What is a secondary pollutant found in photochemical smog?

Peroxyacetyl Nitrate (PAN) is a secondary pollutant that forms in photochemical smog. This compound is created when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight. This process occurs during warm, sunny days when emissions from vehicles and industrial sources combine with natural airborne compounds.

Secondary pollutants, such as PAN, are particularly concerning because they can have harmful effects on human health and the environment. PAN is an eye irritant and can cause respiratory issues, making it a significant component of photochemical smog, which is more prevalent in urban areas with heavy traffic.

In contrast, carbon monocyclics, carbon dioxide, and methane are either primary pollutants or greenhouse gases, but they do not classify as secondary pollutants within the context of photochemical smog. Primary pollutants are directly emitted into the atmosphere, while secondary pollutants are formed through chemical reactions in the atmosphere. Understanding the distinction between these types of pollutants is critical for monitoring air quality and formulating environmental regulations.