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CLEAN AIR ACT. 1956 - INVESTIGATION OF AIR POLLUTION
As from the commencement of the national survey of air pollution on the 1st April,
1961, the method of expressing concentrations of both smoke and sulphur dioxide was
changed to "microgrammes per cubic metre". Prior to this date the amount of smoke was
given in "milligrammes per 100 cubic metres" and that of sulphur dioxide in "parts per
million by volume".
In the following tables, which show the results recorded (to date) during the year
ending 31st March, 1962, compared with those of the previous year and with the average
of the 5 years ended 31st March, 1960, all figures are given in "microgrammes per cubic
metre". It should be noted that, from available records, the smoke figures prior to
April, 1961, can only be given correct to the nearest 10 microgrammes.
As the D.S.I.R's statistical year does not end until 31st March, 1962, it is not
yet possible to state how the current year's figures compare with those of previous
years. For the six summer months ended 30th September, 1961, the average amount of
smoke (51 microgrammes per cubic metre) showed a marked decrease compared with the
amount for the summer of 1960 (70 microgrammes per cubic metre) and with the average
for the 5 previous summers (80 microgrammes per cubic metre), whereas the average
amount of summer sulphur dioxide has remained constant at about 100 microgrammes per
cubic metre. It is too soon to make any valid comparison of winter results for 1961/62.

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