Mitigating Black Carbon
What are we doing about black carbon?
BC's short atmospheric lifetime (days to weeks), combined with its strong warming potential, means that targeted strategies to reduce BC emissions can be expected to provide climate benefits within the next several decades.
In evaluating mitigation options, it is important to remember that BC is emitted with other particles and gases, such as sulfur dioxide (SO2), nitrogen oxides (NOx), OC and CO2. Some of these co-emitted pollutants exert a cooling effect on climate. This has to be taken into account in evaluating the net effect of BC mitigation options.
The net climate effect of reducing emissions from BC sources on climate depends partly on the relative balance between BC and other co-emitted pollutants. Some combustion sources emit more BC than others. For example, the particles emitted by mobile diesel engines are about 75% BC, while particle emissions from biomass burning are dominated by OC. Reductions in emissions from BC-rich sources have the greatest likelihood of providing climate benefits.
Mitigation actions for BC will produce different climate results depending on the region, season, and sources in the area where emissions reductions occur.
Key U.S. Programs
U.S. mobile source BC emissions are projected to decline by 86% by 2030 due to regulations already promulgated.
BC emissions from mobile diesel engines (including on-road, nonroad, locomotive, and commercial marine engines) in the United States are being controlled through two primary mechanisms:
- emissions standards for new engines, including requirements resulting in use of diesel particulate filters (DPFs) in conjunction with ultra low sulfur diesel fuel; and
- retrofit programs for in-use mobile diesel engines, such as EPA’s National Clean Diesel Campaign and the SmartWay Transport Partnership Program.
New engine requirements have resulted in a 32% reduction in BC emissions from U.S. mobile sources between 1990 and 2005. As vehicles and engines meeting new regulations are phased into the fleet, a further 86% reduction in BC emissions from mobile sources is projected from 2005 to 2030, leading to a total decline of 90% in BC emissions between 1990 and 2030. Such regulations have been effective in reducing emissions of BC from on-road vehicles (mainly diesel trucks), and nonroad diesel engines, locomotives, and commercial marine vessels. Read more details on EPA’s regulatory requirements for mobile sources
Most of the mobile source reductions are concentrated in the diesel fleet, which is responsible for 93% of mobile source BC emissions. Reductions can be achieved via application of diesel particulate filters (DPFs) combined with ultra low sulfur diesel fuel. DPFs typically eliminate more than 90% of diesel PM and can reduce BC by as much as 99%.
Diesel retrofits for in-use engines can achieve additional BC emissions reductions to complement new engine regulations. There are currently available, cost-effective diesel retrofit strategies that can reduce harmful emissions from in-use engines substantially. EPA’s National Clean Diesel Campaign has provided grant funds to support diesel engine retrofits, repowers, and replacements.
Regulations limiting direct emissions of particles (including BC) affect more than 40 categories of industrial sources in the United States, including coke ovens, cement plants, industrial boilers, and stationary diesel engines. While these standards and emission limits are not targeted toward BC emissions specifically, they are clearly having a positive impact on reducing these emissions.
Analysis of historical data indicates that controls on industrial sources, combined with improvements in technology and broader deployment of cleaner fuels such as natural gas, have helped reduce U.S. black carbon emissions more than 70% since the early 1900s.
Available control technologies and strategies include direct PM2.5 reduction technologies such as fabric filters (baghouses), electrostatic precipitators (ESPs), and diesel particulate filters (DPFs).
Emissions of all pollutants from residential wood combustion (RWC) are currently being evaluated as part of EPA’s ongoing review of emissions standards for residential wood heaters, including hydronic heaters, woodstoves, and furnaces.
Mitigation options include providing alternatives to wood, replacing inefficient units or retrofitting existing units. Visit EPA's Burn Wise website for more information.
Open Biomass Burning
Open biomass burning, including both prescribed fires and wildfires, represents a potentially large but less certain portion of the U.S. BC inventory. These sources emit much larger amounts of OC compared to BC. The percent of land area affected by different types of burning is uncertain, as are emissions estimates. Wildfires account for approximately 68% of BC emissions from open biomass burning in the United States, although this varies significantly from year to year.
Appropriate mitigation measures depend on the timing and location of burning, resource management objectives, vegetation type, and available resources. For wildfires, expanding domestic fire prevention efforts may help to reduce BC emissions.
Climate and Clean Air Coalition: On February 16, 2012, Secretary of State Hillary Rodham Clinton announced the Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants, a new global initiative to seize the opportunity of realizing concrete benefits on climate, health, food and energy resulting from reducing short-lived climate pollutants. The coalition will focus efforts on reducing black carbon, hydrofluorocarbons (HFCs), and methane. The founding coalition partners are Bangladesh, Canada, Ghana, Mexico, Sweden, and the United States, together with the UN Environment Programme. For more information, see: http://www.state.gov/r/pa/prs/ps/2012/02/184055.htm.
Long Range Trans-boundary Air Pollution: An Ad Hoc Expert Group on Black Carbon was initiated to assess the available information on black carbon and articulate a rationale for addressing near-term and regional/Arctic climate change impacts of air pollution along with impacts on human health and ecosystems. The Group concluded that there is general consensus that mitigation of BC will lead to positive regional impacts by reducing BC deposition in areas with snow and ice. There is also general consensus that reducing primary PM will benefit public health. Less certain are the direction and magnitude of the global radiative forcing associated with BC.
You will need Adobe Reader to view the Adobe PDF files on this page. See EPA's PDF page to learn more.
View the complete report from the UNECE (PDF) (25pp, 208k)
Arctic Council: Task Force on Short Lived Climate Forcers: An Assessment of Emissions and Mitigation Options for Black Carbon for the Arctic Council (PDF) (173pp, 4.5 MB) – This report compiles and compares national and global BC emissions inventories, examines emission trends and projections, synthesizes existing policies and programs, and identifies additional emission BC mitigation opportunities for Arctic Council Nations.
United Nations Environment Program:
- Integrated Assessment of Black Carbon and Tropospheric Ozone – The United Nations Environment Program initiated an assessment designed to provide an interface between knowledge and action, science and policy, and to provide a scientifically credible basis for informed decision-making regarding short lived climate forcers.
- Towards an Action Plan for Near-term Climate Protection and Clean Air Benefits (PDF) - This document is designed to inform decision makers about additional opportunities to slow the observed rate of climate change and at the same time achieve air quality benefits over the next two to four decades.
- Near-term Climate Protection and Clean Air Benefits: Actions for Controlling Short-Lived Climate Forcers (PDF) - This report addresses the mitigation of short-lived climate forcers (SLCFs) and its key role in air pollution reduction, climate protection and sustainable development.
The International Maritime Organization Marine Environment Protection Committee
The committee agreed to a work plan on addressing the impact in the Arctic of black carbon emissions from ships and instructed the Sub-Committee on Bulk Liquids and Gases (BLG) to: develop a definition for black carbon emissions from international shipping; consider measurement methods for black carbon and identify the most appropriate method for measuring black carbon emissions from international shipping; investigate appropriate control measures to reduce the impacts of black carbon emissions from international shipping in the Arctic; and submit a final report to MEPC 65 in 2014.
Global Alliance for Clean Cookstoves: