Wonder if anyone would know what is the average thermal emissivity value of air relative to blackbody at near room temperatures? I am looking for that magical number between 0 and 1. Looked everywhere but couldn't find the value.
I am trying to enumerate thermal losses when heating air inside an envelope made of Polyethylene with very high transmissivity and hence low emissivity. I am thinking that actual radiative thermal losses of air itself might play an important role with regard to the temperature of the heated air. I am completely neglecting convective and conductive heat loss at this stage. (I understand that these are actually major contributors to the thermal balance.)