Abstract
Combined absorption and emission spectra have been recorded in the atmospheric window from 770 to 1,250 cm^−1^ both in London and in the relatively clean air of Ascot, Berks. The absorption spectra have been partially analysed in terms of selective and continuous extinction. The continuous extinction outweighs the selective in both Ascot and London. There is good agreement between the observed selective absorption and existing theoretical and laboratory data upon gases known to be present in the atmosphere.
The opacity of the continuum shows an increase towards low frequency, and it is much greater in London than in Ascot; in both places it is positively correlated with water vapour. The average effective emission temperature of the continuum is not significantly different from that of water vapour.
The only hypothesis which seems to fit all the observations is that in London the continuum extinction is largely caused by aerosol extinction while in Ascot this is only of minor importance. This requires that the extinction at Ascot be caused by wings of distant lines; this old suggestion of Elsasser is re‐examined and found to be plausible.
Attention is drawn to the important contribution which the continuum can make to the heat balance of the atmosphere below 2 km.