The geometrical configuration plumes diffusing with the atmosphere has been a function of the air vertical stability. The smoke plumes were classified by Church into five types and later Hewson was added the sixth type. The description is given below:
- Looping plumes take place when there has been a super-adiabatic lapse rate and solar heating. The large thermal eddies in the unstable air may bring the plume to the ground level periodically. In general, however, the direction of the plume with the surrounding air occurs rather rapidly.
- Coning plume gets resulted in when the vertical air temperature gradient has been between dry adiabatic and isothermal, the air being slightly unstable with some horizontal and vertical mixing occurring. Coning is most likely to occur during cloudy or windy periods.
- Fanning plumes spread out horizontally but do not mix vertically. Fanning plumes take place when the air temperature increases with altitude (inversion). The plume rarely reaches the grounds level unless the inversion is broken by surface heating or the plume encounters a hill. At night, with light winds and clear skies, fanning plumers are most probable.
- Lofting plumes diffuse upward but not downwards and occur when there is a super-adiabatic layer above a surface inversion. A lofting plume will generally not reach the ground surface.
- Fumigation causes the high pollutant concentration plume reaching the ground level along the length of the plume and is caused by a super-adiabatic lapse rate be4neath an inversion. The super-adiabatic lapse rate at the ground level occurs due to the solar heating. This condition has been favored by clear skies and light winds.
Application of meteorology in air pollution problems: The utilization of meteorological data in the air resource management program gives rise to formidable problems. We know that meteorological conditions vary tremendously from one day to another, from one season to another, and from location to another. There are times and places when almost any amount of pollution can get dispersed readily, while at other times and in other places, normally minor emissions can be a problem. We have yet to learn how to modify the weather so that it will be most favorable to good ventilation and adequate dispersion of air pollutants. We must take it as it comes and adapt man’s activities to its variations. Theoretically all major pollution sources not subject to control at the source could be located in those areas where atmospheric dispersion processes were most favorable, or could be so operated that emissions were nil or at a minimum during times of adverse conditions. These alternatives are commonly known as land-use control and meteorological control, respectively. Land-use control entails consideration of air pollution factors in zoning decisions. Meteorological control of pollutant emissions has been simple in concept, maximum emissions are allowed when good atmospheric dispersion may be expected; they are minimized when the air is stagnant. Controls of this nature have often been used where emissions could be interrupted or post-poned without unbearable economic penalty.