What occurs when primary pollutants react with each other or with natural substances?

When primary pollutants react with each other or with natural substances in the environment, they form what are known as secondary pollutants. Primary pollutants are those that are directly emitted from a source, such as carbon monoxide from vehicles or sulfur dioxide from industrial processes. When these substances undergo chemical reactions, often in the presence of sunlight, heat, or other environmental factors, new compounds can be created, which are classified as secondary pollutants.

An example of a secondary pollutant is ozone, which can form in the atmosphere when nitrogen oxides and volatile organic compounds react under sunlight. These secondary pollutants can contribute to various environmental and health issues, such as respiratory problems and ecological damage.

The other options refer to different environmental phenomena or types of pollution that do not directly arise from the chemical reactions of primary pollutants. For instance, acidic precipitation results from the deposition of acids, typically formed by the reaction of certain primary pollutants, but it is not the process of creating secondary pollutants directly. Thermal inversion describes a situation where warmer air traps cooler air at the surface, potentially leading to increased pollution, but it is not related to the chemical composition of pollutants. Smog, typically a mix of smoke and fog, represents a type of air pollution but does not define the process of forming secondary pollutants