You could always make a function such as:
f[n_]:=WolframAlpha["air density" <> ToString[n] <> " meters",{{"Result",1},"NumberData"}]
But there is a function in a package for this data, which will be easier to use and quicker:
http://reference.wolfram.com/language/StandardAtmosphere/ref/MeanDensity.html
Needs["StandardAtmosphere`"]
Table[MeanDensity[Quantity[i, "Meters"]], {i, 1, 1000, 100}]
If you want to remove the units from the data, use QuantityMagnitude:
Table[QuantityMagnitude[MeanDensity[Quantity[i, "Meters"]]], {i, 1, 1000, 100}]
