A modelling study of air quality impact of odd-even day traffic restriction scheme before, during and after the 2008 Beijing Olympic Games

Abstract. Systematic air pollution control measures were designed and implemented to improve air quality for the 2008 Beijing Olympics. This study focuses on the evaluation of the air quality impacts of a short-term odd-even day traffic restriction scheme (TRS) implemented before, during and after the Games, based on modelling simulation by a well validated urban-scale air quality model. Concentration levels of CO, PM₁₀, NO₂ and O₃ were predicted for the pre- (10–19 July), during- (20 July–20 September) and post-TRS (21–30 September) periods, based on the on-line monitored traffic flows on a total of 334 road segments constituting the 2nd, 3rd, 4th Ring Roads (RR) and the major Linkage Roads (LRs) that were subject to the TRS policy and distributed around the main urban area of Beijing, and on the hourly sequential meteorological data from a representative Observatory. Subsequently, we used the predictions and observations at a roadside air quality monitoring site to evaluate the model, based on a widely used statistical framework for model evaluation, as well as on the dependence of model performance on time-of-the-day and on wind direction, and the model predictions turned out satisfactory. Results showed that daily average concentrations on the 2nd, 3rd, 4th RR and LRs during the TRS period decreased significantly, by about 35.8%, 38.5%, 34.9% and 35.6% for CO, about 38.7%, 31.8%, 44.0% and 34.7% for PM₁₀, about 30.3%, 31.9%, 32.3% and 33.9% for NO₂, and about 36.7%, 33.0%, 33.4% and 34.7% for O₃, respectively, compared with the pre-TRS period. Besides, hourly average concentrations were also reduced significantly, particularly for the morning and evening peaks for CO and PM₁₀, for the evening peak for NO₂, and for the afternoon peak for O₃. Consequently, both the daily and hourly concentration level of CO, PM₁₀, NO₂ and O₃ conformed to the CNAAQS (China National Ambient Air Quality Standards) Grade II during the Games. Besides, a notable ozone weekend effect was revealed for the pre- and post-TRS periods, and was virtually removed for the during-TRS period. In addition, notable reduction of concentration levels were achieved in different regions of Beijing in response to the TRS policy, with the air quality in the downwind northern and western regions improved most significantly. The TRS policy was therefore effective in improving short-term air quality in Beijing during the Games.