1. The problem statement, all variables and given/known data Determine the mass of air above a certain area on a typical winter day between ground level and 470m. 2. Relevant equations 3. The attempt at a solution I found the total area which I need to find the mass of air for, which gave me 2.05x10^9m^2 I times that by the height of 470m, which gave me the volume, 9.66x10^11m^3 Now I think I need to find the density of air as a function of altitude, I am unsure on how to find the average density, do i need to find an equation and integrate? any help would be appreciated thanks.