Peroxyacetyl nitrate (PAN), an eye irritant, is produced by:

• Photochemical Smog Components: Photochemical smog is an oxidizing mixture that forms when sunlight reacts with primary pollutants like hydrocarbons and nitrogen oxides ($$\text{NO}_x$$) emitted from automobiles and industries.
• Secondary Pollutants: This solar-driven chemical reaction yields powerful secondary pollutants, primarily ozone ($$\text{O}_3$$) and peroxyacetyl nitrate (PAN).

Conclusion:

PAN is a characteristic component formed exclusively in secondary photochemical smog pathways during sunny, warm weather conditions.

Answer: Option D — Photochemical smog