Peroxyacetyl nitrate (PAN) and its production in classical smog:

Peroxyacetyl nitrate (PAN) is a secondary air pollutant that is formed through a complex series of reactions involving volatile organic compounds (VOCs) and nitrogen oxides (NOx). It is known to be an eye irritant and can cause respiratory problems in humans.

Classical smog:
Classical smog, also known as London smog or sulfurous smog, is a type of air pollution that occurs in industrialized areas with high levels of coal burning. This type of smog is characterized by the presence of sulfur dioxide (SO2) and particulate matter, which are emitted from industrial processes and combustion of fossil fuels.

Production of PAN in classical smog:
PAN is produced through a series of photochemical reactions that occur in the presence of sunlight. These reactions involve the oxidation of VOCs, such as hydrocarbons, and the nitrogen oxides emitted from vehicle exhaust and industrial processes.

The production of PAN in classical smog can be explained as follows:

1. Emission of nitrogen oxides (NOx): Industrial processes, power plants, and vehicles release nitrogen oxides into the atmosphere. These nitrogen oxides can include nitrogen dioxide (NO2) and nitric oxide (NO).

2. Reaction of nitrogen oxides with volatile organic compounds (VOCs): In the presence of sunlight, nitrogen oxides react with VOCs, such as hydrocarbons, to form peroxyacyl radicals (R-CO-O2) and NO2. This reaction is known as the peroxyacyl radical mechanism.

3. Formation of peroxyacetyl radicals: The peroxyacyl radicals formed in the previous step can undergo further reactions to form peroxyacetyl radicals (CH3C(O)O2). This reaction involves the oxidation of the peroxyacyl radicals by oxygen (O2).

4. Reaction of peroxyacetyl radicals with nitrogen dioxide: The peroxyacetyl radicals can react with nitrogen dioxide (NO2) to form peroxyacetyl nitrate (PAN) and nitrogen monoxide (NO). This reaction is known as the PAN formation reaction.

5. Accumulation of PAN: PAN can accumulate in the atmosphere, especially in areas with high levels of VOCs and nitrogen oxides. It is a stable compound and can be transported over long distances.

Conclusion:
PAN, an eye irritant, is produced in classical smog through a series of photochemical reactions involving nitrogen oxides and volatile organic compounds. These reactions occur in the presence of sunlight and result in the formation of PAN, which can contribute to the harmful effects of smog on human health.