the average daily concentration had exceeded the standard in 2015 and even exceeded 500 μg·m−<sup>3</sup> in several days, most of the days were decreasing, indicating that the air quality in Beijing was improving year by year. The average daily concentration during the implementation of enhanced control and emission-reduction measures during APEC in 2014 and the 2015 Military Parade was compared with the same period in 2013, and it was found that although the average daily concentration during the 2014 APEC and 2015 Military Parade was below 100 μg·m<sup>−</sup>3, most of the average daily concentrations during the military parade were below 50 μg·m<sup>−</sup>3, which is significantly lower than the average daily concentration during the APEC military parade, indicating that the emission reduction effect during the military parade was better, which may be related to the weather situation at that time. In the same period as the parade in 2014 and 2013 or the same period as APEC in 2013 and 2015, the average daily concentration of the parade was more than 100 μg·m<sup>−</sup>3, especially in the same period as APEC in 2013 and 2015. The average daily concentration on some days was more than 300 μg·m<sup>−</sup>3. It showed that enhanced control and emission-reduction measures greatly contributed to the reduction in PM2.5. In addition, after entering autumn and winter in 2015, the PM2.5 concentration reached its peak, and the average daily concentration even reached 500 μg·m−<sup>3</sup> on some days, indicating that Beijing's air pollution sources were complex [6], and air quality assurance measures still need to be enhanced.

As can be seen from Table 3, the effective samples from 2013 to 2015 were 344, 362, and 360 days, respectively, and the three-year mean valid sample was 355 days, accounting for 97.3% in the whole year. The annual average of AQI in 2013, 2014, and the three-year period was 88.2, 90.53, and 87.49, respectively, which were all higher than 83.75 in 2015. The average AQI in 2015 during the Military Parade with the IECERM was only 19.27, far less than the average of the other two years and the three-year period. In addition, the enhanced control and emission-reduction measures were implemented during APEC in 2014; however, the annual average AQI in 2014 was higher than the annual average in 2013 and the three-year period, which may be related to the worse weather situation in 2014. The annual average AQI in the three-year period was 87.49. For the purpose of achieving the goal of GB-3095-2012 s-level standard and first-level standard, the annual average of AQI should be reduced by 60.00% and 82.46%, respectively. The average of the normal year is the average of 2013 and 2014. The average of the normal year during the Military

Parade was 64.63, which was reduced by 70.40% compared with the average AQI during the Military Parade. It had achieved the goal of GB-3095-2012 level-2 standard, which was still some distance from the level-1 standard. All these indicated that the enhanced control and emission-reduction measures had made a certain contribution to the improvement of Beijing's air quality, but to achieve the goal of better annual air quality, all parties still needed to coordinate control and joint efforts.

**Figure 8.** Daily mean value of PM2.5 in monitoring sites of the Olympic Center from 2013 to 2015. Notes: The unit on the *y*-axis is μg·m<sup>−</sup>3. The vertical green line and red line show the comparison over the same period when the 2015 Military Parade and 2014 APEC for three years from 2013 to 2015, respectively. The transverse red line shows the concentration of PM2.5 is 115 μg·m<sup>−</sup>3.


**Table 3.** Changes in AQI over the same period from 2013 to 2015 during the Military Parade.

To compare the changes in the Air Quality Index for the same period of three years during the Military Parade in Beijing, Tables 4 and 5 provide the days with their pollution level and the average value of AQI for the three years before, during, and after the IECERM, respectively, i.e., before the IECERM (5 August to 19 August), during the IECERM (20 August to 3 September), and after the IECERM (4 September to 18 September). It could be seen that the number of good days during the Military Parade in 2015 was 35 days (Table 4), accounting for 77.78% of the effective days, higher than 66.67% and 68.89% in 2013 and 2014, respectively. The number of days with mild and moderate pollution was nine days, less than fourteen and thirteen days in 2013 and 2014, respectively. There was one day of heavy pollution in 2013 and 2014 and none in 2015. According to the average value of AQI, except for mild pollution (AQI between 76 and 115), the average value of AQI in other intervals in 2015 was lower than the average value of AQI in 2013 and 2014. In addition, Table 5 showed the days' pollution levels and the average AQI for the same period in three years during the IECERM. It was found the days in 2015 were all fine which have implemented the measures, with twelve days of excellent and three days of good. In 2013 and 2014, the number of fine days without measures was 11 and 8, accounting for 73.33% and 53.33%, respectively. The results suggested that the IECERM contributes significantly to the improvement of air quality in Beijing [30].


**Table 4.** Changes in AQI over the same period from 2013 to 2015 before, during, and after the IECERM.

