ENVELOPED IN SOOT

New Zealand Times, Volume LIV, Issue 12660, 21 January 1927, Page 3

ENVELOPED IN SOOT

LONDON’S SMOKE FOGS MTS DARKEST HOURS GREAT LOSS OF SUNSHINE At the top of a tall building in Victoria street, London, is a quiet little room where everything known about the habits and peculiarities of smokefogs is filed and indexed, says a writer in “Tit-Bits.” Here we met Dr Owens. Britain’s leading professor of fogs^ “Hundreds of tons of soot float in the air during a London smoke-fog,” said Dr Owens. “If the fog is 300ftto 400 ft deep, about 200 to 250 tons of soot, are suspended over the city. And this weight of soot is jjroduced in about three hours by the fires lighted on a winter’s morning.” Although the wind sweeps most of this smoke away, much of it settles on houses and streets. In 1919, for instance, an average of 370 tons settled on every square mile, which means that upwards of 60,000 tons were deposited over the whole city. The year 1924 showed the remarkably reduced figure of approximately 300" tons per square mile. 17 MILLION TONS “London burns something like 17,000,000 tons of coal a year,” Dr Owpns continued, “and tlie wind is its best ventilator. To illustrate the effect of wind on. the atmosphere of a great city it is best to imagine a single chimney belching smoke into a steady wind. With the wind blowing at four miles an hour, one hour’s smoke is distributed over four miles. If it falls to one mile an hour, however, the same amount of smoke is stretched over one mile and is four times as dense.” Apart from foggy days, the quantity of smoke and other impurities floating in London’s atmosphere varies each

hour. From midnight until about 5 a.m. tho air is comparatively pure. But at 7 o’clock on week-days it thickens rapidly, reaching its depsest at about ten o’clock. After this it clears gradually, with a slight increase at six in the evening. On Sundavs the densest period is at about eleven o’clock. In the same way, most great cities have their clearest and thickest periods, which vary considerably. SUNSHINE SHUT OFF Nearly 50 per cent, of the sunshine London should reoeive is shut off by its smoke pall. During bad fogs over a million particles float in every cubic incli of London air, while on even an ordinary winter’s day 70,000 is a moderate estimate. “Occasionally shaped like kidneys, soot particles are usually formed irregularly ” says Dr Owens. “Numbers of rouna, glassy-looking particles are frequently found, however. Sometimes red and sometimes yellow, these are derived from the fuel ash’ from fires.” An hourly record of the amount of impurity ,in the air is kept by an ingenious automatic apparatus invented by Dt Owens. A disc of absorbent white paper, 7in in diameter, is divided into twenty-four divisions similar to the face of a clock. This is attached tc the top of a machine, which causes it to revolve completely once in a day and night. The disc is protected from the air in such a way that only one littlo round spot, l-3in in diameter, situated near its edge, is exposed at one time. When tho first spot has absorbed as much of the impurity in the air as it can hold and has become discoloured, another is exposed automatically. In this way two or more dark patches, varying in shade according to the condition of the atmosphere, are made on tho white disc each hour. When these are compared with a set scale of ten shades, ranging from white to nearly black, winch are known to represent definite “weights” of impurity, the number of tons of soot Hooting in tho air at any given time can be calculated.

“Soot particles are light and settle very slowly,” Dr Owens concluded. “Sfiot from the top of a chimney 100 ft high into porfcotly still air, they would take nearly three weeks to settle. When a strong wind is blowing they often travel hundreds of miles before touching ground.” Curiously enough, most London fogs occur on Wednesdays and fewest on Saturdays.