Review on the atmosphere

1.) the three elements that determine air density are temperature, pressure, and humidity
2.) air pressure is the result of the height of a column of air above a datum (reference point).
3.) with increasing altitude, air pressure decreases, which causes air density to decreases
4.) the atmosphere is warmed from below
5.) with increasing altitude, air temperature decreases and this tends to increase air density
6.) the combined effect of pressure and temperature changes with increasing altitude causes an overall decrease in air density.
7.) the standard atmosphere (ISA, international standard atmosphere) assumes that seal level pressure is 29.92 and seal level air temperature is 59.degrees Fahrenheit. The temperature lapse rate is 3.5degrees Fahrenheit/1000 feet.
8.) a low density altitude results when pressure is higher (than 29.92), temperature is lower, and the moisture content is dryer.