CE2038 U1 Notes

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AIR POLLUTION MANAGEMENT

Unit : 1

Definition:

Air pollution may be defined as the presence in the air (outdoor atmosphere) of one

or more contaminants or combinations thereof in such quantities and of such durations as

may be or tend to be injurious to human, animal or plant life, or property, or which

unreasonably interferes with the comfortable enjoyment of life or property or conduct of

business. Air pollution is any atmospheric condition in which certain substances are

present in such concentrations that they can produce undesirable effects on man and his

environment.

Substances like gases, radioactive materials and many others,

a) Example for gases substances like sulphur oxides, nitrogen oxides, carbon

monoxide, hydrocarbons etc.,

b) Example for particulate matter like smoke, dust, fumes, aerosols.

Most of these substances are naturally present in the atmosphere in low

(background) concentration and usually considered to be harmless.

Particulate substance can be considered an air pollutant only. When its

concentration is relatively high compared with the background value and causes

adverse effects.

For e.g. sulphur dioxide, if present in the atmosphere in concentration greater than

the background value of 2x10-4 ppm and cause measurable effects on humans,

animals, plants or property, then only it is clarified as a air pollutant.

Classification of air pollutants:

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The variety of matter emitted into the atmosphere by natural and anthropogenic

sources. It’s classified into two categories,

a) Primary pollutants

b) Secondary pollutants

a) Primary pollutants:

Those that are emitted directly from the sources. Typically pollutants included under

this category,

Particulate matter for eg, ash, smoke, dust, fumes, mist and spray.

Inorganic gases such as sulphur dioxide, hydrogen sulphide, nitric

oxide, ammonia, carbon monoxide, carbon dioxide and hydrogen

fluoride, olefinic and aromatic hydrocarbons.

Radioactive compounds.

b) Secondary pollutants:

Those that are formed in the atmosphere by chemical interactions.

Among primary pollutants and normal atmospheric constituents.

Secondary pollutants such as ,

Sulphur trioxide, Nitrogen dioxide, PAN (peroxyacetyl nitrate), Ozone,

Aldehydes, Ketones, and various Sulphate and Nitrate salts are

included in this category.

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Particulate Matter and Gaseous Pollutants:

Particulate Matter:

In general the term “particulate” refers to all atmospheric substances that are not

gases. They can be suspended droplets or solid particles or mixtures of the two.

Particulates can be composed of inert or extremely reactive materials ranging in size from

100 µm down to 0.1µm and less. The inert materials do not react readily with the

environment not do they exhibit any morphological changes as a result of combustion or

any other process, Where as the reactive materials could be further oxidized or may react

chemically with the environment.

The classification of various particulates may be made as follows;

Dust :

It contains particles of the size ranging from 1 to 200µm. These are formed by

natural disintegration of rock and soil or by the mechanical processes of grinding and

spraying.

They have large settling velocities and are removed from the air by gravity and

other inertial process Fine dust particles at act as centers of catalysis for many of the

chemical reactions taking place in the atmosphere.

Smoke :

It contains fine particles of the size ranging from 0.01 to 1 µm which can be

liquid or solid, and are formed by combustion or other chemical process. smoke may

have different colours depending on the nature of materials burnt.

Fumes:

There are solid particles of the size ranging from 0.1 to 1µm and are normally

released from chemical or metallurgical processes.

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Mist:

It is made up of liquid droplets generally smaller than 10µm which are

formed by condensation in the atmosphere or are released from industrial

operations.

Fog:

It is the mist in which the liquid is water and is sufficiently dense to obscure

vision.

Aerosols:

In this category are included all air – borne suspensions ether solid or liquid,

these are generally smaller than 1 µm.

Particles in the size range 1 to 10µm have measureable settling velocities but

are readily stirred by air movements, whereas particles size 0.1 – 1 µm have small

settling velocities. These below 0.1µm, a submicroscopic size found in urban air,

undergo random Brownian motion resulting from collisions among individual

molecules.

Fig 2.1 compares the size of atmospheric particulates from various sources.

Most particulates in urban air have sizes in the range 0.1- 10µm. The finest and the

smallest particles are the ones which cause significant damage to health.

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Virus

(Aitken

Tobacco

Deposition In

carbon

Oil

Sea

Combustion nuclel

Nucles)

Condensation

Smoke

respiratory

Mist, fog,

Black

smoke

Salt nuclel

(Large

Nuclel

Coal

Fly

Cement

track

cloud

insecticide

Bacteria

Particles)

Dust

Ash

Pollen

Dust

droplets

dust

0.001 0.01 0.1 1.0 10 100

Fig 1.1. Sizes of Atmospheric particulate matter.

SMOG

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Gaseous pollutants:

Of all the different types of particulates in the atmosphere, the presence of trace

elements such as cadmium, lead, nickel and mercury may constitute the greatest health

hazard. Many of the trace metals are toxic and are concentrated in the finest of particulate

matter in a variety of combined forms such as oxides, hydroxides, sulphates and nitrates.

Oxides of Sulphur:

i) The most important oxide emitted by pollution sources is sulphur dioxide

(So2).

ii) So2 is a colourless gas with characteristics, sharp, pungent odour.

iii) It is moderately soluble in water (11.3 g/100ml) forming weakly acidic

sulphurous acid (H2So3).

iv) In a polluted atmosphere, So2 reacts photochemically or catalytically with

other pollutants or normal atmospheric constituents to form sulphur

trioxide, sulphuric acid and salts of sulphuric acid.

v) Sulphur trioxide (S02) is generally emitted along with S02, at about 1 – 5

percent of the S02 concentration.So3 rapidly combines with moisture in the

atmosphere to form sulphuric acid which has a low dew point.

vi) Both S02 and S03 are relatively quickly washed out of the atmosphere by rain

or settle out as aerosols.

Nitrogen oxides:

i) Of the six or seven oxides of Nitrogen, only three Nitrous oxide (N2O), Nitric

oxide (NO), and Nitrogen dioxide (NO2) – are formed in any appreciable

quantities in the atmosphere.

ii) Often NO and NO2 are analysed together in air and are referred to as NOx.

iii) Nitric oxide is a colourless, odourlessgas produced largely by fuel

combustion. It is oxidized to NO2 in a polluted atmosphere through

photochemical secondary reactions.

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iv) Nitrogen dioxide is a brown pungent gas with an irritating odour which can

be detected at concentrations of about 0.12ppm.

v) It absorbs sunlight and initiates a series of photochemical reactions.

vi) NO2 is probably produced by the oxidation of NO by ozone. Nitrogen dioxide

is of major conern as a pollutant.It is emitted by fuel combustion and Nitric

acid plants.

Carbon monoxide:

i) It constitutes the single largest pollutant in the urban atmosphere.

ii) CO is colourless, odourless and tasteless and has a birling point of – 192’c.

iii) It has a strong affinity towards the hemoglobin of the bloodstream and is a

dangerous asphysciant.

iv) Carbon monoxide is present in small concentrations (0.1 ppm) in the natural

atmosphere and has a residence time of about six months.

v) The main sources of CO in the urban air smoke and exhaust fumes of many

devices burning coal, gas or oil.

Hydrocarbons:

i) The gaseous and volatile liquid hydrocarbons are of particular interest as air

pollutants.

ii) In the saturated class methane is by far the most abundant hydrocarbons

present in an urban atmosphere.

iii) The hydrocarbons in air by themselves alone cause no harmful effects. They

are of concern because the hydrocarbons undergo chemical reactions in the

presence of sunlight and nitrogen oxides forming photochemical oxidants of

which the predominant one is ozone.

iv) Methane has very low photochemical activity as compared to that of other

hydrocarbons. For this reason, it is the non- methane hydrocarbon

concentration that is of interest while considering air pollution.

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Sources of Air pollution

Sources of air pollution refer to the various locations, activities or factors which are

responsible for the releasing of pollutants into the atmosphere. These sources can be

classified into two major categories which are:

Anthropogenic sources (human activity) mostly related to burning different kinds of fuel

"Stationary Sources" include smoke stacks of power plants, manufacturing

facilities (factories) and waste incinerators, as well as furnaces and other types

of fuel-burning heating devices

"Mobile Sources" include motor vehicles, marine vessels, aircraft and the effect

of sound etc.

Chemicals, dust and controlled burn practices in agriculture and forestry

management. Controlled or prescribed burning is a technique sometimes used in

forest management, farming, prairie restoration or greenhouse gas abatement.

Fire is a natural part of both forest and grassland ecology and controlled fire can

be a tool for foresters. Controlled burning stimulates the germination of some

desirable forest trees, thus renewing the forest.

Fumes from paint, hair spray, varnish, aerosol sprays and other solvents

Waste deposition in landfills, which generate methane. Methane is not toxic;

however, it is highly flammable and may form explosive mixtures with air.

Methane is also an asphyxiant and may displace oxygen in an enclosed space.

Asphyxia or suffocation may result if the oxygen concentration is reduced to

below 19.5% by displacement

Military, such as nuclear weapons, toxic gases, germ warfare and rocketry

Natural sources:

Dust from natural sources, usually large areas of land with little or no vegetation

Methane, emitted by the digestion of food by animals, for example cattle

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Radon gas from radioactive decay within the Earth's crust. Radon is a colorless,

odorless, naturally occurring, radioactive noble gas that is formed from the decay of

radium. It is considered to be a health hazard. Radon gas from natural sources can

accumulate in buildings, especially in confined areas such as the basement and it is

the second most frequent cause of lung cancer, after cigarette smoking

Smoke and carbon monoxide from wildfires

Vegetation, in some regions, emits environmentally significant amounts of VOCs on

warmer days. These VOCs react with primary anthropogenic pollutants—

specifically, NOx, SO2, and anthropogenic organic carbon compounds—to produce a

seasonal haze of secondary pollutants.[6]

Volcanic activity, which produce sulfur, chlorine, and ash particulates

Emission inventory

An emission inventory is an accounting of the amount of pollutants discharged into

the atmosphere. An emission inventory usually contains the total emissions for one or

more specific greenhouse gases or air pollutants, originating from all source categories in a

certain geographical area and within a specified time span, usually a specific year.

An emission inventory is generally characterized by the following aspects:

Why: The types of activities that cause emissions,

What: The chemical or physical identity of the pollutants included,

Where: The geographic area covered,

When: The time period over which emissions are estimated,

How: The methodology to use.

Emission inventories are compiled for both scientific applications and for use in policy

processes.

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Effects of air pollution;

The pollutants are to overwhelm the natural scavenging ability of the atmosphere.

As a result, the concentrations of the pollutants persist at levels which are much higher

than the allowable background levels.

This is particularly true for urban and other industrial regions where the pollutants

adversely affect the health of humans and animals and cause plant and material damage.

Effects of Human Health:

Adverse effects of air pollution may be divided into two classes

i) Acute effects

ii) Chronic effects

Acute effects manifest themselves immediately upon short term exposure to air

pollutants at high concentrations, and chronic effects become evident only after continuous

exposure to low levels of air pollution.

Epidemiological studies are statistical surveys on the effects of air pollution on

human populations under natural conditions. Such studies are extremely important, but

due to the multiplicity of unknown factors it is not possible to establish a cause effect

relationship.

Toxicological studies are conducted in the laboratory under controlled conditions.

The effect of several variables such as pollutants concentration, exposure duration,

temperature, humidity, etc., can be experimentally studied.

Even though there experimental studies can clearly demonstrate a direct cause

effect relationship between certain pollutants and sickness or death, their relevance to

natural setting is sometimes questionable.

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Respiratory Effects:

Pollutants may enter the body by a number of ways. They can cause eye and skin

irritation. Certain particulates may be swallowed asa result of internal respiratory cleaning

action or certain pollutants could even be ingested. But the primary mode of pollutant

transfer into the human body is through the respiratory system.

The respiratory systemic composed primary of two lungs and the air passages

which lead to them. The air passages begin at the nose and mouth, and include windpipe

(trachea) and its two branches known as bronchi.

Particulate matter inhaled may be deposited in various regions of the respiratory

system depending on particle size. Particle above 10µm are almost wholly retained in the

nose.

The health risk is primarily from the deposition of the particles smaller than 0.5µm

in the alveoli where they cause damage to the respiratory organs.

Air pollution effects on Vegetation

The most obvious damage caused by air pollutants to pollutants to vegetation

occurs in the leaf structure. The surface of a leaf is covered by a waxy layer known as the

cuticle.

Its chief functions are the protection of the inner tissues from excessive moisture

loss and the admission of carbon dioxide and oxygen to these internal tissues. The leaf

surface is penetrated by a large number of openings called the stomata’s.

The damage caused by air pollutants is of several types like necrosis, chlorosis and

epinasty. The dead areas on a leaf structures are referred to as necrosis. Chlorosis is the

loss or reduction of chlorophyll and lead to the yellowing of the leaf.

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Epinasty is a downward curvature of the leaf due to higher rate of growth on the

upper surface, and the dropping of leaves called abscission. Few plant species are spared

damage on exposure to one or more of the principle air pollutants.

In general, the pollutants enter the inner tissue through the stomata, where they

destroy the chlorophyll and disrupt photosynthesis. The adverse effects range from

reduction in growth rate to death of the plant. The effect of particulates on vegetation is not

well known. However, some specific dusts have been observed to cause damage.

Cement dust deposited on leaves, on combination with mist or light rain, forms

incrustation. Plugging of stomata may occur, resulting in plant damage.

Chemicals such as arsenic and fluorides when deposited on the leaves can poison

animals.

Effects of Air pollution on materials

The damage caused by atmospheric pollutants to materials is a well known

phenomenon. Particulates such as soot, dust and fumes soil painted surface, fabrics and

buildings, and because of their abrasive nature, particulates can cause damage to exposed

surface when they are driven by wind at high velocities. Through their own corrosiveness

or in the presence of SO2 and moisture, they can accelerate the corrosion of steel, copper,

zinc and other metals.

The most notorious pollutant responsible for metallic corrosion is sulphur dioxide.

It has been reported that corrosion of hard metals such as steel begins at annual mean

concentrations of 0.02ppm (52µg /m3).

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SO2 is readily absorbed by leather and causes its disintegration. Paper is also

discolored by SO2 and becomes brittle and fragile. Sulphuric acid mist in the atmosphere

causes deterioration of structural materials such as marble and limestone.

Ozone is a very reactive substance. Much of the degradation of materials, such as

fabrics and rubber, now attributed to weathering is caused primarily by ozone.

The fading of fibers and the cracking of rubber are attributed to ozone’s oxidizing

ability. Nitrogen oxides, although less widely published them ozone, are known to cause

fading in acetate, cotton and rayon fibers at levels of 0.6 -2 ppm over 2 – 3 month period. It

has been observed that particulate Nitrates attack and damage nickel – brass alloys in the

presence of moisture.

Global warming

Global warming refers to the rising average temperature of Earth's atmosphere and

oceans and its projected continuation. In the last 100 years, Earth's average surface

temperature increased by about 0.8 °C (1.4 °F) with about two thirds of the increase

occurring over just the last three decades. Warming of the climate system is unequivocal,

and scientists are more than 90% certain most of it is caused by increasing concentrations

of greenhouse gases produced by human activities such as deforestation and burning fossil

fuels. These findings are recognized by the national science academies of all the major

industrialized countries.

Climate model projections are summarized in the 2007 Fourth Assessment Report

(AR4) by the Intergovernmental Panel on Climate Change (IPCC). They indicate that during

the 21st century the global surface temperature is likely to rise a further 1.1 to 2.9 °C (2 to

5.2 °F) for their lowest emissions scenario and 2.4 to 6.4 °C (4.3 to 11.5 °F) for their

highest. The ranges of these estimates arise from the use of models with differing

sensitivity to greenhouse gas concentrations.

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An increase in global temperature will cause sea levels to rise and will change the

amount and pattern of precipitation, and a probable expansion of subtropical deserts.

Warming is expected to be strongest in the Arctic and would be associated with continuing

retreat of glaciers, permafrost and sea ice. Other likely effects of the warming include more

frequent occurrence of extreme weather events including heat waves, droughts and heavy

rainfall events, species extinctions due to shifting temperature regimes, and changes in

agricultural yields. Warming and related changes will vary from region to region around

the globe, with projections being more robust in some areas than others.[12] In a 4 °C world,

the limits for human adaptation are likely to be exceeded in many parts of the world, while

the limits for adaptation for natural systems would largely be exceeded throughout the

world. Hence, the ecosystem services upon which human livelihoods depend would not be

preserved.

Initial causes of temperature changes (external forcings)

Greenhouse effect schematic showing energy flows between space, the atmosphere,

and earth's surface. Energy exchanges are expressed in watts per square meter (W/m2).

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This graph, known as the "Keeling Curve", shows the long-term increase of

atmospheric carbon dioxide (CO2) concentrations from 1958–2008. Monthly CO2

measurements display seasonal oscillations in an upward trend; each year's maximum

occurs during the Northern Hemisphere's late spring, and declines during its growing

season as plants remove some atmospheric CO2.

External forcing refers to processes external to the climate system (though not

necessarily external to Earth) that influence climate. Climate responds to several types of

external forcing, such as radioactive forcing due to changes in atmospheric composition

(mainly greenhouse gas concentrations), changes in solar luminosity, volcanic eruptions,

and variations in Earth's orbit around the Sun. Attribution of recent climate change focuses

on the first three types of forcing. Orbital cycles vary slowly over tens of thousands of years

and at present are in an overall cooling trend which would be expected to lead towards an

ice age, but the 20th century instrumental temperature record shows a sudden rise in

global temperatures.

Mitigation

Reducing the amount of future climate change is called mitigation of climate change.

The IPCC defines mitigation as activities that reduce greenhouse gas (GHG) emissions, or

enhance the capacity of carbon sinks to absorb GHGs from the atmosphere. Many countries,

both developing and developed, are aiming to use cleaner, less polluting, technologies.:192

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Use of these technologies aids mitigation and could result in substantial reductions in CO2

emissions. Policies include targets for emissions reductions, increased use of renewable

energy, and increased energy efficiency. Studies indicate substantial potential for future

reductions in emissions.

To limit warming to the lower range in the overall IPCC's "Summary Report for

Policymakers" means adopting policies that will limit emissions to one of the significantly

different scenarios described in the full report. This will become more and more difficult,

since each year of high emissions will require even more drastic measures in later years to

stabilize at a desired atmospheric concentration of greenhouse gases, and energy-related

carbon-dioxide (CO2) emissions in 2010 were the highest in history, breaking the prior

record set in 2008.

Since even in the most optimistic scenario, fossil fuels are going to be used for years

to come, mitigation may also involve carbon capture and storage, a process that traps CO2

produced by factories and gas or coal power stations and then stores it, usually

underground

Ozone depletion

Image of the largest Antarctic ozone hole ever recorded (September 2006), over the

Southern pole

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Ozone depletion describes two distinct but related phenomena observed since the

late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's

stratosphere (the ozone layer), and a much larger springtime decrease in stratospheric

ozone over Earth's Polar Regions. The latter phenomenon is referred to as the ozone hole.

In addition to these well-known stratospheric phenomena, there are also springtime polar

troposphere ozone depletion events.

The details of polar ozone hole formation differ from that of mid-latitude thinning,

but the most important process in both is catalytic destruction of ozone by atomic

halogens.[1] The main source of these halogen atoms in the stratosphere is photo

dissociation of man-made halocarbon refrigerants (CFCs, freons, halons). These

compounds are transported into the stratosphere after being emitted at the surface. [2]

Both types of ozone depletion were observed to increase as emissions of halo-carbons

increased.

CFCs and other contributory substances are referred to as ozone-depleting

substances (ODS). Since the ozone layer prevents most harmful UVB wavelengths (280–

315 nm) of ultraviolet light (UV light) from passing through the Earth's atmosphere,

observed and projected decreases in ozone have generated worldwide concern leading to

adoption of the Montreal Protocol that bans the production of CFCs, halons, and other

ozone-depleting chemicals such as carbon tetrachloride and trichloroethane. It is suspected

that a variety of biological consequences such as increases in skin cancer, cataracts, damage

to plants, and reduction of plankton populations in the ocean's photic zone may result from

the increased UV exposure due to ozone depletion.

Ozone cycle overview

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The ozone cycle Three forms (or allotropes) of oxygen are involved in the ozone-

oxygen cycle: oxygen atoms (O or atomic oxygen), oxygen gas (O2 or diatomic oxygen), and

ozone gas (O3 or diatomic oxygen). Ozone is formed in the stratosphere when oxygen

molecules photo dissociate after absorbing an ultraviolet photon whose wavelength is

shorter than 240 nm. This converts a single O2 into two atomic oxygen ions. The atomic

oxygen ions then combine with separate O2 molecules to create two O3 molecules. These

ozone molecules absorb UV light between 310 and 200 nm, following which ozone splits

into a molecule of O2 and an oxygen atom. The oxygen atom then joins up with an oxygen

molecule to regenerate ozone. This is a continuing process which terminates when an

oxygen atom "recombines" with an ozone molecule to make two O2 molecules.

O + O3 → 2 O2 chemical equation

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Global monthly average total ozone amount. Layers of the atmosphere (not to scale)

The overall amount of ozone in the stratosphere is determined by a balance

between photochemical production and recombination.

Ozone can be destroyed by a number of free radical catalysts, the most important of

which are the hydroxyl radical (OH·), the nitric oxide radical (NO·), the atomic chlorine ion

(Cl·) and the atomic bromine ion (Br·). All of these have both natural and man-made

sources; at the present time, most of the OH· and NO· in the stratosphere is of natural

origin, but human activity has dramatically increased the levels of chlorine and bromine.

These elements are found in certain stable organic compounds, especially

chlorofluorocarbons (CFCs), which may find their way to the stratosphere without being

destroyed in the troposphere due to their low reactivity. Once in the stratosphere, the Cl

and Br atoms are liberated from the parent compounds by the action of ultraviolet light, e.g.

CFCl3 + electromagnetic radiation → CFCl2 + Cl

The Cl and Br atoms can then destroy ozone molecules through a variety of catalytic

cycles. In the simplest example of such a cycle, a chlorine atom reacts with an ozone

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molecule, taking an oxygen atom with it (forming ClO) and leaving a normal oxygen

molecule. The chlorine monoxide (i.e., the ClO) can react with a second molecule of ozone

(i.e., O3) to yield another chlorine atom and two molecules of oxygen. The chemical

shorthand for these gas-phase reactions is:

Cl + O3 → ClO + O2 – The chlorine atom changes an ozone molecule to ordinary

oxygen

ClO + O3 → Cl + 2 O2 – The ClO from the previous reaction destroys a second ozone

molecule and recreates the original chlorine atom, which can repeat the first

reaction and continue to destroy ozone

The overall effect is a decrease in the amount of ozone. More complicated mechanisms have

been discovered that lead to ozone destruction in the lower stratosphere as well.

Atmosphere by chlorofluorocarbons (CFCs) yearly demonstrates how dangerous CFCs are

to the environment.

Lowest value of ozone measured by TOMS each year in the ozone hole.

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Reductions of up to 70% in the ozone column observed in the austral (southern

hemispheric) spring over Antarctica and first reported in 1985 (Farman et al. 1985) are

continuing. Through the 1990s, total column ozone in September and October have

continued to be 40–50% lower than pre-ozone-hole values. In the Arctic the amount lost is

more variable year-to-year than in the Antarctic. The greatest declines, up to 30%, are in

the winter and spring, when the stratosphere is colder.

Reactions that take place on polar stratospheric clouds (PSCs) play an important

role in enhancing ozone depletion. PSCs form more readily in the extreme cold of Antarctic

stratosphere. This is why ozone holes first formed, and are deeper, over Antarctica. Early

models failed to take PSCs into account and predicted a gradual global depletion, which is

why the sudden Antarctic ozone hole was such a surprise to many scientists.

The ozone hole and its causes

Ozone hole in North America during 1984 (abnormally warm reducing ozone

depletion) and 1997 (abnormally cold resulting in increased seasonal depletion). Source:

NASA

The Antarctic ozone hole is an area of the Antarctic stratosphere in which the recent

ozone levels have dropped to as low as 33% of their pre-1975 values. The ozone hole

occurs during the Antarctic spring, from September to early December, as strong westerly

winds start to circulate around the continent and create an atmospheric container. Within

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this polar vortex, over 50% of the lower stratospheric ozone is destroyed during the

Antarctic spring.

As explained above, the primary cause of ozone depletion is the presence of

chlorine-containing source gases (primarily CFCs and related halocarbons). In the presence

of UV light, these gases dissociate, releasing chlorine atoms, which then go on to catalyze

ozone destruction. The Cl-catalyzed ozone depletion can take place in the gas phase, but it

is dramatically enhanced in the presence of polar stratospheric clouds (PSCs).

These polar stratospheric clouds(PSC) form during winter, in the extreme cold.

Polar winters are dark, consisting of 3 months without solar radiation (sunlight). The lack

of sunlight contributes to a decrease in temperature and the polar vortex traps and chills

air. Temperatures hover around or below −80 °C. These low temperatures form cloud

particles. There are three types of PSC clouds; nitric acid trihydrate clouds, slowly cooling

water-ice clouds, and rapid cooling water-ice(nacerous) clouds; that provide surfaces for

chemical reactions that lead to ozone destruction.[17]

The photochemical processes involved are complex but well understood. The key

observation is that, ordinarily, most of the chlorine in the stratosphere resides in stable

"reservoir" compounds, primarily hydrochloric acid (HCl) and chlorine nitrate (ClONO2).

During the Antarctic winter and spring, however, reactions on the surface of the polar

stratospheric cloud particles convert these "reservoir" compounds into reactive free

radicals (Cl and ClO). The clouds can also remove NO2 from the atmosphere by converting it

to nitric acid, which prevents the newly formed ClO from being converted back into

ClONO2.

The role of sunlight in ozone depletion is the reason why the Antarctic ozone

depletion is greatest during spring. During winter, even though PSCs are at their most

abundant, there is no light over the pole to drive the chemical reactions. During the spring,

however, the sun comes out, providing energy to drive photochemical reactions, and melt

the polar stratospheric clouds, releasing the trapped compounds. Warming temperatures

near the end of spring break up the vortex around mid-December. As warm, ozone-rich air

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flows in from lower latitudes, the PSCs are destroyed, the ozone depletion process shuts

down, and the ozone hole closes.

Most of the ozone that is destroyed is in the lower stratosphere, in contrast to the much

smaller ozone depletion through homogeneous gas phase reactions, which occurs primarily

in the upper stratosphere.

Effects on non-human animals

A November 2010 report by scientists at the Institute of Zoology in London found

that whales off the coast of California have shown a sharp rise in sun damage, and these

scientists "fear that the thinning ozone layer is to blame"

The study photographed and took skin biopsies from over 150 whales in the Gulf of

California and found "widespread evidence of epidermal damage commonly associated

with acute and severe sunburn," having cells which form when the DNA is damaged by UV

radiation. The findings suggest "rising UV levels as a result of ozone depletion are to blame

for the observed skin damage, in the same way that human skin cancer rates have been on

the increase in recent decades."

Effects on crops

An increase of UV radiation would be expected to affect crops. A number of

economically important species of plants, such as rice, depend on cyanobacteria residing on

their roots for the retention of nitrogen. Cyanobacteria are sensitive to UV light and would

be affected by its increase.

Sampling and analysis

Sampling is an important component of any piece of research because of the

significant impact that it can have on the quality of your results (or findings). If you are new

to sampling, there are a number of key terms and basic principles that act as a foundation

to the subject. This article explains these key terms and basic principles. Rather than a

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comprehensive look at sampling, the article presents the sampling basics that you would

need to know if you were an undergraduate or master’s level student about to perform a

dissertation (or similar piece of research).

Principles of Sampling and Analysis

The components of an air pollution monitoring system include the collection or

sampling of pollutants both from the ambient air and from specific sources, the analysis or

measurement of the pollutant concentrations, and the reporting and use of the information

collected. Emissions data collected from point sources are used to determine compliance

with air pollution regulations, determine the effectiveness of air pollution control

technology, evaluate production efficiencies, and support scientific research.

The EPA Office of Research and Development (ORD) has developed Federal

Reference Methods (FRMs) and Federal Equivalent Methods (FEMs) for sampling and

analysis of pollutants in the ambient air and from emissions sources. As technology

changes, EPA updates and revises these methods. FRMs and FEMs can be either manual or

automated. Manual methods are specific techniques that must be followed when collecting

and analyzing an air pollutant sample. An automated method usually refers to an

instrument that has been approved by EPA as meeting the technical requirements for

accurate collection and analysis of a pollutant. In the monitoring stations used throughout

the country, automated methods are primarily used to collect and analyze ambient air on a

continuous basis.

The EPA has established ambient air monitoring methods for the criteria pollutants,

as well as for toxic organic (TO) compounds and inorganic (IO) compounds. The designated

ambient methods for the criteria pollutants are listed on the EPA Ambient Monitoring

Technology Center's (AMTIC) Ambient Air Monitoring Methods for Criteria Pollutants Web

page. In addition, the TO Compendium contains standardized methods for monitoring

VOC's and selected toxic organics, and the IO Compendium contains methods for

monitoring inorganic compounds.

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The methods specify precise procedures that must be followed for any monitoring

activity related to the compliance provisions of the Clean Air Act. These procedures

regulate sampling, analysis, calibration of instruments, and calculation of emissions. The

specific method chosen for an analysis depends on a number of factors, the most important

being the chemical characteristics and state of the pollutant. All the reference methods are

designed to determine the actual concentration of a pollutant in a sample. The

concentration is expressed in terms of mass per unit volume, usually micrograms per cubic

meter (µg/m3).

Source and ambient air sampling

The sampling should be carried out long enough and at a rate that allows collection

of an analytically measureable sample. There are both gaseous and particulate air

pollutants whose concentrations occur at levels below are milligram per cubic metre of air.

A typical air sampling system consists of a sample collector, a flowmeter to measure

the airflow through the collector, and a pump to draw the air sampling equipment. The

flowmeter can be positioned either upstream or downstream from the sample collector if

the pressure drop across the collector is low, but when this is not the case the flowmeter

must be placed upstream of the sample as shown in Fig 1.1 (b). Otherwise, serious errors

can result in the airflow measurement as most of the flowmeters are designed to operate at

and are calibrated at atmospheric pressure.

(a)

Sample Collector Flowmeter Pump

(b)

Flowmeter Sample Collector Pump

Fig 1.1. Typical air sampling setup

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Individual sample collectors are generally grouped into two categories; those that

can be used to collect gaseous pollutants and those used for particulate pollutants.

Collection of Gaseous air pollutants:

Several methods are available for collection of gaseous air pollutants from ambient

atmosphere. The common ones are; the grab sampling, absorption in liquids, adsorption on

a solid material, and freeze – out sampling.

Grab sampling:

In ‘Grab’ sampling the sample is collected by filling an evacuated flask or an

inflatable bag. Plastic bags have been widely for grab sampling and for storage before

analysis.

Bag sampling is subject to losses caused by moisture condensation or diffusion

through the walls of the bag. The losses can be minimized by performing the analysis

immediately following collection.

Grab samples may be taken using rigid wall containers made from glass or stainless

steel. These containers are first evacuated and then filled by allowing air to enter.

Alternatively, a container may be filled with water and then used as a collector simply by

draining away the water which is replaced by the air sample.

Many problems associated with bag samplers are common to rigid containers also

and the containers are often heated by wrapping them with heating tapes or nichrome

wires to prevent condensation during sampling.

Absorbtion in Liquids:

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Absorbtion of gaseous pollutants into a liquid medium is probably the most

commonly employed method of collecting the samples. Absorbtion separates the desired

pollutant from air either through direct solubility in the absorbing medium or by chemical

reaction.

Many different types of collectors are in use, ranging from simple bubbles to

complex devices which provide a high degree of gas – liquid contact.

Probably the most widely used collector is impinge. In the impinge the gas stream is

impinged at high velocity onto a flat surface thus providing good contact between the gas

and the liquid.

Adsorption on Solids:

This method is based on the tendency of gaseous to be adsorbed or the surface of

solid materials. The sample air is passes through o packed column containing a finely

divided solid adsorbent on whose surface the pollutants are retained and concentrated.

The most commonly used solid adsorbents are granular porous solids such as

activated charcoal and silica gel with very large surface area.

After adsorption, the sample gases are described for analysis. This may be

accomplished by heating the adsorbent to volatilize the trapped material or by washing it

with aliquid solvent.

Most organic vapours are analyzed by gas chromatographic technique which

directly uses the adsorption principle.

Freeze – out sampling:

In freeze – out sampling a series of cold traps,which are maintained at progressively

lower temperature,are used to draw the air sample where by the pollutants are condensed.

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The traps are brought to the laboratory,the samples are removed, and analyzed by

means of gas chromatographic,infrared or ultraviolet spectro photometry,mass

spectrometry,or by wet chemical means.

Gaseous Pollutants - Spectrophotometry

Spectrophotometry is one of the most useful and widely used tools available for

quantitative analysis. A spectrophotometer measures the amount of light that a sample absorbs.

The instrument operates by passing a beam of light through a sample and measuring the intensity

of light reaching a detector. Spectrophotometry relies on colorimetric principles and is

commonly used to measure sulfur dioxide (SO2) concentrations. In this method, dyes and

chemicals are combined with a solution containing SO2. The color of the solution results in

different amounts of light being absorbed. The amount of light absorbed indicates the amount of

sulfur dioxide present in the sample.

Figure: Schematic of a UV-VIS spectrophotometer

Ozone can also be analyzed using the monochromatic ultraviolet absorption

spectrophotometry principle. As ultraviolet light at 253.7 nm is passed through the optic

bench, a fixed quantity of "zero air" and ambient air are drawn into the bench. The intensity

of the ultraviolet radiation traversing the optics bench is attenuated by the ozone present

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in the ambient sample. This attenuated signal is detected and compared with the

unattenuated signal from the "zero air" cycle. This difference in intensity is electronically

translated into a reading of ozone present in the ambient air.

Gaseous Pollutants - Chemiluminescence

Figure: Chemical reaction to determine oxides of nitrogen by chemiluminescence

Chemiluminescence methods for determining components of gases originated with

the need for highly sensitive means for determining atmospheric pollutants such as ozone,

oxides of nitrogen, and sulfur compounds. Chemiluminescence is based upon the emission

spectrum of an excited species that is formed in the course of a chemical reaction. Oxides of

nitrogen can be determined by the gas phase reaction of NO with ozone (O3). An ambient

air sample is mixed with excess ozone in a special sample cell. A portion of the NO present

is converted to an activated NO2 which returns to a lower energy state and in the process

emits light. This phenomenon is called chemiluminescence. The intensity of this light can

be measured with a photomultiplier tube and is proportional to the amount of NO in the

sample. A second reaction measures the total oxides of nitrogen in the air sample and in

turn, the concentration of NO2 can be calculated.

Another important chemiluminescence method is used for monitoring atmospheric

ozone. In this instance, the determination is based upon the luminescence produced when

ozone reacts chemically with the dye rhodamine-B absorbed on an activated silica gel

surface or with ethylene. The chemical reaction creates light pulses, which are detected and

counted by a photomultiplier tube. The concentration of ozone is determined by comparing

the number of light pulses created by the sample with the number of light pulses created by

a sample having a known concentration of ozone.

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Gaseous Pollutants - Gas Chromatography (GC)

Figure: Schematic gas chromatography

Gas chromatography (GC) coupled with a flame ionization detector (FID) is

employed for qualitative identification and quantitative determination of volatile organic

compounds (VOCs) in air pollution monitoring. The gas chromatograph, or GC, consists of a

column, oven and detector. In the gas chromatograph, a sample goes to the column,

separates into individual compounds and proceeds through the hydrogen flame ionization

detector. The flame in a flame ionization detector is produced by the combustion of

hydrogen and air. When a sample is introduced, hydrocarbons are combusted and ionized,

releasing electrons. A collector with a polarizing voltage located near the flame attracts the

free electrons, producing a current that is proportional to the amount of hydrocarbons in

the sample. The signal from the flame ionization detector is then amplified and output to a

display or external device.

Gas Chromatography-mass Spectrometry

Gas chromatography-mass spectrometry (GC-MS) instruments have also been used for

identification of volatile organic compounds. Mass spectrometers use the difference in mass-to-

charge ratio (m/z) of ionized atoms or molecules to separate them from each other. Mass

spectrometry is useful for quantification of atoms or molecules and also for determining

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chemical and structural information about molecules. Molecules have distinctive fragmentation

patterns that provide information to identify structural components.

Gaseous Pollutants - Fourier Transform Infrared Spectroscopy (FTIR)

Figure: FTIR can directly measure both criteria pollutants and toxic pollutants in the ambient

air.

Figure: FTIR can directly measure both criteria pollutants and toxic pollutants in the ambient

air.

Fourier Transform Infrared Spectroscopy (FTIR)

Fourier Transform Infrared Spectroscopy (FTIR) can detect and measure both

criteria pollutants and toxic pollutants in ambient air. FTIR can directly measure more than

120 gaseous pollutants in the ambient air, such as carbon monoxide, sulfur dioxide, and

ozone. FTIR technology can also measure toxic pollutants, such as toluene, benzene, and

methanol. The technology is based on the fact that every gas has its own "fingerprint," or

absorption spectrum. The FTIR sensor monitors the entire infrared spectrum and reads the

different fingerprints of the gases present in the ambient air.

Carbon monoxide is monitored continuously by analyzers that operate on the infrared

absorption principle. Ambient air is drawn into a sample chamber and a beam of infrared light is

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passed through it. CO absorbs infrared radiation, and any decrease in the intensity of the beam is

due to the presence of CO molecules. This decrease is directly related to the concentration of CO

in the air. A special detector measures the difference in the radiation between this beam and a

duplicate beam passing through a reference chamber with no CO present. This difference in

intensity is electronically translated into a reading of the CO present in the ambient air, measured

in parts per million.

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