What is a primary characteristic of photochemical smog?

Photochemical smog is primarily characterized by its formation in the presence of sunlight. This type of air pollution occurs when sunlight reacts with pollutants such as nitrogen oxides and volatile organic compounds (VOCs), leading to a series of chemical reactions that create ground-level ozone and other secondary pollutants. The process is closely associated with urban areas where vehicular emissions and industrial activities are prevalent, and its severity is often heightened during warm, sunny days.

While high levels of carbon emissions and the presence of volatile organic compounds contribute to the formation of photochemical smog, it is the role of sunlight in initiating these reactions that distinctly characterizes this phenomenon. The storage of airborne toxins is not a defining feature of photochemical smog but rather pertains to other aspects of air pollution management and risk assessment.