Composition of Earth’s Atmosphere
Atmosphere of Earth is mainly composed of nitrogen (78% by volume) and oxygen (21% by volume) gases. Other constituents account only for about 1% of volume of atmosphere where the major of them is argon (0.93% by volume). These numbers are for dry air. The amount of water vapor in atmosphere can vary significantly from one area to another (It can be as low as several ppm in very cold and dry areas and also as high as several percent in very hot and humid regions). Many other substances having a natural origin or related to human activities can also be present in atmosphere with small amounts varying from time to time and from place to place.