Chapter 19

Air Pollution

Air: The Endangered Global Commons

Mixture of gases: 78% Nitrogen, 21% Oxygen, 0.04% Carbon Dioxide, and others

Contains water vapor and various pollutants

A renewable resource cleansed by natural processes and regenerated by living things

Used by many and protected by few – it suffers from the tragedy that befalls many commons

Natural Air PollutantsSource Pollutants

Volcanoes Sulfur oxides, particulates

Forest fires Carbon monoxide, carbon dioxide, nitrogen oxides, particulates

Wind storms Dust

Plants (live) Hydrocarbons, pollen

Plants (decaying) Methane, hydrogen sulfide

Soil Viruses, dust

Sea Salt particulates

Anthropogenic Pollutants

Generally create long-term threat Power plants, automobiles, factories,

and other human sources emit large quantities in restricted areas

Higher concern because it is produced in localized regions so that concentrations reach potentially dangerous levels

Core Case Study: When Is a Lichen Like a Canary?

Lichens can warn us of bad air because they absorb air as a source of nourishment.

Figure 19-1

Core Case Study: When Is a Lichen Like a Canary?

Some lichen species are sensitive to specific air-polluting chemicals.

After Chernobyl, more than 70,000 reindeer had to be killed because they ate highly radioactive lichens.

Because lichens are widespread, long-lived, and anchored in place, they can help track pollution to its source.

Case study: Isle Royale, MI Evernia lichens sicken or die in the presence of excess sulfur dioxide

Scientists used Evernia to show evidence of sulfur dioxide pollution entering Isle Royale from coal-burning facilities at Thunder Bay, Ontario

STRUCTURE AND SCIENCE OF THE ATMOSPHERE

The atmosphere consists of several layers with different temperatures, pressures, and compositions.

Figure 19-2

Fig. 19-2, p. 440

Atmospheric pressure (millibars)

Temperature

Thermosphere

Pressure

Mesopause

Heating via ozoneMesosphere

Stratopause

Alt

itu

de

(kil

om

eter

s)

Stratosphere Alt

itu

de

(mil

es)

Tropopause

Ozone “layer”

Heating from the earthTroposphere

Temperature (˚C)

Pressure = 1,000 millibars at ground level

(Sea level)

STRUCTURE AND SCIENCE OF THE ATMOSPHERE

The atmosphere’s innermost layer (troposphere) is made up mostly of nitrogen and oxygen, with smaller amounts of water vapor and CO2.

Ozone in the atmosphere’s second layer (stratosphere) filters out most of the sun’s UV radiation that is harmful to us and most other species.

AIR POLLUTION

Some primary air pollutants may react with one another or with other chemicals in the air to form secondary air pollutants.

Figure 19-3

Fig. 19-3, p. 442

Primary Pollutants

CO CO2Secondary Pollutants

SO2 NO NO2

Most hydrocarbons SO3

Most suspended particles HNO3

H2O2 O3 PANs

Most NO3– and SO4

2– salts

Sources Natural Stationary

Mobile

H3SO4

Major Air Pollutants

Carbon oxides: Carbon monoxide (CO) is a highly toxic gas

that forms during the incomplete combustion of carbon-containing materials.

93% of carbon dioxide (CO2) in the troposphere occurs as a result of the carbon cycle.

7% of CO2 in the troposphere occurs as a result of human activities (mostly burning fossil fuels). It is not regulated as a pollutant under the U.S.

Clean Air Act.

Major Air Pollutants

Nitrogen oxides and nitric acid: Nitrogen oxide (NO) forms when nitrogen

and oxygen gas in air react at the high-combustion temperatures in automobile engines and coal-burning plants. NO can also form from lightening and certain soil bacteria. NO reacts with air to form NO2. NO2 reacts with water vapor in the air to

form nitric acid (HNO3) and nitrate salts (NO3

-) which are components of acid deposition.

Major Air Pollutants

Sulfur dioxide (SO2) and sulfuric acid:About one-third of SO2 in the troposphere

occurs naturally through the sulfur cycle.Two-thirds come from human sources, mostly

combustion (S+ O2 SO2) of sulfur-containing coal and from oil refining and smelting of sulfide ores.

SO2 in the atmosphere can be converted to sulfuric acid (H2SO4) and sulfate salts (SO4

2-) that return to earth as a component of acid deposition.

Major Air Pollutants

Suspended particulate matter (SPM):Consists of a variety of solid particles

and liquid droplets small and light enough to remain suspended in the air.

The most harmful forms of SPM are fine particles (PM-10, with an average diameter < 10 micrometers) and ultrafine particles (PM-2.5).

According to the EPA, SPM is responsible for about 60,000 premature deaths a year in the U.S.

Major Air Pollutants

Ozone (O3):Is a highly reactive gas that is a major

component of photochemical smog.It can

Cause and aggravate respiratory illness. Can aggravate heart disease. Damage plants, rubber in tires, fabrics,

and paints.

Major Air Pollutants

Volatile organic compounds (VOCs):Most are hydorcarbons emitted by the

leaves of many plants and methane.About two thirds of global methane

emissions comes from human sources.Other VOCs include industrial solvents

such as trichlorethylene (TCE), benzene, and vinyl chloride. Long-term exposure to benzene can cause

cancer, blood disorders, and immune system damage.

Major Air Pollutants

Radon (Rn):Is a naturally occurring radioactive gas

found in some types of soil and rock.It can seep into homes and buildings

sitting above such deposits.

Major Air PollutantsPollutant Major anthropogenic

sourceHealth effects

Carbon monoxide Transportation Headache, dizziness, death,cardiovascular disease

Sulfur oxides Coal-fired power plants and industries

Respiratory disease, emphysema, bronchitis

Nitrogen oxides Transportation, coal power plants, industries

Lung irritation, bronchitis

Particulates Coal power plants, industries

Irritation of respiratory system, cancer

Hydrocarbons Transportation Unknown

Photochemical oxidants

Transportation, stationary combustion sources

Respiratory irritation, eye irritation, emphysema

URBAN OUTDOOR AIR POLLUTION

Industrial smog is a mixture of sulfur dioxide, droplets of sulfuric acid, and a variety of suspended solid particles emitted mostly by burning coal.In most developed countries where coal and

heavy oil is burned, industrial smog is not a problem due to reasonably good pollution control or with tall smokestacks that transfer the pollutant to rural areas.

Case Study: South Asia’s Massive Brown Cloud

A huge dark brown cloud of industrial smog, caused by coal-burning in countries such as China and India, stretches over much of southeastern Asia.In areas beneath the cloud, photosynthesis is

reduced interfering with crop development.Fine particles and droplets in the cloud appear

to be changing regional climates (including rainfall). May have contributed to floods in 2002 and 2005

which killed thousands of people.

Sunlight plus Cars Equals Photochemical Smog

Photochemical smog is a mixture of air pollutants formed by the reaction of nitrogen oxides and volatile organic hydrocarbons under the influence of sunlight.

Sunlight plus Cars Equals Photochemical Smog

Mexico City is one of the many cities in sunny, warm, dry climates with many motor vehicles that suffer from photochemical smog.

Figure 19-4

Factors Reducing Levels of Outdoor Air Pollution

Settling out – heavier particles settle Rain and snow – cleanse the air pollutant Salty sea spray – wash out particulates

and water-soluble pollutants Winds – sweep away and dilute with

cleaner air Chemical reactions – formation of acid

rain – chemical falls to EarthThe pollutants do not disappear; they are merely

shifted elsewhere or deposited onto other medium

Factors Increasing Levels of Outdoor Air Pollution

Urban buildings – slow wind speed Hills and mountains – reduce flow of air in

valleys Higher temperatures – promote chemical

reactions VOC emissions from certain trees and

plants Grasshopper effect – volatile air pollutants

transported from tropics and temperate forests toward the poles during the winter

Temperature inversions – cause buildup

Grasshopper Effect

Explains sightings of reddish-brown haze over the Arctic

Polar bears, whale sharks, and other top carnivores in Arctic have high levels of DDT, other persistent pesticides, toxic metals, and PCBs in their bodies

Temperature Inversions

Cold, cloudy weather in a valley surrounded by mountains can trap air pollutants (left).

Areas with sunny climate, light winds, mountains on three sides and an ocean on the other (right) are susceptible to inversions.

Figure 19-5

During normal conditions, air temperature decreases with altitude, thus pollutants ascend and mix with atmospheric gases

In a temperature inversion, however, warm air forms a lid over cooler air, thus trapping air pollution

Fig. 19-5, p. 447

Inversion layer Inversion layer

San Diego, CA

City with several million people and motor vehicles in an area with a sunny climate, light winds, mountains on three sides, and the ocean on the other side – conditions ideal for photochemical smog worsened by frequent thermal inversions – example: Los Angeles, CA (Brown-air smog)

Brown-air cities

Early morning traffic provides the ingredients for photochemical smog

Reaches highest levels in early afternoon

Suburbs and surrounding rural areas usually have higher levels of photochemical smog than the cities themselves

Major episodes usually occur during summer

Although anthropogenic pollutants are the most significant sources of air pollution, researchers have found some

instances in which naturally occurring pollutants noticeably affect air quality.

In Atlanta, the trees emit a number of highly reactive hydrocarbons. These chemicals react with nitrogen dioxide from automobiles and other combustion sources to produce ozone. New research shows that hydrocarbons from trees are 50 to 100 times more reactive than hydrocarbons from

human sources.

ACID DEPOSITION

Sulfur dioxides, nitrogen oxides, and particulates can react in the atmosphere to produce acidic chemicals that can travel long distances before returning to the earth’s surface.Tall smokestacks reduce local air

pollution but can increase regional air pollution.

ACID DEPOSITION

Acid deposition consists of rain, snow, dust, or gas with a pH lower than 5.6.

Figure 19-6

Fig. 19-6, p. 448

WindTransformation to sulfuric acid (H2SO4) and nitric acid (HNO3)

Windborne ammonia gas and particles of cultivated soil partially neutralize acids and form dry sulfate and nitrate salts

Wet acid depostion (droplets of H2SO4 and HNO3 dissolved in rain and snow)

Nitric oxide (NO)Sulfur dioxide (SO2) and NO

Dry acid deposition (sulfur dioxide gas and particles of sulfate and nitrate salts)

Acid fogFarm

OceanLakes in deep

soil high in limestone are

buffered

Lakes in shallow soil low in limestone

become acidic

Harmful Effects of Acid Rain Cause or worsen

respiratory disease Attack metallic and

stone objects Decrease

atmosphere visibility Kill fish Deplete soils of vital

plant nutrients Harm crops and

plants

ACID DEPOSITION

Acid deposition contributes to chronic respiratory disease and can leach toxic metals (such as lead and mercury) from soils and rocks into acidic lakes used as sources for drinking water.

ACID DEPOSITION Air pollution is

one of several interacting stresses that can damage, weaken, or kill trees and pollute surface and groundwater.

Figure 19-9

Fig. 19-9, p. 451

Emissions

SO2 NOxAcid deposition

H2O2 O3

Others

Direct damage to leaves & bark

Reduced photo-synthesis and growth

Susceptibility to drought, extreme cold, insects, mosses, & disease organisms

Soil acidification

Tree death

Leaching

of soil nutrients

Release of toxic metal ions

Root damage

Reduced nutrient & water uptakeAcids

Lake

Groundwater

PANs

Acid deposition effect on aquatic ecosystems Fish die if pH drops below 4.5 Aluminum ions are released from

soil, carried into lakes, can clog fish gills

Mercury buildup in fish can affect humans (kidneys, brain)

Note: acid rain can be buffered by limestone, which reduces acidity

Factors which determine how severe the health effects are from mercury exposure

The chemical form of mercury The dose The age of person exposed (fetus

most susceptible) The duration of exposure The route of exposure – inhalation,

ingestion, dermal contact, etc. The health of the person exposed

Methylmercury effects on humans

Impaired neurological development (fetuses, infants, children)

Impacts on cognitive thinking, memory, attention

Impaired peripheral vision Disturbances in sensations (“pins

and needles” feelings) Impairment of speech, hearing,

walking

Acid deposition effect on plants Tree leaves, needles damaged Important nutrients (Ca, Mg)

leached, reducing plant productivity Aluminum ions are mobilized, reduce

plant productivity Lead, cadmium, mercury are

mobilized, reduce plant productivity Plants weakened and become

susceptible to other disease

Forest destroyed due to acid rain

Fig. 19-10, p. 452

Solutions

Acid Deposition

Prevention Cleanup

Reduce air pollution by improving energy efficiency

Add lime to neutralize acidified lakes

Reduce coal use

Add phosphate fertilizer to neutralize acidified lakes

Increase natural gas use

Increase use of renewable energy resources

Burn low-sulfur coal

Remove SO2 particulates & NOx from smokestack gases

Remove NOx from motor vehicular exhaust

Tax emissions of SO2

INDOOR AIR POLLUTION Indoor air pollution usually is a greater

threat to human health than outdoor air pollution.

According to the EPA, the four most dangerous indoor air pollutants in developed countries are:Tobacco smoke.Formaldehyde.Radioactive radon-222 gas.Very small fine and ultrafine particles.

Sick-building Syndrome

Almost one in five commercial building in the U.S. considered “sick”

Symptoms:DizzinessHeadachesSore throatsChronic fatigueRespiratory infectionsDepression

Chloroform

Benzo-a-pyrene

Styrene

Radon-222

Methylene Chloride

Tobacco Smoke

Carbon Monoxide

Asbestos

Nitrogen Oxides

1, 1, 1-Trichloroethane

Particulates

FormaldehydeTetrachloroethylene

Para-dichlorobenzene

Fig. 19-11, p. 453

INDOOR AIR POLLUTION Household dust mites

that feed on human skin and dust, live in materials such as bedding and furniture fabrics.Can cause asthma

attacks and allergic reactions in some people.

Figure 19-12

Case Study: Radioactive Radon

Radon-222, a radioactive gas found in some soils and rocks, can seep into some houses and increase the risk of lung cancer.

Sources and paths of entry for indoor radon-222 gas.

Figure 19-13

HEALTH EFFECTS OF AIR POLLUTION

Your respiratory system can help protect you from air pollution, but some air pollutants can overcome these defenses.

Figure 19-14

How does your respiratory system help protect you from air pollution?

Hairs in your nose Sticky mucus in the lining of your

upper respiratory tract Sneezing Coughing Cilia in your upper respiratory tract

Acute effects vs. chronic effects

Acute health effects

Chronic health effects

May cause immediate effects

Take place over many years at low levels

Shortness of breath

Chronic bronchitis

Eye irritation Emphysema

Irritated throats Bronchial asthma

Lung cancer

HEALTH EFFECTS OF AIR POLLUTION

Normal human lungs (left) and the lungs of a person who died of emphysema (right).

Figure 19-15

Air Pollution is a Big Killer Each year, air pollution prematurely

kills about 3 million people, mostly from indoor air pollution in developing countries.In the U.S., the EPA estimates that

annual deaths related to indoor and outdoor air pollution range from 150,000 to 350,000.

According to the EPA, each year more than 125,000 Americans get cancer from breathing diesel fumes.

PREVENTING AND REDUCING AIR POLLUTION – Clean Air Act

Emission standards for cars Emissions standards for new industries Ambient air quality standards for urban areas –

established by the EPA covers six criteria air pollutantsCarbon monoxideNitrogen oxidesSulfur dioxidesSuspended particulate matter (less than PM-10)Volatile organic compoundsOzoneLead

Solutions: Reducing Outdoor Air Pollution

There are a of ways to prevent and control air pollution from coal-burning facilities.Electrostatic precipitator: are used to

attract negatively charged particles in a smokestack into a collector.

Wet scrubber: fine mists of water vapor trap particulates and convert them to a sludge that is collected and disposed of usually in a landfill.

Electrostatic Precipitator Can remove 99% of

particulate matter Does not remove

hazardous ultrafine particles.

Produces toxic dust that must be safely disposed of.

Uses large amounts of electricity

Figure 19-18

Wet Scrubber

Can remove 98% of SO2 and particulate matter.

Not very effective in removing hazardous fine and ultrafine particles.

Figure 19-18

Filtering air pollutants

Pollutants can be filtered from smokestack gases, precipitated out, or even washed out. The problem with these techniques is that the pollutant must then be disposed of. Disposal in landfills can result in the pollution of groundwater.

Fig. 19-17, p. 459

Solutions

Stationary Source Air Pollution

Prevention

Burn low-sulfur coal

Disperse emissions above thermal inversion layer with tall smokestacks

Remove sulfur from coal

Convert coal to a liquid or gaseous fuel

Remove pollutants after combustion

Shift to less polluting fuels

Tax each unit of pollution produced

Dispersion or Cleanup

Fig. 19-19, p. 460

Solutions

Motor Vehicle Air Pollution

Prevention Cleanup

Emission control devices

Mass transit

Bicycles and walking

Less polluting engines

Less polluting fuels

Improve fuel efficiency

Car exhaust inspections twice a year

Get older, polluting cars off the road

Give buyers large tax write-offs or rebates for buying low-polluting, energy efficient vehicles

Stricter emission standards

Fig. 19-20, p. 461

Solutions

Indoor Air Pollution

Prevention

Cover ceiling tiles & lining of AC ducts to prevent release of mineral fibers

Use adjustable fresh air vents for work spaces

Increase intake of outside airBan smoking or limit it to well ventilated areas

Change air more frequently

Set stricter formaldehyde emissions standards for carpet, furniture, and building materials

Circulate a building’s air through rooftop green houses

Prevent radon infiltration Use exhaust hoods for stoves and appliances burning natural gasUse office machines in well

ventilated areas

Use less polluting substitutes for harmful cleaning agents, paints, and other products

Install efficient chimneys for wood-burning stoves

Cleanup or Dilution

Fig. 19-21, p. 461

What Can You Do?

Indoor Air Pollution

• Test for radon and formaldehyde inside your home and take corrective measures as needed.

• Do not buy furniture and other products containing formaldehyde.

• Remove your shoes before entering your house to reduce inputs of dust, lead, and pesticides.

• Test your house or workplace for asbestos fiber levels and for any crumbling asbestos materials if it was built before 1980.

• Don't live in a pre-1980 house without having its indoor air tested for asbestos and lead.

• Do not store gasoline, solvents, or other volatile hazardous chemicals inside a home or attached garage.

• If you smoke, do it outside or in a closed room vented to the outside.

• Make sure that wood-burning stoves, fireplaces, and kerosene- and gas-burning heaters are properly installed, vented, and maintained.

• Install carbon monoxide detectors in all sleeping areas.