Question

Is carbon dioxide $\left( {C{O_2}} \right)$ a secondary pollutant?

Answer 1

Primary pollutants are the air pollutants which are directly emitted from a source into the atmosphere whereas secondary pollutants are the air pollutants which are formed in the atmosphere as a result of a chemical or physical interactions of the primary pollutants either by themselves or other primary pollutants present in the atmosphere.

Complete answer:
Air pollution occurs when certain gases and particles rise in the atmosphere to such a level that they can cause harmful effects to human health as well as the environment. These gases and particles are known as pollutants that tend to be produced from man-made sources which include burning of fossil fuels but can also occur from natural sources like volcanic eruptions and forest fires.
Now, we know that the carbon dioxide gas is one of the major components of greenhouse gases and is produced as the by-product of the combustion of fossil fuels. As the organic matter burns, chemical energy is released in the form of heat and light. One of the common examples of formation of carbon dioxide is combustion of glucose and reaction takes place as follows:
${C_6}{H_{12}}{O_6} + 6{O_2} \to 6C{O_2} + 6{H_2}O + {\text{ energy}}$
As per observations, $93\%$ of the carbon dioxide gas in the troposphere occurs as a result of the carbon cycle and $7\%$ of carbon dioxide occurs due to human activities generally by burning the fossil fuels.
Thus, we can conclude that the carbon dioxide $\left( {C{O_2}} \right)$ is not a secondary pollutant but a primary pollutant because the natural amount of $C{O_2}$ gas present in atmosphere is the basic need for plants for photosynthesis.

Note:
Remember that primary pollutants can be controlled directly through anthropogenic emissions but the secondary pollutants cannot be controlled directly and require complicated control processes as they are formed by various chemical reactions in the atmosphere.