l 30 final
DESCRIPTION
AIR POLLUTION CONTROL course material by Prof S S JAHAGIRDAR,NKOCET,SOLAPUR for BE (CIVIL ) students of Solapur university. Content will be also useful for SHIVAJI and PUNE university studentsTRANSCRIPT
What do you think why such a difference is there?
L-30 UNIT-VI Photochemical smog
Air Pollution and Control
(Elective - I)
Unit- VI
L-29 Chemistry of air pollution, Chain reactions of hydrocarbons, nitrogen oxide, Sulphuric oxides and intermediates, photochemical smog formation
L-30 Air pollution indices -aerosols, fog, smog index.
Smog
The word ‘smog’ comes from two words: smoke and fog.
Characterize visible combination of smoke and fog
Occurs in highly motorised areas and where inversion conditions prevail in the atmosphere.
e.g. – Los Angeles
It is because of action of sunlight on H-C (Hydrocarbons) and Nitrogen Oxides (NOx) emitted from the automobiles
smogsmog
primary
pollutants
volatile hydrocarbons -VOC
nitrogen oxides
secondary pollutants
ketones,
aldehydes,
PANs,
peroxides,
ozone,
Smog FormationSun
Composition of smog
Nitrogen oxides
Ozone
Aldehydes
Unreacted carbon
Particular matter
Peroxyaceyl nitrate (PAN)
Chemical compounds involved
Molecule Name
and Formula
Two-Dimensional
Representation
Three-
Dimensional
Representation
Nitric Oxide, NO
Nitrogen Dioxide,
NO2
Ozone, O3
Acetaldehyde,
C2H4O (an example of
an Aldehydes)
Peroxyacetyl Nitrate,
C2H3O5N
1,3-Butadiene,
C4H6 (an example of a
volatile organic
hydrocarbon)
smog:smog: variation in day
Early morning traffic increases the emissions of both nitrogen oxides and VOCs as people drive to work.
Later in the morning, traffic dies down and the nitrogen oxides and volatile organic compounds begin to be react forming nitrogen dioxide, increasing its concentration.
As the sunlight becomes more intense later in the day, nitrogen dioxide is broken down and its by-products form increasing concentrations of ozone.
At the same time, some of the nitrogen dioxide can react with the volatile organic compounds to produce toxic chemicals such as PAN.
As the sun goes down, the production of ozone is halted. The ozone that remains in the atmosphere is then consumed by several different reactions.
Colour
Nitrogen dioxide is responsible for the brownish colour of the haze.
The particulates formed and the brown colour of nitrogen dioxide give the air a dirty, ‘smoggy’ appearance.
18
Photochemical smog / LA smogLos Angeles
Photochemical smog / LA smog
LA
Santiago
Las Vegas
Reaction with NO2 UV light energy is absorbed by NO
It moves into high energy state and becomes unstable.
Then decomposes in to NO and O (nascent oxygen)
Nascent oxygen quickly reacts with atmospheric oxygen to form ozone.
This reaction takes place in presence of third body (X).
If nitric oxide is present it reacts with ozone to form NO2 and O2
Chemical reactions :-
NO2 + hv NO* NO + O
O + O2 O3
O3 + NO NO2 +O2
NO2 behaves like catalyst
Aldehydes
Peroxyacyl radical
Acetyl radical
Acetaldehyde
Methyl
Formyl radical
Acetone
Methyl
Acetyl
Factors affecting photochemical reactions Light intensity
Hydrocarbon reactivity.
Ratio of H-C to nitric oxide
Presence of light absorbers
Meteorological variables
Height and intensity of atmospheric inversion
Effects on human health
Headaches
Eyes, nose and throat irritations
Impaired lung function
Coughing and wheezing
smog: effectssmog: effects
PAN’s cause eyes to water and respiratory problems, also catalyses formation of sulphuric acid,
ozone in the troposphere is: an eye irritant and also irritates respiratory system
causes deterioration of rubber as it breaks –C=C-and bleaches dyes
affects leaves and therefore growth/damages crops
reduced visibility
secondary pollutants are toxic to plants
corrosion of building materials by acids and ozone.
Objective Questions1. _________________ is main driving factor
for photochemical smog formation.
2. NO2 acts as ________________.
3. Increase in ozone concentration during day time indicates _____________________ formation.
4. Cracking of rubber takes place because of ______.
5. Photochemical smog occurs in highly _________area.
Theory QuestionsQ1. Write detailed short note on ‘Photo-chemistry of
air pollution’
OR
Explain ‘Photochemical reactions’ in detail.
Q2. Explain effects of photochemical smog.
Video Clip-1
Video Clip-2