Regular Smog Inspections
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Why You Need A Smog Test?
The substances that react with nitrogen oxides to form oxidants (the final product of photochemical smog) are trace hydrocarbons (from incomplete combustion) and the hydroxyl radical. The necessary ingredients for photochemical smog formation are (1) nitrogen oxides, (2) sunlight, and (3) hydrocarbons.
Photochemical smog formation proceeds through a sequence of reactions, all involving a free radical mechanism. Free radicals are generated by photodissociation of nitrogen dioxide, a process that generates ozone and oxygen atoms. Oxygen atoms react with water to form hydroxyl radicals, which in turn react with hydrocarbons to form hydrocarbon radicals. Oxidation of hydrocarbons by the hydroxyl radical leads to the formation of aldehydes. The aldehydes are oxidized further to form aldehyde peroxides and aldehyde peroxyacids. These final substances are the compounds that are so irritating to sensitive biological tissues and cause most of the health problems associates with photochemical smog.
Figure shown below, is a diagram showing the changes in atmospheric concentrations for nitrogen oxide, nitrogen dioxide, non-methane hydrocarbons, aldehydes, and oxidants.