**1. Introduction**

In recent years, a series of temporary emission-reduction measures have been adopted to ensure air quality during some large-scale events at home and abroad, such as the 2002 Busan Asian Games, the 2008 Beijing Olympic Games, the 2010 Guangzhou Asian Games, and the 2014 APEC Meeting in Beijing. Many scholars have studied air quality from the aspect of air quality protection measures. For example, Li L et al. [1] used the WRF-CMAQ

**Citation:** Huang, B.; Deng, M.; Gao, Q.; Ma, Z.; Chen, M. Study on Improving the Air Quality with Emission Enhanced Control Measures in Beijing during a National Parade Event. *Atmosphere* **2022**, *13*, 1019. https://doi.org/ 10.3390/atmos13071019

Academic Editors: Duanyang Liu, Kai Qin and Honglei Wang

Received: 11 May 2022 Accepted: 15 June 2022 Published: 24 June 2022

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model to simulate the concentration of PM2.5 under the condition of no control measures and temporary industrial control measures or carried out the evaluation of effect of control measures on air-quality improvement during the Nanjing Youth Olympic Games based on actual observation data. Wang et al. [2] found that during the APEC meeting in 2014, the overall air quality of Shijiazhuang city was better than that of the same period in 2013, and the mass concentration of all air pollutants except for O3 decreased significantly. Lee et al. [3] conducted a study on PM10, CO, NO2, and SO2 of 13 air sub-stations during the traffic restriction period of the 2002 Busan Asian Games in South Korea and found that the concentrations of these pollutants all decreased significantly. Beig et al. [4] used the WRF-Chem model to evaluate and found that if effective emission-reduction measures were not taken during the event, the air quality improvement effect would be limited. Liu et al. [5] found in their study that the contribution of early progressive emission reduction to SO2, NO2, VOC, and other pollutants was greater than that of temporary emission-reduction measures. Li et al. [6] analyzed the improvement in air quality in Beijing during APEC and found that compared with the same period in 2013, the concentration of PM2.5 significantly decreased during APEC in 2014, and the air quality was dominated by fine weather, indicating that enhanced emission-reduction measures had a significant effect on the improvement in air quality in Beijing.

Studies showed that different weather situations, different seasons, and different pollution sources have different impacts on pollutant concentrations [7–12]. Therefore, a lot of research has been conducted on weather conditions during major events. For example, Li et al. [13] analyzed the variable characteristics of air quality and pollution meteorological conditions in Guangzhou during the Guangzhou Asian Games and pointed out that the air quality during the Asian Games could be guaranteed under the influence of strong emission-reduction measures implemented by the government and good weather conditions. Yu et al. [14] analyzed the weather conditions during the Asian Youth Games and found that due to the influence of afternoon thundershowers and typhoons, the weather conditions during the Asian Youth Games were good for the diffusion of pollutants, and the air quality was significantly better than that of the same period in 2011 and 2012. Chen et al. [15] studied the impact of meteorological conditions on air quality during the Shanghai World Expo. Although the joint prevention and control measures of air quality during the Shanghai World Expo made pollution emissions lower than in normal years, the transport and diffusion of atmospheric circulation still led to three pollution events during the Shanghai World Expo when the meteorological conditions were unfavorable. The results indicated that meteorological conditions are one of the main factors affecting the air quality during the Shanghai World Expo. In addition, some scholars studied the formation mechanism of pollution under different control measures [16–28].

In honor of the 70th-anniversary victory of the Chinese People's War of Resistance against Japanese Aggression and the World Anti-Fascist, a grand ceremony was held on 3 September 2015 in China. So as to protect Beijing's air quality during the Military Parade, six provinces around Beijing jointly implemented a series of control measures and regional joint prevention, including odd–even license plate restrictions, industrial production and suspension. During this period, Beijing's air quality reached grade one (excellent) weather for 15 consecutive days, and on September 3rd, there were blue skies and white clouds, widely known as "Military Parade blue". At present, scholars have evaluated the effect of emission reduction during the Military Parade [29,30].

Different from previous studies, this study conducted a comparative study on the air quality of Beijing before, during, and after the implementation of the enhanced control measures for the 2015 military parade, as well as during the same period in 2013 and 2014. In addition, a comparative analysis of the improvement effect of air quality between the 2014 APEC and the 2015 Military Parade was also carried out. Meanwhile, emission enhanced control and reduction measures with regard to Beijing or its surrounding area during the 2015 Military Parade were induced. To explore and analyze the contribution of emission-reduction measures and weather conditions to the improvement of air quality in Beijing, this study can provide data theory for air-quality research before, during, and after the implementation of emission-reduction measures during major activities and scientific support for the implementation of air quality assurance measures during non-activities. The actual mechanism and single-factor research had not been applied in this study, so further study is needed.

Based on the air-quality data of the Beijing Olympic Sports Center released by the China Environmental Monitoring Station, this study compared the changes in Beijing's air quality before, during, and after the implementation of the Military Parade, as well as the same three years in 2013, 2014, and 2015. The discussion of the effect of emission-reduction measures or the influence of weather conditions on Beijing's air quality has important scientific significance and practical value, and at the same time, it could provide scientific and technical support for improving Beijing's air quality.
