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67
There was for the year 1933 another increase in the average carbon-monoxide
content of the air samples taken in Blackwall tunnel, the difference being particularly
marked in the summer quarter, during which eight of the twenty-six samples exceeded
the maximum figure desired, due to some extent to the unusual weather, but
also to the increasing amount of motor traffic passing through both tunnels in the last
few years, the census showing in both cases nearly 100 per cent. more in 1933 than
1928. The ventilation plant at Blackwall tunnel has in the main kept the air in a
satisfactory state during 1933, but on some occasions during the summer its capacity
was somewhat overtaxed. In the Rotherhithe tunnel the conditions have been more
satisfactory and the figures for 1933 were very similar to those of 1932.
Carbonmonoxide
in fire
stations.
It is the practice to run engines of motor vehicles for short periods at intervals
throughout the night and day in order to keep them warm and ready to go to a fire
without delay; it is necessary, particularly on cold nights, to do this with the doors
closed and consequently very little ventilation. During the past year chemical
investigations made at a number of fire stations showed a greater concentration of
carbon-monoxide in the air of the appliance rooms than is desirable, with some
percolation of the polluted air into adjoining rooms. Two different types of apparatus
for passing fumes from the exhaust pipes of the engines directly to the open air,
which had been fitted at stations, were found to be very satisfactory; the carbonmonoxide
in the air in the appliance room immediately behind the engines after
five minutes running only reaching 2 parts per 100,000 and 7 parts per 100,000 for
the two types at the different stations. Although conditions varied greatly at
different stations it was recommended that exhaust gas extraction apparatus should
be installed at all stations. Actually, however, it is understood that the chief
officer of the fire brigade is taking steps to achieve the same results by other means.
Atmospheric
pollution.
The results of observations made in connection with the general scheme of
investigation of atmospheric pollution carried out at stations in various parts of
Great Britain and others made solely for local purposes enable some general picture
to be formed of the incidence of pollution in the air of London. In considering
such results, however, it must be remembered that the air over a region is not
stationary, and that there are innumerable small, and several large, sources of
pollution, the significance of which at the very few places where observations can
be made is constantly varying owing both to changes of the seasons and the force
and direction of winds.
Certain general conclusions can nevertheless be drawn:—
(1) Determination of sulphur gases, of the reaction (alkaline or acid) of rainwater
and of pure water exposed to the air all show that the air of London is, on the
whole, more acid in winter than in summer.
(2) Observations of acidity and of the action of air and rain on bright copper
surfaces show similar seasonal variations pointing to more pollution in winter than
in summer, and to more in London itself than in outer London.
(3) Observations with Owen's air filter show that the air of London, or at least
at places where this instrument has been installed, contains more soot in winter
than in summer.
Visibility.
Observations of horizontal visibility in all directions from the fleche of County
Hall showed that the average visibility was higher in 1933 than the average of the
six preceding years in most months (fig. 5). The visibility in 16 directions averaged
around alternate points of the compass (true north bearings) is shown in fig. 6 for
each month of 1933.
The higher ranges of vision in all months except those of winter when visibility
is low in all directions are as in previous years centred on the south, and the eastern
quadrants as heretofore gives the poorest results. Observations at places east of the
Nore light vessel from the decks of sludge vessels confirm the view previously expressed
that the low winter visibility from the London station must be associated
with urban conditions and not with the river valley; that is, it is associated rather
with atmospheric pollution caused by the greater use of fuel for house, office and
factory warming, and is not due to purely meteorological factors.