INTRODUCTION TO THE ATMOSPHERE
The atmosphere is mainly composed of Nitrogen, Oxygen and Argon which account for 99 % of the composition. Other gases including Neon, Carbon Dioxide, Hydrogen, and Helium are also present in small quantities [1]. The air pressure and density of the atmosphere decreases as the distance from the earth’s surface increases, however the temperature inverts between the four main layers.
It is important to be aware of the molecules present in each layer of the atmosphere and the way in which these molecules affect the rest of the atmosphere, in order to understand the chemical reactions that occur after a volcanic eruption. Molecules in the atmosphere are important to life because they prevent the transmission of harmful solar radiation reaching the earth’s surface, and they maintain a constant surface temperature of the lower troposphere. When this maintained equilibrium is disturbed, following an eruption, this can have negative implications on life.
It is important to be aware of the molecules present in each layer of the atmosphere and the way in which these molecules affect the rest of the atmosphere, in order to understand the chemical reactions that occur after a volcanic eruption. Molecules in the atmosphere are important to life because they prevent the transmission of harmful solar radiation reaching the earth’s surface, and they maintain a constant surface temperature of the lower troposphere. When this maintained equilibrium is disturbed, following an eruption, this can have negative implications on life.
The atmosphere is made of the Troposphere, Stratosphere, Mesosphere and the Thermosphere. The weather on Earth occurs in the troposphere, which extends from the surface of earth and rises to 17 Km along the equator and 7 Km at the poles. 80% of the atmosphere’s mass exists in the troposphere [2] As altitude increases in the troposphere, the temperature decreases, until the Tropopause is met. At this boundary, the temperature stops decreasing with altitude (the temperature inversion occurs). In the troposphere there is also some Ozone (O3) present, which is harmful to living organisms as it irritates the respiratory system and acts as a harmful pollutant.
Above the Tropopause is the stratosphere which extends up to 51 Km high. As the altitude increases in the stratosphere, the temperature increases too. Therefore, the temperature increases from approximately -60 degrees Celsius to near 0 degrees Celsius, as shown in figure 8. The majority of the Ozone is found in the Stratosphere which absorbs ultraviolet radiation, thus protecting life on earth, whereby the ozone layer prevents the transmission of UV-c by 100% and UV-b by 95% [3]. Though after an eruption, the ozone starts to become depleted as a result of reactions which are determined by the emission of halide gases. The halide gases can also act indirectly by acting as heterogeneous catalysts, whereby the reactions occur on dust particles which have also been emitted.
The mesosphere extends above the stratopause, reaching a height of 85 Km and above the mesosphere lays the thermosphere. These two layers are at such a height from the earth’s surface that they are not directly affected by volcanic eruptions and the resulting magmatic plumes, or by the gases emitted.
Above the Tropopause is the stratosphere which extends up to 51 Km high. As the altitude increases in the stratosphere, the temperature increases too. Therefore, the temperature increases from approximately -60 degrees Celsius to near 0 degrees Celsius, as shown in figure 8. The majority of the Ozone is found in the Stratosphere which absorbs ultraviolet radiation, thus protecting life on earth, whereby the ozone layer prevents the transmission of UV-c by 100% and UV-b by 95% [3]. Though after an eruption, the ozone starts to become depleted as a result of reactions which are determined by the emission of halide gases. The halide gases can also act indirectly by acting as heterogeneous catalysts, whereby the reactions occur on dust particles which have also been emitted.
The mesosphere extends above the stratopause, reaching a height of 85 Km and above the mesosphere lays the thermosphere. These two layers are at such a height from the earth’s surface that they are not directly affected by volcanic eruptions and the resulting magmatic plumes, or by the gases emitted.
1: http://en.wikipedia.org/wiki/Atmosphere_of_Earth
Figure 8: http://www.learner.org/courses/envsci/unit/text.php?unit=2&secNum=2
2: http://www.weatherquestions.com/What_is_the_troposphere.htm
3: OCR Chemistry AS, Dave Gent and Rob Ritchie Page 226
Figure 8: http://www.learner.org/courses/envsci/unit/text.php?unit=2&secNum=2
2: http://www.weatherquestions.com/What_is_the_troposphere.htm
3: OCR Chemistry AS, Dave Gent and Rob Ritchie Page 226