Total Weight of Air = Weight of Dry Air + Weight of Water Vapor Mixing Ratio = Mass of Water Vapor / Mass of the Dry Air Consider this: If you have 5 g of water vapor in every 1000 g (1 kg) of dry air, this is the same thing as saying an air sample that weighs 1005 grams , 5 g of which are water vapor, then that air sample has a mixing ratio of 5 g kg-1. Thus, a mixing ratio of 5 g kg-1 tells you the percentage of water vapor in the air. For 5 g kg-1 , the percentage of water vapor in the a_________