Smog is a mix of smoke and fog caused by air pollution. There are two main types: industrial smog from coal burning, containing sulfur dioxide and particulate matter; and photochemical smog from vehicle emissions containing ozone, nitrogen oxides, and other chemicals. Industrial smog causes respiratory issues and acid rain, while photochemical smog causes eye and respiratory irritation. Thermal inversions trap smog near the surface by warm air acting as a lid over polluted cool air. Smog has negative health, environmental, and economic impacts.

1. SMOG
And
its Environmental Effects

2. 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)

3. 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.

4. 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.

5. 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
→
→

6. 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→

7. 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
→
→

8. Reactions of Smog
5. 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

9. 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

10. 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

11. Effects
Effects 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

12. THANK YOU