What is a defining characteristic of secondary pollutants like ozone?

A defining characteristic of secondary pollutants, such as ozone, is that they are not emitted directly into the atmosphere but are formed through chemical reactions involving primary pollutants. These primary pollutants, which can include substances like nitrogen oxides (NOx) and volatile organic compounds (VOCs), interact in the presence of sunlight to create secondary pollutants. Ozone is a key example, typically forming in the lower atmosphere on sunny days when these primary pollutants undergo reactions.

This process highlights the complexity of air quality issues, as the presence and concentration of secondary pollutants can vary greatly depending on local atmospheric conditions, such as temperature and sunlight. Understanding this characteristic is crucial for addressing air pollution and implementing effective regulatory measures.