What are Particulates?Published by MAC on 2005-08-14
What are Particulates?
The Gallon Environment Letter
Canadian Institute for Business and the Environment
Vol. 10, No. 14, August 10, 2005
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Dust (particulate matter) is a significant component of air pollution. Particulates are not a single pollutant but a mix of particles of different sizes, origin, and chemical composition. Regulations have tended to address only size rather than the other aspects of the particle mix.
Coarser particulates may be found near sources of pollution such as power plants, industrial and agricultural operations, and roads. They include cement dust, foundry dust, wind-blown soil dust and coal dust. Finer particulates may be found long distances from sources. Chemical reactions between air pollutants and also between natural compounds such as water and seawater can lead to formation of different types of particles.
Among the features of particulates are:
- Size variations. Particles in the air may range in size from a grain of sand which can be seen with the naked eye down to as small as individual molecules. In between, still too small to be seen, are colloidal particles. Those particles which are 10 micrometers or less in diameter are called PM10 where PM is particulate matter. Smaller particles are 2.5 micrometers or less in diameter and are called PM2.5. PM10 includes the set of PM2.5. (1 micrometre = 1 millionth of a metre)
- Chemical composition. This affects size, for example, sulphur tends to be in fine particles while heavy metals particles are coarser. (See below for the range of material particulates may contain.)
- Sources affect size and chemical composition. Coarse PM is usually from a source due to abrasion and crushing. Particulates may also be altered or created by chemical and physical reactions with gas or liquid pollutants.
- Size affects how particles disperse. Coarse particles settle closer to where they were created than fine particles. Fine particulates can be airborne for days or months and transported 1000 km or 10,000 km.
- Secondary particle creation. It isn't just a matter of what goes up must come down. Particles are also formed by chemical reactions in the air. Fine particles are often created from gas to particle conversion reactions, from evaporation of water from contaminated fog or cloud droplets and condensing of volatile organic compounds, metals and incomplete combustion.
- Different types. Particles are variously described as aerosols (very small particles, liquid or solid which are formed by reactions of gases atomization of liquids or dispersion of dusts), haze (contains particles which reduce visibility), mists (contain liquid particles), smoke (contains particles from incomplete combustion) and biological.
- Particles may be made up of a wide range of material including: Aluminium, iron, calcium, silicon from coal combustion, rock mining, soil erosion, vehicle debris such as engine and brake linings, automobile and truck tire fragments, general debris and waste remnants.
- Soot and carbon black. These particles are emitted from car and truck exhausts, furnaces, incinerators, power generation, and steel making. These types of pollutants are particularly bad because they may play a role in further chemical reactions. Carbon black is a carrier of gases and other particulate pollution.
- Fly ash. When coal is burned, the mineral content which is not combustible is converted to ash. The bottom ash, a heavy part, is deposited and collected.
- Fly ash particles which are partially collected by stacks and scrubbers also escape to the atmosphere in small particles which harm plants and people. Asbestos. When particles of this material are breathed in, it causes asbestosis, a type of pneumonia, as well as cancer. International programs have been put in place to reduce use and exposure to asbestos although Canada is still a producer and exporter.
- Toxic metals. Lead particles are less present in the air in many developed countries where leaded fuel has been banned but they a growing concern in other countries. Mercury from power plants and volcanoes in the atmosphere is toxic, travels long distances and some is in particulate form. Beryllium with its high toxicity is a growing problem because of its use in electronic equipment and instrumentation.
- Radioactive. Naturally occuring radon decays to form products which adhere to atmospheric particles. Burning fossil fuels introduces radioactivity in the fly ash as do nuclear testing and nuclear accidents.
- Biological material: Particulates may contain plant and insect fragments, pollen, fungus, bacteri, virus, and mould spores.
Effects of Particles
The effects depend on the nature of the particles such as their size and toxicity as well as on how long the particles stay in the air and the results of chemical and physical interactions.
Among the effects are:
- Reduction of visibility.
- Dust covering. For example, Michaelangelo's David was recently cleaned of 500 years of accumulated dust. Curators found that, soon after the cleaning, dust brought in by the many visitors was accumulating again. Restoration of art can change the fundamental nature of the artistic piece.
- Fostering chemical reactions in the atmosphere affecting weather and air pollution impacts.
- Certain sized particles scatter light affecting weather and climate.
- Health effects. Particulates are associated with higher rates of circulatory and respiratory diseases. Effects can include heart attacks, pneumonia, harmful impacts on chronic lung diseases, increased risk of lung cancer and reduced survival rates from cardio-respiratory effects. Coarser particles damage nasal and upper respiratory passages. Small particles may enter deep into the lungs and the blood stream or lymph system damaging organs. Increases in hospital visits and more frequent and severe asthma may also result.
Controlling Particulate Matter
Many companies offer air pollution control equipment and services to remove particles from operations and waste streams but not all are effective for all particulate matter. Cost is often a barrier to the take-up of technology.
Among the control measures are:
- Sedimentation. Gases are stored in large spaces and over time, the larger particles settle out through the force of gravity.
- Dry centrifugal collectors. Particles are separated from the air stream by spinning or fans so that the particles are forced outward to be collected.
- Filtration. Fabric filters collect dust in tube bags in baghouses.
- Scrubbers. Gas is passed through a section with a narrow waist. A scrubbing liquid is broken by the passing gas into droplets which capture particles.
- Electrostatic Precipitors. The particles gain a charge when the gas is passed through current and are attracted to a surface for later removal. This is similar to the principle used by household air cleaners and the problem is that the process may also produces ozone which is toxic.
- Pollution prevention to avoid creation of air pollution in general and particulates in particular is another approach. Energy conservation and alternate energy sources may have a role to play in reducing particulates.
Manahan, Stanley. Fundamentals of Environmental Chemistry. Boca Raton, Florida: Lewis Publishers, 2000.
September 12, 2005
Environmental News Service (ENS)
WASHINGTON, DC - The U.S. Environmental Protection Agency (EPA) has issued a new air quality rule proposing the steps that state, local and tribal governments can take to reduce fine particle pollution (PM2.5) in areas that do not meet the EPA's standards.
EPA Administrator Stephen Johnson said, "New clean air rules will reduce pollution from power plants, industrial facilities, and on and off road vehicles and equipment. As these rules take effect over the next decade, EPA projects that air quality will improve across the country, helping to ensure that all Americans can work, exercise and play in cleaner, healthier air."
The proposed rule, known as the PM2.5 Implementation Rule, describes the planning framework and requirements for state, local and tribal governments to consider when developing their plan to reduce air pollution to meet the fine particle pollution standards.
Areas meeting the standard must show how they will ensure that fine particle pollution levels remain below the standards. Reducing fine particle pollution is a critical element of the administration's comprehensive national clean air strategy and will result in deep and sustained reductions in air pollution, Johnson said. The strategy includes EPA's recent Clean Diesel Program to reduce pollution from highway, nonroad and stationary diesel engines, the Clean Air Interstate Rule to reduce pollution from power plants in the eastern United States, and the Clean Air Visibility Rule.
Fine particles, about 1/30th the size of an average human hair, are emitted by power plants and factories burning fossil fuels such as coal, automobiles, and diesel powered vehicles such as buses and trucks.
These fine particles are also formed in the atmosphere when gases such as sulfur dioxide, nitrogen oxides, and volatile organic compounds - all of which are also products of fuel combustion - are transformed in the air by chemical reactions.
These particles, known as PM2.5 because they are 2.5 micrometers or smaller in size, have been associated with serious health problems including cardiovascular disease, chronic bronchitis and asthma attacks.
EPA issued the PM2.5 standards in 1997 and designated areas as attainment or nonattainment with the standard in December 2004. Nonattainment areas must meet the standards by 2010.
Johnson estimates that meeting these standards will prevent at least 15,000 premature deaths; 75,000 cases of chronic bronchitis; 10,000 hospital admissions for respiratory and cardiovascular disease; hundreds of thousands of occurrences of aggravated asthma; and 3.1 million days when people miss work because they are suffering from symptoms related to particle pollution exposure.
But clean air advocates became suspicious when the EPA issued the 464 page rule proposal late on a Friday afternoon at a time when few people will read it.
Frank O'Donnell of the non-profit Clean Air Watch says he has begun reading it, and soon found that the EPA is proposing to give another break to the electric power industry. EPA is proposing new loopholes that could permit electric power plants in dirty-air areas to avoid tough pollution controls, O'Donnell said.
Under this proposal, power companies would NOT have to install reasonably available pollution controls as long as they are located in states that participate in the cap and trade program that EPA calls the Clean Air Interstate Rule.
"This is yet another gift to the electric power industry," O'Donnell said, "one that could subject breathers to unnecessarily high levels of fine-particle pollution, which has been linked to premature death and numerous health problems."
Last year, the EPA listed areas of the country out of compliance with the national health standard for fine particle pollution that was set in 1997. This is a companion rule which is supposed to outline for states how they are supposed to meet those standards.
"One glaring loophole," says O'Donnell, is that the EPA is proposing that power plants, EGUs in the jargon of the bureaucracy, would not have to install reasonably available pollution controls if the state in question participates in the regional cap-and-trade program under the Clean Air Interstate Rule.
Installation of reasonably available pollution controls has been a minimal requirement in the past for big sources of pollution located in areas that violate public health standards.
Many states and environmentalists have pointed out that the interstate rule will not be adequate to meet public health standards in many areas.
Under this new proposal, O'Donnell says, a power plant would not necessarily have to be controlled at all, even if it is contributing to local pollution problems.
The rule is found at: http://www.epa.gov/pmdesignations/documents/Sep05/PM25_impl_rule_and_preamble_090805.pdf
Basic information about the Clean Air Interstate Rule is found at: http://www.epa.gov/CAIR/basic.html
The EPA will accept public comment on this proposal for 60 days from the date the notice appears in the Federal Register. For more information, visit: http://www.epa.gov/pmdesignations