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Description
Detailed consideration of the mechanisms of air pollution dispersion, with laboratory demonstration and film of field conditions.
Detailed consideration of the mechanisms of air pollution dispersion, with laboratory demonstration and film of field conditions.
| Module code and title: | PT272, Environmental control and public health |
|---|---|
| Item code: | PT272; 07 |
| First transmission date: | 30-08-1975 |
| Published: | 1975 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:24:08 |
| + Show more... | |
| Producer: | David Jackson |
| Contributor: | Julian Hunt |
| Publisher: | BBC Open University |
| Keyword(s): | Air pollution; Chimney construction; Schlieren photography; Wind tunnels |
| Footage description: | Julian Hunt, against a skyline of chimneys, introduces the programme which deals with air pollution dispersion. Shots of car exhausts and chimney plumes. A bromine-air model is used to show how poisonous gases diffuse very slowly. A demonstration of entrainment is given by a salt water plume in fresh water, using Schlieren photography to show the dilution. Hunt explains the connection. Schlieren photo of heated fluid in a saucepan. Similar currents occur in the movement of cumulus cloud over a plain, film. Discussing wind dispersion, Hunt explains how wind tunnel experiments show non-turbulent wind does not mix pollution but real wind does. Eddies disperse pollution towards the ground. Convective motions combined with wind cause vertical looping of smoke plumes. Several filmed examples. Contrasted with a plume in cool evening air. A demonstration using a tank containing layers of fresh and salty water and balls of varying density shows how particles find their level according to density. Movement is damped out when there is no vertical eddying caused by convection. Another example shows what happens in neutral conditions: neither stable nor unstable. Examples of neutral, stable and unstable atmospheric conditions. Pollution in Santiago, Chile shows layering. Similar aerial views of London in winter. Hunt explains the stable inversion layer which acts as a lid and - when lowered to ground level - causes fog. Hunt explains the factors which determine how chimney plumes are bent over by the air. Wind tunnel demonstrations at Warren Spring Laboratory show the effect of variations in buoyancy and momentum. Actual examples. Explains the need for high chimneys to ensure wider dispersion before plumes reach the ground. A demonstration with water plume and dye shows how dispersion differs over hills, due to the speed up of flow over the ridge. Models and photos of dispersion over or beside hills in varying conditions. Hunt describes various problems with chimneys and tall buildings. Models illustrate the difficulties. Summary of factors to be considered in siting and controlling chimneys. Credits over film of London smog of 1952. |
| Master spool number: | 6HT/71702 |
| Production number: | 00525_5185 |
| Videofinder number: | 2890 |
| Available to public: | no |
