Which of the following is NOT a characteristic of primary pollutants?

Primary pollutants are substances that are emitted directly into the atmosphere and can affect air quality upon release. They can originate from both natural sources, such as volcanic eruptions and wildfires, as well as from anthropogenic activities like vehicle emissions and industrial processes. Some common examples of primary pollutants include carbon monoxide, sulfur dioxide, and nitrogen oxides.

While primary pollutants can indeed pose health risks, it is not accurate to state that they are always harmful to human health. The impact of a primary pollutant on health depends on several factors, including the concentration of the pollutant, duration of exposure, the specific health sensitivities of individuals, and existing environmental conditions. There are situations where low levels of certain pollutants may not lead to harmful effects or may even be within safe exposure limits. Therefore, not all primary pollutants are categorically harmful, which supports the rationale for why this characteristic does not accurately define them.