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

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

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

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

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

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)

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

Smog investigation https://www.youtube.com/watch?v=JVcFps_gWpk In LA https://www.youtube.com/watch?v=MOQjK3LWoK8

Humidity in urban areas is lower (why?)

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.

Humidity 2 Humidity is also affected seasonally with 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.

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

Photochemical smog https://www.youtube.com/watch?v=s2sHIyvN0aE Mix of smogs https://www.youtube.com/watch?v=PBqyQ4TFevI

Additionally – think about these… 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?

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