Air and Air Pollution - EDHSGreenSea.netedhsgreensea.net/APES/apespdfs/unit12pptA.pdfThe Atmosphere...
Transcript of Air and Air Pollution - EDHSGreenSea.netedhsgreensea.net/APES/apespdfs/unit12pptA.pdfThe Atmosphere...
Air and Air Pollution
The Atmosphere
• Four layers:
Troposphere
extends from surface to 17km
75% of total mass of atmosphere
where weather occurs, air currents etc.
78% N2, 21% O2, 1% Ar, .036% CO2
varying amounts of H2O vapor (1-4%)
highest atmospheric pressure
temperature decreases with altitude
ends at tropopause
The Atmosphere
Stratosphere
extends from 17km to 48km
contains less matter than troposphere
ozone layer (1000x more than trop.)
very little water vapor (1000x less than trop)
very calm, no weather, suspended matter will stay formany years, little mixing at tropopause
temperature rises as you increase altitude (because molecules are absorbing greater amount of sun’s energy)
ends at the stratopause
The Atmosphere
Mesosphere
extends from 48 to 80km
characterized by a temperature reversal with
decreasing temps as you go up
ends at the mesopause
The Atmosphere
Thermosphere
extends from 80kn to 1600km
ionized gases
temperatures increase as you go up because molecules
are being constantly bombarded by high energy
radiation
ionosphere - lower portion, aurora borealis
there is no end to the thermosphere, it just gradually
fades into space
Diagram of the Atmosphere
What is air pollution?
• Any chemical or object in the atmosphere in
quantities and for a duration that that causes
harm to humans, other forms of life and
materials
• Natural and human-caused forms of
pollution can be identical, or different
Natural Air Pollution
• Volcanoes:
– ash, sulfur compounds
– acid mists, toxic gases
• Sea spray and decaying vegetation:
– sulfur compounds
• Forest fires:
– suspended particles
– CO2
• Plants
– volatile chemicals
– pollen, spores, etc.
• Wind/storms
Human-caused Pollution
• Primary pollutants
– chemicals that are harmful in the form in which
they are released into the environment.
• Secondary pollutants
– chemicals which are modified and become
harmful after mixing in the troposphere with
other chemicals
– the sun provides the energy for many of these
reactions
Major Types of Pollutantsdesignated by Clean Air Act of 1970
• Sulfur Oxides
• Carbon Oxides
• Particulates
• Hydrocarbons (VOCs)
• Nitrogen Oxides
• Photochemical Oxidants
• Lead
Sulfur Oxides (SO2)
• Humans cause 1/4 of sulfur emissions (180mill) yearly by
burning fossil fuels (coal)
• Other sources are sea spray, organisms and volcanoes
• reduce visibility by as much as 80%
Human Caused SO2 Production
•Human causes
are primarily
coal burning for
electricity and
oil refining
•emissions of
SO2=
19,900,000
metric tons
Reactions of Sulfur Dioxide
• SO2 + O2 SO3
• SO3 + H2O H2SO4
• H2SO4 + H2O H3O+ + SO4
2-
Nitrogen Oxides (NO2)
• Created by burning of fossil fuels when gas reaches 650F
• At this point, nitrogen combines with oxygen to make
nitrogen oxides
• Major component of Photochemical Smog (mixture of
pollutants formed with sunlight)
Human Caused NOx Production
• Produced by a
combination of fuel
burning for electricity
and transportation
• Annual emissions =
21,300,000 metric
tons
Reactions of Nitrogen Oxides
• N2 + O2 NO
• NO + O2 NO2
• NO2 + H2O HNO3 + NO
Carbon Oxides
• Most of CO2 emitted each
year is produced by
respiration and is balanced by
photosynthesis
• Anthropogenic CO and CO2
are produced by burning
fossil fuels
• Carbon dioxide causes global
warming (more later)
Human-caused CO production
• Carbon monoxide is
formed by the incomplete
burning of fossil fuels
• Most is produced through
burning of gas in
transportation
• It is destructive because it
binds to hemoglobin in
place of O2
Metals and Halogens
• lead, mercury, arsenic nickel, etc.
• lead occurs in trace amounts in fuels (leaded
gas)
• others are mined, and released in ore smelting
• mercury is produced by burning wastes and
coal
• halogens are used in aerosols (CFCs)
• HF is produced by the burning of coal
Particulate Matter
• Particulate matter is solid
or liquid material
suspended in a gaseous
medium
• Obvious forms of pollution
because they reduce
visibility and leave dirt
• Hurt respiratory tissues,
long lasting effects
• Farming, volcanoes, fires
and desertification cause
Particulate Matter Production
• PM-10 particulate
matter - matter that
that is less than
10microns in diameter
(most dangerous)
Volatile Organic Compounds
(VOCs)
• Organic chemicals that are gases
• Plants are the largest sources
• Examples:450 mil tons isoprene C5H8
450 mil tons terpenes C10H15
400 mil tons methane CH4
• These are turned into CO and CO2 in theatmosphere
VOC’s emitted by humans
• Humans are responsible for 20% of annual VOC emission
VOC’s emitted by humans
• Most are produced in
paint and cleaning
solution formation
• Some are also
produced in the
burning of fuel for
transportation
Ozone and Photochemical Oxidants
• Although atmospheric ozone is beneficial,
ground level ozone is a serious pollutant
• Ozone is produced by a series of secondary
reactions
• Ozone acts as an oxidizing agent can be
damaging to living tissue as well as plastics
and rubber
Production of Photochemical Oxidants
and Photochemical Smog
• NO2 + UV NO + O (free radical)
• O + O2 O3
• NO + VOC NO2 + PAN (peroxylacyl
nitrates) + aldehydes
• O3, NO2 and PANs are called
photochemical oxidants because they react
with chemicals in the atmosphere or your
body that they shouldn’t
Production of Photochemical Oxidants
and Photochemical Smog
Picture of Photochemical Smog
What is Industrial Smog?
• In cities where are large amount of coal is
burned, a smog is produced that is rich in
soot particles, sulfurous compounds and
water vapor
• Can be found in any industrialized city
where the primary energy source is coal
Effects of Topography:
Thermal/Temperature Inversion
• Normally the air near the Earth’s surface is
warmest because the sun strikes the Earth
and the energy is radiated back into the air
• The warm surface air carries the pollutants
up into the air
• At night, the surface air is cool, and the
higher air is warm. Thermal inversion.
Effects of Topography:
Thermal/Temperature Inversion
• Under the right conditions, a high pressure
(warm) air current will come in above the
surface air, and trap the surface air and
prevent it from rising
• When this happens, the high pollution
surface air cannot escape, and smog levels
rise dramatically--L.A. summers, Santa
Anas
Effects of Topography:
Thermal/Temperature Inversion
Effects of Topography:
Thermal/Temperature Inversion
•In L.A. sea breezes and descending warm air cause
air pollution to be trapped against the foothills.
• Pollution is highest against the hills (in the valley)
where the pollution accumulates
Long Range Transport of Pollution
• Pollution is carried to
the poles by air
currents
• Polar areas have
pesticides, heavy
metals, sulfates, soot
etc.
• Inuits have higer
levels of PCBs than
any population
Effects of pollution on the
environment
• Acid deposition
• Buildings and monuments
• Visibility
What is acid deposition?
• Acid deposition is the deposition of wet
(acidic rain, fog, snow or clouds) or dry
(acidic particles) on the Earth’s surface as a
result of air pollutants
Review: pH
• The pH scale is a
logarithmic scale
which represents the
amount of H+ ions in
solution
• Neutral pH is 7.0
• Note: normal rain
water is slightly acidic
(5.0-5.6)
Acid Deposition
• As previously discussed, nitrogen and sulfur
compounds react in the air to form acids.
• These acids are then brought back to the
earth in a form of precipitation
• Typical rain in the Eastern U.S. is 4.3
• It can be as low as 3.0 (vinegar) or 2.3
(lemon juice - 1000x more acidic than
normal rainwater)
Effect of soils on acid deposition
• Soils have the ability to buffer acid.
• Soils high in CaCO3 (calcite, baking soda,
present in limestone) can neutralize much of
the acid
• Application of CaCO3 (lime)is a reasonable
remedy, but it is expensive
• Soils that are low in CaCO3 are very
susceptible to acid deposition
Where is acid deposition a problem?
• Downwind from coal burning plants
• Eastern U.S. and Canada and Eastern Europe
Where is acid deposition a problem?
• Canada receives much of the acid deposition
caused by U.S. factories
What are the effects of acid deposition?
PLANTS
• Leaf damage
– chlorosis, a disease caused by the die-off of
chlorophyll, causes discoloring and dying of
leaves
• Weakening of plants
– plants are often weakened by acid deposition
which makes them more susceptible to disease
•
What are the effects of acid
deposition? Forest damage
What are the effects of acid deposition?
AQUATIC ENVIRONMENTS
• Major problem in Scandinavia (18,000 lakes in
Sweden are so acidic that fish won’t live)
• Decrease in fish populations
– increase acidity causes mercury and aluminum to leach
out of rocks and compounds to become more dangerous
– acidity can interfere with uptake of oxygen
– interferes with nutrient cycling
– reproductive stage is one most interfered with
– acid shock: spring thaw
The effects of pollution on
BUILDINGS & MONUMENTS
• Limestone buildings are easily eroded by acid
precipitation
• Soot darkens and eats away at structures
The effects of pollution on
BUILDINGS & MONUMENTS
• The frieze from the
Nike temple on the
Acropolis is going to
have to be removed
because it is being
eroded by acid rain.
Think about it –
thousands of years of
exposure – now it goes!
The effects of pollution on
VISIBILITY
• Visibility has decreased much over the last
100 years
• As much as 80% visibility is reduced over
an area 3000km across in the Eastern U.S.
in summer
• Effects in Southern California are well
known to all of us
What is indoor pollution?
• Indoor pollution is generally 2-5x greater
indoors than outdoors
• Significant problem because people spend
most of their time indoors
• smoking, formaldehyde, asbestos, radon
• SCHOOLS POOR INDOOR AIR
QUALITY
What are the effects of pollution
on human health?
• Most health problems occur in the respiratory track
because that is how air pollutants get into the body
• Your body has natural defenses, but they can be
overwhelmed
• Can reduce life expectancy by 5-10 years, or
increase risk of disease by 15-50x depending on
where you live (maybe 150,000-350,000 per year in
U.S.
• Most significant is smoking, which is preventable
What are the effects of pollution
on human health?
• Diseases:
– asthma
– lung cancer
– chronic bronchitis
– emphysema
Controlling Air Pollution:
Regulations
• Clean Air Acts of 1970, 1977, and 1990
1. Establishment of National Ambient Air QualityStandards (NAAQS) for seven major pollutants(primary standards)
2. Prevention of deterioration
3. National emission standards
4. Specific targets for reductions of sulfur,nitrogen compounds, carbon monoxide anddioxide
Controlling Air Pollution:
Particulate Removal
• Filters
– removes particulates by trapping them in a mesh filter
– low maintenance
• Electrostatic Precipitators
– most common in power plants
– Particulates pick up a charge as they pass between
electrodes. Then they are attracted by a charged
collecting plate
– high efficiency and cost
Controlling Air Pollution:
Particulate Removal
Controlling Air Pollution:
Sulfur Removal
• Changing or cleaning fuels
• Limestone injection
– mixing limestone with coal during burning removes
sulfur, but creates slag
• Fluidized bed combustion
– limestone and coal are burned in a bed, suspended
by pressurized air. Sulfur is drawn off as it is
created, and heat transfer is more efficient
– can use higher sulfur coal
Controlling Air Pollution:
Sulfur Removal• Scrubbing (flue gas desulfurization)
– gases are bubbled through a slurry (watery mixture of
limestone)
– the gases react, and the sulfur is removed
– sludge produced must be disposed of carefully
Controlling Air Pollution:
Nitrogen Oxides
• Controlling fuel to air mixtures carefully
• Exhaust recycling
– burn once, then recycle and burn air again to
reduce emissions
• Catalytic converters use catalysts to
increase the burning of the fuel to decrease
CO and NO2 production (90% effective in
non-diesel engines) They do increase CO2
Controlling Air Pollution:
Hydrocarbons
• Monitor fuel/oxygen ration to maximize
complete burning
• Cars now do this with an oxygen sensor in
the tailpipe.
THE GOOD NEWS
• Pollution control measures are working
• The health of the world’s air (on average) is
getting better
• The air in L.A. is the best that it has been in
30-40 years
• Although our CO2 emissions continue to
increase, other pollutants are decreasing
Trends in Car Emissions
Ambient Air Pollutants
Megacities
•• SCRUBBERSSCRUBBERS::
installed oninstalled on
smoke stacksmoke stack
to reduceto reduce
pollutantspollutants
•• CatalyticCatalytic
ConvertersConverters
Air Pollution in the U.S.•• However, levels of many pollutants are stillHowever, levels of many pollutants are still
higher than recommended by the EPA in manyhigher than recommended by the EPA in many
urban areasurban areas
•• In addition, more cars are being produced andIn addition, more cars are being produced and
this is offsetting gains in air qualitythis is offsetting gains in air quality
Air Pollution in Developing
Countries
•• IndustrializationIndustrialization
–– As it proceeds air pollution increasesAs it proceeds air pollution increases
–– more cars, more factories, etcmore cars, more factories, etc
–– very few regulations and advanced technologiesvery few regulations and advanced technologies
compounds pollution problemscompounds pollution problems
Mexico City•• WorldWorld’’s Fourth largest city: boasts the s Fourth largest city: boasts the worldworld’’ss
worst airworst air
–– TopographyTopography
(similar to L.A.)(similar to L.A.)
–– 3 million motor3 million motor
vehicles, no smogvehicles, no smog
controls: most burncontrols: most burn
leaded gas leaded gas
Mexico City•• WinterWinter
•• Summer Summer
Mexico City•• What has been done to improve air quality?What has been done to improve air quality?
–– switching to unleaded gas, phase out old cars and switching to unleaded gas, phase out old cars and
impose driving restrictions when air quality is veryimpose driving restrictions when air quality is very
badbad
Remote Regions••
Global Distillation EffectGlobal Distillation Effect
–– Certain Pollutants are volatile and can be carried inCertain Pollutants are volatile and can be carried in
air currents to remote locationsair currents to remote locations
•• Lake Lake NyosNyos, , CamaroonCamaroon
Lake Nyos••
CO2 seeped into deep lake: kept in bottom waterCO2 seeped into deep lake: kept in bottom water
by pressure & thermoclinesby pressure & thermoclines
•• Released Released explosivelyexplosively,,
covered nearby covered nearby
villages villages
Axphixiation
Aftermath
Remote Regions•• Open Hearth FiresOpen Hearth Fires
–– often poorly in ventillatedoften poorly in ventillated
homeshomes
–– can have worse pollutioncan have worse pollution
levels than a dirty urban citylevels than a dirty urban city
Remote Regions•• DDTDDT and other and other
organochlorine compoundsorganochlorine compounds
and banned in manyand banned in many
countries, yet keep turningcountries, yet keep turning
up there due to this effectup there due to this effect
Remote Regions••
Arctic and Antarctic regions are especially atArctic and Antarctic regions are especially at
risk due to theirrisk due to their
fragile foodfragile food
ecologyecology