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5
Atmospheric Pollution.
For many years before the war your Worshipful Committee maintained a Deposit Gauge on the
roof of your premises at 20, Golden Lane. This was destroyed by enemy action and no further observations
were practicable till 1948. when you authorised the replacement of this gauge and the installation
of additional apparatus at Golden Lane and in Finsbury Circus for the more exact measurement of
atmospheric pollution.
At the end of the first complete year of observations I have considered how I may present some
results to you. In future years I shall be able to show comparisons with previous years, though so
many factors, particularly of wind and weather, influence the monthly readings in stations in the
very centre of London, that only over a period of years can sound deductions be drawn as to the
upward or downward trend of atmospheric pollution.
Meanwhile I have thought it justifiable to endeavour to compare atmospheric pollution in the
City with other areas in London; a busy manufacturing area and a rural area. Again I must enter
the caveat that over a period of one year only wide variations are of significance for the purpose of
comparison.
I am indebted to Mr. W. R. McGrath, who is in charge of the various instruments for compiling
the following report, and to Mr. S. H. Richards, Superintendent of Observations (Atmospheric
Pollution), Department of Scientific and Industrial Research, for kindly reading the draft and making
numerous valuable suggestions.
I am indebted to Mr. W. G. C. Neale, a Sanitary Inspector in the Department, for the
photographs of the various instrument*.
The Measurement of Atmospheric Pollution.
The deposit gauge was the earliest instrument used by local authorities in this country for
measuring atmospheric pollution. The one positioned at Golden Lane in the City of London for many
years prior to the war was destroyed by enemy action in September, 1940.
In 1948, to enable observations to be restarted, the following instruments were installed:—
At Golden Lane—(1) A deposit gauge.
(2) A smoke filter and volumetric sulphur dioxide apparatus.
(3) A lead-peroxide apparatus.
At Finsbury Circus Gardens—(4) A lead-peroxide apparatus.
The main purpose of (1) is to keep a check on deposited pollution during the reconstruction
period, of (2) to do the same for smoke anti for sulphur-dioxide. (3) and (4) will enable a comparison
to be made-of sulphur-dioxide pollution in two different areas of the City. Observations with similar
instruments are being made by other local authorities in many districts, including the London area.
Impurity in the atmosphere can take the form of (a) solid or liquid particles which may be so
large that they settle out rapidly, or so small that they remain suspended for a very long time; and
(4) gaseous impurity, such as sulphur-dioxide produced by the combustion of the sulphur present in
fuels, which is dispersed and remains in the air until it is absorbed by rain, or by substances with
which it comes into contact.
It is of interest to note that, according to an estimate made by the Director of Fuel Research,
of the Department of Scientific and Industrial Research, in 1945, from about 180 million tons of coal
burnt per annum in Great Britain, there are emitted annually 2.3 million tons of smoke, 0.5 million
tons of ash, and 5.0 million tons of sulphur dioxide. Nearly half of the smoke is produced in domestic
grates, although these consume less than one quarter of the coal. Some four-fifths of the ash and
sulphur dioxide come from industrial undertakings.
Deposited Matter.
The deposit gauge collects, by means of a funnel-shaped glass bowl, solid and liquid material
deposited from the air. The material passes down a connecting pipe into a glass bottle. At the end of
each month the contents of the bottle are analysed by the Public Analyst into the following components
: Water, undissolved matter, and dissolved impurities. The undissolved matter includes
soot and ash ; among the dissolved impurities arc found sulphur, chlorine and lime. The results from
the deposit gauge are normally expressed as tons deposited per square mile per month.
Most types of atmospheric pollution are collected by the deposit gauge. Thus, the ash of the insoluble
matter, sometimes with the addition of small quantities of wind-blown dust, is the ash emitted
from chimneys. Similarly, the sulphate in solution is mainly derived from the sulphur-dioxide emitted
from chimneys. There is also a connection between deposits of combustible matter (including tar)
and the smoke emitted from chimneys; though the combustible matter in the deposit gauge may
include particles of grit including unburnt coal and coke.
Table 1 shows the mean monthly rates of deposit during 1949, of the materials collected in the
deposit gauge at Golden Lane.