Note 37 — Chapter V · NITROGEN AND AIR

Whilst formed in the air these oxidising substances (N2O3, ozone and hydrogen peroxide) at the same time rapidly disappear from it by oxidising those substances which are capable of being oxidised. Owing to this instability their amounts vary considerably, and, as would be expected, they are met with to an appreciable amount in pure air, whilst their amount decreases to zero in the air of cities, and especially in dwellings where there is a maximum of substances capable of oxidisation and a minimum of conditions for the formation of such bodies. There is a causal connection between the amount of these substances present in the air and its purity—that is, the amount of foreign residues of organic origin liable to oxidation present in the air. Where there is much of such residues their amount must be small. When they are present the amount of organic substances must be small, as otherwise they would be destroyed. For this reason efforts have been made to apply ozone for purifying the air by evolving it by artificial means in the atmosphere; for instance, by passing a series of electrical sparks through the ventilating pipes conveying air into a building. Air thus ozonised destroys by oxidation—that is, brings about the combustion of—the organic residues present in the air, and thus will serve for purifying it. For these reasons the air of cities contains less ozone and such like oxidising agents than country air. This forms the distinguishing feature of country air. However, animal life cannot exist in air containing a comparatively large amount of ozone.