EE-Unit-II Atmospheric Composition

Why do I care? The composition of the atmosphere, among other things, determines its ability to transmit sunlight and trap infrared light, leading to potentially long-term changes in climate.

The atmosphere is concentrated at the earth’s surface and rapidly thins as you move upward, blending with space at roughly 100 miles above sea level. The atmosphere is actually very thin compared to the size of the earth, equivalent in thickness to a piece of paper laid over a beach ball.  However, it is responsible for keeping our earth habitable and for producing weather.

Figure A

The atmosphere is composed of a mix of several different gases in differing amounts.  The permanent gases whose percentages do not change from day to day are nitrogen, oxygen and argon.  Nitrogen accounts for 78% of the atmosphere, oxygen 21% and argon 0.9%.  Gases like carbon dioxide, nitrous oxides, methane, and ozone are trace gases that account for about a tenth of one percent of the atmosphere.  Water vapor is unique in that its concentration varies from 0-4% of the atmosphere depending on where you are and what time of the day it is.  In the cold, dry artic regions water vapor usually accounts for less than 1% of the atmosphere, while in humid, tropical regions water vapor can account for almost 4% of the atmosphere.  Water vapor content is very important in predicting weather.

Greenhouse gases whose percentages vary daily, seasonally, and annually have physical and chemical properties which make them interact with solar radiation and infrared light (heat) given off from the earth to affect the energy balance of the globe.  This is why scientists are watching the observed increase in greenhouse gases like carbon dioxide and methane carefully, because even though they are small in amount, they can strongly affect the global energy balance and temperature over time.