Final answer:
Primary pollutants are directly emitted from sources (e.g., sulfur dioxide, nitrogen oxides, carbon monoxide, particulate matter), while secondary pollutants form in the atmosphere through reactions (e.g., ozone). Some pollutants can be both primary and secondary like NOx and particulate matter.
Step-by-step explanation:
Primary pollutants are emitted directly from sources. Examples include sulfur dioxide (SO2), nitrogen oxides (NOx), carbon monoxide (CO), and particulate matter. Secondary pollutants, on the other hand, are not directly emitted. Instead, they form in the atmosphere through chemical and physical reactions. Common examples are ozone (O3) and some types of particulate matter. It's worth noting, however, that certain pollutants can both be considered primary and secondary, such as NOx and particulate matter, depending upon the circumstances of their creation and release into the environment.
Learn more about Primary and Secondary Pollutants