- The combustion of fossil fuels produces primary pollutants that may generate secondary pollutants and lead to photochemical smog, the levels of which can vary by topography, population density and climate.
- Photochemical smog has significant impacts on societies and living systems.
- Photochemical smog can be reduced by decreasing human reliance on fossil fuels.
Knowledge and understanding:
- Primary pollutants from the combustion of fossil fuels include carbon monoxide, carbon dioxide, black carbon or soot, unburned hydrocarbons, oxides of nitrogen, and oxides of sulfur.
- In the presence of sunlight, secondary pollutants are formed when primary pollutants undergo a variety of reactions with other chemicals already present in the atmosphere.
- Tropospheric ozone is an example of a secondary pollutant, formed when oxygen molecules react with oxygen atoms that are released from nitrogen dioxide in the presence of sunlight.
- Tropospheric ozone is highly reactive and damages plants (crops and forests), irritates eyes, creates respiratory illnesses and damages fabrics and rubber materials. Smog is a complex mixture of primary and secondary pollutants, of which tropospheric ozone is the main pollutant.
- The frequency and severity of smog in an area depends on local topography, climate, population density, and fossil fuel use.
- Thermal inversions occur due to a lack of air movement when a layer of dense, cool air is trapped beneath a layer of less dense, warm air. This causes concentrations of air pollutants to build up near the ground instead of being dissipated by “normal” air movements.
- Deforestation and burning, may also contribute to smog.
- Economic losses caused by urban air pollution can be significant.
- Pollution management strategies include:
- altering human activity to consume less fossil fuels—example activities include the purchase of energy-efficient technologies, the use of public or shared transit, and walking or cycling
- regulating and reducing pollutants at the point of emission through government regulation or taxation
- using catalytic converters to clean the exhaust of primary pollutants from car exhaust
- regulating fuel quality by governments
- adopting clean-up measures such as reforestation, regreening, and conservation of areas to sequester carbon dioxide.
Applications and skills:
- Evaluate pollution management strategies for reducing photochemical smog.
- The global rise of urbanization and industrialization has led to an increase in urban air pollution.
Theory of knowledge:
- Environmental problems are often emotive—under what circumstances should we maintain a detached relationship with the subject matter under investigation?
- Climate change—causes and impacts (7.2)
- Acid deposition (6.4)
- Stratospheric ozone (6.2)
- Humans and pollution (1.5)
- Investigating ecosystems (2.5)