1、第一章 大气概述1 大气的组成2 大气的结构Atmosphere (air) is: a mixture of gases held to Earth by gravity. Earths primary means of transporting energy and moisture over its surface. an insulator and shield . relatively thinEarth (including its atmosphere) has a radius of about 6500 km. The atmosphere is only about 100
2、 km thickless than 2% of the Earths thickness. Despite its relative shallowness, the atmosphere contains considerable mass: 5.14 X 10E15 kg thats a mass equivalent to 5.65 billion million tons, the amount of water that would fill a lake the size of California to a depth of 13 km (7.7 miles)Atmospher
3、ic density decreases with altitude1. About 97% of the atmosphere is within 30 km (18 miles) of the surface.2. 75% is compressed below 10,700 m or 35,100 feet (7 miles)which is to say, within the troposphereAtmospheric density decreases with altitudeDensity: the amount of mass of a substance (express
4、ed in kilograms) contained in a unit of volume (1 cubic meter)Atmospheric density decreases with altitudeIn gases, individual molecules have no attachment to each other and move about randomly.Sothere is no definite limit to the amount of mass that can exist in a given volumemolecules can always be
5、added to or removed from the volumeResult change in densityAtmospheric density decreases with altitudeMean free path the average distance a molecule travels before colliding with anotherNear Earths surfacemean free path is a mere 0.0001 mm150 km (93 miles) above sea level (i.e., in the thermosphere)
6、 a molecule travels about 10 m before colliding with another Permanent gases (constant proportion in the atmosphere) 99.999 % of atmospheric mass Nitrogen, Oxygen, Argon, Neon, Helium, Krypton(氪 ), Xenon(氙 ), Hydrogen Variable gases (small percentage, but impact the behavior of the atmosphere) Water
7、 Vapor, Carbon Dioxide, Ozone, Methane(甲烷 ) Homosphere(均质层 ) lowest 80 km - region of chemical homogeneity Heterosphere(非均质层 ) region above the homosphere - lighter gases (H and He)1 大气的组成Evolution of the Atmosphere 4.5 billion years ago: hydrogen and helium primary atmosphere was lost to space secondary atmosphere: gases released by volcanic eruptions - outgassing - WV, CO2 , and other gases from the earth interior Ultimately, photosynthesis reduced carbon dioxide and added oxygen to the atmosphere
