Transcript SMOG - Virginia K. Fox Translations

SMOG
And 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:
2SO2  O2  2SO3
• Metallic Particulates act as a catalyst for this reaction.
• In addition, free radicals from NO2 also speed up the
reaction:
NO + uv light  NO + O
2
SO2 + O  SO3
Reactions of Smog
• The formation of Secondary Pollutants in
Photochemical Smog.
1. Formation of NOx:
N 2(g) + O 2(g)  2NO (g)
2NO (g) +O 2(g)  2NO 2(g)
2. Photo-Dissociation of nitrogen dioxide to produce
oxygen atoms:
NO2(g) + uv light  NO(g) + O(g)
Reactions of Smog
3. Atomic oxygen forms Ozone:
O(g) + O2(g)  O3(g)
4. Formation of organic free radicals:
3O + HC  HCO3
-orO3 + HC  HCO3
Reactions of Smog
5. Formation of photochemical “soup” containing
hundreds of chemicals including PANs:
R-CH=CH-R + O3  RCH=O + R-O  + CH-O 
hydrocarbon
alkanal
free radicals
R-CH=O + O + uv light  R-C=O +  OH
free radical
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
Cooler Air
Cooler Air
Winds disperse pollutants worldwide
Warm air layer
Pollutants dissociate upwards
Pollutants trapped
at surface
Warmer Air
Normal Conditions
Cool Air trapped at surface
Thermal Inversion
Related Research
ANY QUESTIONS?