particulate pollution and stratospheric pollution

8/8/2019 Particulate Pollution and Stratospheric Pollution

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Air pollution is the introduction of chemicals, particulatematter, or biological materials that cause harm or discomfortto humans or other living organisms, or damages the naturalenvironment into the atmosphere.

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The atmosphere is a complex dynamic naturalgaseous system that is essential to support life on

planet Earth. Stratospheric ozone depletion due toair pollution has long been recognized as a threat tohuman health as well as to the Earth's ecosystems.

Indoor air pollution and urban air quality are listed astwo of the world's worst pollution problems in the2008 Blacksmith Institute World's Worst PollutedPlaces report.

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Particulates, alternatively known to as particulate matter(PM) or fine particles and also called soot, are tinysubdivisions of solid or liquid matter suspended in a gasor liquid. In contrast, aerosol refers to particles and thegas together.

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Sources of particulate matter can be man

made or natural. Air pollution and waterpollution can take the form of solid particulatematter, or be dissolved. Salt is an example of a

dissolved contaminant in water, while sand isgenerally a solid particulate.

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To improve water quality, solid particulates can be removed by

water filters or settling, and is referred to as insolubleparticulate matter. Dissolved contaminants in water are oftencollected by distilling - allowing the water to evaporate and thecontaminants to return to particle form and precipitate.

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Some particulates occur naturally, originating fromvolcanoes, dust storms, forest and grassland fires,living vegetation, and sea spray. Human activities, suchas the burning of fossil fuels in vehicles, power plantsand various industrial processes also generatesignificant amounts of aerosols. Averaged over theglobe, anthropogenic aerosols those made by humanactivities 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 tohealth hazards such as heart disease, altered lungfunction and lung cancer.

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Among the most common categorizations imposed on particulatesare those with respect to size, referred to as fractions. As particles areoften non-spherical (for example, asbestos fibers), there are manydefinitions of particle size. The most widely used definition is theaerodynamic diameter . A particle with an aerodynamic diameter of

10 micrometers moves in a gas like a sphere of unit density (1 gramper cubic centimeter) with a diameter of 10 micrometers. PMdiameters range from less than 10 nanometers to more than 10micrometers. These dimensions represent the continuum from a fewmolecules up to the size where particles can no longer be carried by agas.

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The notation PM 10 is used to describe particles of 10 micrometers or less and PM 2.5 representsparticles less than 2.5 micrometers inaerodynamic diameter.

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But because no sampler is perfect in the sensethat no particle larger than its cutoff diameterpasses the inlet, all reference methods allow ahigh margin of error. These are alsosometimes referred to with other equivalent

numeric values. Everything below 100 nm,down to the size of individual molecules isclassified as ultrafine particles (UFP or UP).

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N ote that PM 10-PM2.5 is the difference of PM 10 andPM2.5 , so that it only includes the coarse fraction of

PM10 .

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F raction Size range

PM10 (thoracic fraction)


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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 10excludes particles in a smaller size range, e.g. PM 2.5, usuallyreported separately in the same work. Such a case is sometimesemphasized with the difference notation, e.g. PM 10-PM2.5. Other

exceptions may be similarly specified.

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This is useful when not only the upper boundof a fraction is relevant to a discussion. Thefacts that some particle size ranges requiregreater filter strength and the smallest onescan outstrip the body's ability to keep them

out of cells both serve to guide understandingof related public policy, environment, andhealth topics.

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The composition of aerosol particles depends on their source.Wind-blown mineral dust tends to be made of mineral oxides

and other material blown from the Earth's crust; this aerosolis light-absorbing. Sea salt is considered the second-largestcontributor in the global aerosol budget, and consists mainly

of sodium chloride originated from sea spray; otherconstituents of atmospheric sea salt reflect the compositionof sea water, and thus include magnesium, sulfate, calcium,potassium, etc. In addition, sea spray aerosols may containorganic compounds, which influence their chemistry. Sea saltdoes not absorb.

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Secondary particles derive from the oxidation of primarygases such as sulfur and nitrogen oxides into sulfuric acid(liquid) and nitric acid (gaseous). The precursors for theseaerosols i.e. the gases from which they originate may havean anthropogenic origin (from fossil fuel combustion) and anatural 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. This is mainly because the presence of sulfate andnitrate causes the aerosols to increase to a size that scatterslight effectively.

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Organic matter (OM) can be either primary or secondary, thelatter part deriving from the oxidation of VOCs; organic materialin the atmosphere may either be biogenic or anthropogenic.Organic matter influences the atmospheric radiation field byboth scattering and absorption. Another important aerosol typeis constitute of elemental carbon (EC, also known as bl ack car b on , 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 thecarbonaceous fraction of aerosols.

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The chemical composition of the aerosol directly affects howit interacts with solar radiation. The chemical constituentswithin the aerosol change the overall refractive index. Therefractive index will determine how much light is scatteredand absorbed.

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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 amatter of hours whereas the smallest particles(less than 1 micrometer) can stay in theatmosphere for weeks and are mostly

removed by precipitation.

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Diesel particulate matter is highest near the

source of emission. Any info regarding DPMand the atmosphere, flora, height, anddistance from major sources would be usefulto determine health effects.

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All aerosols both absorb and scatter solar and terrestrialradiation. This is quantified in the S ing l e Scattering A lb edo(SSA), the ratio of scattering alone to scattering plusabsorption ( extinction ) of radiation by a particle. The SSAtends to unity if scattering dominates, with relatively littleabsorption, and decreases as absorption increases, becomingzero for infinite absorption.

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For example, sea-salt aerosol has an SSA of 1,

as a sea-salt particle only scatters, whereassoot has an SSA of 0.23, showing that it is amajor atmospheric aerosol absorber.

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Aerosols, natural and anthropogenic, can affect the climate bychanging the way radiation is transmitted through theatmosphere. Direct observations of the effects of aerosols are

quite limited so any attempt to estimate their global effectnecessarily involves the use of computer models. TheIntergovernmental Panel on Climate Change, IPCC, says: W hi l ethe radiative forcing due to greenhouse gases may b edetermined to a reasona bl y high degree of accuracy... theuncertainties re l ating to aeroso l radiative forcings remain l arge,and re l y to a l arge extent on the estimates from g l ob a l mode ll ing studies that are difficu l t to verify at the present time .

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A graphic showing the contributions (at 2000,relative to pre-industrial) and uncertainties of various forcings is available here

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Sulfate AerosolSulfate aerosol has two main effects, direct and indirect. Thedirect effect, via albedo, is to cool the planet: the IPCC's bestestimate of the radiative forcing is -0.4 watts per squaremeter with a range of -0.2 to -0.8 W/m but there aresubstantial uncertainties. The effect varies strongly

geographically, with most cooling believed to be at anddownwind of major industrial centres.

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Modern climate models attempting to deal with theattribution of recent climate change need to include sulfate

forcing, which appears to account (at least partly) for theslight drop in global temperature in the middle of the 20thcentury. The indirect effect (via the aerosol acting as cloudcondensation nuclei, CC N , and thereby modifying the cloudproperties -albedo and lifetime-) is more uncertain but is

believed to be a cooling.

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B lack carbonBlack carbon (BC), or carbon black, or elemental carbon (EC),often called soot, is composed of pure carbon clusters, skeletonballs and buckyballs, and is one of the most importantabsorbing aerosol species in the atmosphere. It should bedistinguished from organic carbon (OC): clustered or aggregatedorganic molecules on their own or permeating an EC buckyball.BC from fossil fuels is estimated by the IPCC in the FourthAssessment Report of the IPCC, TAR, to contribute a globalmean radiative forcing of +0.2 W/m (was +0.1 W/m in theSecond Assessment Report of the IPCC, SAR), with a range +0.1

to +0.4 W/m

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The large number of deaths and other health problemsassociated with particulate pollution was first demonstratedin the early 1970s and has been reproduced many timessince. PM pollution is estimated to cause 22,000-52,000deaths per year in the United States (from 2000) and 200,000deaths per year in Europe.

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The effects of inhaling particulate matter that have been widely studied in humansand animals now include asthma, lung cancer, cardiovascular issues, and prematuredeath. 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 can penetrate the deepest part of the lungs. Larger particles are generally filtered in the nose and throat and do notcause problems, but particulate matter smaller than about 10 micrometers,referred to as PM 10 , can settle in the bronchi and lungs and cause health problems.The 10 micrometer size does not represent a strict boundary between respirableand non-respirable particles, but has been agreed upon for monitoring of airborneparticulate matter by most regulatory agencies. Similarly, particles smaller than 2.5micrometers, PM 2 .5, tend to penetrate into the gas exchange regions of the lung,and very small particles (< 100 nanometers) may pass through the lungs to affectother organs. In particular, a study published in the Journal of the American

Medical Association indicates that PM 2.5 leads to high plaque deposits in arteries,causing vascular inflammation and atherosclerosis a hardening of the arteriesthat reduces elasticity, which can lead to heart attacks and other cardiovascularproblems. Researchers suggest that even short-term exposure at elevatedconcentrations could significantly contribute to heart disease.

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Researchers at the Johns Hopkins Bloomberg School of Public Healthhave conducted the largest nationwide study on the acute healtheffects of coarse particle pollution. Coarse particles are airborne

pollutants that fall between 2.5 and 10 micrometers in diameter.The study, published in the May 14, 2008, edition of JAMA, foundevidence of an association with hospital admissions forcardiovascular diseases but no evidence of an association with thenumber of hospital admissions for respiratory diseases. After taking

into account fine particle levels, the association with coarse particlesremained but was no longer statistically significant.

The smallest particles, less than 100 nanometers (nanoparticles),may be even more damaging to the cardiovascular system.

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There is evidence that particles smaller than 100 nanometers can passthrough cell membranes and migrate into other organs, including thebrain. It has been suggested that particulate matter can cause similar

brain damage as that found in Alzheimer patients. Particles emittedfrom modern diesel engines (commonly referred to as DieselParticulate Matter, or DPM) are typically in the size range of 100nanometers (0.1 micrometer). In addition, these soot particles alsocarry carcinogenic components like benzopyrenes adsorbed on their

surface. It is becoming increasingly clear that the legislative limits forengines, which are in terms of emitted mass, are not a proper measureof the health hazard. One particle of 10 m diameter hasapproximately the same mass as 1 million particles of 100 nmdiameter, 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 suggestionsto limit the particle surface area or the particle number.

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A further complexity that is not entirely documented is how

the shape of PM can affect health. Of course the dangerousfeathery shape of asbestos is widely recognised to lodge itself in the lungs with often dire consequences. Geometricallyangular shapes have more surface area than rounder shapes,which in turn affects the binding capacity of the particle toother, possibly more dangerous substances.

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Particulate matter can clog stomatal openingsof plants and interfere with photosynthesisfunctions. In this manner high particulate

matter concencentrations in the atmospherecan lead to growth stunting or mortality insome plant species.

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Climate effects can be extremely catastrophic; sulfur dioxideejected from the eruption of Huaynaputina probably causedthe Russian famine of 1 6 01 - 1 6 03, leading to the deaths of

two million.

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Particles can affect the climate in two different ways. The "directeffect" is caused by the fact that the particles scatter and absorb solarand infrared radiation in the atmosphere. As particles become The

"indirect effect" of particles are more complex and more difficult toassess. Changes in the number concentration of aerosols in theatmosphere causes variations in the population and size of clouddroplets. There is a set amount of water available for clouds. The watercan form large droplets within the clouds, which causes precipitation (amajor removal mechanism for aerosols).

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The addition of PM into the atmosphere causes thewater to condense on to the particles. This results in

more, but smaller droplets in the clouds, whichincreases the cloud albedo. In addition to increasingthe albedo, this effect tends to decrease the chanceof precipitation. If precipitation is suppressed, this

results in excess water remaining in the atmosphere

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Due to the health effects of particulate matter, maximumstandards have been set by various governments. Many urbanareas in the U.S. and Europe still frequently violate theparticulate standards, though urban air on these continentshas become cleaner, on average, with respect to particulatesover the last quarter of the 20th century. Much of thedeveloping world, especially Asia, exceed standards by such awide margin that even brief visits to these places may beunhealthy.

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The most concentrated particulate matter pollution tends tobe in densely populated metropolitan areas in developingcountries. The primary cause is the burning of fossil fuels bytransportation and industrial sources.

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Particulate matter studies in Bangkok Thailand indicated a

1.9% increased risk of dying from cardiovascular disease, and1.0% risk of all disease for every 10 micrograms per cubicmeter. Levels averaged 6 5 in 199 6 , 6 8 in 2002, and 52 in 2004.Decreasing levels may be attributed to conversions of dieselto natural gas combustion as well as improved regulations.

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M ost Polluted World Cities by P M

Particulate matter,g/m 3 (2004)

City

16 9 Cairo, Egypt150 Delhi, India

128 Kolkata, India (Calcutta)

125 T ianjin, China

123 Chongqing, China

109 Kanpur, India

109 Lucknow, India

104 Jakarta, Indonesia

101 Shenyang, China


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particulate pollution and stratospheric pollution

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