Primary & Secondary Pollutants (DP IB Environmental Systems & Societies (ESS))

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

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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 (NO_x): 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 (SO_x): 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 (NO_x) 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