Objective: To understand the characteristics of size and concentration of the ultrafine particles (UFPs) during the 2008 Olympics in Beijing, as well as the influencing factors for number concentration of UFPs.
Methods: Ultrafine particle monitor model 3031, manufactured by USA TSI Co., was used to monitor the daily number concentration of 20-500 nm particles, and descriptive analysis was conducted based on the data collected.
Results: During the Olympics, the mean value of number concentration for 20-100 nm particulate matter is 5 920.43 particles/ cm3. Particles ranging 30-50 nm account for the largest portion(23.49%) among particles of all sizes. There are two peak values on the curve of 24 hours' number concentration for 20-100 nm particles, respectively, at noon and evening.
Conclusion: This paper indicates that the number concentration of ultrafine particles registered considerable reduction in the 2008's Olympics compared to the pre-Olympics years. And observation of the curves indicated that the number concentrations of the UFPs with bigger size are related to traffic volume, whereas for smaller size UFPs, illumination may be a more important influencing factor. Also there are significant correlations between number concentration and temperature as well as relative humidity.