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Evaluating and Addressing the Leakage Problems of Black Carbon Mitigation in China’s Domestic Sector Yuan Xu*,†,‡ and Junfeng Liu*,§ †
Department of Geography and Resource Management & Institute of Environment, Energy and Sustainability, The Chinese University of Hong Kong, Hong Kong, China ‡ Shenzhen Research Institute, The Chinese University of Hong Kong, Shenzhen, China § Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing, China to fully use their leftover agricultural wastes after switching fuels, while field burning, with intensive black carbon emissions, is one of the cheapest and most commonly adopted solutions. The severity of these leakage problems could be evaluated from the perspectives of absolute amounts, as well as temporal and spatial shifts of emissions. Whether the leakage problems may increase or decrease overall black carbon emissions depends on two major factors. On the one hand, only a proportion of the agricultural wastes that are replaced in the domestic sector will be burned in the field. On the other hand, black carbon emission factors in stoves and field burning are different. On average for China, field burning has a 45% lower emission factor than cooking stoves;2 the change will be about 57% lower for wheat residues, 67% lower for rice residues but 32% higher for maize residues.3 Accordingly, significant reduction of black carbon emissions could still happen despite the leakage problems. Furthermore, the leakage problems shift the seasonal distribution of black carbon emissions. Cooking is a yearround activity and heating is for cold months, while field burning is mostly concentrated in harvest seasons, especially June and October.4 The June field burning peak is lower and somewhat coincides with the start of the Monsoon season, he Kyoto Protocol and the newly signed Paris Agreement resulting in faster wet deposition and a shorter lifetime of black did not specifically regulate the mitigation of black carbon, carbon, whereas the October peak is much more intensive and a type of particulate matter with significant warming potential the lifetime of black carbon longer.5 Radiative forcing induced and health impacts. However, under the more decentralized by black carbon over the Himalayas and Tibetan Plateau is the regime on climate mitigation in the Paris Agreement, individual strongest in spring but much lower in autumn.5 The temporal countries could deliberate more freely on mitigating greenshift due to fuel switching accordingly moves a significant house gases, including black carbon. The domestic sector in amount of black carbon emissions from months with greater East and South Asia as well as the rest of the developing world impacts to months with lesser impacts, which is likely beneficial has the greatest overall impacts, particularly on the climateto further constraining the warming potential. sensitive Arctic surface temperature.1 Fuel switching is often In addition to its climate impacts, black carbon is also a major recognized as one of the most effective technical methods to air pollutant. The leakage problems spatially move year-round reduce black carbon emissions from cooking and heating indoor air pollution (from cooking) outdoors, which is stoves. Agricultural wastes with high emission factors of black concentrated at high levels in the harvest season. However, carbon could be replaced by, for example, liquefied petroleum because of human proximity to indoor emissions vs outdoor gas (LPG) with negligible emissions. The nearly 100% emissions (where there is much better dispersion), fuel mitigation efficiency of this fuel switching is largely for the in switching will still have significant net benefits on public health situ emissions, but it does not fully take into consideration the despite the leakage problems. lifecycle of the replaced agricultural wastes causing leakage We conclude that fuel switching in the domestic sector is an problems. effective method in controlling black carbon-induced warming With rapid economic growth, rural residents in China and and pollution. Nevertheless, the leakage problems should be other emerging economies have been rapidly climbing an carefully addressed for more effective black carbon mitigation. “energy ladder”, replacing biomass with cleaner fuels, resulting in significant cobenefits of black carbon mitigation in the domestic sector. However, serious leakage problems might Received: April 25, 2016 compromise the net effects. Many rural households are unable
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© XXXX American Chemical Society
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DOI: 10.1021/acs.est.6b02046 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Environmental Science & Technology One solution could be to integrate it into CO2 mitigation schemes for encouraging better use of agricultural wastes with economic incentives. China has renewed its CO2 mitigation goal in the ongoing 13th Five-Year Plan (2016−2020) to reduce CO2 intensity by 18%, and in its Intended Nationally Determined Contribution to achieve peak emissions in around 2030. To reach these goals, led by seven regional pilot emissions trading schemes, a national scheme is being planned, for full implementation in 2019. Agricultural wastes and other types of biomass could be formally recognized as carbonneutral fuels in the emissions trading schemes. Because these schemes generally include industrial emitters (and boilers for concentrated heating services) but not domestic households, the latter’s decision to climb the “energy ladder” would not be affected while the former could be encouraged, through earning CO2 emission permits, to consume agricultural wastes with modern technologies despite their relatively high costs.
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AUTHOR INFORMATION
Corresponding Authors
*(Y. X.)
[email protected]. *(J. L.) jfl
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This research is funded by the General Research Fund of the Hong Kong Research Grants Council (2120485), the National Basic Research Program of China (2012CB955803) and the South China Program at The Chinese University of Hong Kong (6903795).
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REFERENCES
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DOI: 10.1021/acs.est.6b02046 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
