1. Introduction North China, or Huabei region, located between 32°- 42°N latitude in eastern China, is one of the most severely polluted regions in China. There are many large and strong emission sources in Beijing (BJ), Tianjin (TJ), Tangshan (TS) and Shijiazhuang (SJZ) in Huabei. The chemical characteristics of air masses from these cities are expected to be very different. A regional chemical transport model coupled with the tracer tagging method are used to investigate the ozone production efficiency (OPEx) from those polluted cities. Model description The regional chemical transport model coupled with an on-line tracer tagging method was used （ Ma et al., 2002 ）. The meteorological information was provided by MM5. The model domain covers the entire Huabei region. In the horizontal, the model includes 91×61 grid with 10km resolution. In the vertical the model is divided unequally into 30 layers. The anthropogenic emissions in Huabei region are obtained from Zhao et al (2012) with 10km resolution as shown in Fig.1. The initial and boundary conditions of chemical species were from the EMAC global model. The simulation period was from 8:00 UTC 1 April to 23:00 UTC16 May 2006. Results M.Xue, J. Z. Ma (mjz@cams.cma.gov.cn) Chinese Academy of Meteorological Sciences, Beijing, China Reference Xue et al., AE, 71, 122-130,. doi:http://dx.doi.org/10.1016/j.atmosenv.2013.01.045,2013. Fig. 2 Average distributions of O 3, NO x /NO y, P(O 3 ), NO x, NO y and NO z at 14:00 BJT for the simulation period Ozone production efficiency calculated for different cities in North China Fig. 3 Average contributions of emitted NO x from tagged regions (BJ, TJ, TS and SJZ) to the NO x and NO y concentraions at 14:00 BJT for the simulation period Fig. 4 Calculated OPEx for BJ 、 TJ 、 TS and SJZ urban plumes for 12:00-14:00 BJT during the simulation period Fig. 5 Simulated gases and NO z attributions to different emission regions and categories at Xin’an for 14:00 BJT at each cloud-free day. Colors for the label of days represents the site was influenced dominantly by air masses from BJ (read), TJ (green) or TS (blue) on that day Fig.1 Anthropogenic emissions of CO (a), VOC (b), NO x (c), and NO x from industrial (d), traffic (e) and other (f) in the central area of Huabei. Other refers to emissions from civil and biomass burning. Dark solid cycle indicates the Xin’an site. Conclusions The estimated OPEx for BJ,TJ,TS and SJZ plumes is very different, with the values of 3.35, 2.75, 1.43 and 2.33 mol mol -1 respectively. The estimated OPEx in BJ, TJ, TS air masses arriving at Xin’an are comparable to those in their general pollution plumes. A lower OPEx in TS than BJ and TJ air masses indicates a remarkable difference in the chemical characteristics of pollution plumes from different pollution centers in North China. Fig. 6 Calculated OPEx at Xin’an site for 12:00-14:00 BJT. Red, green and blue data points indicate the days influenced dominantly by BJ, TJ and TS air masses Literature cited Ma et al., JGR, 107(D22), 4660, doi:10.1029/2001jd001354,2002. Zhao et al., ACP, 12, 481-501, doi:10.5194/acp-12-481-2012, 2012.