Transcript Understanding Our Environment

Air: Climate and Pollution
Chapter 9
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Outline:
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Atmosphere and Climate
Climate Change
 El Nino
 Human Causes
Climate and Pollution
 Kinds of Pollution
 Sources
 Transport
Effects of Air Pollution
Air Pollution Control
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ATMOSPHERE AND CLIMATE
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Weather - A description of short-term
physical conditions of the atmosphere.
Climate - A description of the long-term
weather pattern in a particular area.
 Weather and climate are primary
determinants of biomes and ecosystem
distribution.
 The atmosphere has 4 distinct zones of
contrasting temperature due to difference
in absorption of solar energy:
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Troposphere
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Troposphere:layer of air immediately
immediately adjacent to the Earth’s surface.
 Ranges in depth from 18 km over the
equator to 5 km over the poles.
 Air circulates in convection currents.
 Air temperature drops rapidly with
increasing altitude.
 Contains 75% of total air mass.
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A Layered Envelope
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Stratosphere
 Extends from troposphere to about 50 km.
 Similar composition to Troposphere, but
much more dilute.
 Temperature increases with altitude.
 Almost no water vapor and 10 times more
of ozone (O3) than in the troposphere.
 Relatively calm
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Stratosphere contd.
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This ozone layer absorbs UV radiation which
makes the stratosphere warmer towards the
top.
Since UV normally damages living tissues,
absorption of UV by stratosphere protects life
on Earth.
The ozone layer over Antartica is depleting
which will results in filtration of UV to the
earth and causes skin cancer, mutations,
crop failure etc.
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A Layered Envelope
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Above the Stratosphere , the temperature
decreases creating the Mesosphere, the middle
layer runs upto 85 km. Minimum temperature is
about - 80o C
Thermosphere, the heated layer, begins at
about 85 km, runs for 600 km a layer of highly
Ionized gases and high temperatures.
Ionosphere – is the lower part of lower
thermosphere which has high energy radiation
which causes highly charged particles to glow
called Aurora borealis (northern lights) &
A.australis (southern light)
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Atmospheric Temperature Changes
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Energy and the Greenhouse Effect
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Solar Radiation
 Solar energy not evenly distributed over the
globe.
 Of solar energy reaching outer atmosphere:
- 25% reflected
- 25% absorbed
- 50% reaches earth’s surface
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Solar Radiation
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Visible light passes through atmosphere
undiminished.
Ultraviolet light is absorbed by ozone in the
stratosphere.
Infrared radiation is absorbed by carbon
dioxide and water in the troposphere.
 Albedo – surfaces that have high reflectivity
- Fresh clean snow
90%
- Dark soil
3%
- Net average of earth
30%
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Solar Radiation
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Solar Radiation
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Most solar energy reaching the earth is visible
light.
 Energy re-emitted by the earth is mainly
infrared radiation (heat energy).
- Longer wavelengths are absorbed in the
lower atmosphere, trapping heat close to
the earth’s surface.
- Greenhouse Effect (atmosphere is
considered as a green house, transmit
sunlight but traps heat inside).
- Increasing atmospheric CO2 due to human
activities appears to be causing global
warming and the Greenhouse effect.
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Convection and Atmospheric Pressure
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Water vapor contains a large amount of
energy stored as latent heat.
 Evaporation converts solar energy into
latent heat stored in evaporated water.
 When water vapor condenses, this latent
heat is released.
 The redistribution of heat and water around
the globe is essential to life on earth.
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Why Does It Rain ?
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Water vapor condenses,releasing latent heat
causes air to rise, cool, and lose more water
vapor.
 Rising, expanding air creates an area of
relatively high pressure at the top .
 Air flows out of high-pressure zone
towards areas of low-pressure.
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Why Does It Rain ?
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Subsiding air is compressed as it
approaches the earth’s surface where it piles
up and creates an area of high pressure at
the surface.
 Air flows out of this region back towards
low pressure, closing the cycle.
If condensation nuclei (tiny particles of
smoke, dust,spores, volcanic ash etc.)are
present, or if temperatures are low enough,
condensation will lead to precipitation.
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Why it Rains? Contd.
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Anytime when air is rising ,clouds, snow or
rain might form.
Cooling occurs because of changes in
pressure.
Air cools as it rises (as pressure increases)
and if the air is moist it is likely to rain.
When air is sinking it warms up as it
approaches the surface (increasing
pressure).Available moisture evaporates.
Rainfall rarely occur in areas of high moisture
( refer pg 199).
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CLIMATE CHANGE
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Periodic weather cycles detected (periodic
weather changes).Reasons:
 Solar magnetic cycles (changes in the
sunlight intensity).
 Milankovitch Cycles studied by a Serbian
scientist and he observed a Periodic shifts
in earth’s orbit and its axis of rotation.
 The above changes results in change in
distribution and intensity of sunlight
reaching the earth.
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El Nino
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La Nina, El Nino or the Southern oscillation:
A pool of warm surface water most of the
years is held by the equatorial trade wind
between Indonesia and the South America
and moves this current westwards towards
Indonesia.
Every 3-5 years the low-pressure system
breaks in Indonesia.
This giant pool of warm water moves
backward and forward between Indonesia
and S America, this effect is called EL Nino.
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El Nino Southern Oscillation
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Large pool of warm surface water in Pacific
Ocean moves back and forth between
Indonesia and South America.
 Most years, the pool is held in western
Pacific by steady equatorial trade winds.
 Every three-five years the Indonesian low
pressure system collapses and the mass
of warm surface water surges back east.
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El Nino Southern Oscillation
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During an El Nino year, the northern jet stream
(normally over Canada) pulls moist air from the
Pacific over the U.S.This is accompanied by
intense storms and heavy rains (from California
across the midwest States).
The counterpart to El Nino is La Nina when the
eastern tropical Pacific cools down.
During intervening La Nina years, hot, dry
weather is often present (California to midwest)
Together these cycles are called El Nino
Southern Oscillation (ENSO)
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El Nino Southern Oscillation
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Human-Caused Global Climate Change
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IPCC (Intergovernmental Panel on Climate Change
(2001) released report stating “recent changes in
the world’s climate have had discernable impacts
on physical and biological systems.”
 Concluded human activities must be at least
partially responsible.
 Noted that the earth’s surface temperature has
risen by about 0.6 0C(1.1 0F) and IPCC
concluded that human is partially to be blamed(
Green house gases-CO2, methane,nitrous oxide).
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Aerosol Effects
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Burning fossil fuels, forests and grasslands
and other human activities releases 30
billions of CO2 per year.
Aerosols counteract Greenhouse effect.
Aerosols( sulphate and soot) produced by
same activities ) have a tendency to reflect
sunlight and cool surface air temperatures.
 Short-lived, thus effects are temporary.
 Mt. Pinatubo erupted in 1991 and ejected
enough ash and sulfate particles to cool
global climate about 1o C for nearly a year.
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Current Evidence of Climate Change
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Precipitation increased 1% in last century.
Artic sea ice thinning.
Alpine glaciers retreating.
Coral reefs bleaching.
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International Climate Negotiations
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Kyoto Protocol (1997) signed in Japan as a follow up of the
earth’s summit(1992) in Rio de Janeiro
 160 nations agreed to roll back carbon dioxide, methane,
and nitrous oxide emissions about 5% below 1990 levels
by 2012.
 Also included 3 other green house gases to be reduced:
hydrofluorocarbon (CFC), perfluorocarbon and sulphur
hexafluoride.
 The protocol sets different limits for different countries,
depending on their output before 1990,however poorer
countries like China and India were exempeted from their
emission limit to allow thse countries to develop.
 They also argued that wealthier countries created this
mess and they should sort out this problem.
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Controlling Greenhouse Emissions
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Switch to renewable energy sources such as
solar, wind, biomass etc.
CO2 is lives longer in the atmosphere than
Methane and other greenhouse gases.
Capture and Store CO2:
 Increase plantations of trees and farmland
 Inject CO2 into underground strata or deep
ocean (Read pg 208 for details).
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Climate & Air Pollution
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According to EPA (Env. Protection Agency),
US releases 147 million metric tons of air
pollution(excluding CO2) per year and world
wide emission of these pollutants is 2 billion
metric tons per year.
Major Kinds of Pollutants: Primary and
secondary pollutants.
Primary pollutants are released in a hamrful
way e.g Factory smoke and secondary
pollutants become hazardous after reactions
in the air.
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CLIMATE AND AIR POLLUTION
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Photochemical oxidants (compounds formed
with solar energy) e.g atmospheric acids are
probably the most important secondary
pollutants.
Fugitive emissions - Do not go through
smokestack e.g dust from soil erosions, rock
crushing, building constructions.
Conventional Pollutants - Group of seven major
pollutants that contribute the largest volume of
air-quality degradation (sulphur dioxide, carbon
monoxide, particulates,volatile organic
compounds,nitrogen oxide,ozone,and lead).
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Conventional Pollutants
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US Clean Air Act designated seven major
(conventional or criteria) pollutants for which
maximum ambient (Air around us) air levels are
mandated. EPA sets allowable limits for
concentrations of these pollutants:
 Sulfur Dioxide
 Carbon Monoxide
 Particulates
 Hydrocarbons
 Nitrogen Oxides
 Photochemical Oxidants
 Lead
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Major Pollutants
Unconventional Pollutants
- Compounds produced in less volume
than conventional pollutants, but are
especially toxic or hazardous
(e.gAsbestos,benzene, mercury etc.)
 Aesthetic Degradation
- Reduce quality of life (e.g
noise,odors,dust particles etc.)
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Lead and Other Toxic Elements
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Toxic metals and halogens are chemical
elements that are toxic when concentrated
and released in the environment.
 Metals
- Lead, mercury, arsenic, nickel, beryllium,
cadmium, thallium, uranium, cesium,
and plutonium.
 Halogens
- Fluorine, chlorine, bromine, and iodine.
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Stratospheric Ozone
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Discovered stratospheric ozone levels were
dropping rapidly during September and
October.
 Occurring since at least 1960.
At ground-level, ozone is a pollutant, but in
the stratosphere it screens UV radiation.
 A 1% decrease in ozone results in a 2%
increase in UV rays reaching the earth.
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Stratospheric Ozone
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Pollution and chemical reactions has led to a
phenomenon known as ozone “hole”.
The ozone hole is thinning of the ozone
layer of the stratosphere.
Chlorofluorocarbon (CFCs) and other gases
are the principal agent for ozone depletion.
Ozone(O3) aborbs UV rays which harms
plants and animal tissues.
A 1% loss of ozone could result in a million
extra human skins cancers per year.
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EFFECTS OF AIR POLLUTION
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Human Health
 EPA estimates each year 50,000 people
die prematurely from illnesses related to air
pollution.
- Likelihood of suffering ill health is related
to intensity and duration of exposure.
 Inhalation is the most common route,
but absorption through the skin and
consumption via food can also occur.
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Effects of Air Polution
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Consequences of breathing dirty air leads to
increased probability of heart attack,lung
diseases and cancers.
250 000 people in US suffer from pollution
related bronchitis per year
Conditions are much worse in developing
countries.
City dwellers are more prone to pollutant
related diseases than countryside dwellers.
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Acid Deposition
Acid Precipitation/Acid rain: - Deposition of wet,
acidic solutions or dry, acidic particles from the
air.
 pH scale ranges from 0-14:
7 = Neutral; <7 = Acidic; >7 = Basic
 Unpolluted rain generally has pH of 5.6.
 Rain water react with CO2 in the air and
carbonic acid is formed.
 Rainfall acidity thus falls to pH 4.3.
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AIR POLLUTION CONTROL
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Reducing Pollution
 Most effective strategy for controlling
pollution is to minimize polluting activities.
 Best effective strategy is to conserve
energy: reducing electricity
consumption,insulating homes and
offices,better public transport to reduce air
pollution.
 Alternative energy source: wind & solar.
 Technological advances
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Air Pollution Control contd.
Particulate Removal – Filtering Air
Emission : Remove particles physically
by trapping them in a porous mesh
which allows air to pass through but
holds back solids.
Removal of sulfur, Nitrogen oxides
,hydrocarbon and others by advance
technology.
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Reducing Pollution
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Sulfur Removal
 Fuel Switching
- Switch from soft coal with a high sulfur
content to low sulfur coal.
 Limestone Injection
- Can reduce sulfur emissions by 90% by
mixing crushed limestone with coal
before it is fed into a boiler.
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CLEAN AIR LEGISLATION
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Clean Air Act (1963) - First national air
legislation pollution control.
Clean Air Act (1970) rewrote original Act.
 Identified critical pollutants.
 Established ambient air quality standards
mainly:
Primary Standards – to protect human
health
Secondary Standards –to protect materials,
environment, and comfort.
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Clean Air Act
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Since 1970 the Clean Air Act has been modified &
amended: Revision in1990 and have addressed
principal problems :
 Acid Rain
 Urban Smog
 Toxic Air Pollutants
 Ozone Protection
 Marketing Pollution Rights
 Fugitive emissions of volatile organics
 Ambient ozone, soot, and dust.
 NOx emissions (Nitrogen oxides)
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CURRENT AND FUTURE CONDITIONS
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Read while you relax
In the United States, air quality has improved
dramatically in the last decade in terms of
major large-volume pollutants.
 Cities where pollution is largely from traffic
still have serious air quality problems.
Major metropolitan areas of many developing
countries are growing at explosive rates, and
environmental quality is very poor.
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