At near-IR wavelengths atmospheric temperature has the dominant effect on flux levels in astronomical observing windows. The temperature at the top of the inversion layer, rather than at ice level, determines the amount of the thermal emission. The amount of aerosols, however, has a significant effect on both the atmospheric flux and the transmission. Water vapour content, over the range of values encountered on the Antarctic plateau, plays little role in determining these levels. In the mid-IR windows, up to and including the 20 m window, aerosol content plays the primary role in determining flux and transmission levels for the atmosphere.
Temperature plays a secondary role in determining the flux levels.
Water vapour content has a marginal role. Aerosols play a negligible role. Flux levels only show a small range of variation with water vapour content, instead being set by the temperature. Flux levels are directly proportional to absolute temperature. We stress that these conclusions are valid only for exceptionally cold, dry sites, such as those on the Antarctic plateau.