1. Fog, Pollution and Precipitation
L/O: to be able to describe how precipitation, fog and pollution vary between rural and urban areas

2. When do we get fog in cities? (or anywhere for that matter)

3. What is an anticyclone? Air is sinking – not rising (pressure?)
Lack of fronts means wind may be light
Conditions: dry settled and bright
Summer: Hot dry weather
Winter: Clear skies, cold nights and frost
In winter also related to fog because cold forces moisture to condense at low altitudes

6. Fog Pollution particulates are hygroscopic
Through the day water attaches to pollution particles
As the air cools at night, fog forms

7. Fog continued More fogs in urban areas (100% more) Last longer
More intense
Lower visibility
Lower sunshine levels in cities.

8. Pollution effects Oxides of Nitrogen (NOx’s) Carbon Monoxide (CO)
Weathering of buildings, rain, haze
Carbon Monoxide (CO)
Heart probs, headaches and fatigue
Photochemical oxidants (Ozone O3 and peroxyacetal nitrate PAN)
Smog, plant damage, headaches, eye irritation and chest pains)

9. Pollution from what? Suspended particulates Sulphur dioxide (SO2)
Burning fossil fuels
V small (micro metres)
Spoil buildings
Act as carcinogens
Fog/smog
Sulphur dioxide (SO2)
Haze, acid rain, respiratory problems, damage to plants

10. Smog investigation
In LA

11. Humidity in urban areas is lower (why?)

12. Why is there a greater incidence of fog in urban areas? (7 marks)
How are precipitation and fog related to particulate concentration? (8 marks)

13. Humidity 1
Humidity is another part of the climate, which is affected by the temperature of the air. Relative humidity can be up to 6% lower in an urban area as the air is warmer meaning it can hold more moisture, however the lack of vegetation and surfaces limit evapotranspiration.

14. Humidity 2
The humidity is also affected seasonally with the humidity being about 2% lower in the winter as the air is generally cooler so the air can hold less moisture and in the summer it can be up to 10% lower as the air is much warmer, which is increased by the land surfaces within the urban area that absorb heat due to the dark colour of the buildings and road surfaces.
For example in London the temperature in the city centre is warmer than the outer edge. This means that the air in the city centre has the ability to hold more moisture; however the lack of open water in the centre of London means there is little evapotranspiration so the humidity is lower.

15. Precipitation How is it different? Why?? More thunder storms
More convective storms of greater intensity
Why??
UHI generates convection
High rise and mix of building heights = more turbulence and vertical motion
Water vapour from industry
Hygroscopic nuclei = raindrop formation
Friction from urban area slows fronts

16. Photochemical smog
Mix of smogs

17. Today Write a definition for hygroscopic
How is precipitation different in rural and urban areas? Why does this occur?
Why is fog more common in urban areas?
How does air pollution vary with the time of year?