Measurements of the amount of ozone in the earth’s atmosphere and its relation to other geophysical conditions

Abstract

Several attempts have been made to determine the amount of ozone in the earth’s atmosphere during recent years. Until 1920 only chemical methods were employed, and these yielded very discordant results, the difficulty being to separate the chemical action of ozone from that of other oxidizing constituents of the atmosphere. Rayleigh in England, and Götz in the Alps, have shown that there cannot be more than a very small amount of ozone in the air near the earth’s surface. The first accurate measurements of the total amount of ozone in the atmosphere over any given region were made by Fabry and Buisson, who measured spectroscopically the intensity of the ultra-violet absorption band in the solar spectrum, which is due to ozone in the earth’s atmosphere. From measurements made on 14 days in May and June, 1920, they found the amount of ozone to be equivalent to a layer of pure ozone about 3 mm. thick at normal temperature and pressure. Small variations were observed from day to day. Ozone has a very strong absorption band, extending from about 3300 Å towards the shorter wave-lengths and reaching a maximum at about 2550 Å, and a weak band in the visible, which, however, absorbs some 4 per cent, of the solar energy at 6000 Å, and only rather narrow bands in the infra-red at about 9.5μ and 4.5μ (whose width and intensity are not accurately known) ; therefore its equilibrium temperature under solar and terrestrial radiation is high. It is thus of considerable interest to determine what variations in the amount of ozone take place over a long period, since these may have important relations to other geophysical phenomena.