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Federal agencies should require all diesel-engine vehicles on US Govt funded projects to have black carbon filters, chargeable to project




Black carbon (BC), or “soot”, is the second most powerful cause of global warming, after carbon dioxide. The benefits of reducing BC emissions would be realized almost immediately. The atmospheric lifetime of BC is about five days, while that of CO2 extends beyond a century. We propose that the Department of Transportation, EPA, and other agencies providing funds for construction of highways, sewage and waste disposal facilities, etc. require that all diesel engines have and maintain working BC filters, chargeable to relevant the federal funded contract. 

Most BC emissions are coming from older diesel engines that continue to be used for decades. Although the cost of adding a BC filter is up to a few tens of thousands of dollars, they are not being installed because they are not required and those operating these engines typically don't have the wherewithal to install the filters.

Cutting emissions of BC would lead to a near-immediate reduction in warming and, virtually immediately, start to slow the rate of increase of radiative forcing and global average temperature. The most pronounced effect would be in the region where the emissions are cut.  However, because of the extremely small size of BC particles they can be transported over thousands of miles, so the reduced warming effect would be more extensive. The reduced warming effect would also disproportionately benefit snowy and icy areas, such as the Arctic and mountain snow-packs, because deposited black carbon deposited there decreases reflectivity, thus causing increased solar absorption.

For other emission categories, such as BC from open burning or cooking fires, the BC is co-emitted with other pollutants that may have a cooling effect. Diesel black carbon, however, has minimal co-pollutants, the lowest co-emissions of all major BC sources. Thus, reducing BC emissions from diesels would have a powerful, immediate, and undiluted effect.

There would also be immense human health benefits. 


Category of the action

Mitigation - What U.S. Federal Agencies can do to mitigate climate change

What actions do you propose?


Diesel engine exhaust, which includes not only particles of black carbon (BC), but some gases, is classified by the International Agency for Research on Cancer (IARC) as a known human carcinogen. The chair of the IARC stated that “The scientific evidence was compelling and the Working Group’s conclusion was unanimous: diesel exhaust causes lung cancer in humans.”

Particles of BC emitted by diesel engines are exceedingly fine, allowing them to be carried deep into the lung. Particles of their size are consistently and independently related to the most serious adverse health effects, including cardiopulmonary mortality.

Even though it is second only to carbon dioxide as a cause of global warming, BC is not classified as a “greenhouse gas” under the Kyoto Protocol or accounted for in the EPA compilation of emissions of greenhouse gases. BC also is not included in other international, regional or state agreements designed to reduce global warming.

Controls on BC emissions are generally undertaken at the national level, if at all. Even then, emissions to date have been regulated only for the purpose of protecting health, not reducing global warming. While there has been increasing scientific attention to the warming caused by BC, agreements limiting emissions have almost completely ignored the emerging scientific results.

Diesel engines contributed about 20 percent of global BC emissions in 2000.  Unregulated diesel engines emit nearly five times as much black carbon as allowed under current tailpipe limits adopted by the U.S., Europe and other developed nations.

The turnover of trucks and off-road equipment (e.g. forming tractors, bull dozers, etc.) is slow.  In the absence of programs designed to force retirement of existing trucks, the mean fleet age in three major California ports was 12.7 years.  Over-the-road trucks can easily log millions of miles during their service lives.

In-use programs, such as mandatory exhaust trap retrofits, have been adopted in a very few areas.  Where adopted they succeed in substantially reducing emissions. For example, an accelerated diesel particle filter retrofit and truck replacement program at the Port of Oakland in California achieved a 54 ± 11 percent reduction in the fleet-average BC emissions.

The Administration has a program to reduce emissions from new engines. The requirements should be stringent, and they have been.  Because of new vehicle regulations, emissions of diesel particulate in the United States, Japan, and Canada decreased by 91 percent, 77 percent, and 90 percent, respectively, from 1976 to 2006.

But with the exception of California ports, virtually no action is being taken at the national or state levels to reduce emissions of black carbon from older diesel engines.  These emissions can and need to be reduced, both to limit warming and to achieve important health benefits.

Diesel particulate filters can be installed on existing engines. They sharply reduce black carbon emissions, are not particularly expensive.  For a new heavy-duty truck equipped with a diesel particulate filter in model year 2007, the first year they were required in the United States, manufacturers increased sticker prices by $5,000 to $10,000. However, those operating unfiltered engines typically lack the wherewithal to install the filters. For this reason, they are not required. The Administration does have a voluntary program to assist in installation of the filters on trucks and perhaps other sources, but additional efforts are needed.

Under current practice, the cost of constructing of federal projects ends up being artificially subsidized (given the costs to public health, the environment and climate) because the retrofit of diesel particulate traps is not required. To improve air quality, reduce deaths of those living near highways and minimize future warming caused by emissions of black carbon from existing diesel engines in the United States, we propose that this subsidy of diesel engines be eliminated.


We also propose that the expense of retrofitting diesel engines be borne by the project and those who benefit from the project. In the Federal aid highway program, for example, the President could simply determine that the expenses of a retrofit, like those of planting flowers, be an “eligible project cost.”

Further, we propose that all other agencies providing funding for federal projects  require that all diesel engines used on such projects install and maintain working black carbon filters and that the charge for these can be made to the federally-funded contract.


Who will take these actions?


The key action is for the President to require this step be taken by the agencies.

Where will these actions be taken?


These actions would be taken in the US. One would hope that these actions would be echoed in other nations and be easier to accomplish as a result of the increase in demand and technological improvement that would be generated by this action.

How much will emissions be reduced or sequestered vs. business as usual levels?


A substantial share of US black carbon emissions come from off-road and other uses of diesel engines that have a very slow turnover, resulting in emissions only being controlled by equipment replacement over several-decade cycle times. The black carbon control efforts to date, while to be praised, are not reducing overall black carbon emissions nearly fast enough.

Some actions have been taken on a voluntary basis through an EPA program and there are efforts in polluted areas to reduce contributions from trucks by, for example in the LA Basin, requiring that filters be used on vehicles servicing the region's port facilities, etc. These emission reductions can be accomplished at quite low cost--the problem is that voluntary actions are not enough and funding is insufficient. Federal funding  is involved in a very large number of projects across the country, so having the Federal Government require the use of black carbon filters on all projects would force greater cost-effective action.

What are other key benefits?


Black carbon emissions are a health hazard, reduce visibility, and contribute a strong warming influence. They also impose the cost of soiling. There are thus many benefits to acting.

What are the proposal’s costs?


Costs of black carbon filters are quite modest--for construction equipment in the range of a few tens of thousands of dollars. For road construction projects that are now costing tens of millions of dollars per mile, with total project costs of hundreds of millions of dollars, the incremental cost of a few million, spread across several projects given that most equipment is used and then used again, would very likely be in the noise of project costs.

Importantly, benefits would result not just from limiting the BC emissions while the construction equipment is working on the first project, but also when it is used in public and private projects after first use. Thus, there would be health, welfare, and climate benefits far greater than for just the particular project.

Time line


The Presidential instruction should be able to be completed within months and then be incorporated into federal contract regulations within a year. In that the installation of filters is an existing technology and does not take much time or involve much cost, including appropriate provisions in contracts should be able to be started within one to two years, leading to reductions in black carbon emissions starting within two years. In that black carbon has an atmospheric lifetime of a week or so, the reduction in the warming influence from such actions should also start to be felt within two years.

Related proposals



Bond, T C, S  J Doherty, D W Fahey, P M Forster, and T Bernsten. Bounding the role of black carbon in the climate system: A scientific assessment. Journal of Geophysical Research Atmospheres, 118(11), 5380-5552, 2013.

EPA's Black Carbon Program is described at indicates that they are aiming for 86% control by 2030, basically taking so long as much of the off-road equipment is used for many years before newer, low emission equipment is purchased. While the total reduction proposed is admirable, this is simply not fast enough and the proposed policy step would lead to faster reductions, also at very low cost and also providing other co-benefits to health, etc.