Diesel particulate matter

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. Long-term exposures can lead to chronic, more serious health problems such as cardiovascular disease, cardiopulmonary disease, and lung cancer.

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.

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. One study, reported in the Lancet in 2011, has already revealed that traffic exhaust is the single most serious preventable cause of heart attack in the general public, the cause of 7.4% of all attacks.

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, a 2011 study in The Lancet concluded that traffic exhaust is the single most serious preventable cause of heart attack in the general public, the cause of 7.4% of all attacks.

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. 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.

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.

Effect of engine lubricating oil

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

Regulation

Although the American 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.

References

• Department of Labor, Mine Safety and Health Administration. Diesel Particulate Matter Exposure of Underground Metal and Nonmetal Miners: Final Rule, January 19, 2001. Federal Register 66(13):5706.
• Monforton C. Weight of the Evidence or Wait for the Evidence? Protecting Underground Miners from Diesel Particulate Matter American Journal of Public Health, 2006;96(2):271-276.
• Steenland K, Silverman DT, Hornung DW. "Case control study of lung cancer and truck driving in the Teamsters union." American Journal of Public Health 1990; 80:670-674.
• Steenland, K, Silverman DT, Zaebst D. "Exposure to diesel exhaust in the trucking industry and possible relationships with lung cancer." American Journal of Industrial Medicine 1992; 21:887-890.
• Bruske-Holhfield I, Mohner M, Ahrens W, et al. "Lung cancer risk in male workers occupationally exposed to diesel motor emissions in Germany." American Journal of Industrial Medicine 1999; 36:405-414.
• Wichmann, H.-E. Abschaetzung positiver gesundheitlicher Auswirkungen durch den Einsatz von Partikelfiltern bei Dieselfahrzeugen in Deutschland Umweltbundesamt Berlin 2003. Report 2352, especially page 32
• Umweltbundesamt Berlin Future Diesel. Abgasgesetzgebung Pkw, leichte Nfz und Lkw – Fortschreibung der Grenzwerte bei Dieselfahrzeugen 2003. Report 2353, especially page 25

External links

• Diesel Retrofit in Europe.
• NIOSH Mining Safety and Health Topic: Diesel Exhaust
• Diesel Particulate Matter, a case study at www.defendingscience.org
• Clean School Bus USA, EPA Initiative
• Weight of the Evidence or Wait for the Evidence? Protecting Underground Miners from Diesel Particulate Matter Article by Celeste Monforton. American Journal of Public Health, February 2006.
• U.S. Department of Labor Occupational Safety & Health Administration: Safety and Health Topics: Diesel Exhaust
• Diesel exhaust -- peer reviewed studies by Health Effects Institute

Partculates: see also

• Diesel particulate filter
• Carl Moyer Program