Particulates – also known as particulate matter (PM), suspended particulate matter (SPM), fine particles, and soot – are tiny subdivisions of solid matter suspended in a gas or liquid. In contrast, aerosol refers to particles and/or liquid droplets and the gas together. Sources of particulate matter can be man made or natural. Air pollution and water pollution can take the form of solid particulate matter, or be dissolved.[1] Salt is an example of a dissolved contaminant in water, while sand is generally a solid particulate.
To improve water quality, solid particulates can be removed by water filters or settling, and is referred to as insoluble particulate matter. Dissolved contaminants in water are often collected by distilling, allowing the water to evaporate and the contaminants to return to particle form and precipitate.
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. 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.[2] Increased levels of fine particles in the air are linked to health hazards such as heart disease, altered lung function and lung cancer.
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The composition of aerosols and particles depends on their source. Wind-blown mineral dust [1] tends to be made of mineral oxides and other material blown from the Earth's crust; this particulate is light-absorbing. Sea salt [2] 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.
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). Secondary sulfate and nitrate aerosols are strong light-scatterers. [3] 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 constitute of 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.ii [4]
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.[3]
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.
All aerosols absorb, scatter, and distribute solar and terrestrial radiation. This is quantified in 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.
Particulates and Aerosols, natural and anthropogenic, can affect the climate by changing the way radiation is transmitted through the atmosphere. Direct observations of the effects of aerosols are quite limited so any attempt to estimate their global effect necessarily involves the use of computer models. The Intergovernmental Panel on Climate Change, IPCC, 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 [5].
A graphic showing the contributions (at 2000, relative to pre-industrial) and uncertainties of various forcings is available here.
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 [6] 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, TAR, 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
The large number of deaths[4] and other health problems associated with particulate pollution was first demonstrated in the early 1970s [5] 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)[6] and 200,000 deaths per year in Europe.
The effects of inhaling particulate matter that have been widely studied in humans and animals now include asthma, lung cancer, cardiovascular issues, 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.[7] 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. In particular, 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.[8] 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.[9]
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 contaminate is dependent upon the form in which it exists (aerosol or particulate). Inhalation also depends upon the breathing rate of the subject. [10]
The smallest particles, less than 100 nanometers (nanoparticles), may be even more damaging to the cardiovascular system.[11]
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 number.
A further complexity that is not entirely documented is how the shape of PM can affect health. Of course the dangerous feathery 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). [12]
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.[13] 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.
Health effects on the public are considered to be caused by climate change, which is determined to be a result of increased global temperatures. An increased burden of malnutrition, diahhreal, cardio-respiratory, and infectious diseases, in addition to an increased morbidity and mortality caused by heat waves, floods, and droughts are all thought to be public health effects of global warming. Alarmingly, a change in the distribution of disease vectors, such as insects, is affecting public health, and thought to be initiated by climate change and air pollution. [14]
The primary health concern caused by air pollution, and particulate matter specifically is cardiovascular and respiratory diseases. The idea is that the earth has reached its carrying capacity and our ecological footprint is high across the world, and increasing. The rise of CVD as the leading cause of death in America and developing countries, and the world in general, is resulting in premature mortality that can directly be linked to air pollution. [15]
Particulate matter can clog stomatal openings of plants and interfere with photosynthesis functions.[18] In this manner high particulate matter concentrations in the atmosphere can lead to growth stunting or mortality in some plant species.
Climate effects can be extremely catastrophic; sulfur dioxide ejected from the eruption of Huaynaputina probably caused the Russian famine of 1601 - 1603, leading to the deaths of two million.
Particles can affect the climate in two different ways. The "direct effect" is caused by the fact that the particles scatter and absorb solar and infrared radiation in the atmosphere.[19] The "indirect effect" of particles are more complex and more difficult to assess. Changes in the concentration of aerosols and PM in the atmosphere cause variations in the density and size of cloud droplets. There is a set amount of water available for clouds. The water can form large droplets within the clouds, which causes precipitation (a major removal mechanism for aerosols and source of acid rain). The addition of PM into the atmosphere causes the water to condense on to the particles. This results in more, but smaller droplets in the clouds, which increases the cloud albedo. In addition to increasing the albedo, this effect tends to decrease the chance of precipitation. If precipitation is suppressed, this results in excess water remaining in the atmosphere.[20]
The primary concern for climate effects of air pollution is an increase in global average temperatures. Greenhouse gases produced as a result of human activity trap heat in earth's atmosphere, warming the surface. Urbanization and industrialization is the main cause of airborn particulate matter, and so it follows that air pollution is a more serious threat in densely populated areas. Electricity and heat produced by antiquated methods such as wood burning and coal combustion is still the primary method for sustaining everyday life in developing countries. Climate effects inevitably lead to health effects, which are listed above, but consist mainly of respiratory problems, cardiovascular disease, and premature death. [21]
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. Much of the developing world, especially Asia, exceed standards by such a wide margin that even brief visits to these places may be unhealthy.
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 is 30 ug/m3 (daily average, i.e. 24-hour period, 3 year average, 98th percentile)[22].
In directives 1999/30/EC and 96/62/EC, the European Commission has set limits for PM10 in the air:
| Phase 1 from 1 January 2005 |
Phase 2¹ from 1 January 2010 |
|
|---|---|---|
| Yearly average | 40 µg/m³ | 20 µg/m³ |
| Daily average (24-hour) allowed number of exceedences per year. |
50 µg/m³ 35 |
50 µg/m³ 7 |
¹ indicative value.
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. [23]
Suggested solutions and interventions include fuel gas desulfurization (FGD) technology and electro-static precipitators (ESP) at existing power plants, which are estimated to reduce PM concentrations 10% to 20%. Public awareness must be increased for laws and initiatives such as a 50% rebate on night time electric bills. In February 2011 the "Law on Air Pollution Reduction in the Capital City" was passed. This law includes fines for people and businesses not following limits, and tax incentives to individuals and businesses reducing air pollution. A recent list of the World's worst polluters published by Daily Finance on November 29, 2010 ranks Ulaanbaatar 5th in the world, a real tragedy considering its population only hovers around the 1.3 million mark. [24]
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 UB is 0 C, making it the world's coldest capital city. About 40% of the population in UB 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 UB's PM10 levels are 14 times higher than what is recommended. This also means that UB 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 meter cubed up to a few years ago. The PM levels in Chinese cities are being reduced in recent years. [25]
The United States Environmental Protection Agency (EPA) sets standards for PM10 and PM2.5 concentrations in urban air. (See National Ambient Air Quality Standards.) EPA regulates primary particulate emissions and precursors to secondary emissions (NOx, sulfur, and ammonia). The U.S. climate policy under the Bush administration held a goal to cut greenhouse gases by 18% between 2002 and 2012. Bush set out to encourage energy efficiency renewable energy, and agricultural practices. Under the Obama administration the U.S. climate policy sets out to change Corporate Average Fuel Economy (CAFE) standards to 35.5 miles per gallon by 2016, 4 years ahead of the 2007 schedule. In December 2009 Obama participated in the United Nation's Climate Change Conference. [26]
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.[27] DTSC is exercising its authority under the California Health and Safety Code, Chapter 699, sections 57018-57020.[28] These sections were added as a result of the adoption of Assembly Bill AB 289 (2006). 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 was sent to manufacturers who produce or import carbon nanotubes in California, or who may export carbon nanotubes into the State. 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.[29]
DTSC is expanding the Specific Chemical Information Call-in to members of the nanometal oxides, the latest information can be found on their website.[30]
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.
During November and December 2011, the values for particulate matter concentrations in Skopje, Macedonia have been record high, with daily average of 500. The values are taken from a page supported by the city authorities. [31]
| Most Polluted World Cities by PM[32] | |
|---|---|
| Particulate matter, μg/m3 (2004 and 2011) |
City |
| 508 | Skopje, Macedonia |
| 279 | Korfu, Greece |
| 169 | Cairo, Egypt |
| 150 | Delhi, India |
| 128 | Kolkata, India (Calcutta) |
| 125 | Tianjin, 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.
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