Editing Content :: Admin Scraper

Chapter

Content type

Position

Value

COMPOSITION AND STRUCTURE OF ATMOSPHERE 65 Dust Particles tropopause. The stratosphere is found above the tropopause and extends up to a height of Atmosphere has a sufficient capacity to keep 50 km. One important feature of the small solid particles, which may originate from different sources and include sea salts, fine stratosphere is that it contains theozone layer. soil, smoke-soot, ash, pollen, dust and This layer absorbs ultra-violet radiation and shields life on the earth from intense, harmful disintegrated particles of meteors. Dust form of energy. particles are generally concentrated in the lower layers of the atmosphere; yet, Themesosphere liesabovethestratosphere, convectional air currents may transport them which extends up to a height of 80 km. In this layer,onceagain,temperaturestartsdecreasing to great heights. The higher concentration of with the increase in altitude and reaches up to dust particles is found in subtropical and ° temperate regions due to dry winds in minus 100C at the height of 80 km. The upper limitofmesosphereisknownasthemesopause. comparison to equatorial and polar regions. The ionosphere is located between 80 and 400 Dust and salt particles act as hygroscopic nuclei around which water vapour condenses kmabovethemesopause.Itcontainselectrically to produce clouds. charged particles known as ions, and hence, it is known as ionosphere. Radio waves transmitted from the earth are reflected back S TRUCTURE OF THE ATMOSPHERE to the earth by this layer. Temperature here The atmosphere consists of different layers starts increasing with height. The uppermost with varying density and temperature. Density layeroftheatmosphereabovethethermosphere is highest near the surface of the earth and decreases with increasing altitude. The column of atmosphere is divided into five different layers depending upon the temperature condition. They are: troposphere, stratosphere, mesosphere, thermosphere and exosphere. The troposphere is the lowermost layer of the atmosphere. Its average height is 13 km and extends roughly to a height of 8 km near the poles and about 18 km at the equator. Thickness of the troposphere is greatest at the equator because heat is transported to great heights by strong convectional currents. This layer contains dust particles and water vapour. All changes in climate and weather take place in this layer. The temperature in ° this layer decreases at the rate of 1C for every 165m of height. This is the most important layer for all biological activity. The zone separating the tropsophere from stratosphere is known as the tropopause. The air temperature at the tropopause is about minus 80 C over the equator and about minus o 45 C over the poles. The temperature here is nearly constant, and hence, it is called the Figure 7.1 : Structure of atmosphere Reprint 2026-27