Air Pollution

Chapter 12: Air Pollution

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A brief history of air pollution Types and sources of air pollutants Factors that affect air pollution Air pollution and the urban environment Acid deposition

A Brief History of Air Pollution 

London’s historical problems    

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King Edward I forbid sea coal in 1273 London known for “pea-soup” (dangerous) One “pea-soup” incident caused 700 deaths Term “smog” created around 1911

Disastrous London smog event of 1952  

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Winds died, smog settled over London People could see where they were walking for 5 days Killed 5,000 lives Caused Parliament to pass Clean Air Act of 1956

A Brief History of Air Pollution 

Donora, Pennsylvania pollution episode, 1948 

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Pollution trapped in Monongahela River Valley by inversion (20 people died)

U.S. Clean air act, 1970, 1990 Due to high pollution, Congress passed Clear Air Act (revised in 1977, 1990)  Sets emission standards  Incentives for companies to lower emission 

Principal Air Pollutants 

Primary pollutants 

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Enter atmosphere directly

Secondary pollutants 

Enter atmosphere from chemical reactions

• Globally, a large percentage of air pollution sources are natural. Within localized areas, however, humancaused sources are often the largest contributors.

Principal Air Pollutants 

Particulate matter – solid particles and liquid droplets small enough to remain suspended (aerosols).  

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Not poisonous - soot, smoke, dust, pollen More dangerous – asbestos, arsenic, oil, sulfuric acid

PM10 – Particulates with diameters < 10 micrometers    

Small enough to penetrate into lungs Can remain in air for long time Wind can carry great distances Asian dust can transport dust long distances

Principal Air Pollutants

Principal Air Pollutants 

PM2.5 – Particulates with diameters < 2.5 micrometers Penetrate farther into lungs  Found in diesel soot and are carcinogenic (school buses, traffic corridors) 

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Removed by rain, snow, ice crystals

Principal Air Pollutants 

Carbon Monoxide – major pollutant in cities. Colorless, odorless, poisonous gas 60 million metric tons enter U.S. air annually. Half from highway vehicles.  Extremely dangerous and can kill quickly in poorly ventilated areas. 

Principal Air Pollutants 

Sulfur dioxide – comes from sulfurcontaining fossil fuels. Colorless. Comes from power plants, heating devices, paper mills, volcanoes Can form into secondary pollutants (sulfur trioxide, sulfuric acid  Hurt breathing and certain plants 

Principal Air Pollutants 

Volatile organic compounds – organic compounds mainly made of hydrogen and carbon 

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Methane, benzene, formaldehyde, chlorofluorocarbans

Nitrogen oxides – formed when nitrogen combines with oxygen during fuel combustion  

Nitrogen dioxide, nitric oxide (NOx) Vehicles, power plants, garbage dumps

• Along with ozone, VOCs and NOx are major components of photochemical smog.

Ozone in the Troposphere  

Photochemical smog – formed when chemical reaction takes place with sunlight Ozone – Dangerous at surface. Irritates eyes, lungs. Can cause asthma and bronchitis 

Causes several billions of dollars in loss from crop yield

• Photochemical smog is a problem on most major cities of the world.

Ozone in the Troposphere

Ozone in the Stratosphere 

Relationship to ultraviolet radiation Ozone layer shields surface from UV radiation  UV can cause skin cancer  Eye cataracts  Hurt immune system 

Ozone in the Stratosphere 

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Ozone broken down into O2 and O when UV hits it Chloroflucarbons (CFCs) where used in hairsprays, deodorants, propellants until 1987 (Montreal Protocol) Stable at surface, enter stratosphere from t-storms, near jet streams

Ozone in the Stratosphere 

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Sunlight breaks off the Chlorine and it breaks up ozone CFCs are very longlasting One CFC can destroy 100,000 Ozone molecules

Ozone in the Stratosphere

Ozone in the Stratosphere

Air Pollution: Trends and Patterns 

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Primary air quality standards – standards set up to protect human health secondary air quality standards- standards set up to protect visibility, crops, and buildings Nonattainment areas – areas that do no meet air quality standards • Secondary air pollutants are particularly difficult to control, because they are not emitted directly into the atmosphere.

Air Pollution: Trends and Patterns 

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80 millions Americans breathing air not meeting one standard Air Quality Index (AQI) – includes carbon monoxide, sulfur dioxide, nitrogen dioxide, particulate matter, ozone Highest pollutant is one used in index  Anything higher than 100 is unhealthy 

Fig. 12-11, p. 338

The Role of the Wind

The Role of the Wind 

Dilution – mixing air pollution in a greater volume of air. Can create problems downwind

• “Dilution is the solution to pollution” - in the 1950s this motto led to the construction of tall smokestacks for large factories. Pollution was released higher in the atmosphere where winds were stronger. Air quality improved locally but suffered downwind.

The Role of Stability and Inversions  

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Temperature lapse rates Inversions inhibit vertical movement. Keep pollutants in a layer Mixing depth – the depth of the mixing layer (the layer from the surface to the top of the inversion)

• The mixing layer can often be easily seen from an airplane.

The Role of Stability and Inversions

The Role of Topography 

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Cold air drainage – air drains downhill over night, carrying pollutants Air blockage by mountain ranges. Mountains block the progress of flow. Blocks pollutants from moving out of the region

The Role of Topography

Severe Air Pollution Potential  

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Many sources (clustered close together) High pressure (becomes stationary, light winds) Inversions (inhibits vertical movement) Stagnation (pollutants unable to disperse) Valley (pollutants accumulate) • Some locations, like Los Angeles and Mexico City, have an unfortunate combination of surrounding topography, frequent inversions, abundant emissions and plentiful sunlight perfect conditions for photochemical smog.

Air Pollution and the Urban Environment 

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Urban heat island – cities are warmer than rural areas Country breeze – Return breeze in circulation

Acid Deposition 

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Dry deposition – when pollutants slowly settle to ground Wet deposition – when pollutants are carried to ground by rain, snow Acid rain effects

• Strangely enough, an acidified lake looks crystal clear and beautiful. But the beauty is false; it’s only clear because nothing is alive in it.