T HE work of the Advisory Committee on Atmospheric Pollution has

removed the question of the greatness of the smoke evil from the region of surmise to that of ascertained fact. Systematic examination and measure- ment of pollution of the air by smoke was initiated by the appointment of this Committee in 1912, and a large mass of information has been collected since then.

The methods of measurement need not be gone into in detail. It will be sufficient to say that three separate methods have been adopted :— (a) The collection of deposit from the air in gauges of known area exposed- under suitable conditions, and the subsequent examination and analysis of the deposit.

(b) The measurement of suspended impurity which is so finely divided as not to deposit readily, such measurement being made by an automatic instrument which filters two litres of air through a small disc of filter paper, making three or four such filtrations per hour. This brings out the hourly distribution of the impurity. d (c) The trapping of suspended matter by means of a special "dust counter," and its subsequent examination micro- scopically, by which means both the number of suspended particles and their dimensions and nature can be examined.

Smoke may be divided into two main types—industrial and domestic. Domestic smoke is produced in far greater quantity per ton of coal burnt than is the industrial variety. In the former something like 5 per cent, of the coal burnt is emitted from the chimney in the form of smoke, while in the latter the amount is probably under per cent. Domestic smoke differs in its nature from factory smoke. The domestic grate or range does not permit of such complete combustion as in the boiler furnace, one result of which is that a large percentage -of tar and carbonaceous matter appears in the domestic soot, the tar amounting to between 20 per cent. and 40 per cent, of the weight of the soot, and this gives it adhesive properties by which it is enabled to stick to the leaves of plants and the surface of buildings. There is little or no tar in the smoke from the industrial furnace for steam raising and the like, and much less carbonaceous soot.• " A highly injurious constituent of smoke is contributed by the sulphur in the coal. The sulphur is emitted chiefly in the form of sulphur oxides, which ultimately form sulphuric acid. For each 1 per cent. of sulphur in the coal burnt-about 50 lbs. of sulphuric acid are produced per ton of coal. This sulphuric acid comes down with the rain to poison the soil in the neighbourhood of our cities, and to destroy our historic buildings. We have, from this cause, about three -million tons of sulphuric acid poured into the air over these islands per year.

This would not all be prevented if there were no smoke ; but the smoke particles aggravate the trouble as they have the power of absorbing this acid and thus concen- trating it upon wherever they may settle.

The amount of soot which is ejected from our chimneys • per year may be taken as approximately 2i million tons. -Some of this settles in the neighbourhood of its source, while much of it is carried by the wind over the whole country. In this soot there are about 500,000 tons of

tar.

In the .aceorarmying table the deposit from the air' at

different places is shown for the year 1928-24. It will be seen that the quantity varies greatly in different places. The figures given arc divided into summer and winter deposits as the winter is the time when domestic smoke is produced in greatest quantity.

DEPOSIT FROM THE Alit DURING YEAR 1923-24. (in tons per %guar,. mile.) Total Solids. Sulphates.

Sum- Win- Stations. Summer, Winter. Annual. mer. ter. Annual.

542 310 842 — — 344 316 660 31 32 392 247 639 22 20 236 204 440 24 22 205 222 427 25 33 256 170 426 36 24 194 210 404 27 31 181 212 393 23 33 208 169 377 27 21 173 203 376 20 35 160 160 320 21 20 143 145 288 14 19 129 118 247 10 14 112 118 230 14 14 60 102 162 9 15 60 68 128 7 9 33 36 69 9 10 The above figures are arranged in order of total annual deposit (see columns 3 and 0).

The table is self-explanatory and does not call for much remark. The total annual deposit varies from 69 tons per square mile at Malvern to 842 at Rochdale.

The summer deposit is usually, but not always, slightly less than the winter as a large amount of dust is produced in the summer. The total annual deposit for London averaged 288 tons per square mile, this being the average of eight stations, while the average of eight stations in Glasgow gave 320 tons per square mile. The average annual deposit of sulphates in London (estimated as SO3) amounted to 33 and in Glasgow to 41 tons per square mile.

A word of warning may be given with reference to the table of deposits shown. It must not be inferred that the highest deposits in this table indicate the smokiest city in the country. We have not got observations in all and there are, doubtless, smokier cities, but they are not always anxious to take measurements, or to face the facts and try to remedy the evil.

Suspended Impurity.

Hourly records of suspended impurity taken by the author's automatic filter show a fairly regular distri- bution in most cities. The clear period in Westminster, for instance, is from midnight to 6 a.m., then, as fires are lighted, there is a rapid increase in impurity to about 10 or 11 a.m., on weekdays, after which there is a fairly steady fall, with another slight rise towards evening, followed by a fall until midnight again. The impurity in the air thus measured is smoke impurity, as its esti- mation depends upon the black discoloration of a filter paper, and the distribution follows closely what would be expected ; it is even noticeable that the maximum in the forenoon is later on Sundays than on weekdays. due to later rising.

Dust Counting.

Observations taken with the author's dust counter show that the suspended matter in the air is excessively finely divided, the diameter of the particles averaging about 1-50,000 of an inch. During thick smoke haze in London the diameter rises to about 1-25,000 of an inch or more. Evidently, the coarser particles have not had time or opportunity to settle. By this instrument the soot from our cities can be detected almost anywhere in the country, and in considerable quantity under suitable conditions. This is important, since people living in the country should realize that the air there is by no means free from city smoke. The author has detected such Rochdale .. ..

Liverpool .. ..

Blackburn .. ..

Birmingham ..

London—Golden Lane St. Helens ..

Kingston-upon-Hull ..

Leeds—Hunslet .. G lasgow—Tol 'cross Pk. Salford Glasgow—average of 8 stations . . . . London—average of 8 stations .. London—Ravenscourt Park London—Wandsworth Common .. Kingston-on-Thames..

Southport .. Malvern (1921-22) .. — 63 42 46 58 60 58 56 48 55 41 32 24 28 24 16 19 suspended matter in the wind- after it had travelled three hundred miles across the North Sea, while smoke haze on the south coast of England has been traced to the manufacturing districts of the Midlands.* Loss of Sunshine.

One result of smoke in the air which has a profound effect upon health is. the cutting off of sunshine. It has been shown that something like 50 per cent, of the winter sunshine which London ought to get is cut off by smoke. The same applies to Manchester and Sheffield (where measurements have been taken), and apart from sunshine the reduction of ordinary daylight in such cities is also of the order of 50 per cent. In the five years 1881-1885, for example, only 17 per cent. of the possible sunshine was received in London .in the winter and 83 per cent, in the summer ; while in the period 1916-1920 45 per cent. was received in the winter and 95 per cent. in the summer. The death rate per 1,000 in London has fallen from 21-3 in 1881 to 12-8 in 1920.

As showing the effect at different times of the year a table is given showing the sunshine at London stations expressed as a percentage of mean values for country stations.t In this table the country stations compared with London are Oxford, Cambridge, Geldeston, South- ampton and Rothamsted, the London station being at Westminster. The figures are derived from observations extending over twenty years.

SUNSHINE AT LONDON STATIONS EXPRESSED AS PERCENTAGE3 OF MEAN VALUES FOR COUNTRY STATIONS.

San. Feb. Mr. Apr. May. June. July. Westminster .. 38 45 55 70 82 8t 83 Aug. Sept. Oct. Nov. Dee. Year.

Westminster .. 86 78 65 46 29 64 •

These figures speak for themselves ; the great logs during the *winter is evident. It is satisfactory, however, to see that the amount of sunshine received by London has gradually increased since 1881.

From the above few data the magnitude of the smoke evil can be gathered and the fact that it is preventable to a great extent may be inferred from the figures showing the increase in the sunshine received in London.