Atmospheric pollution and its causes Revision Notes

Smog is a type of air pollution characterised by a visible haze that reduces air quality and harms health. It primarily forms when volatile organic compounds (VOCs) emitted by industrial processes and vehicle exhausts react with nitrogen oxides (NOx) in the presence of sunlight. This reaction produces ground-level ozone and other photochemical oxidants, which contribute to smog.

Temperature inversion is a meteorological condition that worsens smog. Normally, air temperature decreases with altitude, allowing warm air near the surface to rise and disperse pollutants. However, during a temperature inversion, a layer of warm air sits above cooler air near the ground, trapping pollutants close to the surface. This prevents the dispersal of smog, leading to higher concentrations and more severe pollution episodes.

For example, in a city surrounded by mountains, cold air can become trapped in the valley overnight, with warmer air above, causing pollutants from morning traffic and factories to accumulate and create dense smog.

• VOCs from vehicles and industry react with NOx under sunlight to form smog.
• Temperature inversion traps pollutants near the ground, intensifying smog.
• Urban areas with limited air circulation are more prone to severe smog episodes.

Acid rain forms when sulfur dioxide (SO2) and nitrogen oxides (NOx) gases released by burning fossil fuels combine with water vapour in the atmosphere. These gases undergo chemical reactions to form sulfuric acid (H2SO4) and nitric acid (HNO3), which then fall to the ground as acidic precipitation.

This acidic rain damages aquatic ecosystems by lowering the pH of lakes and rivers, harming fish and other organisms. It also corrodes buildings, especially those made of limestone and marble, and damages forests by leaching nutrients from the soil and harming leaves.

For instance, power stations burning coal emit large amounts of SO2, which can travel hundreds of kilometres before falling as acid rain, affecting areas far from the pollution source.

• SO2 and NOx gases react with water vapour to form sulfuric and nitric acids.
• Acid rain lowers pH of water bodies, harming aquatic life.
• It damages buildings and forests by chemical corrosion and nutrient depletion.

The ozone layer in the stratosphere protects life on Earth by absorbing harmful ultraviolet (UV) radiation from the sun. Chlorofluorocarbons (CFCs), once widely used in refrigeration, air conditioning, and aerosol sprays, release chlorine atoms when broken down by UV light in the stratosphere.

These chlorine atoms catalyse the breakdown of ozone (O3) molecules into oxygen (O2), thinning the ozone layer. This depletion allows more UV radiation to reach the Earth's surface, increasing risks of skin cancer, cataracts, and damaging ecosystems.

An example is the Antarctic ozone hole, a seasonal thinning caused by CFCs and cold stratospheric conditions, leading to increased UV exposure in southern hemisphere regions.

• CFCs release chlorine atoms that destroy ozone molecules in the stratosphere.
• Ozone layer depletion increases harmful UV radiation reaching Earth.
• This leads to health risks and environmental damage.

The greenhouse effect is a natural process where certain gases in the atmosphere trap heat, keeping the Earth warm enough to support life. However, human activities have increased concentrations of greenhouse gases such as carbon dioxide (CO2), methane (CH4), and water vapour, intensifying this effect.

CO2 is mainly released by burning fossil fuels and deforestation, while methane comes from agriculture (e.g., livestock digestion) and landfill sites. These gases absorb infrared radiation emitted by the Earth's surface, trapping more heat and raising global temperatures, a phenomenon known as the enhanced greenhouse effect.

For example, increased CO2 levels from industrial emissions have contributed to global temperature rises observed over the past century, leading to climate change impacts such as more frequent heatwaves and rising sea levels.

• Greenhouse gases trap heat in the atmosphere, warming the planet.
• Human activities increase CO2 and methane, enhancing this effect.
• Enhanced greenhouse effect drives global warming and climate change.