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content of 9.2 parts per 100,000 ; only two samples exceeding the recommended
maximum of 20 parts per 100,000. The great improvement in the atmospheric
conditions brought about by the installation of the new ventilation plant is clearly
proved when these figures are compared with last year's average of 21.5 parts carbon
monoxide per 100,000 and 39 samples above the limit figure. The installation of
the new plant at Rotherhithe was begun, but the exhaust fans in No. 2 and No. 3
shafts only commenced work in November and December respectively, their period
of operation thus being too short to affect appreciably the averages for the whole
year. At Rotherhithe 103 samples were taken, giving an average carbon monoxide
content of 19.6 parts per 100,000; 41 contained more than the limit figure of 20
parts per 100,000. These results are rather worse than those of last year, and
show a great contrast with the improvement at Blackwall. " Suspended matter
in air " determinations were also made regularly at each tunnel and the results
showed general agreement with those of carbon monoxide.
Atmospheric
pollution.
The investigation of atmospheric pollution in the county of London has been
continued, both in connection with the general scheme of the Atmospheric Pollution
Committee of the Department of Scientific and Industrial Research to which the
Council has contributed for many years and of which the chemist is a member,
and in special directions made desirable by the pending erection of large power
stations in the county.
Six standard deposit gauges are erected in open spaces in the county. The
analysis of the water and deposit collected at these places, at the Meteorological
Office, and at stations maintained by the Cities of London and Westminster, afford
the authorities concerned a fair estimate of the total pollution deposited in the
whole of the county. Results obtained at Kew Observatory give information as
to a less polluted district within the metropolitan area, comparable with similar
information obtained by local authorities for districts widely scattered over England
and Wales.
In addition, smaller deposit gauges of a special type, and exposed discs of
copper, yield information concerning local pollution and its effect on metal-work
in places where conditions demand special records. At these places also special
work on the sulphur content of the air is being carried out by a process developed
by the Government chemist. The information thus obtained, supplemented by
records of soot in the air at County Hall and Battersea Park, and other data, will
be of value in connection with the study of emanations from power stations and other
industrial developments in the county.
Visibility.
The question of the range of visibility is intimately connected with that of
atmospheric pollution and observations from the fleche at County Hall and from
sludge ships in the Thames estuary furnish collateral information as to the variations
of efficiency of London air as a medium for the transmission of light.
Observations of horizontal visibility in all directions continued during 1931
showed that on the whole it was higher than the average of the five preceding years.
The subjoined diagram shows the mean distance in all directions at which objects
could be distinguished at mid-day in each month of 1931 and of the preceding
quinquennium, and is self explanatory.
The range of visibility was greatest in the quadrant S.E. to S.W. and markedly
so in the summer months June, July and August, as is shown by the second diagram.
During 1931 the visibility in the quadrant N.E. showed a great improvement on the
average of the previous five years.