出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/07/26 15:47:17」(JST)
Atmospheric particulate matter - also known as particulates or particulate matter (PM) - are tiny pieces of solid or liquid matter associated with the Earth's atmosphere. They are suspended in the atmosphere as atmospheric aerosol, a term which refers to the particulate/air mixture, as opposed to the particulate matter alone. However, it is common to use the term aerosol to refer to the particulate component alone.[1] Sources of particulate matter can be man made or natural. They can adversely affect human health and also have impacts on climate and precipitation. Subtypes of atmospheric particle matter include suspended particulate matter (SPM), respirable suspended particle (RSP; particles with diameter of 10 micrometres or less), fine particles (diameter of 2.5 micrometres or less, ultrafine particles, and soot.
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 particulates. Coal combustion in developing countries is the primary method for heating homes and supplying energy. Because salt spray over the oceans is the overwhelmingly most common form of particulate in the atmosphere, anthropogenic aerosols—those made by human activities—currently account for about 10 percent of the total mass of aerosols in our atmosphere.[2]
The composition of aerosols and particles depends on their source. Wind-blown mineral dust[3] tends to be made of mineral oxides and other material blown from the Earth's crust; this particulate is light-absorbing. [4] Sea salt[5] is considered the second-largest contributor in the global aerosol budget, and consists mainly of sodium chloride originated from sea spray; other constituents of atmospheric sea salt reflect the composition of sea water, and thus include magnesium, sulfate, calcium, potassium, etc. In addition, sea spray aerosols may contain organic compounds, which influence their chemistry. Sea salt does not absorb light.[citation needed]
Secondary particles derive from the oxidation of primary gases such as sulfur and nitrogen oxides into sulfuric acid (liquid) and nitric acid (gaseous). The precursors for these aerosols—i.e. the gases from which they originate—may have an anthropogenic origin (from fossil fuel or coal combustion) and a natural biogenic origin. In the presence of ammonia, secondary aerosols often take the form of ammonium salts; i.e. ammonium sulfate and ammonium nitrate (both can be dry or in aqueous solution); in the absence of ammonia, secondary compounds take an acidic form as sulfuric acid (liquid aerosol droplets) and nitric acid (atmospheric gas), all of which may contribute to the health effects of particulates.[6]
Secondary sulfate and nitrate aerosols are strong light-scatterers.[7] This is mainly because the presence of sulfate and nitrate causes the aerosols to increase to a size that scatters light effectively.
Organic matter (OM) can be either primary or secondary, the latter part deriving from the oxidation of VOCs; organic material in the atmosphere may either be biogenic or anthropogenic. Organic matter influences the atmospheric radiation field by both scattering and absorption. Another important aerosol type is elemental carbon (EC, also known as black carbon, BC): this aerosol type includes strongly light-absorbing material and is thought to yield large positive radiative forcing. Organic matter and elemental carbon together constitute the carbonaceous fraction of aerosols.[8] Secondary organic aerosols, tiny "tar balls" resulting from combustion products of internal combustion engines, have been identified as a danger to health.[9]
The chemical composition of the aerosol directly affects how it interacts with solar radiation. The chemical constituents within the aerosol change the overall refractive index. The refractive index will determine how much light is scattered and absorbed.
The composition of particulate matter that generally causes visual effects such as smog consists of sulphur dioxide, nitrogen oxides, carbon monoxide, mineral dust, organic matter, and elemental carbon also known as black carbon or soot. The particles are hydroscopic due to the presence of sulphur, and SO2 is converted to sulphate when high humidity and low temperatures are present. This causes the reduced visibility and yellow color.[10]
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In general, the smaller and lighter a particle is, the longer it will stay in the air. Larger particles (greater than 10 micrometers in diameter) tend to settle to the ground by gravity in a matter of hours whereas the smallest particles (less than 1 micrometer) can stay in the atmosphere for weeks and are mostly removed by precipitation. Diesel particulate matter is highest near the source of emission. Any info regarding DPM and the atmosphere, flora, height, and distance from major sources would be useful to determine health effects.
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Particulate matter emissions are highly regulated in most industrialized countries. Due to environmental concerns, most industries are required to operate some kind of dust collection system to control particulate emissions. These systems include inertial collectors (cyclone collectors), fabric filter collectors (baghouses), wet scrubbers, and electrostatic precipitators.
Cyclone collectors are useful for removing large, coarse particles and are often employed as a first step or "pre-cleaner" to other more efficient collectors. Fabric filters or baghouses are the most commonly employed in general industry.[11] They work by forcing dust laden air through a bag shaped fabric filter leaving the particulate to collect on the outer surface of the bag and allowing the now clean air to pass through to either be exhausted into the atmosphere or in some cases recirculated into the facility. Common fabrics include polyester and fiberglass and common fabric coatings include PTFE (commonly known as Teflon©). The excess dust buildup is then cleaned from the bags and removed from the collector. Wet scrubbers pass the dirty air through a scrubbing solution (usually a mixture of water and other compounds) allowing the particulate to attach to the liquid molecules. Electrostatic precipitators electrically charge the dirty air as it passes through. The now charged air then passes by large electromagnetic plates which attract the charged particle in the airstream collecting them and leaving the now clean air to be exhausted or recirculated.
Atmospheric aerosols affect the climate of the earth by changing the amount of incoming solar radiation and outgoing terrestrial long wave radiation retained in the earth's system. This occurs through several distinct mechanisms which are split into direct, indirect[12][13] and semi-direct aerosol effects. The aerosol climate effects are the biggest source of uncertainty in future climate predictions.[14] The Intergovernmental Panel on Climate Change, Third Assessment Report, says: While the radiative forcing due to greenhouse gases may be determined to a reasonably high degree of accuracy... the uncertainties relating to aerosol radiative forcings remain large, and rely to a large extent on the estimates from global modelling studies that are difficult to verify at the present time.[15]
The Direct aerosol effect consists of any direct interaction of radiation with atmospheric aerosol, such as absorption or scattering. It affects both short and longwave radiation to produce a net negative radiative forcing.[16] The magnitude of the resultant radiative forcing due to the direct effect of an aerosol is dependent on the albedo of the underlying surface, as this affects the net amount of radiation absorbed or scattered to space. e.g. if a highly scattering aerosol is above a surface of low albedo it has a greater radiative forcing than if it was above a surface of high albedo. The converse is true of absorbing aerosol, with the greatest radiative forcing arising from a highly absorbing aerosol over a surface of high albedo.[12] The Direct aerosol effect is a first order effect and is therefore classified as a radiative forcing by the IPCC.[14] The interaction of an aerosol with radiation is quantified by the Single Scattering Albedo (SSA), the ratio of scattering alone to scattering plus absorption (extinction) of radiation by a particle. The SSA tends to unity if scattering dominates, with relatively little absorption, and decreases as absorption increases, becoming zero for infinite absorption. For example, sea-salt aerosol has an SSA of 1, as a sea-salt particle only scatters, whereas soot has an SSA of 0.23, showing that it is a major atmospheric aerosol absorber.
The Indirect aerosol effect consists of any change to the earth's radiative budget due to the modification of clouds by atmospheric aerosols, and consists of several distinct effects. Cloud droplets form onto pre-existing aerosol particles, known as cloud condensation nuclei (CCN).
For any given meteorological conditions, an increase in CCN leads to an increase in the number of cloud droplets. This leads to more scattering of shortwave radiation i.e. an increase in the albedo of the cloud, known as the Cloud albedo effect, First indirect effect or Twomey effect.[13] Evidence supporting the cloud albedo effect has been observed from the effects of ship exhaust plumes[17] and biomass burning[18] on cloud albedo compared to ambient clouds. The Cloud albedo aerosol effect is a first order effect and therefore classified as a radiative forcing by the IPCC.[14]
An increase in cloud droplet number due to the introduction of aerosol acts to reduce the cloud droplet size, as the same amount of water is divided between more droplets. This has the effect of suppressing precipitation, increasing the cloud lifetime, known as the cloud lifetime aerosol effect, second indirect effect or Albrecht effect.[14] This has been observed as the suppression of drizzle in ship exhaust plume compared to ambient clouds,[19] and inhibited precipitation in biomass burning plumes.[20] This cloud lifetime effect is classified as a climate feedback (rather than a radiative forcing) by the IPCC due to the interdependence between it and the hydrological cycle.[14] However, it has previously been classified as a negative radiative forcing.[21]
The Semi-direct effect concerns any radiative effect of caused by absorbing atmospheric aerosol such as soot, apart from direct scattering and absorption, which is classified as the direct effect. It encompasses many individual mechanisms, and in general is more poorly defined and understood than the direct and indirect aerosol effects. For instance, if absorbing aerosols are present in a layer aloft in the atmosphere, they can heat surrounding air which inhibits the condensation of water vapour, resulting in less cloud formation.[22] Additionally, heating a layer of the atmosphere relative to the surface results in a more stable atmosphere due to the inhibition of atmospheric convection. This inhibits the convective uplift of moisture,[23] which in turn reduces cloud formation. The heating of the atmosphere aloft also leads to a cooling of the surface, resulting in less evaporation of surface water. The effects described here all lead to a reduction in cloud cover i.e. an increase in planetary albedo. The semi-direct effect classified as a climate feedback) by the IPCC due to the interdependence between it and the hydrological cycle.[14] However, it has previously been classified as a negative radiative forcing.[21]
Sulfate aerosol has two main effects, direct and indirect. The direct effect, via albedo, is a cooling effect that slows the overall rate of global warming: the IPCC's best estimate of the radiative forcing is -0.4 watts per square meter with a range of -0.2 to -0.8 W/m² [24] but there are substantial uncertainties. The effect varies strongly geographically, with most cooling believed to be at and downwind of major industrial centres. Modern climate models addressing the attribution of recent climate change take into account sulfate forcing, which appears to account (at least partly) for the slight drop in global temperature in the middle of the 20th century. The indirect effect (via the aerosol acting as cloud condensation nuclei, CCN, and thereby modifying the cloud properties -albedo and lifetime-) is more uncertain but is believed to be a cooling.
Black carbon (BC), or carbon black, or elemental carbon (EC), often called soot, is composed of pure carbon clusters, skeleton balls and buckyballs, and is one of the most important absorbing aerosol species in the atmosphere. It should be distinguished from organic carbon (OC): clustered or aggregated organic molecules on their own or permeating an EC buckyball. BC from fossil fuels is estimated by the IPCC in the Fourth Assessment Report of the IPCC, 4AR, to contribute a global mean radiative forcing of +0.2 W/m² (was +0.1 W/m² in the Second Assessment Report of the IPCC, SAR), with a range +0.1 to +0.4 W/m²
Volcanoes are a large natural source of aerosol, and have been linked to changes in the earth's climate, often with consequences for the human population. Eruptions linked to changes in climate include the 1600 eruption of Huaynaputina which was linked to the Russian famine of 1601 - 1603,[25][26][27] leading to the deaths of two million, and the 1991 eruption of Mount Pinatubo which cause a global cooling of approximately 0.5°C lasting several years.[28][29] Research tracking the effect of light-scattering aerosols in the stratosphere during 2000 and 2010 and comparing its pattern to volcanic activity show a close correlation. Simulations of the effect of anthropogenic particles showed little influence at present levels.[30][31]
Aerosols are also thought to affect weather and climate on a regional scale. The failure of the Indian Monsoon has been linked to the suppression of evaporation of water from the Indian Ocean due to the semi-direct effect of anthropogenic aerosol.[32]
Recent studies of the Sahel drought[33] and major increases since 1967 in rainfall over the Northern Territory, Kimberley, Pilbara and around the Nullarbor Plain have led some scientists to conclude that the aerosol haze over South and East Asia has been steadily shifting tropical rainfall in both hemispheres southward.[32][34]
The latest studies of severe rainfall declines over southern Australia since 1997[35] have led climatologists there to consider the possibility that these Asian aerosols have shifted not only tropical but also midlatitude systems southward.
Increased levels of fine particles in the air as a result of anthropogenic particulate air pollution "is consistently and independently related to the most serious effects, including lung cancer[36] and other cardiopulmonary mortality."[37] The large number of deaths[38] and other health problems associated with particulate pollution was first demonstrated in the early 1970s[39] 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)[40] and contributed to ~370,000 premature deaths in Europe during 2005.[41]
The effects of inhaling particulate matter that have been widely studied in humans and animals now include asthma, lung cancer, cardiovascular issues, respiratory diseases, birth defects, and premature death. The size of the particle is a main determinant of where in the respiratory tract the particle will come to rest when inhaled. Because of their small size, particles on the order of ~10 micrometers or less (PM10) can penetrate the deepest part of the lungs such as the bronchioles or alveoli.[42] Larger particles are generally filtered in the nose and throat via cilia and mucus, but particulate matter smaller than about 10 micrometers, referred to as PM10, can settle in the bronchi and lungs and cause health problems. The 10 micrometer size does not represent a strict boundary between respirable and non-respirable particles, but has been agreed upon for monitoring of airborne particulate matter by most regulatory agencies.
Similarly, particles smaller than 2.5 micrometers, PM2.5, tend to penetrate into the gas exchange regions of the lung, and very small particles (< 100 nanometers) may pass through the lungs to affect other organs. Penetration of particles is not wholly dependent on their size; shape and chemical composition also play a part. Therefore simple nomenclature can be used to distinguish between the different degrees of relative penetration of a PM particle into the cardiovascular system. Inhalable particles penetrate no further than the bronchi as they are filtered out by the cilia, Thoracic particles can penetrate right into terminal bronchioles whereas PM which can penetrate to alveoli and hence the circulatory system are termed respirable particles.
A study published in the Journal of the American Medical Association indicates that PM2.5 leads to high plaque deposits in arteries, causing vascular inflammation and atherosclerosis — a hardening of the arteries that reduces elasticity, which can lead to heart attacks and other cardiovascular problems.[43] The World Health Organization (WHO) estimates that "... fine particulate air pollution (PM(2.5)), causes about 3% of mortality from cardiopulmonary disease, about 5% of mortality from cancer of the trachea, bronchus, and lung, and about 1% of mortality from acute respiratory infections in children under 5 yr, worldwide." doi:10.1080/15287390590936166 PMID 16024504. Researchers suggest that even short-term exposure at elevated concentrations could significantly contribute to heart disease. A 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.[44]
The smallest particles, less than 100 nanometers (nanoparticles), may be even more damaging to the cardiovascular system.[45]
There is evidence that particles smaller than 100 nanometers 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 nanometers (0.1 micrometer). 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 is clearly much less hazardous, as it probably never enters the human body — and if it does, it is quickly removed. Proposals for new regulations exist in some countries, with suggestions to limit the particle surface area or the particle count (numerical quantity).
A further complexity that is not entirely documented is how the shape of PM can affect health. Of course the dangerous needle-like shape of asbestos is widely recognised to lodge itself in the lungs with often dire consequences. Geometrically angular shapes have more surface area than rounder shapes, which in turn affects the binding capacity of the particle to other, possibly more dangerous substances.
The inhalable dust fraction is the fraction of dust that enters the nose and mouth and may be deposited anywhere in the respiratory tract. The thoracic fraction is the fraction that enters the thorax and is deposited within the lung airways and the gas-exchange regions. The respiratory fraction is what is deposited in the gas exchange regions (alveoli).[46]
The site and extent of absorption of inhaled gases and vapors are determined by their solubility in water. Absorption is also dependent upon air flow rates and the partial pressure of the gases in the inspired air. The fate of a specific contaminant is dependent upon the form in which it exists (aerosol or particulate). Inhalation also depends upon the breathing rate of the subject.[47]
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 micrometers in diameter.[48] 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.
Particulate matter studies in Bangkok Thailand indicated a 1.9% increased risk of dying from cardiovascular disease, and 1.0% risk of all disease for every 10 micrograms per cubic meter. Levels averaged 65 in 1996, 68 in 2002, and 52 in 2004. Decreasing levels may be attributed to conversions of diesel to natural gas combustion as well as improved regulations.[49]
The Mongolian government agency has recorded a 45% increase in the rate of respiratory illness in the past five years. Bronchial asthma, chronic obstructive pulmonary disease and interstitial pneumonia are the most common ailments treated by area hospitals. Levels of premature death, chronic bronchitis, and cardiovascular disease are increasing at a rapid rate.[10]
Particulate matter can clog stomatal openings of plants and interfere with photosynthesis functions.[50] In this manner high particulate matter concentrations in the atmosphere can lead to growth stunting or mortality in some plant species.
Due to the health effects of particulate matter, various governments have created regulations both for the emissions allowed from certain types of pollution sources (motor vehicles, industrial emissions etc.) and for the ambient concentration of particulates. 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.[citation needed] Much of the developing world, especially Asia, exceed standards by such a wide margin that even brief visits to these places may be unhealthy.[citation needed]
In Canada the standard for particulate matter is set nationally by the federal-provincial Canadian Council of Ministers of the Environment (CCME). Jurisdictions (provinces) may set more stringent standards. The CCME standard for particulate matter 2.5 (PM2.5) is 30 μg/m3 (daily average, i.e. 24-hour period, 3 year average, 98th percentile).[51]
The European Union has set limits for particulates in the air:[52]
| PM10 since 1 January 2005 |
PM2.5¹ from 1 January 2015 |
|
|---|---|---|
| Yearly average | 40 µg/m³ | 25 µg/m³ |
| Daily average (24-hour) Allowed number of exceedences per year |
50 µg/m³ 35 |
None
None |
¹ Target value entered into force 1.1.2010. Limit value enters into force 1.1.2015.
Hong Kong has set limits for particulates in the air:[53]
| PM10 | PM2.5 | |
|---|---|---|
| Yearly average | 55 µg/m³ | None |
| Daily average (24-hour) Allowed number of exceedences per year |
180 µg/m³ 1 |
None
None |
Hong Kong has proposed new limits on particulates and is planning to enforce them around 2014. Proposed limit on PM10 is 50 µg/m³ yearly average and 100 µg/m³ daily average. Proposed limit on PM2.5 is 35 µg/m³ yearly average and 75 µg/m³ daily average. Both daily averages may be exceeded 9 times per year.[54]
Japan has set limits for particulates in the air:[55][56]
| PM10[57] | PM2.5 since 21 September 2009 |
|
|---|---|---|
| Yearly average | None | 15 µg/m³ |
| Daily average (24-hour) Allowed number of exceedences per year |
100 µg/m³ or 200 µg/m³[58]
None |
35 µg/m³
None |
South Korea has set limits for particulates in the air:[59][60]
| PM10 since 4 December 2006 |
PM2.5 from 1 January 2015 |
|
|---|---|---|
| Yearly average | 50 µg/m³ | 25 µg/m³ |
| Daily average (24-hour) Allowed number of exceedences per year |
100 µg/m³ None |
50 µg/m³
None |
The United States Environmental Protection Agency (EPA) has set standards for PM10 and PM2.5 concentrations.[61] (See National Ambient Air Quality Standards)
| PM10 daily limit since 1987[62] |
PM2.5 daily limit since 2006 |
|
|---|---|---|
| Yearly average | None | 15 µg/m³ |
| Daily average (24-hour) Allowed number of exceedences per year |
150 µg/m³ 1 |
35 µg/m³ None |
In October 2008, the Department of Toxic Substances Control (DTSC), within the California Environmental Protection Agency, announced its intent to request information regarding analytical test methods, fate and transport in the environment, and other relevant information from manufacturers of carbon nanotubes.[63] DTSC is exercising its authority under the California Health and Safety Code, Chapter 699, sections 57018-57020.[64] These sections were added as a result of the adoption of Assembly Bill AB 289 (2006).[64] They are intended to make information on the fate and transport, detection and analysis, and other information on chemicals more available. The law places the responsibility to provide this information to the Department on those who manufacture or import the chemicals.
On January 22, 2009, a formal information request letter[65] was sent to manufacturers who produce or import carbon nanotubes in California, or who may export carbon nanotubes into the State.[66] This letter constitutes the first formal implementation of the authorities placed into statute by AB 289 and is directed to manufacturers of carbon nanotubes, both industry and academia within the State, and to manufacturers outside California who export carbon nanotubes to California. This request for information must be met by the manufacturers within one year. DTSC is waiting for the upcoming January 22, 2010 deadline for responses to the data call-in.
The California Nano Industry Network and DTSC hosted a full-day symposium on November 16, 2009 in Sacramento, CA. This symposium provided an opportunity to hear from nanotechnology industry experts and discuss future regulatory considerations in California.[67]
DTSC is expanding the Specific Chemical Information Call-in to members of the nanometal oxides, the latest information can be found on their website.[68]
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Key points in the Colorado Plan include reducing emission levels and solutions by sector. Agriculture, transportation, green electricity, and renewable energy research are the main concepts and goals in this plan. Political programs such as mandatory vehicle emissions testing and the prohibition of smoking indoors are actions taken by local government to create public awareness and participation in cleaner air. The location of Denver next to the Rocky Mountains and wide expanse of plains makes the metro area of Colorado's capital city a likely place for smog and visible air pollution.
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U.S. counties violating national PM2.5 standards
|
U.S. counties violating national PM10 standards
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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.[citation needed]
Mongolia's capital city Ulaanbaatar, is affected by choking air pollution caused by coal and wood burning stoves used for heating and cooking. The new market economy of the country and its very cold winter seasons have led to the formation of Ger districts, where 60% of the coldest capital city in the world's population resides. The resulting air pollution problem is characterized by very high concentrations of airborne particles, particulate matter, and by less severe sulphur dioxide and nitrogen oxide levels. Measurements carried out in UB shows that PM is by far the most serious component of the air pollution problem.[10]
During the winter months in particular, urban air obscures vision, and negatively impacts human health. The air pollution also affects the visibility in the city to such an extent that airplanes on some occasions are prevented from landing at the local airport. The annual average temperature in Ulaanbaatar is 0 C, making it the world's coldest capital city. About 40% of the population in Ulaanbaatar Mongolia lives in apartments, about 80% of them supplied with central heating systems from 3 combined heat and power plants (CHP). The power plants consumed almost 3.4 million tons of coal in 2007. The pollution control technology is in poor condition.
In addition to stack emissions, another unaccounted for source in the emission inventory is the fly ash from the ponds where fly ash is disposed. Removed fly ash is sent to settling tanks where the sedimented dust is collected and sent to the ash pond. These ash ponds are continually subjected to wind erosion in the dry season.
In Ulaanbaatar, Mongolia annual seasonal average particulate matter concentrations have been recorded as high as 279. To put this in perspective, the World Health Organization's recommended PM10 level is 20. This means that Ulaanbaatar's PM10 levels are 14 times higher than what is recommended. This also means that Ulaanbaatar has left Northern China's most polluted cities in its wake. Compared to such high concentrations, some cities in Northern China and South Asia also had concentrations above 200 micrograms per cubic meter up to a few years ago. The PM levels in Chinese cities are still extreme in recent years, reaching an all-time high in Beijing on Jan. 12, 2013, of 993 micrograms per cubic meter.[10]
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| リンク元 | 「SPM」「浮遊粒子状物質」 |
| 関連記事 | 「matter」「suspend」「particulate」「matt」 |