Mr. Gerding's Biology

6.3 Photochemical smog

Significant Ideas:

• 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 Understandings:

• 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. 

Application and Skills:

• Evaluate pollution management strategies for reducing photochemical smog.

International-mindedness:

• 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?