Characteristics of Ground Ozone Concentration over Beijing from 2004 to 2015: Trends, Transport, and Effects of Reductions

Based on the hourly ozone monitoring data during 2004–2015 in urban area and at DL background station in Beijing, a comprehensive discussion of the characteristics of ozone concentration was conducted. Annual concentration of daily maximum 1 h ozone (O3 1 h) was all increasing at urban sites (1.79 ppbv yr−1) and DL background station (2.05 ppbv yr−1) while daily maximum 8 h average ozone concentration (O3 8 h) was increasing in urban area (1.14 ppbv yr−1) and slightly decreasing at DL background station (−0.47 ppbv yr−1) from 2004 to 2015 due to different ozone sensitivity regimes and ratios of NO2/NO. Diurnal variation of ozone peaks obtained at downwind DL station were about 1 h later than that in urban area from May to October in different years and concentration of ozone at a DL background station was much higher than that of urban sites. Moreover, the difference of ozone peaks between urban sites and DL background station was significantly becoming smaller in recent years, which may be related to the regional ozone transport and the expansion urbanization of Beijing. Based on the joint efforts of regional air pollution prevention and control,Beijing achieved Sep 3 military blue. Calculated average concentrations of CO, NO2, and O3 in S2 (Aug 20~31, 2015) and S3 (Sep 01~03, 2015) decreased by 31.48 %, 43.97 %, and 13.21 % at urban sites, and by 20.93 %, 57.10 %, and 23.62 % at DL station, respectively compared with those in S1 (Aug 01~19,2015) and S4 Sep 04~30, 2015). A reduction of local anthropogenic emissions such as VOCs and NOx could reduce ozone efficiently especially in downwind areas of Beijing and made the ozone peaks decrease significantly and appear 2~3 h earlier compared to the scenarios of no emission reductions. Compared to the increasing ozone during Asia-Pacific Economic Cooperation (APEC)meeting period,to decrease the ozone concentration in Beijing, VOCs emissions should be reduced larger and be controlled stricter than that of NOx in Beijing and the policy of regional air pollution joint prevention and control should still be promoted unswervingly and jointly in the further.