Why variation of ground-level O3 differed during air quality control for APEC and Parade

Ozone (O3) is an important photochemical product, which represents the atmospheric oxidants capacity. The increasing ground-level O3 in Beijing attracts people's attention and became an urgent thing to manage in recent years. In the autumn of 2014 and summer of 2015, Asia-Pacific Economic Cooperation (APEC) China 2014 and the 2015 China Victory Day parade (Parade) were held in Beijing. Thus, spell of emission restrictions was conducted for improving the air quality for the two great events, respectively. Previous studies indicated that significant reduction in the emissions of primary anthropogenic pollutants had been achieved, and the monthly averaged concentration of CO, SO2, NOx (NO + NO2) and NMHCs were decreased by 30%-60% for both events. In contrast to the obvious reduction in primary pollutants, O3 increased by 42% in APEC but decreased by 33% in Parade, which was surprising as the control measures are almost the same during the two events. The regional transport from the surrounding areas contributed lot in APEC, and the non-linearity relationship of O3 and its precursors may be another reason. A zero-dimensional box model based on the compact Regional Atmospheric Chemical Mechanism version 2 (RACM 2) was applied to chase down the internal factor to determine the O3 variation. The EKMA plot showed that / was the important role to effect photochemical regime as well as ozone production efficiency. Except that, the influence of NO-O3 titration effect and low photolysis frequencies in autumn also contributed to that. As high / does help O3 control and NOx continues to fall down due to the government policy, reactivity-based regulations for VOC controls are more cost-effective. With source profile and annual PMF analysis of source apportionment by related studies, we suggest solvent use should be focus on involving VOC control.