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

2. 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

4. Precipitation How is it different? –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 Also increase of PPT down wind SNOW???

5. Fog Humidity in urban areas is lower (why?) At night urban areas retain humidity (as air doesn’t cool so fast) Pollution particulates are hygroscopic Through the day water attaches to pollution particles As the air cools at night, fog forms Especially in river valleys (more water vapour)

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

7. Pollution Suspended particulates –Burning fossil fuels –V small (micro metres) –Spoil buildings –Act as carcinogens –Fog/smog Sulphur dioxide (SO 2 ) –Haze, acid rain, respiratory problems, damage to plants

8. Pollution cont… Oxides of Nitrogen (NO x ’s) –Weathering of buildings, rain, haze Carbon Monoxide (CO) –Heart probs, headaches and fatigue Photochemical oxidants (Ozone O 3 and peroxyacetal nitrate PAN) –Smog, plant damage, headaches, eye irritation and chest pains)

9. 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? What are the major pollutants in urban areas and what effects do they have? How does air pollution vary with the time of year?

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