SMOGAnd

its Environmental Effects

History of Smog

• Name comes from a mix of “Smoke” and “Fog”

• First observed in London during the industrial revolution

• There are 2 types of smog: Industrial Smog (London) and Photochemical Smog (Los Angeles)

Industrial Smog (Reducing)

• Source: Pollution from the burning of coal and oil that contains sulfur

• Consists mainly of: Sulfur Dioxide, Sulfur Trioxide, soot and ash (particulate matter) and sulfuric acid

• It can cause breathing difficulties in humans, plus acid rain damage to plants, aquatic systems, and metal or stone objects

• London and Chicago have problems with industrial smog.

• Methods of reducing this smog: Alkaline Scrubbers reduce SO2 and SO3 levels; electrostatic precipitators reduce particulates.

Photochemical Smog (Oxidizing)

• Source: Mainly automobile pollution• Contains: Nitrogen Oxides, Ozone, Alkanals, Peroxyacyl

Nitrates (PANs), plus hundreds of other substances• Effects: PANs cause eyes to water and can damage plants,

O3 irritates eyes and deteriorates rubber and plants, NOx causes acid rain.

• First observed in LA in the 1940s, Manila and Mexico City also experience this kind of smog

• Catalytic Converters change NO to N2, Lean burning engines reduce Nox, but create more CO and Hydrocarbons.

Reactions of Smog

• Sulfur Dioxide can be oxidized to Sulfur trioxide, a secondary pollutant:

• Metallic Particulates act as a catalyst for this reaction.

• In addition, free radicals from NO2 also speed up the reaction:

2 2 32SO O 2SO

2

2 3

NO + uv light NO + O

SO + O SO

Reactions of Smog

• The formation of Secondary Pollutants in Photochemical Smog.

1. Formation of NOx:

2. Photo-Dissociation of nitrogen dioxide to produce

oxygen atoms:

2(g) 2(g) (g)

(g) 2(g) 2(g)

N + O 2NO

2NO +O 2NO

2(g) (g) (g)NO + uv light NO + O

Reactions of Smog

3. Atomic oxygen forms Ozone:

4. Formation of organic free radicals:

(g) 2(g) 3(g)O + O O

3

3 3

3O + HC HCO

-or-

O + HC HCO

Reactions of Smog5. Formation of photochemical “soup” containing

hundreds of chemicals including PANs:

3R-CH=CH-R + O RCH=O + R-O + CH-O

hydrocarbon alkanal free radicals

R-CH=O + O + uv light R-C=O + OH

free radical

PAN = Peroxyacetyl nitrate

Thermal Inversions• Abnormal arrangement of air masses

– A warmer layer of air is trapped between two layers of colder air– This causes pollutants to be trapped near the earth’s surface

• Can form when hills or mountains stop horizontal winds, causing pollutants to collect over a city.

• Warm air collects over the polluted air, acting as a lid to stop the pollutants from being dispersed.

• In London, 1952, a thermal inversion lasting several days resulted in the deaths of several thousand people, most severely affecting the very old and young

• Thermal inversions worsen any type of smog

Thermal Inversions

Normal Conditions

Cooler Air

Winds disperse pollutants worldwide

Warmer Air

Pollutants dissociate upwards

Thermal Inversion

Cooler Air

Warm air layer

Cool Air trapped at surface

Pollutants trapped at surface

EffectsEffects on human health

•Headaches•Eyes, nose and throat irritations•Impaired lung function•Coughing and wheezing

Damage to materials•Ozones causes rubber to deteriorate

Effects on the atmosphere•Reduce visibility

Toxicity to plants•

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