Atmos. Chem. Phys. Discuss., 13, 3379-3418, 2013
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How to improve the air quality over mega-cities in China? – Pollution characterization and source analysis in Shanghai before, during, and after the 2010 World Expo
K. Huang1,2, G. Zhuang1, Y. Lin1, Q. Wang1, J. S. Fu2, Q. Fu3, T. Liu1, and C. Deng1
1Center for Atmospheric Chemistry Study, Department of Environmental Science and Engineering, Fudan University, Shanghai, 200433, China
2Department of Civil and Environmental Engineering, The University of Tennessee, Knoxville, TN 37996, USA
3Shanghai Environmental Monitoring Center, Shanghai, 200030, China

Abstract. Three field campaigns were conducted before, during, and after the 2010 World Expo in Shanghai, aiming to understand the response of secondary aerosol components to both control measures and human activities. In spring, PM2.5 averaged 34.5 ± 20.9 μg m−3 with a severe pollution episode influenced by a floating dust originating from northwestern China on 26–28 April, right before the opening of the Expo. With the approaching of Expo, significant increasing trend of SNA (SO42−, NO3, and NH4+) concentrations was observed from 20 April 20 to 2 May, attributing to the enhanced human activities. Nitrate had the most significant daily increasing rate of 1.1 μg m−3 d−1 due to enhanced vehicle emission. In summer, two intensive pollution episodes were found to be a mixed pollution of SNA with biomass burning due to loose control of post-harvest straw burning. Compared to the spring and summer of 2009, NO3 increased 12–15% while SO42− showed reductions of 15–30%. Continuous desulphurization of SO2 emission from power plants in recent years was responsible for the lowered SO42−, while enhanced traffic emission due to tremendous Expo visitors was the major contributor to the increased NO3. In the autumn phase of the Expo before the closing of the Expo (20–30 October), the air quality over Shanghai was much better than ever before. However, the air quality rapidly plummeted as soon as the Expo was announced closed. SNA increased 3–6 folds to be 42.1 and 68.2 μg m−3 on 31 October and 1 November, respectively, as compared to 20–30 October. Of which, nitrate increased most with ~ 5–8 folds, indicating the serious impact from enhanced vehicle emission. The anthropogenic Ca as a tracer from construction dust increased from 2.88 ± 1.85 μg m−3 during the Expo to be 6.98 ± 3.19 μg m−3 during the post-Expo period, attributing to the resumption of construction works after the Expo. Compared to the autumn of 2009, all the ion components increased in 2010, owing to the lifting of emission control measures after the Expo. SO42− was found least increased while NO3 and Ca2+ had tremendous increases of 150% and 320%, respectively. No successive control measures with the loose regulations after the Expo were responsible for this jump of the bad quality. The ratio of NO3/SO42− in PM2.5 over Shanghai had a significant increasing trend from ~0.3 in the early 2000s to more than 1.0 in 2010, indicating the increasing role of mobile sources. Reducing NOx emission will be China's priority in the future to improve the air quality over the mega-cities. In addition, lowering mineral aerosol components (e.g. Ca2+) was also demonstrated to be beneficial for alleviating air pollution in China.

Citation: Huang, K., Zhuang, G., Lin, Y., Wang, Q., Fu, J. S., Fu, Q., Liu, T., and Deng, C.: How to improve the air quality over mega-cities in China? – Pollution characterization and source analysis in Shanghai before, during, and after the 2010 World Expo, Atmos. Chem. Phys. Discuss., 13, 3379-3418, doi:10.5194/acpd-13-3379-2013, 2013.
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