Density of Air

From Wind wiki

If your area of study is close to sea level, and is in a region with moderate climate, using the value of 1.225 kg./m3 is a reasonable estimation.

pV=nRT

, where p is the pressure of the air, V is the volume of the gas, n is the number of moles, R is the universal gas constant and T is the absolute temperature of the gas.

Density, ρ, is simply the number of molecules of the ideal gas in a certain volume, in this case, a molar volume, which may be mathematically expressed as:

ρ=p/RT

While air temperature data is not too hard to come by (and is relatively cheap to measure even if you don't have data already), air pressure data can be tougher to find. If air pressure data for your region is unobtainable, you can estimate density as just a function of site elevation and temperature with the following expression:

ρ=(p_0/RT) e^(((-gz)/RT) )

, where p_0 is the sea level atmospheric pressure, g is gravitational acceleration, 9.81 m/s2, and z is the elevation above sea level.