Emissions and Pollutants

Engine emissions undergo chemical reactions in atmosphere known largely as ‘photochemical’ reactions and give rise to other chemical species which are hazardous to health and environment. Linkage of engine emissions and air pollutants is shown in Fig. 1.5.

TSP = Total suspended particulate matter in air
PAN = Peroxy- acetyl nitrate

Photochemical Smog

Photochemical smog is a brownish-gray haze resulting from the reactions caused by solar ultraviolet radiations between hydrocarbons and oxides of nitrogen in the atmosphere. The air pollutants such as ozone, nitric acid, organic compounds like peroxy- acetylnitrates or PAN ( CH₃CO-OO-NO₂) are trapped near the ground by temperature inversion experienced especially during winter months. These chemical substances can effect human health and cause damage to plants. The photochemical reactions are initiated by nitrogen oxides emitted by vehicles into atmosphere. A simple set of reactions leading to photochemical smog formation is as follows:

is energy of a photon and UV is ultraviolet light radiations .