环境化学课件.pptx

Atmospheric Structure The atmosphereThe atmosphere is a thin blanket of gas that envelops the earth.The gases that make up the atmosphere are held close to the earth by the pull of gravity.With increasing distance from the earth’s surface, the temperature, density, and composition of the atmosphere gradually changeOn the basis of air temperature, the atmosphere can be divided vertically into four major layers. Atmospheric structure TroposphereThe troposphere is the layer from the earth’s surface to the tropopause, which is at 10-15 km altitude depending on latitude and time of year. (Mt. Everest 8.85km)As altitude increases, air temperature decreases at a rate of about 3.5o per 1000 ft. The tropopause has a temperature of about –57oC.The lower part of the troposphere interacts directly with the surface of the earth–this part of the troposphere is generally called air.The atmosphere in this layer is heated from below by convection and radiation from the earth’s surface.Most of our weather occurs in the troposphere. StratosphereThe stratosphere is the layer above the troposphere and extends to about 50km.The temperature rises with increasing altitude, reaching a maximum of about –1oC at the stratopause.The ozone layer is in the stratosphere. Ozone absorbs UV, causing the rising temperature with altitude in this layer.The temperature structure keeps the air calm in this layer. (That’s why jet aircraft fly in the lower stratosphere!) MesosphereThe mesosphere extends from the top of stratopause to ~80 km.In the mesosphere, the temperature decreases with altitude. ThermosphereThe layer of air above mesosphere is called thermosphere.In the thermosphere, temperature rises with altitude, caused by absorption of UV solar radiation by N2 and O2. The lower atmosphereThe troposphere and the stratosphere together are called the lower atmosphere.The lower atmosphere account for 99.9% of total atmospheric mass The lower atmosphere is the domain of main interest from an environmen