The major constituent of the photochemical oxidants is:

The major constituent of photochemical oxidants is ozone. Ozone is a secondary pollutant formed by the reaction of sunlight with primary pollutants, such as volatile organic compounds (VOCs) and nitrogen oxides (NOx). The presence of these chemicals in the atmosphere, along with the intense ultraviolet radiation from sunlight, leads to the photolytic reactions that produce ozone in the lower atmosphere, particularly in urban environments where traffic and industrial activities emit these precursors.

Ozone plays a crucial role in air quality and is a significant component of smog, which can have adverse effects on human health and the environment. It can cause respiratory problems, lead to decreased lung function, and exacerbate preexisting health conditions. Because of its formation and impact, ozone is considered a major constituent of photochemical oxidants, highlighting its importance in environmental health assessments and regulations related to air quality management.