Diesel exhaust

Diesel exhaust
A diesel-powered truck emitting sooty exhaust gas while starting its engine.

Diesel exhaust (known as clag when emitted by diesel locomotives, or diesel engine emissions in scientific papers) is the exhaust gas of a diesel engine.

In diesel engines, conditions in the engine differ from the spark-ignition engine, since power is directly controlled by the fuel supply, rather than by controlling the air supply. Thus when the engine runs at low power, there is enough oxygen present to burn the fuel, and diesel engines only make significant amounts of carbon monoxide when running under a load.

Diesel exhaust is well known for its characteristic smell; but in Britain this smell in recent years has become much less (while diesel fuel getting more expensive) because the sulfur is now removed from the fuel in the oil refinery, plus the effect of catalytic converters.

Diesel exhaust has been found to contain many toxic air contaminants. Among these pollutants, fine particle pollution is perhaps the most important as a cause of diesel's deleterious health effects.



Diesel particulate matter (DPM), sometimes also called diesel exhaust particles (DEP), is the particulate component of diesel exhaust, which includes diesel soot and aerosols such as ash particulates, metallic abrasion particles, sulfates, and silicates. When released into the atmosphere, DPM can take the form of individual particles or chain aggregates, with most in the invisible sub-micrometre range of 100 nanometers, also known as ultrafine particles (UFP) or PM0.1.

Health effects

Diesel combustion exhaust is a major source of atmospheric soot and fine particles, which is a fraction of air pollution implicated in human heart and lung damage. Diesel exhaust also contains nanoparticles. Since the study of the detrimental health effects of nanoparticles (nanotoxicology) is still in its infancy, the full extent of negative health effects from nanoparticles produced by all types of diesel are unknown.

The main particulate fraction of diesel exhaust consists of fine particles. Because of their small size, inhaled particles may easily penetrate deep into the lungs. The rough surfaces of these particles makes it easy for them to bind with other toxins in the environment, thus increasing the hazards of particle inhalation. Exposures have been linked with acute short-term symptoms such as headache, dizziness, light-headedness, nausea, coughing, difficult or labored breathing, tightness of chest, and irritation of the eyes and nose and throat[citation needed]. Long-term exposures can lead to chronic, more serious health problems such as cardiovascular disease, cardiopulmonary disease, and lung cancer[citation needed].

In 2001, the mortality within the German population (82 million people) was according to the official report 2352 of the Umweltbundesamt Berlin (Federal Environmental Agency of Germany) at least 14400 people because of Diesel soot exposure.

The study of nanoparticles and nanotoxicology is still in its infancy, but the full health effects from nanoparticles produced by all types of diesel are unknown. It is already clear enough, however, that the health detriments of fine particle emissions are severe and pervasive. Although one study found no significant evidence that short term exposure to diesel exhaust results in adverse extra-pulmonary effects, effects that are often correlated with an increase in cardiovascular disease,[1] a 2011 study in The Lancet concluded that traffic exposure is the single most serious preventable trigger of heart attack in the general public, the cause of 7.4% of all attacks; although, it is impossible to tell how much of this effect is due to the stress of being in traffic and how much is due to exposure to exhaust.[2]

Variation with engine conditions

The types and quantities of nanoparticles can vary according to operating temperatures and pressures, presence of an open flame, fundamental fuel type and fuel mixture, and even atmospheric mixtures. As such, the resulting types of nanoparticles from different engine technologies and even different fuels are not necessarily comparable. In general, the usage of biodiesel and biodiesel blends results in decreased pollution. One study has shown that the volatile component of 95% of diesel nanoparticles is unburned lubricating oil.[3] Long term effects still need to be further clarified, as well as the effects on susceptible groups of people with cardiopulmonary diseases.

Diesel engines can produce black soot (or more specifically diesel particulate matter) from their exhaust. The black smoke consists of carbon compounds that were not combusted, because of local low temperatures where the fuel is not fully atomized. These local low temperatures occur at the cylinder walls, and at the outside of large droplets of fuel. At these areas where it is relatively cold, the mixture is rich (contrary to the overall mixture which is lean). The rich mixture has less air to burn and some of the fuel turns into a carbon deposit. Modern car engines use a diesel particulate filter (DPF) to capture carbon particles and then intermittently burn them using extra fuel injected directly into the filter. This prevents carbon buildup at the expense of wasting a small quantity of fuel.

The full load limit of a diesel engine in normal service is defined by the "black smoke limit", beyond which point the fuel cannot be completely combusted. As the "black smoke limit" is still considerably lean of stoichiometric, it is possible to obtain more power by exceeding it, but the resultant inefficient combustion means that the extra power comes at the price of reduced combustion efficiency, high fuel consumption and dense clouds of smoke. This is only done in specialized applications (such as tractor pulling competitions) where these disadvantages are of little concern.

When starting from cold, the engine's combustion efficiency is reduced because the cold engine block draws heat out of the cylinder in the compression stroke. The result is that fuel is not combusted fully, resulting in blue and white smoke and lower power outputs until the engine has warmed. This is especially the case with indirect injection engines, which are less thermally efficient. With electronic injection, the timing and length of the injection sequence can be altered to compensate for this. Older engines with mechanical injection can have mechanical and hydraulic governor control to alter the timing, and multi-phase electrically controlled glow plugs, that stay on for a period after start-up to ensure clean combustion—the plugs are automatically switched to a lower power to prevent their burning out.

Particles of the size normally called PM10 (particles of 10 micrometres or smaller) have been implicated in health problems, especially in cities. Some modern diesel engines feature diesel particulate filters, which catch the black soot and when saturated are automatically regenerated by burning the particles.

All diesel engine exhaust emissions can be significantly reduced by using biodiesel fuel.

Effect of engine lubricating oil

One study has shown that the volatile component of 95% of diesel nanoparticles is unburned lubricating oil.[4] Long term effects still need to be further clarified, as well as the effects on susceptible groups of people with cardiopulmonary diseases.

Chemical components

Diesel engines produce very little carbon monoxide as they burn the fuel in excess air even at full load, at which point the quantity of fuel injected per cycle is still about 50 percent lean of stoichiometric.

This is a list of chemical components that have been found in diesel exhaust.

Contaminant Note
acetaldehyde IARC Group 2B carcinogens
acrolein IARC Group 3 carcinogens
aniline IARC Group 3 carcinogens
antimony compounds Toxicity similar to arsenic poisoning
arsenic IARC Group 1 Carcinogens, endocrine disruptor
benzene IARC Group 1 Carcinogens
beryllium compounds IARC Group 1 Carcinogens
biphenyl It has mild toxicity.
bis(2-ethylhexyl)phthalate endocrine disruptor
1,3-butadiene IARC Group 2A carcinogens
cadmium IARC Group 1 Carcinogens, endocrine disruptor
chlorobenzene It has "low to moderate" toxicity.
chromium compounds IARC Group 3 carcinogens
cobalt compounds
cresol isomers
cyanide compounds
dibutyl phthalate endocrine disruptor
1,8-dinitropyrene Carcinogen
dioxins and dibenzofurans
ethyl benzene
formaldehyde IARC Group 1 Carcinogens
inorganic lead endocrine disruptor
manganese compounds
mercury compounds IARC Group 3 carcinogens
methanol It may cause blindness.
methyl ethyl ketone It may cause birth defect.
naphthalene IARC Group 2B carcinogens
nickel IARC Group 2B carcinogens
3-Nitrobenzanthrone One of the strongest carcinogens known
phenol endocrine disruptor
polycyclic organic matter, including polycyclic aromatic hydrocarbons (PAHs)
selenium compounds IARC Group 3 carcinogens
styrene IARC Group 2B carcinogens
toluene IARC Group 3 carcinogens
xylene isomers and mixtures: o-xylenes, m-xylenes, p-xylenes IARC Group 3 carcinogens


Some problems associated with the exhaust gases (nitrogen oxides, sulfur oxides) can be mitigated with further investment and equipment; some diesel cars now have catalytic converters in the exhaust.

All diesel engine exhaust emissions can be significantly reduced by using biodiesel fuel. Oxides of nitrogen do increase from a vehicle using biodiesel, but they too can be reduced to levels below that of fossil fuel diesel, by changing fuel injection timing.

Occupational effects

Exposure to diesel exhaust and diesel particulate matter (DPM) is a known occupational hazard to truckers, railroad workers, and miners using diesel-powered equipment in underground mines. Adverse health effects have also been observed in the general population at ambient atmospheric particle concentrations well below the concentrations in occupational settings.

Recently, concerns have been raised in the USA regarding children's exposure to DPM as they ride diesel-powered schoolbuses to and from school. The Environmental Protection Agency (EPA) has established the Clean School Bus USA initiative in an effort to unite private and public organizations in curbing student exposures.


Although the US Mine Safety and Health Administration issued a health standard in January 2001 designed to reduce exposure in underground metal and nonmetal mines, on September 7, 2005, MSHA published a notice in the Federal Register proposing to postpone the effective date from January 2006 until January 2011.

To rapidly reduce particulate matter from heavy-duty diesel engines in California, the California Air Resources Board created the Carl Moyer Program to provide funding for upgrading engines ahead of emissions regulations. In 2008 the California Air Resources Board also implemented the 2008 California Statewide Truck and Bus Rule which requires all heavy-duty diesel trucks and buses, with a few exceptions, that operate in California to either retrofit or replace engines in order to reduce diesel particulate matter.

See also

External links


  1. ^ http://www.blackwellpublishing.com/isth2005/abstract.asp?id=46528 Exposure to Diesel Nanoparticles Does Not Induce Blood Hypercoagulability in an at-Risk Population (Abstract)
  2. ^ Nawrot, Perez, Künzli, Munters, Nemery Public health importance of triggers of myocardial infarction: comparative risk assessment The Lancet Volume 377, Issue 9767, Pages 732 - 740, 26 February 2011 http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2810%2962296-9/abstract doi:10.1016/S0140-6736(10)62296-9
    "Taking into account the OR and the prevalences of exposure, the highest PAF was estimated for traffic exposure (7.4%)... "
    "… [O[dds ratios and frequencies of each trigger were used to compute population-attributable fractions (PAFs), which estimate the proportion of cases that could be avoided if a risk factor were removed. PAFs depend not only on the risk factor strength at the individual level but also on its frequency in the community. ... [T]he exposure prevalence for triggers in the relevant control time window ranged from 0.04% for cocaine use to 100% for air pollution. ... Taking into account the OR and the prevalences of exposure, the highest PAF was estimated for traffic exposure (7.4%) ...
  3. ^ On-line measurements of diesel nanoparticle composition and volatility
  4. ^ http://dx.doi.org/10.1016/S1352-2310(02)01017-8 On-line measurements of diesel nanoparticle composition and volatility
  5. ^ Diesel Exhaust Toxicants mindfully.org

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