Transcript Photochemical smog

Photochemical Smog
Lecture-2
Photochemical smog ??
Noxious mixture of highly reactive and oxidizing
air pollutants including:
 Oxides of Nitrogen (NOx)
 Volatile organic compounds
 Troposphere Ozone
 Peroxyacetyl Nitrates (PAN)
Generation Mechanism:
Three ingredients required:
 Ultraviolet Light
 Hydrocarbons
 Nitrogen oxides
• HC
• NO
UV Light
• O3
• PANs
• Other Oxidants
(Aldehydes, Ketones etc)
Photochemical Reaction
Generation Mechanism contd..
Photochemical Reactions:
Troposphere Ozone:
 NO2 + h
 O + O2
NO + O
O3
Sources:
 Exhaust gases From Motor vehicles
 Unburnt Hydrocarbons
Photochemical Reaction Contd..
2.) Volatile Organic Compounds (VOC)
Carbon-based molecules such as Aldehydes,
Ketones and Hydrocarbons
RCH3 + 2O2 + 2NO
RCHO + 2NO2 + H2O
Sources:
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Paint thinners, solvents and petroleum constituents
Trees: emits isoprene and terpenes
Methane from termites, cows and cultivation
Photochemical Reaction Contd..
3.) Peroxyacetyl Nitrates (PAN)
Are secondary pollutants formed from
peroxyacid radicals and NO2
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CH3CHO + OH•
CH3C•O + H2O
CH3C•O + O2
CH3C(O)OO• (acetylperoxy)
CH3C(O)OO• + •NO2
CH3C(O)OONO2
(PAN)
Effects on human health:
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Ozone
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Cause acute respiratory problems
Aggravate asthma
Cause temporary decreases in lung function in healthy adults
Lead to hospital admissions and emergency room visits
Impair the body's immune system
Peroxyacetylnitrate (PANs)
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Respiratory and eye irritants
Mutagenic- causing skin cancer
Effects on human health contd..
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Volatile organic compounds (VOCs)
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Global warming- Methane
Carcinogenic- benzene
Form Ozone