Atmospheric systems and societies
Domain 7 covers atmospheric structure and composition, energy balance, circulation, air pollution and stratospheric ozone. The exam tests albedo, the greenhouse effect, smog, acid deposition and ozone depletion.
Core rules
- The troposphere holds most mass and water vapour and is where weather occurs; temperature falls with altitude. The stratosphere contains the ozone layer; temperature rises with altitude because ozone absorbs UV.
- Albedo is the fraction of incoming solar radiation reflected. Absorbed solar radiation = incoming × (1 - albedo).
- The natural greenhouse effect keeps Earth warm; enhanced greenhouse effect results from added greenhouse gases.
- Photochemical smog forms when sunlight acts on nitrogen oxides and volatile organic compounds, producing ozone at ground level.
- Acid deposition forms from sulfur dioxide and nitrogen oxides; ozone depletion is driven mainly by chlorine and bromine from CFCs and halons.
Worked example
Incoming solar radiation at the top of the atmosphere is 340 W m⁻². With albedo 0.30, the surface-atmosphere system absorbs 340 × 0.70 = 238 W m⁻². Reasoning: albedo reduces the energy available; the absorbed energy must be balanced by longwave emission and other fluxes. If ice cover falls, albedo falls, more solar energy is absorbed, warming increases ice melt - a positive feedback. This is distinct from ozone depletion, which lets more UV-B through but is not the main driver of tropospheric warming.
Traps
- Confusing the ozone hole with climate change; they share some causes but are different problems.
- Saying the greenhouse effect is unnatural; the natural effect is essential.
- Treating smog ozone as beneficial; stratospheric ozone is protective, tropospheric ozone is a pollutant.
- Ignoring that albedo feedback can be positive.
- Assuming acid deposition is only a local issue; it can travel long distances.