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Stemming PM2.5 Pollution in China: Re-evaluating the Role of Ammonia, Aviation and Non-exhaust Road Traffic Emissions Yunhua Chang,†,§,∥ Xuejun Liu,*,‡ Anthony J. Dore,⊥ and Kaihui Li† †
State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China ‡ College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China § Graduate University of the Chinese Academy of Sciences, Beijing 100049, China ∥ College of Geography and Environmental Science, Northwest Normal University, Lanzhou 730070, China ⊥ Centre for Ecology and Hydrology, Edinburgh, Bush Estate, Penicuik, Midlothian EH26 0QB, U.K. (I). AGRICULTURAL AND NON-AGRICULTURAL NH3 EMISSIONS In reactions with sulphuric acid (formed by oxidation of precursor SO2 emissions), nitric acid (formed by oxidation of precursor NO x emissions) and hydrochloric acid, NH 3 emissions are involved in the formation of ammonium salts, which contribute between 20% and 80% of total PM2.5 mass. Although gaseous NH3 tends to deposit near to its sources, a rapid reaction to form NH4+ aerosols mean that it can be involved in long-range transportation in the particulate phase from rural sources to urban receptors. In EU27, emissions of NH3 have decreased 21% between 1990 and 2010, mainly in response to regional control measures such as the Gothenburg Protocol. NH3 emissions from agricultural sector, most notably animal manure and fertilizer application, are particularly problematic in China because food security is the top priority in the world’s most populous country. By comparison, determining the complex types of non-agricultural NH3 sources (e.g., coal combustion and waste incineration, sewage, and landfill) is more uncertain, and the magnitude of nonWorld Bank report in 2007 estimated that 750 000 agricultural NH3 emissions can be neglected at a large scale. premature deaths a year in China are blamed on air Nevertheless, petrol vehicles fitted with catalytic converters may pollution levels (http://go.worldbank.org/FFCJVBTP40). The provide much larger NH3 emissions than previous estimates.1 issue is causing growing alarm. Over the past year, China has Given China’s expanding auto market, it is clear that measurements of NH3 emissions from transport sources implemented a series of aggressive plans to phase out its coalwould be valuable, especially in the street canyons of fired power plants, run more cars and buses on natural gas, and megacities. raise standards for vehicle emissions. Earlier in 2012, a more comprehensive air quality standard set 35 and 70 μg m−3 as (II). EMISSIONS OF PM2.5 AND THEIR PRECURSORS FROM CIVIL AVIATION China’s annual and daily PM2.5 limits, respectively. Moreover, Civil aviation accounts for approximately 3.5% of global 74 cities in the Beijing-Tianjin-Hebei region, Yangtze River greenhouse-gas emissions (http://www.sourcewatch.org/ Delta and Pearl River Delta, plus the inland Chongqing index.php?title=Greenhouse_gas_emissions_from_the_ municipality and all provincial capitals, have been required to international_aviation_industry). Airports are known to be publish daily reports on PM2.5 concentrations by the end of major sources of PM2.5, volatile organic compounds (VOCs), 2012. If all goes to plan, a substantial emission reduction of HC, CO, NOx, SO2, and other numerous hazardous air pollutants. Although there have been significant improvements PM2.5 and its precursors (mainly NOx and SO2) could be in fuel efficiency in the past few years, this has been outweighed achieved from road traffic and the electricity supply sector. by the increase in air traffic. In 2011, China’s civil aviation While based on scientific knowledge, we argue that there are industry achieved a transport turnover volume (including still three uncontrolled parts in China, which could significantly affect China’s megacities such as Beijing, Shanghai, and Received: November 8, 2012 Guangzhou to meet a rigorous and constant compliance with Accepted: November 26, 2012 Published: December 4, 2012 the PM2.5 standard.
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© 2012 American Chemical Society
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dx.doi.org/10.1021/es304806k | Environ. Sci. Technol. 2012, 46, 13035−13036
Environmental Science & Technology
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besides the existing measures, a comprehensive strategy to control these three neglected emission sources is needed to meet the new air quality standard (Figure 1). But then again, it should be noted that more research is necessary to reduce uncertainty in these emission sources.
passenger and cargo turnover) of 57.7 billion ton·km, an increase of 3.9 billion ton·km over the previous year. This includes a passenger turnover volume which was 40.4 billion ton·km in 2011, a rise of 12.2% compared with the year 2010 (http://www.caac.gov.cn/I1/K3/201205/ P020120507306080305446.pdf). During the next four to five years, China will build another 45 airports, expanding the number of airports in the country to 220. A recent study indicated that fuel consumption in 2010 on domestic flights in China was 12.1 million (metric) tons; HC, CO, NOx, and SO2 emissions were 4600, 39700, 154100, and 9700 tons, respectively.2 A fact that must not be ignored is that excepting emissions while cruising, most of the remaining pollutants were disproportionally concentrated in China’s three biggest and busiest airports: Beijing, Shanghai, and Guangzhou. Therefore, determining the extent of aircrafts’ contribution to pollution levels in the three megacities is of critical importance.
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AUTHOR INFORMATION
Corresponding Author
*Phone: 0086-991-7885367; fax: 0086-10-62731016; e-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was funded by the National Natural Science Foundation of China (Project 41005001) and by the ‘Hundred Talents Program’ of the Chinese Academy of Sciences.
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(III). NON-EXHAUST PM2.5 FROM ROAD TRAFFIC While the regulation of exhaust emissions from road traffic has been well established, currently non-exhaust particle emissions
REFERENCES
(1) Sutton, M. A.; Dragosits, U.; Tang, Y. S.; Fowler, D. Ammonia emissions from non-agricultural sources in the UK. Atmos. Environ. 2000, 34, 855−869. (2) Fan, W.; Sun, Y.; Zhu, T.; Wen, Y. Emissions of HC, CO, NOx, CO2, and SO2 from civil aviation in China in 2010. Atmos. Environ. 2012, 56 (1), 52−57. (3) Ketzel, M.; Omstedt, G.; Johansson, C.; During, I.; Pohjolar, M.; Oettl, D.; Gidhagen, L.; Wahlin, P.; Lohmeyer, A.; Haakana, M.; Berkowicz, R. Atmos. Environ. 2007, 41 (40), 9370−9385. (4) Garg, B. D.; Cadle, S. H.; Mulawa, P. A.; Groblicki, P. J.; Laroo, C.; Parr, G. A. Environ. Sci. Technol. 2000, 34 (21), 4463−4469. (5) Iijima, A.; Sato, K.; Yano, K.; Tago, H.; Kato, M.; Kimura, H.; Furuta, N. Atmos. Environ. 2007, 41 (23), 4908−4919.
Figure 1. Schematic illustration of the comprehensive PM2.5 control strategy.
from tire wear, brake wear, road surface abrasion and turbulent resuspension in the wake of passing traffic are unabated. Emissions from non-exhaust sources are found partly in the fine fraction and mostly in the coarse fraction; therefore they have been addressed to see whether these might provide a potential solution to lower atmospheric PM levels in urban areas. Using data from eight street locations in five European countries, Ketzel et al. showed that a large part (about 50−85% depending on the location) of the total PM10 emissions originates from non-exhaust emissions.3 Another U.S. brake wear test study concluded that on average 86% and 63% of the airborne PM was PM10 and PM2.5, respectively. 4 A recent research in Japan demonstrated that between 74% and 92% of brake abrasion particles (on the basis of number concentration) were emitted as PM2.5, corresponding to 12−36% of total particle mass.5 Although no similar studies have been undertaken in China, the results from Japan highlighted a universal fact that the effects of traditional measures relying on the exhaust part of urban road traffic emissions would be significantly undermined by non-exhaust PM2.5 emissions. In conclusion, stemming PM2.5 pollution in megacities largely depends on the mitigation of non-agricultural NH3, civil aviation, and non-exhaust road traffic emissions. Therefore, 13036
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