1. Pollution Management
5.7 Urban Air Pollution

2. Assessment Statements
5.7.1 State the source and outline the effects of tropospheric ozone.
5.7.2 Outline the formation of photochemical smog.
5.7.3 Describe and evaluate pollution management strategies.

3. 5.7.1 State the source and outline the effects of tropospheric ozone.
Unlike other pollutants, ozone is not directly emitted from human-made sources in large quantities.
Ozone occurs naturally in the upper atmosphere, but the chemical reactions between volatile organic compounds, Nitrogen Oxides, and sunlight can produce ground level ozone.
Volatile Organic Compounds (VOCs) are compounds able to evaporate into gases and take part in photochemical reactions including methane, alcohol, and ethane.

4. 5.7.1 State the source and outline the effects of tropospheric ozone.
The main sources of VOCs and nitrogen oxides are road transport, solvent release from drying paints, glues or inks, and petrol handling and distribution.
In humans it irritates eyes, causes breathing difficulties, cause lung damage, and may increase susceptibility of infection.
Ozone damages crops and forests by affecting photosynthesis thereby leading to reduced yields.
It can react with fabrics and rubber materials.

5. 5.7.2 Outline the formation of photochemical smog.
Photochemical smog refers to poor air quality caused by a mixture of nitrogen oxides and VOCs. It is associated with high air pressure, as these have weak winds and are not dispersed.
Summer smog occurs on calm sunny days when ozone is formed. The ozone mixes with acid aerosols, aldehydes, hydrogen peroxide, and peroxacetyl nitrate. It then drifts to the suburbs and rural area.

6. 5.7.2 Outline the formation of photochemical smog.
Winter smog is caused by temperature inversions (layer of warm air keeping pollutants trapped) and high levels of sulfur dioxide and other pollutants caused by increased heating usage.
In addition cars are less efficient in the winter and release large amounts of carbon monoxide and hydrocarbons.
Urban areas surrounded by high ground are at higher risk as cold air sinks reinforcing the inversion.