Download Smog

SMOG
Application of Collision Theory
http://www.toronto.cbc.ca/features/smog/
Smog
• “Smog” is a term that was coined about
100 years ago.
• Smog forms when smoke emissions are
mixed with moist foggy air.
• The proper name is photochemical
smog and it is produces a hazy, yellowbrown sky.
• It is caused by the action of sunlight on
nitrogen oxides (NOx) and hydrocarbon
emissions from automobiles.
• Smoggy air contains CO, NO, NO2, CxHy,
and O3.
• On smog alert days, breathing is
uncomfortable, and the sky ‘looks ugly’.
• One of the most dangerous components
of smog is ozone, O3.
• Ground level ozone, O3, forms when the
nitrogen monoxide from vehicle exhaust
combines with O2 in the air.
Smog Reaction Mechanism
Step 1:
Step 2:
Step 3:
Step 4:
NO + O2 → NO3
NO3 + NO → 2 NO2
2 NO2 → 2 NO + 2 O
2 O + 2 O2 → 2 O3
Identify all : 1) intermediates
2) Catalysts
Hooray for ozone production??
– in the upper atmosphere, ozone
absorbs ultraviolet (uv) light and
protects life on earth from the
dangerous effects of uv light.
– at ground level it irritates the respiratory
tract and eyes, increases the risk of
heart or lung disease, causes plant
leaves to become brittle, bleaches
colour from fabrics, and breaks down
the elasticity of rubber.
Ozone is a nasty chemical at ground level!
Question: How do we deal with it?
– Based on the mechanism provided
above, one way of preventing ozone
formation at ground level is to get rid of
the catalyst for the production of
monoxygen.
The Catalytic Converter
Modern catalytic converters have two
purposes.
1. One is to convert carbon monoxide
and nitrogen monoxide to nitrogen and
carbon dioxide.
2. The other is to convert unburned
hydrocarbons (which are responsible
for PAN's - another component of
smog) to carbon dioxide and water
The Catalytic Converter
The Catalytic Converter
- There are different designs of catalytic
converters on the market.
- The catalysts may vary from one to
another.
- Common catalysts include:
Pd, Pt, Rh, Ni2O3 ,Cu2O, & Cr2O3
- The internal honeycomb design
maximizes the surface area available
for contact between the exhaust gases
from the engine and the metal or metal
oxide catalysts
Reaction Mechanism using catalyst
Step 1:
Step 2:
Step 3:
Step 4:
2 CO(g) → 2 CO(ad)
NO(g) → N(g) + O(g)
N(g) + NO(g) → N2(g) + O
2 CO(ad) + 2 O(g) → 2 CO2(g)
Lead and Catalytic
Converters
Leaded gasoline molecules
have four ethyl (CH3CH2-)
groups bonded to a central
lead atom.
They burn evenly in car
engines reducing a condition
called engine ‘knock’ (which
is associated with burning
straight chain alkanes).
Leaded gasoline banned by 1990 in
Canada because:
1. of the poisonous effects of lead.
2. of its effect on the efficiency of catalytic
converters.
- Lead not only poisons people, it also
"poisons" converters by binding to the
catalysts.
- Once it becomes covered in an
impurity like lead, a converter can no
longer adsorb CO and NO molecules.
MTBE and Branched Hydrocarbons
• The replacement for leaded gasoline
molecules are highly branched
hydrocarbons like 2,2,4-trimethylpentane.
• However, the need for oxygen in gasoline
has led to the use of an ether called
methyl tert-butyl ether or MTBE.
MTBE and Branched Hydrocarbons
• It provides more oxygen to the combustion
reaction and helps increase the amount of
oxygen going into the converter to get rid
of unburned hydrocarbons.
• MTBE use is controversial. In gas tanks,
it is not a problem, but is a problem in
ground water and wells because it is a
suspected carcinogen. It is finding its way
into water supplies in cities and towns
because of sloppy filling practices and
gasoline spills.
• Handout:
Smog, Catalytic converters and You.
Textbook Readings MHR
page 802: Automobile Engines
(paragraph 1)
Textbook Practice Items MHR
page 487: item 19