1. Starter Individually Write down everything you can remember about Ozone…

2. Urban Air Pollution Learning outcomes: All of you should be able to: State the source of tropospheric ozone Most of you should be able to: Outline the effect of tropospheric ozone Outline the formation of photochemical smog

3. Tropospheric Ozone 10% of ozone in the Earth’s atmosphere is in the Troposphere. Nitrogen dioxide NO 2 –the brown haze that forms over cities Hydrocarbons come from burning fossil fuels and speed up the formation of NO 2. Nitrogen oxides and VOCs come from road transport, solvent release and petrol handling

4. The reactions between nitrogen oxides and VOCs are photochemical (they happen in the presence of heat and sunlight)… So when do you think the concentrations of tropospheric ozone will be the highest? In the troposphere, Ozone is known as a secondary pollutant… Why do you think this is?

5. Examples of ozone damage Black-eyed Susan Coneflower Snap beans Damages crops and forests; in humans it irritates eyes, causes breathing difficulties and may increase susceptibility to infection. Highly reactive and can damage fabrics and rubber Ozone degrades chlorophyll so photosynthesis and productivity are reduced.

6. Formation of photochemical smog Smog over Mexico City Sometimes called Los Angeles-type smog Ozone, nitrogen oxides and gaseous hydrocarbons interact with strong sunlight. Complex reactions create many chemicals e.g. VOCs, carbon monoxide and nitrogen oxides. A mixture of about 100 different air pollutants with ozone as the main one

7. The occurrence of photochemical smog It is governed by a number of factors… In pairs can you come up with some possibilities? HINT: think about Mexico City and China Local topography e.g. cities lying in valleys, sheltered from the wind. Thermal inversion (warm days a warmer layer of air above the city prevents air from rising. Climate – rain clears smog Population density Fossil fuel use

8. London-type smog Completely different… Occurs at low temperatures. Main pollutants include sulphur dioxide and smoke particles from burning coal. Caused a lot of deaths until the introduction of the clean air act.