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Air Pollution (1).ppt
1. Air Pollution
Atmospheric Composition, Green house effects: Definition, impact of greenhouse gases on
the global climate and consequently on sea water level, agriculture and marine food,.
Global warming and its consequence, Control of Global warming. Lapse rate: Ambient
lapse rate Adiabatic lapse rate, atmospheric stability, temperature inversion (radiation
inversion).
Atmospheric dispersion: Maximum mixing depth, ventilation coefficient, effective stack
height, smokestack plumes.
Definition of pollutants and contaminants, Primary and secondary pollutants: emission
standard, criteria pollutant.
Sources and effect of different air pollutants- Suspended particulate matter, oxides of
carbon, oxides of nitrogen, oxides of sulphur, particulate, PAN. Smog, Photochemical smog
and London smog. Acid Rain
Depletion Ozone layer: CFC, destruction of ozone layer by CFC, impact of other green house
gases, effect of ozone modification.
Standards and control measures: Industrial, commercial and residential air quality
standard, control measure (ESP. cyclone separator, bag house, catalytic converter, scrubber.
2. Components of Environment:
Atmosphere: Sphere of Air
Hydrosphere: Sphere of Water
Lithosphere: Sphere of soil /sand/rock
Biosphere: Sphere of Living Organisms
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Structure of Atmosphere:
Troposphere Stratosphere MesosphereIonosphere
(Thermosphere)Magnetosphere (Exosphere)
Troposphere: All leaving beings are here.
Composition N2-78%, O2-21%, CO2-0.04%, Inert gas 0.94% (Helium, Neon,
Argon, Xenon, Radon), Traces 0.03% + Water Vapour.
Extends 8-10km of the polar latitude. Contains 80% of the atmospheric mass. The
virtual temperature gradient is 5Deg C in the lower and 7deg per km in the upper
regions of the troposphere. The junction of Troposphere and Stratosphere (upper
portion of Tropo and lower portion of Strato) is called Tropopause.
3. Stratosphere: The layer above Tropopause. About 50km above the earth surface. Rich
layer of Ozone (O3) gas. The main components are Ozone, Oxygen and Atomic Oxygen. UV
energy , coming from the Sun, is absorbed in this layer. Very essential for the living beings.
Mesosphere: The layer above Stratosphere. Extends upto 85km above the earth’s surface.
Concentration of Ozone gas is lower here and decreases with height. Absorption of Solar
Radiation is also less due to the less presence of ozone. Oxygen (O2) and Nitrogen
Monoxide (NO). This layer often contains various Clouds. This layer is also responsible for
reflecting all sound waves moving upwards from the Earth Surface. NO is the mostly found
in this region.
Thermosphere/Ionosphere: The region above Mesosphere or the Mesopause (junction of
Mesosphere & Ionosphere). Here Temperature rises rapidly with increasing altitude.
500km above the earth surface. O2, NO and atomic oxygen (O) are found here. Maximim
temperature can reach 1200Deg C here. This region is high electrical conductor as charged
particles are produced from O2, NO, O. Due to absorption of UV radiation charged positive
ions are formed (NO+, O+).
Magnetosphere: approximately 2000km above the earth surface. This is empty space and
mostly unknown. Having very high temperature and associated to dark black
interplanetary space.
5. Nitrogen (N2): A relatively inert gas and fundamental to all living systems. Through the
nitrogen cycle nitrogen is removed from the atmosphere and becomes part of living
organisms. This process is realized by nitrogen fixation by soil bacteria, and by way of
lighting through precipitation. Nitrogen returns to the atmosphere mainly by biomass
combustion and denitrification.
Oxygen (O2) has also very important relations with life. Oxygen exchange between the
atmosphere and biosphere is realized by photosynthesis and respiration.
Argon (Ar) in the atmosphere is the third most abundant gas.
6.
7.
8. Dependence of saturated water vapour pressure from air temperature. The higher the
temperature, the greater water vapour can be held by the air.
9. Greenhouse Effect:
Greenhouse: A greenhouse is a house made of glass. It has glass walls and a glass roof.
People grow tomatoes and flowers and other plants in them. A greenhouse stays warm
inside, even during winter. Sunlight shines in and warms the plants and air inside. But the
heat is trapped by the glass and can't escape. So during the daylight hours, it gets
warmer and warmer inside a greenhouse, and stays pretty warm at night too.
10. If the greenhouse effect is
too strong, Earth gets warmer
and warmer. This is what is
happening now. Too much
carbon dioxide and other
greenhouse gases (carbon
dioxide, methane, nitrous
oxide, ozone)in the air are
making the greenhouse effect
stronger. (Global Warming)
11.
12. Effects of Global Warming on Climate Changes
Rising concentration of greenhouse gases generally produce an
increase in the average temperature of the earth. This results in
melting of polar ice, rise in sea level, loss of land, wormer temperature.
Impact of greenhouse gases on
the global climate:
Wormer temperature - ? Explain
Melting of polar ice - ? Explain
Rise in sea level - ? Explain
Loss of land – ? Explain
River routes may change – ? Explain
Just Imagine !!!
13. Effects of Global Warming on Climate:
Adding greenhouse gases has little effect on incoming short-wave solar
radiation, but increases the amount of outgoing long-wave terrestrial
radiation that is absorbed in the lower atmosphere. The result is
warming of the lower atmosphere (commonly known as the enhanced
greenhouse effect, or global warming). Potentially, there are other
effects on our climate also – changes in rainfall distribution and
storminess, for example.
Effects of Global Warming on the sea level:
Earth’s oceans are warming and sea levels are rising as a result of
increasing concentrations of greenhouse gases in the atmosphere.
Indeed, around 93 percent of the additional heat created by global
warming has so far been absorbed into the oceans. As water warms, it
expands. This expansion has been the major cause of sea-level rise,
with a smaller component from land-based glaciers and ice sheets. In
the twentieth century, global average sea levels increased by 19 cm.
Over time, the contribution from ice melting is expected to increase
substantially
14. Effects of Global Warming on Agriculture:
First of all the increased amount of CO2 can accelerate the
photosynthesis process. This might be harmful for the plants.
Moreover, there are innumerable potential effects climate change
could have on agriculture. It could affect crop growth and quality,
livestock health, and pests. Climate change could affect farming
practices, as well as pest control and the varieties of crops and
animals that could be raised in particular climactic areas. The
timing of crops production would be hampered. These could, in
turn, affect the availability and price of agriculture products as
well as the costs of doing business.
How Economy depends on Global Warming?...???
15. Effects of Global Warming on Marine Food:
There might be a downfall on marine food production. Global
warming can cause collapse in ocean’s food chain.
Researchers discovered that there would be “limited scope” for
acclimation to warmer waters and acidification. Limited species
will survive negative effects of rising CO2, with an expected large
reduction in species diversity and abundance globally.
Microorganisms will be an exception, they are expected to
increase in number and diversity. This will directly decrease the
marine foods production and imbalance the ecosystem.
Microorganisms are v v strong. They can survive in difficult
situations but other marine animals (fishes mainly) cant. That
means we cant get enough marine foods and our Economy may
go down !!!
16. How to control Global Warming?
1. Reduce, Reuse, RecycleReduce waste by choosing reusable products instead of disposables. Buy products with minimal packaging. Recycle
paper, plastic, newspaper, glass and aluminum cans. By recycling half of your household waste, you can save 1088kg of carbon dioxide every
year.
2. Use Less Heat and Air Conditioning
Add insulation to your walls and attic, it can lower your heating costs more than 25 percent, by reducing the amount of energy you need to heat
and cool your home. Turn down the heat while you're sleeping at night or away during the day, and keep temperatures moderate at all times.
Setting your thermostat just 2 degrees lower in winter and higher in summer could save about 907kg of carbon dioxide each year.
3. Change your lightbulbs
Replace regular light bulbs with compact fluorescent light (CFL) bulbs. CFLs last 10 times longer than incandescent bulbs, use two-thirds less
energy, and give off 70 percent less heat.
4. Drive less and drive smarter
Go surfing with friends, Walk and ride your bike more and check out options for carpooling to work or school. When you do drive, make sure
your car is running efficiently. For example, keeping your tires properly inflated can improve your petrol mileage by more than 3 percent.
5. Buy Energy-Efficient Products
When it's time to buy a new car, choose one that offers good mileage. Home appliances now come in a range of energy-efficient models, and
compact florescent bulbs are designed to provide more natural-looking light while using far less energy than standard light bulbs.
Avoid products that come with excess packaging especially molded plastic and other packaging that can't be recycled.
6. Use Less Hot Water
Set your water heater at a lower tempreture to save energy and buy low-flow showerheads to save hot water and about 350 pounds of carbon
dioxide yearly. Wash your clothes in warm or cold water to reduce your use of hot water and the energy required to produce it.
7. Use the "Off" Switch
Save electricity and reduce global warming by turning off lights when you leave a room, and using only as much light as you need. And
remember to turn off your television, video player, stereo and computer when you're not using them. It's also a good idea to turn off the water
when you're not using it. While brushing your teeth, shampooing the dog or washing your car, turn off the water until you actually need it for
rinsing. You'll reduce your water bill and help to conserve a vital resource.
8. Plant a Tree or two
If you have the means to plant a tree, start digging. During photosynthesis, trees and other plants absorb carbon dioxide and give off oxygen. A
single tree will absorb approximately one ton of carbon dioxide during its lifetime.
9. Keep an eye on your local beach
It’s your responsibility to look after your local spot. Keep an eye on changes, pick up litter, use your local status to increase respect for the ocean
environment.
10. Encourage Others to Conserve
Share information about recycling and energy conservation with your friends, neighbors and co-workers, and take opportunities to encourage
public officials to establish programs and policies that are good for the environment.
These 10 steps will take you a long way toward reducing your energy use and your monthly budget. And less energy use means less dependence
on the fossil fuels that create greenhouse gases and contribute to global warming and the raising of temperatures in our oceans.
17. Ambient Lapse Rate (ELR)
The rate of change in air temperature with altitude is called Lapse
Rare. It is the rate at which Earth's atmospheric temperature
decreases with an increase in altitude, or increases with the
decrease in altitude.
Adiabatic Lapse Rate (ALR)
When air moves upward in the atmosphere it experiences less
pressure so the air expands and cools down. But the surrounding
air gains heat and becomes hotter. At this scenario, if there is no
heat transfer across the boundary along with the movement of
air, this process is called adiabatic. Under this condition the rate
is called Adiabatic Lapse Rate.
18. Dry Adiabatic Lapse Rate(DALR)
When the packet of moving air is dry and the temperature is more
than dew point , the ALR is called DALR.
Saturated Adiabatic Lapse Rate (SALR)
If the air is saturated with moisture, and the temperature is less
than the dew point, the adiabatic lapse rate is called Saturated
Adiabatic Lapse Rate (SALR)
.
Heat capacity is a measurable physical quantity equal to the ratio
of the heat added to (or removed from) an object to the resulting
temperature change
19. Atmospheric Stability
It determines the ability of pollutants to disperse vertically into the
atmosphere and its ability to dilute pollution. Difference between ELR
& ALR determines atmospheric stability
Conditions:
(1) ELR>ALR = Unstable atmosphere (Internal temperature of the air
is higher than the surroundings, its density becomes lower and air
goes up)
(2) ELR<ALR = Stable atmosphere (Internal temp of air is lower than
the surroundings. Its density becomes higher and air goes down)
(3) ELR=ALR = Atmosphere is neutrally stable. (Internal temperature
of air is same of surroundings and it gets no force to go up or
down)
20. Sub-Adiabatic Lapse Rate
When ELR<ALR the atmosphere is stable and this prevailing lapse
rate is called Sub-Adiabatic Lapse Rate
Super-Adiabatic Lapse Rate
When ELR>ALR the rate of cooling is faster than ALR, the condition
of atmosphere under such circumstances is called Super-Adiabatic
Lapse Rate.
Smog
Smog is combination of Fog & Smoke.
21. Temperature Inversion
Normally, air temperature decreases with the increase of
Altitude. But, in unusual case, if temperature increases
with increasing altitude, this phenomenon is called
Temperature Inversion. Here Laps rate is Negative.
Cause of Temperature Inversion:
(a) Radiation Inversion
(b) Subsidence Inversion
(c) Advective Inversion
22. Radiation inversions
The most common type of inversion. Radiation inversions generally
happen in places where it cools off a lot at night. During the day
time, the Sun heats the earth. During night time the ground and the
air cools much faster than the heating up. This creates an Inversion.
We can feel it more during the Winter season. Without Sunlight this
phenomenon cannot happen. In the morning Radiation Inversion
gradually stops.
23. Atmospheric dispersion :
Atmospheric dispersion modeling is the mathematical simulation of
how air pollutants disperse in the ambient atmosphere.
Maximum mixing depth
The amount of air available to dilute pollutants is related to the
wind speed and to the extent to which emissions can rise into the
atmosphere
Mixing mixing depth is measured from the surface of the Earth. The
warmer and lighter air gows upwards and coos down. Now at a
time, this air will reach to a certain height where its temperature
and density becomes equal to the surrounding air. This height is
known as Mixing mixing depth .
24. Ventilation coefficient
The product of the maximum mixing depth & the average wind
speed In a certain region is called ventilation coefficient.
Higher wind speed will disperse the wind comparatively quicker
and if the wind speed is low the dispersion will be slower.
Wind speed & concentration of air pollutants are inversely
proportional to each other.
25. Effective Stack Height:
The dispersion of emmited gases from the source of their
production is known as Plune and the source is called Stack.
Effective Stack Height (H) = h + Δh
h= stack height
Δh= plume height
26. Smokestack plumes:
is formed whenever pollutants emitted from a source into the atmosphere
continuously over a period of time
Major factors that influence the dispersion of smokestack plumes:
1. Local atmospheric stability (determines the rate of vertical mixing and
dilution of the plume).
2. 2. Winds (control the distance that the pollution can travel and the areas
that will be affected).
Behavior of smokestack plumes
(a) When the atmosphere is neutrally stable, the plume cones, or spreads in
all directions as it travels from the stack.
(b) If the atmosphere is stable, the plume cannot spread vertically but can
disperse horizontally, producing a fan.
(c) Fumigation occurs when stack emissions are dispersed to the ground by
the overturning of the atmosphere below an inversion layer.
(d) Looping occurs in an unstable atmosphere where upward and downward
motions in large turbulent eddies are equally likely.
(e) The injection of stack emissions above a stable stratified layer results in a
lofting of the emissions.
27. Pollutants and Contaminants
The Contaminant is the substance that was introduced by man into the
environment by any means while the pollutant may be induced by man or may
be present in the natural environment. The Contaminant is a term mostly used to
the sources of pollution that are caused due to substances that have been made
by human beings.
Primary & Secondary Pollutants
A primary pollutant is an air pollutant emitted directly from a source.
A secondary pollutant is not directly emitted as such, but forms when
other pollutants (primary pollutants) react in the atmosphere.
Emission Standard
Emission standards are the legal requirements governing air pollutants released
into the atmosphere. Emission standards set quantitative limits on the
permissible amount of specific air pollutants that may be released from specific
sources over specific timeframes. They are generally designed to achieve air
quality standards and to protect human life.
28. Criteria Pollutants:
The criteria pollutants are carbon monoxide, lead, nitrogen dioxide,
ozone, particulate matter, and sulfur dioxide. Criteria pollutants are
the only air pollutants with national air quality standards that define
allowable concentrations of these substances in ambient air.
30. Photochemical smog
Photochemical smog is the chemical reaction of sunlight, nitrogen
oxides and volatile organic compounds in the atmosphere, which
leaves airborne particles and ground-level ozone.
This pollutants include:
Aldehydes
Nitrogen oxides,
particularly nitric oxide and nitrogen dioxide
Peroxyacyl nitrates
Tropospheric ozone
Volatile organic compounds
31. Photochemical smog
• 1st observed in Los Angeles,
USA.
• Main components were
hydrocarbon, oxides of
nitrogen and ozone.
• This is oxidising type of smog.
• Temperature of this smog is
greater than 25 ̊C.
• Mid summer is ideal condition
for its formation.
• Subsidence inversion is
suitable for this type of smog.
Sulphurous Smog
• 1st observed in London.
• Main components were
hydrocarbon, oxides of sulphur
and ozone.
• This is reducing type of smog.
• Temperature of this smog is
less than 5 ̊C.
• Early morning is the ideal
condition for its formation.
• Radiation inversion is suitable
for this type of smog.
32. Sources and effect of different air pollutants
1. Carbon Monoxide (CO): Carbon Monoxide is a highly toxic and dangerous pollutant, infamous
for its lack of identifying color and smell. At one point, this gas was extremely prevalent in
homes for use in domestic heating before it was found to be unsuitable, and it has since been
replaced by much safer solutions such as natural gas and electricity. However, this gas is far from
extinct in human use.
Sources: Most commonly, Carbon Monoxide is produced by combustion engines running
without modern catalytic convertors. Other common sources of Carbon Monoxide are old gas
and fuel appliances, incinerators, and even cigarettes.
Effects: Carbon Monoxide can have a profound effect on the environment as it is extremely
poisonous, and can contribute to very dangerous ground-level air and ozone conditions.
2. Lead (Pb): Lead has long been known to be a dangerous substance. Once commonplace in
nearly all gas and aviation fuels, there has since been tremendous effort to reduce the amount
of lead found in these substances. Since the introduction of lead-free gasoline, the volume of
lead in the atmosphere has dropped enormously.
Sources: While efforts have been made to remove lead from fuel, it continues to be present in
some aircraft fuel. Similarly, the outpouring of lead from metal processing plants, and the
release of lead from waste processes such as incineration and battery acid production means
that there is still enough lead in the air to recognize it as a dangerous pollution.
Effects: Lead can not only poison humans, but it also has a profound effect upon natural
ecosystems. Contaminating air, soil, and water, lead can cause damage to flora and fauna alike.
33. 3. Ozone (O3): Ozone is not inherently bad. After all, the ozone layer is one of the major
protections mankind has against harmful solar radiation. However, ground level Ozone has
become a major problem in recent years.
Sources: Ground level Ozone is formed by chemical reactions between multiple different oxides
found in the air, which – when exposed to sunlight – can form new compounds and leave Ozone
as a by-product. The majority of the emissions which make up Ozone come from the usual
suspects such as car exhausts, factory processing, electric utilities and power plants, and even
some chemical solvents.
Effects: Ozone is a dangerous substance for most living organisms, and as such an increase in
ground level Ozone has a notable effect on human health as well as the overall health of multiple
ecosystems on land and in the seas.
4. Nitrogen Dioxide (NO2): Nitrogen Dioxide is one of the oxides which can react to produce
Ozone, but that is far from its only negative effect. Nitrogen Dioxide is one of the gases that one
most commonly thinks to when considering air pollution: thick, brown, and choking, it is one of
the more visibly harmful pollutants.
Sources: Nitrogen Dioxide, like many other pollutants, is most often released into the atmosphere
by the burning of fossil fuels in car engines, airplane engines, factories, and power plants.
Effects: In addition to being a choking and obstructive gas in the air, Nitrogen Dioxide also has the
propensity to react with other agents to form nitric acid and organic nitrates, contributing to
the formation of acid rain.
Needless to say, Nitrogen Oxide has a huge effect on humans, increasing the likelihood of
respiratory problems, cancers, and other lung problems. Acid rains produced by Nitrogen Dioxide
are extremely harmful to plants and animals across the world, and can lead to further problems in
water systems.
34. 5. Sulfur Dioxide (SO2): Sulfur Dioxide is a substance most closely associated with the steam age
and locomotives, as the biggest culprit in its production is coal combustion. However, these days
are not so far gone as you may have thought.
Sources: To this day, locomotives, ships, planes, and other equipment still produce huge
volumes of Sulfur Dioxide. Industrial processes, particularly ore extraction and purification, are
also producers of the gas.
Effects: Sulfur Dioxide, like Nitrogen Dioxide, is a compound which often mixes with
other pollutants in the air to form harmful acids, but it is also harmful on its own. Common
effects of Sulfur Dioxide poisoning are respiratory problems, eye problems, and even heart and
circulatory problems. Importantly, Sulfuric Acid, created by the mixing of sulfur with water, is a
potent acid which is not only destructive to human property but also to trees, soils, and water
systems.
6. Particulate Matter (PM): Particulate Matter is something a lot more visible and tangible than
the components listed above, but is no less dangerous or harmful. The matter generally consists
of soot, dirt, and chemical byproducts produced through combustion or chemical mixing.
Sources: Particle matter is produced by nearly every single process involving chemicals and
fuels, as well as more innocuous processes such as farming and road construction. Any process
which produces a physical byproduct will generally result in particulate matter.
Effects: Particle Matter ranges from annoying to extremely dangerous, often hampering visibility
on roads and causing respiratory problems. Particulate Matter is associated with a range of
heart, lung, and eye conditions in humans, and is also linked to an increased likelihood of
developing cancers later in life.
35. What Can We Do To Help Reduce Air Pollution?
Raise awareness. Whether it be through joining non-profits, activist groups, or even
just posting about the matter online, raising people’s awareness about air pollution
and its causes is an important step in reducing the problem around the world.
Try to minimize travel in cars and airplanes. While driving is often unavoidable, there
are many who could quite easily cut down on their fuel consumption by making use of
public transportation or even bikes. Similarly, making use of a more fuel-efficient
vehicle is a good way to make the car travel you do undertake much less harmful.
Keeping a car serviced and safe will dramatically improve its fuel-efficiency and reduce
the volume of emissions it releases. Airplanes are among the worst contributors to air
pollution, so consider staying in the country when vacationing.
Conserve energy where possible. Since electricity production releases a huge number
of air pollutants, using as little energy as possible can help minimize the amount
produced in any one day. If you spread the message too, you can have a
noticeable impact on electricity production. Simply changing lightbulbs to energy
efficient alternatives, turning off appliances when not in use, and reducing the
amount of time spent in front of the television or on the computer are good starts.
36. Make use of 3 R’s. Who wouldn’t have heard of 3 words Reduce, Reuse and Recycle.
Reduce simple means reducing the consumption of goods like plastic bags that can
hurt the environment. Reuse means reusing the same thing for some different
purpose; like reusing the old jar for storing cereals or pulses. Recycling stands for
recycling old items so that they can be made into some useful products again.
Get your car’s engine tune up. Keeping your car’s engine tune up will make sure
that it does not consume more fuel and gives you a better mileage.
Keep tires properly inflated. Cars consume more gasoline when tires are not
properly inflated. Keep the air pressure to optimum level will reduce your impact on
the environment.
Make use of renewable electricity where possible. Installing your own solar panels
for even small tasks can help to conserve electricity which would otherwise be
provided by power plants.
Get energy audit done for your home. Get energy audit done and ask the auditor
about changes that you can make in order to ensure that your home is as energy
efficient as possible. They can give you recommendations that will help you out and
even save you money in the long run.
37. Consider going green. There are various ways to go green without even spending a
extra penny. For e.g.: use public mode of transportation instead of car, opt for eco-
friendly hotels when go out on a holiday, buy items with less packaging, buy energy-
efficient appliances, use daylight as much as possible, avoid buying plastic water
bottles, and many more.
Plant trees and plants, as these can help to increase the amount of breathable air
available, and reduce levels of certain pollutants that cause harm to the
40. Suspended particulate matter (SPM)
Atmospheric aerosol (a colloidal suspension of particles dispersed in air or gas.)
particles, also known as atmospheric particulate matter, particulate matter (PM),
particulates, or suspended particulate matter (SPM) are microscopic solid or liquid
matter suspended in Earth's atmosphere.
SPM consists of microscopically small solid particles or liquid droplets suspended in
the air. The smaller the particles, the deeper they can penetrate into the respiratory
system and the more hazardous they are to breathe
How to control SPM:
a. Stop smoking; if you do smoke, do not smoke indoors.
b. Mulch garden refuse instead of burning it.
c. Limit the use of fireplaces and wood stoves; when using these appliances, make sure
d. that wood is being burned properly. ...
e. Switch to cleaner burning appliances.
42. PAN
Peroxyacyl nitrates (also known as Acyl peroxy nitrates, APN or PANs)
are powerful respiratory and eye irritants present in photochemical
smog. They are nitrates produced in the thermal equilibrium between
organic peroxy radicals by the gas-phase oxidation of a variety of
volatile organic compounds (VOCs), or by aldehydes and other
oxygenated VOCs oxidizing in the presence of NO2.
Example,
peroxyacetyl nitrate, CH3COOONO2:
Hydrocarbons + O2 + NO2 + light → CH3COOONO2
The general equation is:
CxHyO3 + NO2 → CxHyO3NO2
59. What is Ozone Layer Depletion?
Ozone layer depletion, is simply the wearing out (reduction) of the
amount of ozone in the stratosphere. Unlike pollution, which has
many types and causes, Ozone depletion has been pinned down to
one major human activity. Industries that manufacture things like
insulating foams, solvents, soaps, cooling things like Air
Conditioners, Refrigerators and ‘Take-Away’ containers use
something called chlorofluorocarbons (CFCs). These substances are
heavier than air, but over time, (2-5years) they are carried high into
the stratosphere by wind action.
Depletion begins when CFC’s get into the stratosphere. Ultra violet
radiation from the sun breaks up these CFCs. The breaking up action
releases Chlorine atoms. Chlorine atoms react with Ozone, starting
a chemical cycle that destroys the good ozone in that area. One
chlorine atom can break apart more than 100,000 ozone molecules.
60.
61. Effects of Ozone depletion
• Skin cancer.
• Eye and lung Irritation.
• Reduced photosynthesis.
• Affects crop productivity.
• Affects weather pattern through interference
with oxygen.
62. How Ozone Depletion Affects UV Levels?
Humans: High levels of UV Rays cause non-melanoma skin cancer. Additionally, it plays a
major role in malignant melanoma development. UV is also linked to cataracts (a disease of
the eye which clouds the eye’s lens).
Plants: The damage that extreme UV levels has on plants is one that our eyes do not see
much, but humans can feel the impact. Plant growth, as well as its physiological and
developmental processes are all affected negatively. These include the way plants form,
timing of development and growth, distribution of plant nutrients and metabolism, etc.
These changes can have important implications for plant competitive balance, animals that
feed on these plants, plant diseases, and biogeochemical cycles.
Marine (or water) Ecosystems Phytoplankton form the foundation of aquatic food webs.
These usually grow closer to the surface of water, where there is enough sunlight. Changes
in UV levels is known to affect the development and growth of phytoplankton, and naturally,
the fish that feed on them. UV radiation is also know to have affect the development stages
of of fish, shrimp, crab, amphibians and other animals. When this happens, animals in the
upper food chain that feed on these tiny fishes are all affected.
Effects on Biogeochemical Cycles: The power of higher UL levels affect the natural balance
of gasses (and greenhouse gases) in the biosphere: e.g., carbon dioxide (CO2), carbon
monoxide (CO), carbonyl sulfide (COS) and ozone. Changes in UV levels can cause
biosphere-atmosphere feedback resulting from the atmospheric buildup of these gases.
63. What is Ozone Hole?
Top atmospheric researchers confirm that Ozone levels vary by season and
latitude. Sometime in 1979, it was observed the there considerable Ozone
depletion in the upper latitudes, Arctic and Antarctic. This massive stretch of
ozone depletion (hole) is estimated to be about the size of America. Particularly in
the antarctic, satellite images were released showing a disturbing thinning of the
ozone layer. The phenomenon is what we usually call the Ozone hole, and it was
most observed over the Antarctic every year during the spring. In the winter,
temperatures drop below -78°C (-109°F) in the Poles (Antartic). Thin clouds form
of ice, nitric acid, and sulphuric acid mixtures. Chemical reactions on the surfaces
of ice crystals in the clouds release active forms of CFCs. This sets the ozone
depletion going by spring, a lot of depletion has occurred. Why does the Ozone
hole only occur in the Antarctic? Researchers say it is not only in the Antarctic, but
in many places in other latitudes where populations are dense. It is believed that
these places have cloud types that aid in the chemical reactions that cause ozone
depletion. In spring, temperatures begin to rise, the ice evaporates, and the ozone
layer starts to recover.
64. CFC (Chlorofluorocarbons):
Chlorofluorocarbons are fully halogenated paraffin hydrocarbons that
contain only carbon, chlorine, and fluorine, produced as volatile
derivative of methane, ethane, and propane.
How do CFC destroy the ozone (O3) layer?
When ultraviolet light waves (UV) strike CFC (CFCl3) molecules in the
upper atmosphere, a carbon-chlorine bond breaks, producing a chlorine
(Cl) atom. The chlorine atom then reacts with an ozone (O3) molecule
breaking it apart and so destroying the ozone.
65.
66.
67. Engineering systems for air
pollution control:
Devices for particulate emission
1. Baghouse filter
2. Cyclone separator
3. Scrubber
4. Catalytic converter
5. Electrostatic precipitator
68. Baghouse Filter
Fabric filters offer the following
Advantages:
(1) They can achieve very high
collection efficiencies even
for very small particles;
(2) They can be used for a wide
variety of particles;
(3) They can operate over a
wide range of volumetric
flow rates; and
(4) They require only moderate
pressure drops
Disadvantages:
(1) Cannot operate In higher
temperature
(2) Needs large area for
effective filtration
Design of Baghouse Filter:
69. Baghouse Filter Mechanism:
Bag filters are also known as bag houses or fabric filters.
They are surface filters where dust collects in a layer on the
fabric and the layer becomes the effective filter. Bags made
of woven cloth or felt or membrane are connected to a
shaking mechanism. Dust-laden air flows upwards into the
filter bags. The dust collects on the inside of bags. When dust
accumulates to a certain level (depending on build up of
resistance), gas flow is stopped and the bags are shaken. The
dust falls into the hopper below.
70. Cyclone separator:
Cyclone separators are gas cleaning devices that utilize the
centrifugal force created by a spinning gas stream to separate
particles from a gas. The gas flow is forced to follow the curved
geometry of the cyclone while the inertia of particles in the flow
causes them to move toward the outer wall, where they collide and
are collected
71. Scrubber
Used to remove SO2 from flue gas. These are of two types.
(a) Wet method: Here limestone (CaCO3) is mixed with water and
slurry is made and sprayed into flue gases. Chemical reaction
occurs and calcium sulphite CaSO3 is produced that precipitate
out. Removed as sludge. Removal of SO2 is done here.
Reaction: CaCO3+SO2+H2OCaSO3.H2O+CO2
(a) Dry method: Here lime (CaO) is used for the removal of SO2.
Comparatively less effective. And costly due to the use of lime.
Reaction: CaO+SO2+H2OCaSO3.2H2O
73. Catalytic Converter:
To control the emission from motor engine, this is used. Basically
such device CO & Hydrocarbone are Oxidised to CO2 & NO2/NO.
74. Use:
In order to reduce air pollution, modern automobiles are
equipped with a device called a catalytic converter that reduces
emissions of three harmful compounds found in car exhaust.
Removes:
Carbon monoxide (a poisonous gas)
Nitrogen oxides (a cause of smog and acid rain)
Hydrocarbons (a cause of smog)
The catalyst used in a catalytic converter is a combination of
platinum (Pt), palladium (Pd), and rhodium (Rh). These metals
coat a ceramic honeycomb (or ceramic beads) contained within a
metal casing that is attached to the exhaust pipe. The catalytic
converter’s honeycomb structure provides the maximum surface
area on which reactions can take place while using the least
amount of catalyst.
76. Electrostatic precipitator:
Used to separate very small particles (~1µm). High voltage
(100,000V) is applied to the wires connected to the grounded
plates. The corona discharge in the wire ionizes the incoming gas
and the charged molecules towards grounded plate & adhere to
the grounded surface (according to their charges). Now they are
separated by fluid flush or gravitational force.
Corona discharge: Corona discharge is an electrical discharge
brought on by the ionization of a fluid such as air surrounding a
conductor that is electrically charged.
