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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.



• 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



•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


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!


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


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


Particulate Removal


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


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


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


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

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