Everything about Particulate totally explained
Particulates, alternatively referred to as
particulate matter (PM) or
fine particles, are tiny particles of solid or liquid suspended in a gas. In contrast,
aerosol refers to particles and the gas together. Sources of particulate matter can be man made or natural. Some particulates occur naturally, originating from
volcanoes,
dust storms,
forest and
grassland fires, living vegetation, and
sea spray. Human activities, such as the burning of
fossil fuels in vehicles,
power plants and various industrial processes also generate significant amounts of aerosols. Averaged over the globe,
anthropogenic aerosols—those made by human activities—currently account for about 10 percent of the total amount of aerosols in our atmosphere. Increased levels of fine particles in the air are linked to health hazards such as
heart disease, altered lung function and
lung cancer.
Scale classification
Among the most common categorizations imposed on particulates are those with respect to size, referred to as fractions. As particles are often non-spherical (for example,
Asbestos fibers), there are many definitions of
particle size.
The most widely used definition is the
aerodynamic diameter. A particle with an
aerodynamic diameter of 10
micrometer moves in a gas like a sphere of unit density (1 gram per cubic centimeter) with a diameter of 10
micrometer.
PM diameters range from less than 10
nanometers to more than 100
micrometers. These dimensions represent the continuum from a few
molecules up to the size where particles can no longer be carried by a gas.
The notation PM
10 is used to describe particles of 10 micrometers or less and PM
2.5 represents particles less than 2.5 micrometers in
aerodynamic diameter. .
But because no sampler is perfect in the sense that no particle larger than its
cutoff diameter passes the inlet, all reference methods allow a high margin of error.
These are also sometimes referred to with other equivalent numeric values. Everything below 100 nm, down to the size of individual molecules is classified as
ultrafine particles (UFP or UP).
| fraction |
size range |
| PM10 (thoracic fraction) |
<=10 μm |
| PM2.5 (respirable fraction) |
<=2.5 μm |
| PM1 |
<=1 μm |
| Ultrafine (UFP or UP) |
<=0.1 μm |
| PM10-PM2.5 (coarse fraction) |
2.5 μm - 10 μm |
Note that PM
10-PM
2.5 is the difference of PM
10 and PM
2.5, so that it only includes the coarse fraction of PM
10.
These are the formal definitions. Depending on the context, alternative definitions may be applied. In some specialized settings, each fraction may exclude the fractions of lesser scale, so that PM
10 excludes particles in a smaller size range, for example PM
2.5, usually reported separately in the same work . Researchers suggest that even short-term exposure at elevated concentrations could significantly contribute to heart disease.
Researchers at the Johns Hopkins Bloomberg School of Public Health have conducted the largest nationwide study on the acute health effects of coarse particle pollution. Coarse particles are airborne pollutants that fall between 2.5 and 10 microns in diameter. The study, published in the May 14, 2008, edition of JAMA, found evidence of an association with hospital admissions for cardiovascular diseases but no evidence of an association with the number of hospital admissions for respiratory diseases. After taking into account fine particle levels, the association with coarse particles remained but was no longer statistically significant.
The smallest particles, less than 100 nanometers (
nanoparticles), may be even more damaging to the cardiovascular system.
There is evidence that particles smaller than 100 nanometres can pass through cell membranes and migrate into other organs, including the brain. It has been suggested that particulate matter can cause similar brain damage as that found in
Alzheimer patients. Particles emitted from modern
diesel engines (commonly referred to as
Diesel Particulate Matter, or DPM) are typically in the size range of 100 nanometres (
0.1 micrometres). In addition, these
soot particles also carry
carcinogenic components like
benzopyrenes adsorbed on their surface. It is becoming increasingly clear that the legislative limits for engines, which are in terms of emitted mass, are not a proper measure of the health hazard. One particle of 10 µm diameter has approximately the same mass as 1 million particles of 100 nm diameter, but it's clearly much less hazardous, as it probably never enters the human body - and if it does, it's quickly removed. Proposals for new regulations exist in some countries, with suggestions to limit the particle surface area or the particle number.
The large number of deaths and other health problems associated with particulate pollution was first demonstrated in the early 1970s and has been reproduced many times since. PM pollution is estimated to cause 22,000-52,000 deaths per year in the United States (from 2000) and 200,000 deaths per year in
Europe.
Regulation
Due to the health effects of particulate matter, maximum standards have been set by various governments. Many
urban areas in the U.S. and Europe still frequently violate the particulate standards, though urban air on these continents has become cleaner, on average, with respect to particulates over the last quarter of the 20th century.
United States
The
United States Environmental Protection Agency (EPA) sets standards for PM
10 and PM
2.5 concentrations in urban air. (See
National Ambient Air Quality Standards.) EPA regulates primary particulate emissions and precursors to secondary emissions (
NOx,
sulfur, and
ammonia).
EU legislation
In
directives 1999/30/EC and 96/62/EC, the
European Commission has set limits for PM
10 in the air:
¹ indicative value.
Affected areas
| Most Polluted World Cities by PM |
Particulate matter,
μg/m3 (2004) |
City |
| 169 |
Cairo, Egypt |
| 161 |
Beijing, China |
| 150 |
Delhi, India |
| 128 |
Kolkata, India (Calcutta) |
| 125 |
Taiyuan, China |
| 123 |
Chongqing, China |
| 109 |
Kanpur, India |
| 109 |
Lucknow, India |
| 104 |
Jakarta, Indonesia |
| 101 |
Shenyang, China |
The most concentrated particulate matter pollution tends to be in densely populated metropolitan areas in developing countries. The primary cause is the burning of fossil fuels by transportation and industrial sources.
Aerosol science
The field of
aerosol science and technology has grown in response to the need to understand and control natural and manmade aerosols.
Further Information
Get more info on 'Particulate'.
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