Assessment of traffic-related air pollution in the urban streets before and during the 2008 Beijing Olympic Games traffic control period

In order to investigate the air quality and the abatement of traffic-related pollution during the 2008 Olympic Games. we select 12 avenues in the urban area of Beijing to calculate the concentrations of PM10, CO. NO2 and O-3 before and during the Olympic traffic controlling days, with the OSPM model. Through comparing the modeled results with the measurement results on a representative street, the OSPM model is validated as sufficient to predict the average concentrations of these pollutants at street level, and also reflects their daily variations well, i.e. CO presents the similar double peaks as the traffic flow, PM10 concentration is influenced by other sources. Meanwhile, the model predicts O-3 to stay less during the daytime and ascend in the night, just opposite to NO2, which reveals the impact of photochemical reactions. In addition, the predicted concentrations on the windward side often exceed the leeward side, indicating the impact of the special street shape, as well as the wind. The comparison between the predicted street concentrations before and during the Olympic traffic control period shows that the overall on-road air quality was improved effectively, due to the 32.3% traffic flow reduction. The concentrations of PM10, CO and NO2 have reduced from 142.6 mu g m(-3), 3.02 mg m(-3) and 118.7 mu g m(-3) to 102.0 mu g m(-3), 2.43 mg m(-3) and 104.1 mu g m(-3). However, the different pollutants show diverse changes after the traffic control. PM10 decreases most, and the reduction effect focusing on the first half-day even clears the morning peak, whereas CO and NO2 have even reductions to minify the daily fluctuations on the whole. Opposite to the other pollutants, ozone shows an increase of concentration. The average reduction rate of PM10. CO, NO2 and O-3 are respectively 28%, 19.3%, 12.3% and -25.2%. Furthermore, the streets in east, west, south and north areas present different air quality improvements, probably induced by the varied background pollution in different regions around Beijing, along with the impact of wind force. This finding suggests the pollution control in the surrounding regions, not only in the urban area. (C) 2009 Elsevier Ltd. All rights reserved.