Black carbon
Encyclopedia
- Not to be confused with Carbon blackCarbon blackCarbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its...
. For the cell phone, see Samsung SGH-D900Samsung SGH-D900The Samsung SGH-D900, also known as the Ultra Edition 12.9 or Black Carbon, is a slider-style mobile phone created by Samsung Electronics that was announced in Q3 2006. It is marketed as the world's thinnest slider phone. Since the end of 2006, a Wine Red edition was added and 2007 marked the...
In Climatology
Climatology
Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences...
, black carbon or BC is a climate forcing agent formed through the incomplete combustion of fossil fuel
Fossil fuel
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...
s, biofuel
Biofuel
Biofuel is a type of fuel whose energy is derived from biological carbon fixation. Biofuels include fuels derived from biomass conversion, as well as solid biomass, liquid fuels and various biogases...
, and biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
, and is emitted in both anthropogenic and naturally occurring soot
Soot
Soot is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as cenospheres,...
. It consists of pure carbon in several linked forms. Black carbon warms the Earth
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
by absorbing heat in the atmosphere and by reducing albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
, the ability to reflect sunlight, when deposited on snow and ice. Black carbon stays in the atmosphere for only several days to weeks, whereas CO2 has an atmospheric lifetime of more than 100 years. The term black carbon is also used in soil sciences and geology, referring either to deposited atmospheric BC or to directly incorporated BC from vegetation fires. Especially for the tropics, BC in soils significantly contributes to fertility as it is able to adsorb important plant nutrients.
Early history
Smoke or soot was the first pollutant to be recognized as having significant environmental impact yet one of the last to be studied by the contemporary atmospheric research community. Faraday recognized that soot was composed of carbon and that it was produced by the incomplete combustion of carbon-containing fuels. Soot is composed of a complex mixture of organic compounds which are weakly absorbing in the visible spectral region and a highly absorbing black component which is variously called “elemental”, “graphitic” or “black carbon”. The term elemental carbon has been used in conjunction with thermal and wet chemical determinations and the term graphitic carbon suggests the presence of graphiteGraphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
-like micro-crystalline structures in soot as evidenced by Raman Spectroscopy
Raman spectroscopy
Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system.It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range...
of Rosen and Novakov. The term black carbon is used to imply that this soot component is primarily responsible for the absorption of visible light as shown by Yasa et al. and Rosen et al. For consistency, in this paper, we will use the term black carbon (BC) as a synonym for both the elemental and graphitic component of soot as suggested by Novakov.
The disastrous effects of coal pollution on human health and mortality in the early 1950s in London led to the UK Clean Air Act of 1956. This act led to dramatic reductions of soot concentrations in the United Kingdom which were followed by similar reductions in US cities like Pittsburg and St. Louis. These reductions were largely achieved by the decreased use of soft coal for domestic heating by switching either to “smokeless” coals or other forms of fuel, such as fuel oil and natural gas. The steady reduction of smoke pollution in the industrial cities of Europe and United States caused a shift in research emphasis away from soot emissions and the almost complete neglect of black carbon as a significant aerosol constituent, at least in the United States. In the 1970s, however, a series of studies largely conducted by the Novakov group at Lawrence Berkeley Lab substantially changed this picture and demonstrated that black carbon as well as the organic soot components continued to be a large component in urban aerosols across the United States and Europe which led to improved controls of these emissions. Obviously, in the less-developed regions of the world where there were very limited or no controls on soot emissions the air quality continued to degrade as the population increased. It was not generally realized until many years later that from the perspective of global effects the emissions from these regions were extremely important.
Most of the developments mentioned above relate to air quality in urban atmospheres. The first indications of the role of black carbon in a larger, global context came from studies of the Arctic Haze phenomena, first described by Mitchell. Black carbon was identified in the Arctic haze aerosols by Rosen et al. and in the Arctic snow by Clarke and Noone.
In general, aerosol particles can effect the radiation balance leading to a cooling or heating effect with the magnitude and sign of the temperature change largely dependent on aerosol optical properties, aerosol concentrations, and the albedo of the underlying surface. A purely scattering aerosol will reflect energy that would normally be absorbed by the earth-atmosphere system back to space and leads to a cooling effect. As one adds an absorbing component the aerosol, it can lead to a heating of the earth-atmosphere system if the reflectivity of the underlying surface is sufficiently high. Early studies of the effects of aerosols on atmospheric radiative transfer on a global scale assumed a dominantly scattering aerosol with only a small absorbing component, since this appears to be a good representation of naturally occurring aerosols. However, as discussed above, urban aerosols have a large black carbon component and if these particles can be transported on a global scale then one would expect a heating effect over surfaces with a high surface albedo like snow or ice. Furthermore, if these particles are deposited in the snow an additional heating effect would occur due to reductions in the surface albedo.
In the late 1970s and early 1980s surprisingly large ground level concentrations of black carbon were observed throughout the western Arctic by Rosen et al. and modeling studies indicated that they could lead to heating over polar ice. One of the major uncertainties in modeling the effects of the Arctic haze on the solar radiation balance was limited knowledge of the vertical distributions of black carbon. During 1983 and 1984 as part of the NOAA AGASP program, the first measurements of such distributions in the Arctic atmosphere were obtained with an aethalometer which had the capability of measuring black carbon on a real-time basis. These measurements showed substantial concentrations of black carbon found throughout the western Arctic troposphere including the North Pole. The vertical profiles showed either a strongly layered structure or an almost uniform distribution to 8 kilometers with concentrations within layers as large as those found at ground level in typical mid-latitude urban areas in the United States as shown by Rosen et al. The absorption optical depths associated with these vertical profiles were large as evidenced by a vertical profile over the Norwegian arctic where absorption optical depths of 0.023 to 0.052 were calculated respectively for external and internal mixtures of black carbon with the other aerosol components. The average optical depths over all the AGASP flights which included eight vertical profiles over the Alaskan, Canadian, and Norwegian Arctic was also large with values respectively of 0.013 and 0.030 for an external and internal mixture as shown by Rosen and Hansen. Optical depths of these magnitudes lead to a substantial change in the solar radiation balance over the highly reflecting Arctic snow surface during the March–April time frame of these measurements. This is illustrated by the calculations of Porch and McCracken and Cess, who have modeled the Arctic aerosol for an absorption optical depth of 0.021 (which is close to the average of an internal and external mixtures for the AGASP flights), under cloud-free conditions, and a surface albedo of 0.8 and obtain an increase in the surface-atmosphere energy absorption of 7 Wm−2 averaged over the day for March 15 at 70 °N. These heating effects were viewed at the time as potentially one of the major causes of Arctic warming trends as described in Archives of Dept. of Energy, Basic Energy Sciences Accomplishments.
Radiative Forcing Estimates
Estimates of black carbon’s globally averaged direct radiative forcing vary from the IPCCIntergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...
’s estimate of + 0.34 watts per square meter (W/m2) ± 0.25, to a more recent estimate by V. Ramanathan and G. Carmichael of 0.9 W/m2.
The IPCC also estimated the globally averaged snow albedo effect of black carbon at +0.1 ± 0.1 W/m2.
Based on the IPCC estimate, it would be reasonable to conclude that the combined direct and indirect snow albedo effects for black carbon rank it as the third largest contributor to globally averaged positive radiative forcing since the pre-industrial period. In comparison, the more recent direct radiative forcing estimate by Ramanathan and Carmichael would lead one to conclude that black carbon has contributed the second largest globally averaged radiative forcing after carbon dioxide (CO2), and that the radiative forcing of black carbon is “as much as 55% of the CO2 forcing and is larger than the forcing due to the other greenhouse gasses (GHGs) such as CH4, CFCs, N2O, or tropospheric ozone.”
Table 1 : Estimates of Black Carbon Radiative Forcing, by Effect
| Source | Direct Effect | Semi-Direct Effect | Dirty Clouds Effect | Snow/Ice Albedo Effect | Total |
| IPCC (2007) | 0.34 ± 0.25 | - | - | 0.1 ± 0.1 | 0.44 ± 0.35 |
| Jacobson (2001, 2004, and 2006) | 0.55 | - | 0.03 | 0.06 | 0.64 |
| Hansen (2001, 2002, 2003, 2005, and 2007) | 0.2 - 0.6 | 0.3 ± 0.3 | 0.1 ± 0.05 | 0.2 ± 0.1 | 0.8 ± 0.4 (2001) 1.0 ± 0.5 (2002) »0.7 ± 0.2 (2003) 0.8 (2005) |
| Hansen & Nazarenko (2004) | - | - | - | ~ 0.3 globally 1.0 arctic |
- |
| Ramanathan (2007) | 0.9 | - | - | 0.1 to 0.3 | 1.0 to 1.2 |
Table 2: Estimated Climate Forcings (W/m2)
| Component | IPCC (2007) | Hansen, et al. (2005) |
|---|---|---|
| CO2 | 1.66 | 1.50 |
| BC | 0.05-0.55 | 0.8 |
| CH4 | 0.48 | 0.55 |
| Tropospheric Ozone | 0.35 | 0.40 |
| Halocarbons | 0.34 | 0.30 |
| N2O | 0.16 | 0.15 |
Reduction of black carbon emissions
In its 2007 report, the IPCC estimated for the first time the direct radiative forcingRadiative forcing
In climate science, radiative forcing is generally defined as the change in net irradiance between different layers of the atmosphere. Typically, radiative forcing is quantified at the tropopause in units of watts per square meter. A positive forcing tends to warm the system, while a negative...
of black carbon from fossil fuel emissions at + 0.2 W/m2, and the radiative forcing of black carbon through its effect on the surface albedo of snow and ice at an additional + 0.1 W/m2. More recent studies and public testimony by many of the same scientists cited in the IPCC’s report estimate that emissions from black carbon are the second largest contributor to global warming after carbon dioxide emissions, and that reducing these emissions may be the fastest strategy for slowing climate change.
Since 1950, many countries have significantly reduced black carbon emissions especially from fossil fuel sources, primarily to improve public health from improved air quality, and “technology exists for a drastic reduction of fossil fuel related BC” throughout the world.
Given black carbon’s relatively short lifespan, reducing black carbon emissions would reduce warming within weeks. Because black carbon remains in the atmosphere only for a few weeks, reducing black carbon emissions may be the fastest means of slowing climate change in the near-term. Control of black carbon, particularly from fossil-fuel and biofuel sources, is very likely to be the fastest method of slowing global warming in the immediate future, according to Dr. Mark Jacobson of Stanford University, and he believes that major cuts in black carbon emissions could slow the effects of climate change for a decade or two. Reducing black carbon emissions could help keep the climate system from passing the tipping points for abrupt climate change
Abrupt climate change
An abrupt climate change occurs when the climate system is forced to transition to a new state at a rate that is determined by the climate system itself, and which is more rapid than the rate of change of the external forcing...
s, including significant sea-level rise from the melting of Greenland and/or Antarctic ice sheets.
“Emissions of black carbon are the second strongest contribution to current global warming, after carbon dioxide emissions,” according to Ramanathan
Veerabhadran Ramanathan
Veerabhadran Ramanathan is Victor Alderson Professor of Applied Ocean Sciences and director of the Center for Atmospheric Sciences at the Scripps Institution of Oceanography, University of California, San Diego. He has contributed to many areas of the atmospheric sciences including developments to...
and Carmichael. They calculate black carbon’s combined climate forcing at 1.0–1.2 W/m2, which “is as much as 55% of the CO2 forcing and is larger than the forcing due to the other [GHGs] such as CH4, CFCs, N2O or tropospheric ozone.” Other scientists estimate the total magnitude of black carbon’s forcing between + 0.2 to 1.1 W/m with varying ranges due to uncertainties.2 (See Table 1.) This compares with the IPCC’s climate forcing estimates of 1.66 W/m2 for CO2 and 0.48 W/m2 for CH4. (See Table 2.) In addition, black carbon forcing is two to three times as effective in raising temperatures in the Northern Hemisphere and the Arctic than equivalent forcing values of CO2.
Jacobson calculates that reducing fossil fuel and biofuel soot particles would eliminate about 40% of the net observed global warming. (See Figure 1.) In addition to black carbon, fossil fuel and biofuel soot contain aerosols and particulate matter that cool the planet by reflecting the sun’s radiation away from the Earth. When the aerosols and particulate matter are accounted for, fossil fuel and biofuel soot are increasing temperatures by about 0.35 °C.
Black carbon alone is estimated to have a 20-year Global Warming Potential
Global warming potential
Global-warming potential is a relative measure of how much heat a greenhouse gas traps in the atmosphere. It compares the amount of heat trapped by a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide. A GWP is calculated over a specific time...
(GWP) of 4,470, and a 100-year GWP of 1,055-2,240. Fossil fuel soot, as a result of mixing with cooling aerosols and particulate matter, has a lower 20-year GWP of 2,530, and a 100-year GWP of 840-1,280.
The Integrated Assessment of Black Carbon and Tropospheric Ozone published in 2011 by the United Nations Environment Programme and World Meteorological Organization calculates that cutting black carbon, along with tropospheric ozone and its precursor, methane, can reduce the rate of global warming by half and the rate of warming in the Arctic by 2/3s, in combination with CO2 cuts. By trimming “peak warming”, such cuts can keep current global temperature rise below 1.5˚C for 30 years and below 2˚C for 60 years, in combination with CO2 cuts. (FN: UNEP-WMO 2011.) See Table 1, on page 9 of the UNEP-WMO report. UNEP and World Meteorological Organization, INTEGRATED ASSESSMENT OF BLACK CARBON AND TROPOSPHERIC OZONE, SUMMARY FOR DECISION MAKERS (June 2011).
The reduction of CO2 as well as SLCFs could keep global temperature rise under 1.5˚C through 2030, and below 2C through 2070, assuming CO2 is also cut.UNEP and World Meteorological Organization, INTEGRATED ASSESSMENT OF BLACK CARBON AND TROPOSPHERIC OZONE, SUMMARY FOR DECISION MAKERS (June 2011). Please see the graph on page 12 of the UNEP-WMO report. UNEP and World Meteorological Organization, INTEGRATED ASSESSMENT OF BLACK CARBON AND TROPOSPHERIC OZONE, SUMMARY FOR DECISION MAKERS (June 2011).
Black carbons effect on Arctic ice and Himalayan glaciers
According to the , “the presence of black carbon over highly reflective surfaces, such as snow and ice, or clouds, may cause a significant positive radiative forcing.” The IPCC also notes that emissions from biomassBiomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
burning, which usually have a negative forcing, have a positive forcing over snow fields in areas such as the Himalayas.
According to Dr. Charles Zender of the University of California, Irvine
University of California, Irvine
The University of California, Irvine , founded in 1965, is one of the ten campuses of the University of California, located in Irvine, California, USA...
, black carbon is a significant contributor to Arctic ice-melt, and reducing such emissions may be “the most efficient way to mitigate Arctic warming that we know of”. The “climate forcing due to snow/ice albedo change is of the order of 1.0 W/m2 at middle- and high-latitude land areas in the Northern Hemisphere and over the Arctic Ocean.” The “soot effect on snow albedo may be responsible for a quarter of observed global warming.” “Soot deposition increases surface melt on ice masses, and the meltwater spurs multiple radiative and dynamical feedback processes that accelerate ice disintegration,” according to NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
scientists Dr. James Hansen and Dr. Larissa Nazarenko. As a result of this feedback process, “BC on snow warms the planet about three times more than an equal forcing of CO2.” When black carbon concentrations in the Arctic increase during the winter and spring due to Arctic Haze
Arctic Haze
Arctic haze is the phenomenon of a visible reddish-brown haze in the atmosphere at high latitudes in the Arctic due to air pollution. A major distinguishing factor of Arctic haze is the ability of its chemical ingredients to persist in the atmosphere for an extended period of time compared to other...
, surface temperatures increase by 0.5 °C. Black carbon emissions also significantly contribute to Arctic ice-melt, which is critical because “nothing in climate is more aptly described as a ‘tipping point’ than the 0 °C boundary that separates frozen from liquid water—the bright, reflective snow and ice from the dark, heat-absorbing ocean.”
Black carbon emissions from northern Eurasia, North America, and Asia have the greatest absolute impact on Arctic warming. However, black carbon emissions actually occurring within the Arctic have a disproportionately larger impact per particle on Arctic warming than emissions originating elsewhere. As Arctic ice melts and shipping activity increases, emissions originating within the Arctic are expected to rise.
In some regions, such as the Himalayas, the impact of black carbon on melting snowpack and glaciers may be equal to that of CO2. Warmer air resulting from the presence of black carbon in South and East Asia over the Himalayas contributes to a warming of approximately 0.6 °C. An “analysis of temperature trends on the Tibetan side of the Himalayas reveals warming in excess of 1 °C.” BC record based on a shallow ice core drilled from the East Rongbuk glacier showed a dramatic increasing trend of BC concentrations in the ice stratigraphy since the 1990s, and simulated average radiative forcing caused by BC was nearly 2 W m−2 in 2002. This large warming trend is the proposed causal factor for the accelerating retreat of Himalayan glaciers, which threatens fresh water supplies and food security in China and India.
Major emitters of black carbon
By Region: Developed countries were once the primary source of black carbon emissions, but this began to change in the 1950s with the adoption of pollution control technologies in those countries. Whereas the U.S. emits about 21% of the world’s CO2, it emits 6.1% of the world’s soot. The European Union and United States might further reduce their black carbon emissions by accelerating implementation of black carbon regulations that currently take effect in 2015 or 2020 and by supporting the adoption of pending International Maritime Organization (IMO) regulations. Existing regulations also could be expanded to increase the use of clean diesel and clean coal technologiesClean coal technology
Clean coal technology is a collection of technologies being developed to reduce the environmental impact of coal energy generation. When coal is used as a fuel source, the gaseous emmissions generated by the thermal decomposition of the coal, include sulphur dioxide, nitrogen dioxide, carbon...
and to develop second-generation technologies.
Today, the majority of black carbon emissions are from developing countries and this trend is expected to increase. The largest sources of black carbon are Asia, Latin America, and Africa. China and India together account for 25-35% of global black carbon emissions Black carbon emissions from China doubled from 2000 to 2006. Existing and well-tested technologies used by developed countries, such as clean diesel and clean coal, could be transferred to developing countries to reduce their emissions
Black carbon emissions “peak close to major source regions and give rise to regional hotspots of black carbon—induced atmospheric solar heating.” Such hotspots include “the Indo-Gangetic plains in South Asia; eastern China; most of Southeast Asia including Indonesia; regions of Africa between sub-Sahara and South Africa; Mexico and Central America; and most of Brazil and Peru in South America.”. Approximately three billion people live in these hotspots.
By Source: Approximately 20% of black carbon is emitted from burning biofuels, 40% from fossil fuels, and 40% from open biomass burning, according to Ramanathan. Similarly, Dr. Tami Bond of the University of Illinois, Urbana Champaign, estimates the sources of black carbon emissions as follows:
- 42% Open biomass burning (forest and savanna burning)
- 18% Residential biofuel burned with traditional technologies
- 14% Diesel engines for transportation
- 10% Diesel engines for industrial use
- 10% Industrial processes and power generation, usually from smaller boilers
- 6% Residential coal burned with traditional technologies
Black carbon sources vary by region. For example, the majority of soot emissions in South Asia are due to biofuel cooking, whereas in East Asia, coal combustion for residential and industrial uses plays a larger role. In Western Europe, traffic seems to be the most important source since high concentrations coincide with proximity to major roads or participation to (motorized) traffic.
Fossil fuel and biofuel soot have significantly greater amounts of black carbon than climate-cooling aerosols and particulate matter, making reductions of these sources particularly powerful mitigation strategies. For example, emissions from the diesel engines and marine vessels contain higher levels of black carbon compared to other sources. Regulating black carbon emissions from diesel engines and marine vessels therefore presents a significant opportunity to reduce black carbon’s global warming impact.
Biomass burning emits greater amounts of climate-cooling aerosol
Aerosol
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...
s and particulate matter than black carbon, resulting in short-term cooling. However, over the long-term, biomass burning may cause a net warming when CO2 emissions and deforestation are considered. Reducing biomass emissions would therefore reduce global warming in the long-term and provide co-benefits of reduced air pollution, CO2 emissions, and deforestation. Johannes Lehmann of Cornell University estimates that by switching to slash-and-char from slash-and-burn agriculture, which turns biomass into ash using open fires that release black carbon and GHGs, 12% of anthropogenic carbon emissions caused by land use change could be reduced annually, which is approximately 0.66 Gt CO2-eq. per year, or 2% of all annual global CO2-eq emissions.
Technology for reducing black carbon emissions
Ramanathan notes that “developed nations have reduced their black carbon emissions from fossil fuel sources by a factor of 5 or more since 1950. Thus, the technology exists for a drastic reduction of fossil fuel related black carbon.”Jacobson believes that “[g]iven proper conditions and incentives, [soot] polluting technologies can be quickly phased out. In some small-scale applications (such as domestic cooking in developing countries), health and convenience will drive such a transition when affordable, reliable alternatives are available. For other sources, such as vehicles or coal boilers, regulatory approaches may be required to nudge either the transition to existing technology or the development of new technology.”
Hansen states that “technology is within reach that could greatly reduce soot, restoring snow albedo to near pristine values, while having multiple other benefits for climate, human health, agricultural productivity, and environmental aesthetics. Already soot emissions from coal are decreasing in many regions with transition from small users to power plants with scrubbers.”
Jacobson suggests converting “[U.S.] vehicles from fossil fuel to electric, plug-in-hybrid, or hydrogen fuel cell vehicles, where the electricity or hydrogen is produced by a renewable energy source, such as wind, solar, geothermal, hydroelectric, wave, or tidal power. Such a conversion would eliminate 160 Gg/yr (24%) of U.S. (or 1.5% of world) fossil-fuel soot and about 26% of U.S. (or 5.5% of world) carbon dioxide.” According to Jacobson’s estimates, this proposal would reduce soot and CO2 emissions by 1.63 GtCO2–eq. per year. He notes, however, “that the elimination of hydrocarbons and nitrogen oxides would also eliminate some cooling particles, reducing the net benefit by at most, half, but improving human health,” a substantial reduction for one policy in one country.
For diesel vehicles in particular there are a several effective technologies available. Newer, more efficient diesel particulate filter
Diesel Particulate Filter
A diesel particulate filter is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine. Wall-flow diesel particulate filters usually remove 85% or more of the soot, and under certain conditions can attain soot removal efficiencies of close to 100%...
s (DPFs), or traps, can eliminate over 90% of black carbon emissions, but these devices require ultra-low sulfur diesel
Ultra-low sulfur diesel
Ultra-low-sulfur diesel is a term used to describe diesel fuel with substantially lowered sulfur content...
fuel (ULSD). To ensure compliance with new particulate rules for new on-road and non-road vehicles in the U.S., the EPA first required a nationwide shift to ULSD, which allowed DPFs to be used in diesel vehicles in order to meet the standards. Because of recent EPA regulations, black carbon emissions from diesel vehicles are expected to decline about 70 percent from 2001 to 2020.” Overall, “BC emissions in the United States are projected to decline by 42 percent from 2001 to 2020. By the time the full fleet is subject to these rules, EPA estimates that over 239,000 tons of particulate matter will be reduced annually. Outside of the US diesel oxidation catalysts are often available and DPFs will become available as ULSD is more widely commercialized.
Another technology for reducing black carbon emissions from diesel engines is to shift fuels to compressed natural gas. In New Delhi
New Delhi
New Delhi is the capital city of India. It serves as the centre of the Government of India and the Government of the National Capital Territory of Delhi. New Delhi is situated within the metropolis of Delhi. It is one of the nine districts of Delhi Union Territory. The total area of the city is...
, India, the supreme court
Supreme court
A supreme court is the highest court within the hierarchy of many legal jurisdictions. Other descriptions for such courts include court of last resort, instance court, judgment court, high court, or apex court...
ordered shift to compressed natural gas for all public transport vehicles, including buses, taxis, and rickshaws, resulted in a climate benefit, “largely because of the dramatic reduction of black carbon emissions from the diesel bus engines.” Overall, the fuel switch for the vehicles reduced black carbon emissions enough to produce a 10 percent net reduction in CO2-eq., and perhaps as much as 30 percent. The main gains were from diesel bus engines whose CO2-eq. emissions were reduced 20 percent. According to a study examining these emissions reductions, “there is a significant potential for emissions reductions through the [UNFCCC] Clean Development for such fuel switching projects.”
Technologies are also in development to reduce some of the 133,000 metric tons of particulate matter emitted each year from ships. Ocean vessels use diesel engines, and particulate filters similar to those in use for land vehicles are now being tested on them. As with current particulate filters these too would require the ships to use ULSD, but if comparable emissions reductions are attainable, up to 120,000 metric tons of particulate emissions could be eliminated each year from international shipping. That is, if particulate filters could be shown reduce black carbon emissions 90 percent from ships as they do for land vehicles, 120,000 metric tons of today’s 133,000 metric tons of emissions would be prevented. Other efforts can reduce the amount of black carbon emissions from ships simply by decreasing the amount of fuel the ships use. By traveling at slower speeds or by using shore side electricity when at port instead of running the ship’s diesel engines for electric power, ships can save fuel and reduce emissions.
Reynolds and Kandlikar estimate that the shift to compressed natural gas
Compressed natural gas
Compressed natural gas is a fossil fuel substitute for gasoline , diesel, or propane/LPG. Although its combustion does produce greenhouse gases, it is a more environmentally clean alternative to those fuels, and it is much safer than other fuels in the event of a spill...
for public transport in New Delhi ordered by the Supreme Court reduced climate emissions by 10 to 30%.
Ramanathan estimates that “providing alternative energy-efficient and smoke-free cookers and introducing transferring technology for reducing soot emissions from coal combustion in small industries could have major impacts on the radiative forcing due to soot.” Specifically, the impact of replacing biofuel cooking with black carbon-free cookers (solar, bio, and natural gas) in South and East Asia is dramatic: over South Asia, a 70 to 80% reduction in black carbon heating; and in East Asia, a 20 to 40% reduction.”
Public health
The public health benefits of reduction in the amount of sootSoot
Soot is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as cenospheres,...
and other particulate matter has been recognized for years. However high concentrations persist in industrializing areas in Asia and in urban areas in the West such as Chicago
Chicago
Chicago is the largest city in the US state of Illinois. With nearly 2.7 million residents, it is the most populous city in the Midwestern United States and the third most populous in the US, after New York City and Los Angeles...
. The WHO estimates that air pollution causes nearly two million premature deaths per year. By reducing black carbon, a primary component of fine particulate matter, the health risks from air pollution will decline. In fact, public health concerns have given rise to leading to many efforts to reduce such emissions, for example, from diesel vehicles and cooking stoves.
Regulation of black carbon emissions
Many countries have existing national laws to regulating black carbon emissions, including laws that address particulate emissions. Some examples include:- banning or regulating slash-and-burn clearing of forests and savannas;
- requiring shore-based power/electrification of ships at port, regulating idling at terminals, and mandating fuel standards for ships seeking to dock at port;
- requiring regular vehicle emissions tests, retirement, or retrofitting (e.g. adding particulate traps), including penalties for failing to meet air quality emissions standards, and heightened penalties for on-the-road “super-emitting” vehicles;
- banning or regulating the sale of certain fuels and/or requiring the use of cleaner fuels for certain uses;
- limiting the use of chimneys and other forms of biomass burning in urban and non-urban areas;
- requiring permits to operate industrial, power generating, and oil refining facilities and periodic permit renewal and/or modification of equipment; and
- requiring filtering technology and high-temperature combustion (e.g. super-critical coal) for existing power generation plants, and regulating annual emissions from power generation plants.
The International Network for Environmental Compliance & Enforcement issued a Climate Compliance Alert on Black Carbon in 2008 which cited reduction of carbon black as a cost-effective way to reduce a major cause of global warming.
Black carbon and soil fertility
Up to 30 % of the total carbon stored in soils is contributed by black carbon. Especially for tropical soils BC serves as a reservoir for nutrients. Experiments showed that soils without high amounts of black carbon are significantly less fertile than soils that contain black carbon. An example for this increased soil fertility are the Terra pretaTerra preta
Terra preta is a type of very dark, fertile anthropogenic soil found in the Amazon Basin. Terra preta owes its name to its very high charcoal content, and was indeed made by adding a mixture of charcoal, bone, and manure to the otherwise relatively infertile Amazonian soil, and stays there for...
soils of central Amazonia, which are presumably human-made by pre-Columbian native populations. Terra Preta soils have on average three times higher soil organic matter (SOM) content, higher nutrient levels and a better nutrient retention capacity than surrounding infertile soils. In this context, the slash and burn
Slash and burn
Slash-and-burn is an agricultural technique which involves cutting and burning of forests or woodlands to create fields. It is subsistence agriculture that typically uses little technology or other tools. It is typically part of shifting cultivation agriculture, and of transhumance livestock...
agricultural practice used in tropical regions does not only enhance productivity by releasing nutrients from the burned vegetation but also by adding black carbon to the soil. Nonetheless, for a sustainable management, a slash-and-char
Slash-and-char
Slash-and-char is an alternative to slash-and-burn that has a lesser effect on the environment. It is the practice of charring the biomass resulting from the slashing, instead of burning it as in the slash-and-burn practice....
practice would be better in order to prevent high emissions of CO2 and volatile black carbon. Furthermore, the positive effects of this type of agriculture are counteracted if used for large patches so that soil erosion is not anymore prevented by the vegetation.
See also
- Asian brown cloudAsian brown cloudThe Asian brown cloud is a layer of air pollution that covers parts of South Asia, namely the northern Indian Ocean, India, and Pakistan. Viewed from satellite photos, the cloud appears as a giant brown stain hanging in the air over much of South Asia and the Indian Ocean every year between January...
- Carbon blackCarbon blackCarbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its...
- Global dimmingGlobal dimmingGlobal dimming is the gradual reduction in the amount of global direct irradiance at the Earth's surface that was observed for several decades after the start of systematic measurements in the 1950s. The effect varies by location, but worldwide it has been estimated to be of the order of a 4%...
- Peat bog
- Slash and burnSlash and burnSlash-and-burn is an agricultural technique which involves cutting and burning of forests or woodlands to create fields. It is subsistence agriculture that typically uses little technology or other tools. It is typically part of shifting cultivation agriculture, and of transhumance livestock...
External links
- Why Black Carbon and Ozone Also Matter, in September/October 2009 Foreign AffairsForeign AffairsForeign Affairs is an American magazine and website on international relations and U.S. foreign policy published since 1922 by the Council on Foreign Relations six times annually...
with Veerabhadran RamanathanVeerabhadran RamanathanVeerabhadran Ramanathan is Victor Alderson Professor of Applied Ocean Sciences and director of the Center for Atmospheric Sciences at the Scripps Institution of Oceanography, University of California, San Diego. He has contributed to many areas of the atmospheric sciences including developments to...
and Jessica Seddon Wallack.