Study estimates global black carbon emissions up 72% from 1960-2007; BC emissions intensity down 52%
|Black carbon emissions and BC emissions intensity per year. Credit: ACS, Wang et al. Click to enlarge.|
A study led by a team from Peking University has estimated that global black carbon (BC) emissions increased from 5.3 teragrams/year in 1960 to 9.1 teragrams per year in 2007 (+72%). These estimates are 11-16% higher than produced by in previous inventories, the researchers noted in a paper published in the ACS journal Environmental Science & Technology.
Over the same period, BC emission intensity—the amount of BC emitted per unit of energy production—decreased by 52% for all the regions under assessment, especially China and India.
Improvements in combustion technology and changes in fuel composition had led to an increase in energy use efficiency, and subsequently a decline of BC emission intensities in power plants, the residential sector, and transportation. On the other hand, the BC emission intensities had increased in the industrial and agricultural sectors, mainly due to an expansion of low-efficiency industry (coke and brick production) in developing countries and to an increasing usage of diesel in agriculture in developed countries.—Wang et al.
Black carbon has two deleterious effects on the environment. First, it warms the Earth system by absorbing sunlight and emitting infrared radiation, and by decreasing the ice/snow albedo. The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) said BC has a direct radiative forcing of +0.4 (+0.05 to +0.8) W m−2, and that BC is an important warming species in addition to carbon dioxide and methane.
Second, BC is an important component in ultrafine particles in air and a strong absorbent for various toxic chemicals, and thus is associated with a number of adverse health impacts.
In the new study, the team estimated annual BC emissions from 64 sources in 222 countries/territories for the period from 1960 to 2007 using recompiled fuel consumption and emission factor data sets. Among their findings:
The residential sector is the most important anthropogenic BC emission source. From 1960 to 1988, global BC emissions from the residential sector increased by 37% from 2,226 to 3,021 gigagram (Gg). After 1988, the total emissions leveled off but seem to increase again since the mid-1990s to reach another peak of 2,956 Gg in 2006.
Industrial sector (including diesels used in agriculture) global total emissions were increasing gradually before 1990, even though the emissions from developed countries began to decrease slowly by the end of the 1970s. Emissions surged around 1991, due to rapid economic development and fast growth of energy demand in China. Among all activities, rapid expansion of beehive coke ovens due to increased market demand contributed a large share to this jump, the authors found.
Beehive coke ovens contributed 25% of the total BC emissions in China in 1996, even though only 1.2% of the energy was consumed by this activity, they noted. As a result, global BC emissions in the industrial sector peaked (1,516 Gg) in 1997. In 1996, China banned beehive coke ovens were banned. Although full compliance with this regulation took several years, and not all the beehive ovens in China had disappeared until the beginning of this century, the team found a sharp decline in the emissions during this period. After 2000, BC emissions from this sector in China remained roughly stable, but the increase in other developing countries was accelerated.
BC emissions in the motor vehicle sector in developed countries showed a broad hump peaking around 1978, driven by two opposite forces of an increasing motor vehicles number but decreasing emissions per vehicle. For developing countries, the emissions were increasing continuously over the period, reflecting an increase in the number of vehicles (0.86 and 172 million in 1960 and 2010, respectively).
Although the EFBC [black carbon emission factor] for motor vehicles in developing countries also decreased since the 1990s, the increase in vehicle number has so far overridden the reduction of EFBC. In China, for example, the number of motor vehicles increased from 13 million in 2000 to 78 million in 2010. In addition, a variation in the share of gasoline vs diesel vehicles also influenced the trend. For example, due to policy favoring diesel vehicles and the availability of small diesel engines to engines in cars, the ratio of diesel to gasoline vehicles increased from 0.48 to 1.5 in Europe and from 0.06 to 0.38 in North America during the 1960−2007. This shift leads to 4.3% fewer CO2 emissions, but 59% greater BC emissions, which should be considered for assessing the short versus long-term impacts on climate.—Wang et al.
The team concluded that nascent decrease in BC emission intensities in developing countries, coupled with the decreases in developed countries, will eventually lead to a decrease in total BC emissions in the near future.
Additionally, they noted, the rapid urbanization rates in China and other developing countries in economic transitions are favorable for BC emission reduction. Fuel consumptions in residential and agricultural sectors have the highest BC emission intensities, and thus the highest reduction potential.
Rong Wang, Shu Tao, Huizhong Shen, Ye Huang, Han Chen, Yves Balkanski, Olivier Boucher, Philippe Ciais, Guofeng Shen, Wei Li, Yanyan Zhang, Yuanchen Chen, Nan Lin, Shu Su, Bengang Li, Junfeng Liu, and Wenxin Liu (2014) “Trend in Global Black Carbon Emissions from 1960 to 2007,” Environmental Science & Technology doi: 10.1021/es5021422