PRIMARY AND SECONDARY POLLUTANTS

With industrialization and urbanization, lot of pollutants are released to the environment. It is important to know about the pollutants, their effects and how they are released to the environment in order to minimize their harmful effects. We talk about air pollution, water pollution, soil pollution, noise pollution and various types of other pollutions. Each type of pollution is caused by different pollutants and their sources may vary too. Since all elements in nature are linked together, damage to one element will start a chain reaction and eventually damage the whole system. It will destruct the natural equilibrium too. 

Air pollution is introducing harmful things like chemicals to the atmosphere. In order to categorize as pollutants, these substances should cause damage or harmful to the living organisms, natural environment, or the built environment. An air pollutant could be in the form of a solid particle, liquid droplets or as gases. Some pollutants are natural, and some are man-made. Air pollutants can be categorized into two as primary pollutants and secondary pollutants.

Primary Pollutants

What are Primary Pollutants?

          Primary pollutants are the ones directly emitted into the atmosphere from the source. These can be emitted in natural ways or due to human actions. Gases and ash emitted from a volcanic reaction are primary pollutants emitted in a natural way. Carbon dioxide gas emitted from vehicles is primary pollutants released due to human activities. There are various primary pollutants which are harmful.

Sulphur dioxide, carbon monoxide, nitrogen oxides, volatile organic compounds, particulate matter, peroxyacetyl nitrate, and chlorofluorocarbons are some of the primary pollutants. Sulphur dioxide is produced from volcanoes as well as by industrial processes (where sulphur containing compounds are being subjected to combustion). Nitrogen oxide is produced naturally during lightening. Carbon monoxide and particulate matter are arising from incomplete combustion especially when burning fossil fuels.

Primary pollutants in the air cause serious environmental problems like global warming, acid rains, etc. When considering primary pollutants, the main source for them is the motor vehicles. Fossil fuel burning releases a mixture of primary pollutants. Primary pollutants can also be precursors for the secondary pollutants. There are some pollutants which can be both primary and secondary pollutants. That means while they are being emitted by a source directly, they are made from other pollutants too.

EXAMPLES:

• carbon monoxide (CO)
  • odorless, colorless, poisonous gas
  • created by incomplete combustion (especially bad with older cars)
  • generates headaches, drowsiness, fatigue, can result in death
• oxides of nitrogen (NO_x, NO)
  • NO - nitric oxide
  • emitted directly by autos, industry
• sulfur oxides (SO_x)
• SO₂ - sulfur dioxide
• produced largely through coal burning
• responsible for acid rain problem
• volatile organic compounds (VOCs)
  • highly reactive organic compounds
  • release through incomplete combustion and industrial sources
• particulate matter (dust, ash, salt particles)
• bad for your lungs

Secondary Pollutants

What are Secondary Pollutants?

          Secondary pollutants are not emitted directly to the atmosphere as primary pollutants. Rather they are made in the air using other pollutants. Especially when primary pollutants react or interact with other molecules secondary pollutants are made. Therefore, by releasing primary pollutants to the air, not only it has direct effects, but it affects the atmosphere in an indirect way too.

Ozone is one of the secondary pollutants. It is formed from hydrocarbons and nitrogen oxide in the presence of sunlight. Secondary pollutants cause problems like photochemical smog.

EXAMPLES:

• sulfuric acid H2SO4
  • can cause respiratory problems
• nitrogen dioxide NO₂
  • gives air a brownish coloration
  •  
• ozone O3
• colorless gas
• has a sweet smell
• is an oxidizing agent - lung tissue to rubber products
• irritates the eyes

What is the difference between Primary Pollutants and Secondary Pollutants?

          Primary pollutants are directly emitted into the air by the source. In contrast, secondary pollutants are produced by the reactions between primary pollutants and other molecules.

Primary pollutants are released due to human activities or naturally. However, secondary pollutants are often, made naturally.

Controlling the release of primary pollutants is easier than controlling the ways of secondary pollutant synthesizing.