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due to the varying amount of pollution from local sources. Seasonal fluctuations were
clearly marked at all sites, the generally higher level of pollution in winter being due
to the combined effect of increased coal consumption and the occurrence of meteorological
conditions unfavourable to the dispersion of chimney gases. When the results
are examined over a period of years the main change is a trend towards a slight reduction
in the amounts of tarry matter and smoke ; this can be accounted for by the replacement
of many domestic fires by the more efficient combustion units of blocks of flats.
In the central area of London where the fuel consumption in office blocks and other
centrally-heated buildings exceeds that of local fireplaces, the ratio of smoke (black
suspended matter) to sulphur dioxide is less than that found in more residential areas.
This is attributable to the better combustion conditions obtainable in large furnaces
as compared with small grates burning coal. Use of the automatic sampler enabled a
more detailed analysis to be made of fluctuations of pollution during the daily cycle.
A distinction could be drawn between the effects of domestic and industrial combustion.
For example, on weekdays the smoke to sulphur ratio is at a minimum during the night,
when most domestic fires die down whilst some industry keeps running. At weekends,
when a greater proportion of industry is closed down, and domestic fires are burning
for longer periods, this ratio is found to be higher than for comparable periods during
the week.
The long-term investigation of the common major pollutants of the atmosphere
was supplemented by a special investigation directed towards the detection of various
minor pollutants. In addition dust separated from large volumes of air was examined
for radioactive constituents. The atmosphere has a small content of radioactive matter
arising from natural causes, of which the amount varies from day-to-day with changing
meteorological conditions. There is also a very small proportion of such matter produced
by nuclear explosions. The incidence of both of these sources of radioactivity is being
measured to provide a basis for future comparisons.
By a standing agreement with the Ministries concerned, the Scientific Adviser or
his deputy accompanied the Chief Alkali Inspector of the Ministry of Housing and
Local Government on visits of inspection to test the efficiency of the flue gas working
plants at Battersea and Bankside Power Stations.
Public health
During the year, the water supplies of 19 establishments served by wells were regularly
examined and visits were made to other premises to check the suitability of water from
various sources and to give advice. Of the samples taken 562 were examined bacteriologically,
56 chemically, and 515 for free chlorine content. At three wells some degree
of contamination was found in the untreated water, but chlorination ensured that all
storage water delivered to the services was entirely free of contamination.
A series of 15 whole day meals supplied by day nurseries were examined to ascertain
that adequate standards were being maintained.
The air in the Council's vehicular tunnels under the River Thames was regularly
examined in order to ensure that carbon monoxide, nitrous fumes, lead and soot contents
remained within safe limits. Carbon monoxide was kept within the specified limit on
most occasions at both Blackwall and Rotherhithe tunnels, but the amount of black
suspended matter showed an increase in comparison with previous years. This change is
attributable to the larger proportion of diesel-engined heavy vehicles now in use, which
can be a prolific source of smoke unless carefully maintained and properly driven. The
amount of carbon monoxide produced by the diesel engine is, however, relatively low.
Other work included the examination of disinfectants, and advice was given on
the methods for sterilising such various articles as recorders, plastic tableware, and
firemen's breathing apparatus, also on the steps needed to maintain children's sand pits
in hygienic condition. Powder colours and modelling clay to be used by children were
examined to ensure that toxic pigments were absent. Recommendations were made for
the use of types of synthetic glues which would avoid the risk of dermatitis.
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