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Traffic Optimization: A New Way for Air Pollution Control in China’s Urban Areas Liu Huan† and He Kebin†,* †
School of Environment, Tsinghua University, Beijing 100084, China times in China over past 30 years, which makes it the top 1 source around the country3.
2. CHINA’S DEMANDS ON THE FURTHER VEHICLE EMISSION CONTROLS Nowadays in China, the vehicle emission controls generally rely on the vehicle technology and the oil quality. There have been over 90 vehicle environmental standards defined within 30 years. China has shortened the gap with developed countries by upgrading the emission standards from National I to National IV within 12 years. In last decades, due to the implementation of vehicle emission standards, the growth speed of the pollutant emissions have been much slower than the one of vehicle population. The increase of vehicle population is 60.9% in 2006−2010, whereas the total emissions from vehicles only increased by 6.4%4. However, there are still problems to solve before vehicle emission standards can be fully effective. One of the problems is traffic congestions. The on-board tests show that emission rates in urban areas are highly relevant to congestions. The benefits from new vehicle emission standards are partly offset by traffic congestions.
1. VEHICLES HAVE BECOME THE MAJOR SOURCES OF EMISSIONS During “Eleventh Five-Year”, the total emissions of sulfur dioxide were reduced by 14.3%. On the contrary, however, nitrogen oxides (NOx) and volatile organic compounds (VOC) have been increasing. Ambient concentration of fine particulate matter (PM2.5) and ozone is still at a high level. In big cities, the photochemical smog pollution with vehicle emission pollution characteristics is worsening. In Beijing, Tianjin, the Yangtze River Delta, the Pearl River Delta, the Shandong Peninsula, the Chengdu-Chongqing areas, etc., the annual average PM2.5 concentration reaches around 50−80 μg/m3, which tends to be 4−7 times of U.S. ambient concentration. Vehicle emissions of NOx, VOC, PM2.5 and other pollutants turn to be the major cause of all above. 23% of the fossil fuel-related CO2 emission in the world is generated by transports in 20071. Among this, the ratio of onroad petroleum consumption in China against the one of the world is going to grow from 6% in 2010 to 10−11% up to 2030−2050 following the trend. The research2 estimates on a country level that vehicles contribute 24, 20 and 29% of overall NOx, CO and VOC in China. On an urban level, the proportion may rise to 40−70% for these three major gaseous pollutants, that is, NOx, CO, and VOC. Vehicle is also the second major contributor of PM10 and PM2.5 in Pearl River Delta (21.7% and 35.5%) and the primary local source of PM2.5 in Beijing (22.0%). Vehicle BC emission has also grown 6.8 © 2012 American Chemical Society
3. TRAFFIC OPTIMIZATION: A NEW WAY FOR AIR POLLUTION CONTROL IN CHINA’S URBAN AREAS Although China focuses emission control mainly on vehicle technology, some trials have been actually started on emission reductions by traffic management. Especially during important events, the host city usually adopts vehicle limitation as the primary measure to improve air quality and to solve traffic congestions. The results show that by limiting vehicles which improves traffic conditions, is indeed an effective measure of emission reduction. During the Beijing Olympic Games in 2008, a series of temporary traffic management measures. These measures led to the average traffic flow declined by 32% of the road network inside the sixth-ring road region, and increased the average speed from 25 km/h to 37 km/h. The average speed on highways, arterial roads, and residential roads increased by 34%, 19%, and 23% respectively. The emissions were 24−65% lower than before (HC: 59%, CO: 65%, NOx: 42%, CO2: 39%, and PM: 24%). Among the factors, the mileage decrease contributes 26% reductions of the emission, while the other reductions are Received: May 8, 2012 Accepted: May 10, 2012 Published: May 21, 2012 5660
dx.doi.org/10.1021/es301778b | Environ. Sci. Technol. 2012, 46, 5660−5661
Environmental Science & Technology
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mainly due to the lower emission rates. Generally speaking, good traffic may reduce emissions by 20−50%. Traffic restriction in the Guangzhou Asian Games is another successful case on emission control. Private vehicles are allowed on roads only on alternate days depending on license numbers (odd-numbered vehicles on odd-numbered days and evennumbered vehicles on even-numbered days). The average VKT was reduced by 8.6%, while the emissions of NOx, CO, PM, and VOC were reduced by 30.3%, 44.5%, 24.8%, and 35.6%, respectively. The average speed on arterial roads is 14.93% higher than before, which leads to an improvement on emission rate. During the 2010 Shanghai Expo, government implemented a traffic support program. A number of the government vehicles are forbidden on roads. The measure of limiting private vehicle by license plate tail numbers was prepared as an alternative measure but not carried out. Additionally, because of the longterm vehicle registration control, vehicle population growth in Shanghai has been much slower than in Beijing. According to reports, both the long-term policy and the short-term policy successfully reduced the fuel consumption by vehicles during the Expo. The traffic control measures during the Beijing Olympic Games, the Shanghai World Expo, and the Guangzhou Asian Games show that the control on urban traffic flow will largely reduce vehicle emissions and improve the urban air quality.
4. RECOMMENDATIONS China has not yet implemented the measure of traffic flow optimization to reduce the emissions. To further control criteria pollutants and global warming pollutants, China has to start the environmental friendly transportation optimization in addition to the vehicle technology improvement. It is important to build a methodology and models for environment evaluation over transportation system and to seek for feedbacks to help optimize traffic flow. It is important to find the way to control vehicle pollution while taking into account the traffic demands to achieve the overall goal of energy conservation in China.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work is supported by the National Natural Science Foundation of China (71101078), the special fund of State Key Joint Laboratory of Environment Simulation and Pollution Control.
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REFERENCES
(1) World Energy Outlook 2009; International Energy Agency (IEA): Paris, 2009. (2) Zhang, Q.; Streets, D. G.; Carmichael, G. R.; et al. Asian emissions in 2006 for the NASA INTEX-B mission. Atmos. Chem. Phys. 2009, 9, 5131−5153. (3) Wang, R.; Tao, Sh.; Shen, H.; et al. Global emission of black carbon from motor vehicles from 1960 to 2006. Environ. Sci. Technol. 2012, 46 (2), 1278−1284. (4) China Vehicle Emission Control Annual Report 2011; Ministry of Environmental Protection of the People’s Republic of China (MEP): Beijing, 2011. 5661
dx.doi.org/10.1021/es301778b | Environ. Sci. Technol. 2012, 46, 5660−5661
