Syllabus Edition

First teaching 2015

Last exams 2025

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Primary & Secondary Pollutants

Alistair Marjot

Written by: Alistair Marjot

Reviewed by: Bridgette Barrett

Primary & Secondary Pollutants

  • Air pollution is a significant environmental concern that affects both human health and the environment

    • It consists of primary pollutants directly emitted from sources and secondary pollutants formed through chemical reactions in the atmosphere

    • The combustion of fossil fuels is a major source of primary pollutants

matt-boitor-i74mkr-3op0-unsplash

Photo by Matt Boitor on Unsplash 

Primary pollutants from car exhaust fumes can turn into secondary pollutants

What are Primary Pollutants?

  • Primary pollutants from the combustion of fossil fuels include:

    • Carbon monoxide (CO): a colourless, odourless gas that is harmful to human health and can lead to carbon monoxide poisoning

    • Carbon dioxide (CO2): a greenhouse gas responsible for global warming and climate change

    • Black carbon or soot: fine particulate matter emitted from incomplete combustion, contributing to air pollution and climate change

    • Unburned hydrocarbons: volatile organic compounds (VOCs) released during combustion

    • Oxides of nitrogen (NOx): nitrogen dioxide (NO2) and nitrogen oxide (NO) are key contributors to air pollution, causing respiratory issues and contributing to the formation of smog

    • Oxides of sulfur (SOx): sulfur dioxide (SO2) and sulfur trioxide (SO3) are released during fossil fuel combustion, leading to acid rain and respiratory problems

What are Secondary Pollutants?

  • In the presence of sunlight, primary pollutants undergo a variety of reactions with other chemicals already present in the atmosphere, resulting in the formation of secondary pollutants - some notable examples include:

  • Tropospheric ozone (O3):

    • This is an example of a secondary pollutant formed through a complex series of reactions

    • Oxygen molecules (O2) react with oxygen atoms (O) released from nitrogen dioxide (NO2) in the presence of sunlight

    • Tropospheric ozone is a harmful air pollutant associated with respiratory issues and smog formation

  • Nitrogen oxides (NOx) contribute to the formation of secondary pollutants such as nitric acid (HNO3) and nitrate particles, which contribute to acid rain and particulate matter pollution

  • Understanding the formation and impacts of both primary and secondary pollutants is essential for effective air pollution control and mitigation strategies

  • It highlights the importance of reducing emissions from fossil fuel combustion, promoting cleaner technologies, and implementing measures to mitigate the formation of secondary pollutants

Examiner Tips and Tricks

Regarding primary and secondary pollutants, the use of chemical symbols, formulae or equations is not required for your exams - you just need to remember the names of the pollutants and the process by which tropospheric ozone is formed!

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