Question

Differentiate between primary pollutants and secondary pollutants?

Answer 1

Hint: To answer this question you should know that a primary pollutant is an air pollutant emitted from a source directly into the atmosphere and a secondary pollutant is an air pollutant formed in the atmosphere as a result of interactions between the primary pollutants and other atmospheric components. Now you can find more differences related to both of them.

Complete step by step answer:

You should know that air pollution is defined as the contamination of the atmosphere by substances present at concentrations above their natural levels and capable of producing adverse effects to humans, other living organisms, and the ecosystem in general.
These substances or air pollutants include gases, liquid droplets, and solid particles. They are classified according to the source of emission into two main groups: primary and secondary pollutants.

Primary pollutants -
They are pollutants that are passed into the environment in the form they are produced.
They belong to various categories like particulate, aerosol, reduced, oxidized.
They are less toxic.
They do not show synergism.
Examples of primary pollutants are sulfur dioxide ($SO_{ 2 }$), carbon monoxide (CO), nitrogen oxides ($NO_{ x }$), and particulate matter (PM).

Secondary pollutants -
The pollutants develop as a result of the interaction of primary pollutants and environmental constituents.
They are generally oxidizing.
They are more toxic.
Examples of a secondary pollutant include ozone, which is formed when hydrocarbons (HC) and nitrogen oxides ($NO_{ x }$) combine in the presence of sunlight; $NO_{ 2 }$, which is formed as NO combines with oxygen in the air; and acid rain, which is formed when sulfur dioxide or nitrogen oxides react with water. Major examples of secondary pollutants are photochemical oxidants and secondary particulate matter.

Therefore, we differentiated between primary pollutants and secondary pollutants.

Note: We should also know that the atmospheric concentration of primary pollutants can be controlled in a direct way through the reduction of anthropogenic emissions.
On the contrary, controlling the secondary pollutants is a much more complicated process: the chemical reactions involved in their formation must be understood and interrupted.