PDS AP Environmental Science 8th Period 2010-11

Today in class we began our discussion on Earth’s atmosphere. Earth’s atmosphere is mainly comprised of nitrogen gas at 78%. N₂ is an inert gas (a gas that is non-reactive under normal situations) that does not natural affect humans. Decomposers put nitrogen gas into a useable form through the 3 reactions in the nitrogen cycle: nitrogen fixation, nitrification, and denitrification. The next gas that is in the atmosphere is oxygen, which makes up 21% of our air. O₂ is very different compared to N₂, because oxgyen is highly reactive. O₂ can be split by sunlight to make ozone, which is crucial for people on Earth. The last 1% of the atmosphere is made up primarily of Argon, and there are many other permanent gases (Ne, He, H₂, Xe) and variable gases (H2O, CO₂, CH₄, O₃) that can be found in very small percentages. The percentage of water vapor can vary between 0-4% depending on where it is (the desert would be closer to 0%, while the rainforest would be closer to 4%).

(top picture) http://www.asc-csa.gc.ca/eng/educators/resources/spacesuit/composition.asp

(bottom picture) http://www.aerospaceweb.org/question/atmosphere/atmosphere/layers.gif

The Earth’s atmosphere can be divided into 4 layers, but we will mainly focus on the troposphere and the stratosphere. The atmospheric layers are only about 1/100th of the Earth’s diameter. The first, bottommost layer is the troposphere; this is where weather and human life occur. A nickname for the troposphere is the “weather maker.” The tropopause marks the boundary between the troposphere and the stratosphere. The temperature also starts to raise again after this point until you reach the stratopause. The next layer, the stratosphere, is primarily made up of the ozone layer. The reason that the temperature begins to raise after the tropopause and until it reaches the stratopause, is because in the ozone layer scatters UV rays. Without the ozone layer scattering UV radiation, human life would cease to exist. A nickname for the ozone layer is  ”global sunscreen.”

As you go further up in the atmosphere, pressure decreases because there is less gravity to pull down the air molecules. The concentration of air molecules will increase as the altitude decreases. This is crucial when climbing mountains; if a person climbs too high, the air will get thinner, with less air molecules to breathe. If you were to climb to the top of  Mount Everest, you would be above 2/3 of the air molecules. 99% of the air molecules are below 50% of the atmospheric layers. The atmospheric pressure is 14.7 lb/in² at sea level.

Relative humidity is the ratio of the amount of water vapor actually in the air to the maximum amount of vapor required for saturation at the particular temperature. The relative humidity would be higher on a tropical island than at the desert. High humidity feels hotter to our bodies because it affects the ability of the air to evaporate our sweat. When the humidity is higher, there is more water vapor in the air. This means that it will take longer to evaporate sweat, which we need in order to cool our bodies.

http://en.wikivisual.com/index.php/Air