Difference Between Primary Pollutants and Secondary Pollutants (With Table)

Pollution is one trouble that almost all countries are facing in different intensities. It comes in different types, each affecting a different aspect of the environment such as air, water, land or soil and noise. Amongst these four types, air pollution is considered the most dangerous and impacting, being both visible and invisible at the same time. Air pollution is measured in terms of the pollutants present in the atmosphere at unnatural levels, negatively affecting all living organisms.

The pollutants also vary in their forms, such as solid, liquid and gas. Based on the source from which pollutants are emitted, there are two types of pollutants: – Primary pollutants and secondary pollutants.

Primary Pollutants vs Secondary Pollutants

The difference between primary and secondary pollutants is their sources of emissions. While primary pollutants are emitted from a source, directly into the atmosphere, secondary pollutants are formed as a result of any kind of reaction amongst primary pollutants themselves or between any primary pollutant and any other atmospheric particle.

Comparison Table Between Primary Pollutant and Secondary Pollutant

Parameter of ComparisonPrimary PollutantSecondary Pollutant
Source   Primary pollutants are pollutants that are emitted from a source, directly into the atmosphere.Secondary pollutants are pollutants formed either due to a reaction between primary pollutants themselves or between a primary pollutant and any other atmospheric particle.
Form  Primary pollutants are generally particulate, aerosol, reduced or oxidised.Secondary pollutants are generally oxidising.
EffectPrimary pollutants affect both directly and indirectly, through impacting the atmosphere and through the secondary pollutants respectively.Secondary pollutants might have a limited effect, except in case of ozone, where it is highly reactive.
Control     Controlling primary pollutants can be done directly by controlling anthropogenic emissions.Controlling secondary pollutants is quite complicated since it involves studying the process of its creation.
ExampleSulphur dioxide, carbon monoxide, nitrogen oxides and particulate matter are a few examples of primary pollutants.Ozone, secondary particulate matter, etc are a few examples of secondary pollutants.

What are Primary Pollutants?

Air pollution refers to the contamination of the atmosphere by pollutants found at unnaturally high levels. There are two types of pollutants: – Primary and Secondary. Primary pollutants are pollutants that are directly emitted to the atmosphere by a source.

These pollutants might be emitted either by natural processes such as a volcanic eruption or as a result of man-made actions such as industrial emissions. A primary pollutant is generally found in the form of particulate matter, aerosol, reduced or oxidised. The effect of primary pollutant is both direct and indirect.

Primary pollutants are emitted by a source, directly into the atmosphere, directly affecting all living organisms. They also undergo a chemical reaction, forming secondary pollutants and indirectly affecting the ecosystem. For example, formation of sulphur dioxide is a direct effect of primary pollutant.

Whereas sulphur dioxide reacting with water to form sulphuric acid which is responsible for acid rain is an indirect effect. The two main sources of these pollutants are natural and man-made. And since nothing much can be done about the natural sources, the only way to control primary pollutants is by controlling the anthropogenic emissions such as vehicle and industries.

Few examples of primary pollutants are as follows: –

  1. Sulphur dioxide (SO2)
  2. Carbon monoxide (CO)
  3. Nitrogen oxides (NOx)
  4. Particulate Matter (PM)

What are Secondary Pollutants?

Secondary pollutants are those pollutants that form as a result of a chemical reaction between the primary pollutants themselves or between any primary pollutant and any other particle in the atmosphere. They are generally found in the oxidised form.

Secondary pollutants are said to have limited effect. These pollutants are products of primary pollutants and other atmospheric particles. Thus, they are said to be inert or inactive. However, ozone is an exception to this case. Ozone is formed as a result of photoactivation. This process makes the chemical reaction extremely reactive. Thus, in case of ozone(O3), the effect is not limited.

The main source of secondary pollutants is primary pollutants and secondary pollutants are formed as a result of chemical reaction between primary pollutants and with other atmospheric particles. Thus, it is a challenging task to control the production or emission of secondary pollutants since it involves understanding the complicated process of its creation. Few examples of secondary pollutants are as follows: –

  • Ozone (O3)
  • Nitrogen dioxide (NO2)
  • Sulphur trioxide (SO3)

These are called photochemical oxidants.

  • Secondary particulate matter

Main Differences Between Primary Pollutant and Secondary Pollutant

  1. Primary pollutants are emitted directly into the atmosphere by a source. But secondary pollutants are formed as a result of a chemical reaction between primary pollutants or with any other atmospheric particle.
  2. Primary pollutants are generally found in the form of particulate matter, aerosol, reduced or oxidised. But secondary pollutants are generally in an oxidised form.
  3. While primary pollutants affect the ecosystem in a direct and indirect manner, secondary pollutants have a limited and inert effect. However, ozone is an exception case of secondary pollutant. It undergoes the process of photoactivation, making the chemical reaction highly reactive and dangerous.
  4. Controlling the emission of primary pollutants can be done by reducing the anthropogenic emissions such as vehicle emissions and industrial emissions. However, it is quite a herculean task to control the emission of secondary pollutants because it is formed through a reaction between primary pollutants and with atmospheric particles. Thus, reducing its emissions involves thoroughly understanding the process of its creation and the elements involved.
  5. Sulphur dioxide, nitrogen oxides and particulate matter (PM) are few examples of primary pollutants. But ozone, secondary particulate matter and nitrogen dioxide are few examples of secondary pollutants.

Conclusion

Air pollution is caused by mainly two types of pollutants: – Primary and secondary pollutants. While both these pollutants contaminate the atmosphere, there are certain differences between them.

The main difference between them is their source. While the former is emitted directly into the air, the latter is a product of two primary pollutants or a primary pollutant and any atmospheric particle. Other differences involve their effect, form, examples and how to control them. No matter how many differences, it is important to take adequate measures to keep both the pollutants in check and to keep our environment clean!

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