Discovery of trace substances in air

Nitrogen (N2), oxygen (O2), water vapor (H2O), carbon dioxide (CO2) and rare gases are the permanent main gases in air. Only water shows large variation in its concentration and CO2 is steadily increasing due to fossil fuel burning. Already in 

Ammonia (Scheele, identified nitrogen in alkaline air (NH3) the formula was established in 1785 by Berthollet) was found in air by Scheele in 1786 by observing that a precipitate originated on the cork a bottle containing hydrochloric acid, identified as salt ammonia (NH4CI) and it was later confirmed by Theodore de Saussure in the early 1800s. Still in 1900, it was stated that ammonia never exists freely (i.e., in gaseous form) in air but only in compounds with carbonate and others (Bliicher 1900). 

Prout provided other observations on ... the bleaching qualities of dew, and of the air itself as to the large proportion of oxygen sometimes contained in snow water and in rain water... (p. 570), which we can deduce from current knowledge on the presence of atmospheric oxidants such as H2O2 and photolytic-induced formation of radicals (OH, OJ) in surface water, for example, dew. 

It is notable that Prout s ideas were established before the discovery of ozone by Schonhein in 1839 (Schonbein 1844). The study of H2O2 in air was elosely connected with studying the chemistry of O3 in the nineteenth century (Engler 1879 Rubin 2001). It is remarkable that the existence of H2O2 in air (as gas, as well as dissolved in hydrometeors) was definitely established before 1880 but the existence of O3 was still being discussed around 1880. Definite proof of the existence of O3 in the atmosphere was not provided until the first spectrometric measurements at the end of the nineteenth century (Moller 2004). 

In 1766 Cavendish separated hydrogen from other gases and showed that it burned to water. In connection with Lavoisier s discovery of the role of airy oxygen (1777) it became clear that water is a chemical compound. Only in 1900 was Armand Gautier the first to proclaim the presence of hydrogen in atmospheric air. This was verified in 1902 by Rayleigh s spectroscopic studies in air. 

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