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Domestic smoke differs in this respect, the volume of fuel being so much
smaller, the associated temperature in the region of combustion is much lower with
the result that there is a progressive distillation of the volatile constituents
of bituminous fuel which come off one after another as the appropriate temperature
is reached. In most old-fashioned grates the volume of air passing over the fire
and up the flue is so vast compared with that necessary to burn the fuel that it
cools and condenses these gases as soon as they are produced. They therefore become
entrained in the flue gases and are emitted into the atmosphere. These domestic
smoke particles are extremely small and behave as aerosols and are of an
extremely complex nature They are tarry and hygroscopic and vary in their chemical
content, depending on the temperature of production and whether or not the temperature
in the region of combustion was sufficient to oxidise them and destroy them
It is known that at least one of the components of coal distillation is a carcinogen
(3-4 benz-pyrene) and there are others. Because of the small size of smoke
particles they tend to disperse very widely in the lower atmosphere and because
of their physical property of absorbing moisture the particle size can increase
considerably with the rapid production of haze when meteorological conditions are
suitable.
Whereas the industrial chimney with this occasional black smoke is usually
emitting gases at very high temperature and at very considerable height from a
relatively few sources, the domestic chimney is emitting gases already cooled and
is producing its very considerable filthy atmospheric pollution from numerous
sources relatively close to the ground During the worst period of the year when
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