What are peroxy acetyl nitrates (PANs)?

Peroxy acetyl nitrates (PANs) are classified as secondary pollutants that contribute to the formation of smog. This classification stems from their creation through chemical reactions that occur in the atmosphere, particularly in the presence of sunlight. They are produced when primary pollutants, such as nitrogen oxides and volatile organic compounds (VOCs), react in photochemical processes. As a result, while PANs themselves are not directly emitted from a source, they form as a consequence of reactions involving other pollutants, which is characteristic of secondary pollutants.

This distinction is critical in understanding air quality and pollution dynamics. Because PANs form through photochemical reactions primarily in urban areas with high levels of traffic and industrial activity, they can significantly impact air quality and contribute to the adverse health effects associated with smog. Their presence in the atmosphere is closely monitored, especially during hot, sunny conditions, which favor their formation and accumulation.