How much does one gallon of zero humidity and pollutant free or pure clean and dry air at STP weigh?

Answer 1

At STP, the density of dry air is m/V = p / RT = 101325 N/m2 * 1 m3 / (287 J/kg-K * 273.15 K) = 1.2925 kg/m3. How much one gallon weighs is a simple matter of the volume ratio of one gallon to one cubic meter, so this question doesn't have to be answered again for a different volume.