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 O3 PANs Other Oxidants (Aldehydes, Ketones etc) HC NO UV Light Photochemical Reaction

Generation Mechanism contd..

Photochemical Reactions: Troposphere Ozone: NO2 + h NO + O O + O2 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: 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 CH3CHO + OH• CH3C•O + H2O CH3C•O + O2 CH3C(O)OO• (acetylperoxy) CH3C(O)OO• + •NO2 CH3C(O)OONO2 (PAN)

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

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