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Climate Change, Black Carbon and Clean Diesel

Thanks to the use of ultra-low sulfur diesel fuel, more efficient engines and more effective emissions control technologies, new U.S. clean diesel trucks and buses have significantly lower particulate matter emissions and 99 percent less black carbon emissions than those manufactured before 2004.

Over the last few years there has been growing attention to black carbon and its potential contribution to global warming. The scientific and policymaking communities acknowledge that black carbon plays a role in climate change by heating our planet and altering precipitation patterns. Diesel engines are one of many sources of black carbon emissions. 

Thanks to changes in domestic fuel composition along with advances in engine design and emissions control technology, black carbon emissions have been virtually eliminated from new diesel vehicles and equipment in the U.S. Regulations in place for heavy-duty truck engines beginning in model year 2007 and further tightened rules for model year 2010 engines have required a 98 percent reduction in particulate matter emissions – a leading contributor to black carbon. Other countries have taken note of the advances made in the U.S. and are expanding the introduction of clean diesel technologies in part to reduce black carbon emissions. These clean diesel advances are strongly supported by the United Nations Environment Programme which is advocating their adoption in countries around the world.

We have compiled several definitions, statistics and facts about black carbon and clean diesel technology in order to promote greater understanding about the subject and the shrinking contribution of U.S. diesel emissions to the global black carbon inventory.

What is black carbon?

Black carbon, often equated with elemental carbon, is a component of particulate matter, or soot, produced from the incomplete combustion of fossil fuel, biofuels and biomass.

What are the primary sources of black carbon?

The main sources of black carbon are: 

Globally, diesel engines accounts for 25 percent of all black carbon emissions. In the U.S, the transportation sector accounts for roughly 53 percent of black carbon emissions and diesel engines account for over 90 percent of the transportation sector’s share.

Global Sources of Black Carbon

What is the geographic distribution of black carbon emissions on a global basis?

East Asia, predominantly China, are the largest emitters of black carbon, with the greatest amount of emissions coming from the residential and industrial sectors. The U.S. produces approximately five percent of the world’s fossil-fuel and biofuel soot.

What effect is black carbon believed to have on climate change?

Black carbon is thought by many scientists to have a net warming effect on the earth by absorbing light and turning that energy into heat. It also is believed to darken the surfaces of ice and snow when deposited on them, reducing their ability to reflect light while increasing heat absorption and melting. Black carbon is also understood to contrite to climate change by altering precipitation patterns and cloud formation.

Global Black Carbon Emissions

How does black carbon compare to CO2?

Unlike CO2 which remains in the atmosphere for decades, black carbon remains in the atmosphere for days or weeks and washes out of the atmosphere within a few thousand kilometers of its emission source. Particular concern has been raised about the Arctic, where melting of ice and snow has been accelerated by deposition of wind-blown soot particles. While studies continue to determine the most likely sources affecting the Arctic, the latest research suggests that biomass burning, particularly from Eurasia, is the dominant source of black carbon in Arctic snow.

Are U.S. black carbon emissions rising or falling?

U.S. transportation related black carbon emissions are projected to decline by almost 70 percent between 2005 and 2030. This impressive emissions reduction is achieved by technologies designed to meet regulations already promulgated concerning particulate matter emissions on heavy-duty trucks and off-road equipment such as construction, agricultural and mining equipment.

U.S. Emission of PM 2.5

How does clean diesel technology reduce black carbon?

Thanks to the use of ultra-low sulfur diesel (ULSD) fuel, more efficient engines and more effective emissions control technologies, new clean diesel trucks and buses in the U.S. result in significantly lower particulate matter emissions and 99 percent less black carbon emissions than those manufactured before 2004. Today’s new diesel cars and trucks have advanced filters that trap particulate matter.

The latest clean diesel technology is also standard in many off-road diesel vehicles and equipment such as construction equipment, agricultural vehicles, stationary generators, locomotives and marine vessels designed to meet strict particulate matter and other emissions regulated by the Tier 4 standards established by the U.S. Environmental Protection Agency (EPA). In addition, many older versions of these vehicles and machines can be retrofitted to trap or reduce particulate matter emissions anywhere from 20-90 percent. 

Diesel Particulate Filters

What has the U.S. done to reduce its black carbon emissions form diesel sources?

Over the last decade, the EPA has promulgated several new standards for diesel fuel quality and diesel engine emissions including the introduction of ultra-low sulfur diesel (ULSD) fuel in 2006, the on-highway emission rule for model year 2007 and 2010 trucks and Tier 4 rules for most off-road equipment.

In addition to regulations for new diesel engines, EPA provides grant funding through the National Clean Diesel Funding Assistance Program to help reduce emissions from existing diesel engines through a variety of strategies. Clean diesel funding appropriated between 2008 and 2010 retrofitted, repowered or replaced over 52,000 older engines found in a wide variety of applications from school buses, long haul trucks, construction equipment and even ferryboats. Diesel particulate filters were among the most popular technology choice among vehicle and equipment owners. Retrofit funding provided between 2008 and 2010 resulted in over 12,000 tons of particulate matter emissions eliminated.

Other funds for retrofitting existing diesel vehicles are available through the Federal Highway Administration’s Congestion Mitigation and Air Quality program, national and state supplemental environmental projects and several state government sponsored programs.

Have other countries adopted similar measures to reduce black carbon emissions from diesel sources?

The impressive and dramatic reduction in black carbon from diesel sources in the U.S. has not gone unnoticed by other countries. Most developed economies including Europe, Canada and Japan adopted low sulfur diesel fuel standards along with diesel engine emission rules. The United Nation’s Environment Programme is encouraging developing economies to introduce clean diesel technologies. The first step in the process of introducing clean diesel technologies rests on the availability of low sulfur diesel fuel and the group is working to encourage the production and distribution of low sulfur diesel fuel with a sulfur content of at most 50 parts per million in many developing economies. Other nations with clean fuel standards have adopted modern engine emissions standards – either U.S. or European Union rules – including Argentine, Brazil, Mexico, Chile, Peru, India, Korea, Singapore, Thailand, Russia and Turkey. Yet, diesel emissions are smaller source of black carbon in these emerging economies than other sources including biomass burning for heat, cooking and industrial processes. The United Nations is working to introduce technologies and change practices to reduce these sources of black carbon through cleaner cookstoves and industrial kilns.

Can black carbon emission reductions mitigate climate change?

Black carbon is known to play a role in global warming and climate change and the reduction of black carbon can help reduce the impact of a warming planet. The United Nations estimates that efforts to control all sources of black carbon emissions may ease the rise in global temperatures by 0.5 degrees Celsius. Global warming mitigation through black carbon reduction is regional with the largest temperature reduction occurring in the Artic, Antarctic and Himalayan regions. The World Bank estimates that roughly 16 million tons of crop losses can be reversed due to global controls on diesel source of black carbon.

Regional Temperature Reductions from Black Carbon Control Measure

In the U.S., the state of California implemented measures to control black carbon emissions since the 1960s. Researchers estimate that diesel particulate matter emission reductions achieved in California since the 1980s is equivalent to reducing carbon emissions by 21 million metric tons and is roughly equivalent to five percent of all carbon dioxide emissions.


The introduction of clean ULSD fuel and advanced engine emissions control systems and filters will have dramatically reduced particulate emissions from new diesel engines in all categories. Today the U.S. is estimated to account for about five percent of all black carbon emissions, and is expected to account for only two percent of global on-road vehicle emissions by 2020 as a result of these technology improvements. Modernizing and upgrading existing diesel engines with particulate control technology has proven effective for many applications with the use of clean diesel fuel.


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