1. Photochemical Smog
Lecture-2

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)

3. Generation Mechanism:
Three ingredients required:
Ultraviolet Light
Hydrocarbons
Nitrogen oxides O3
PANs
Other Oxidants
(Aldehydes, Ketones etc) HC NO
UV Light
Photochemical Reaction

4. Generation Mechanism contd..

5. Photochemical Reactions:
Troposphere Ozone:
NO2 + h NO + O
O + O O3
Sources:
Exhaust gases From Motor vehicles
Unburnt Hydrocarbons

6. Photochemical Reaction Contd..
2.) Volatile Organic Compounds (VOC)
Carbon-based molecules such as Aldehydes,
Ketones and Hydrocarbons
RCH3 + 2O2 + 2NO RCHO + 2NO2 + H2O
Sources:
Paint thinners, solvents and petroleum constituents
Trees: emits isoprene and terpenes
Methane from termites, cows and cultivation

7. Photochemical Reaction Contd..
3.) Peroxyacetyl Nitrates (PAN)
Are secondary pollutants formed from peroxyacid radicals and NO2
CH3CHO + OH• CH3C•O + H2O
CH3C•O + O CH3C(O)OO• (acetylperoxy)
CH3C(O)OO• + •NO CH3C(O)OONO (PAN)

8. Effects on human health:
Ozone
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)
Respiratory and eye irritants
Mutagenic- causing skin cancer

9. Effects on human health contd..
Volatile organic compounds (VOCs)
Global warming- Methane
Carcinogenic- benzene
Form Ozone