Thursday, August 8, 2019

Atmospheric and Water Quality Essay Example | Topics and Well Written Essays - 2250 words

Atmospheric and Water Quality - Essay Example Moreover, it also included the effects of ground reflection on the plume. (Sutton, 1947) The basis for this model and various other models is the Generalized Dispersion Equation for A Continuous Point Source Plume. (Beychok, 2005) This equation is: Where: is the cross wind dispersion parameter given as: is the vertical dispersion parameter given as: Where is the vertical dispersion with no reflection, is the vertical dispersion for reflection from the ground, is the vertical dispersion for reflection from an inversion aloft and are given as: is the concentration of emissions given in g/m3 at any given receptor that is located at meters downwind of the emission source, meters crosswind from the emission plume centreline and meters above the level of the ground. is the emission rate of the source pollutant given in g/s is the horizontal wind velocity along the plume’s centreline given in m/s is the height of the emission plume’s centreline above the ground given in m is t he vertical standard deviation of the emission’s distribution given in m is the horizontal standard deviation of the emission’s distribution given in m is the height of the inversion aloft’s bottom from the ground The equation presented above compensates for upward reflection from ground as well as for downward reflection from the bottom of any inversion lids present within the atmosphere. The exponential terms in g3 converge rapidly and in most circumstances assuming m as 1, 2 and 3 provide acceptable solutions. as well as are representative functions of atmospheric stability and delineate the turbulence of the ambient atmosphere and of the downwind distance to the particular receptor. Within this arrangement, the most important variables are the degree of atmospheric turbulence and the height of the emission source. Generally dispersion is directly related to the turbulence. Q2. a. Describe the natural chemical reactions by which stratospheric ozone is created and destroyed. [10 marks] Ozone is produced in the atmosphere as the photochemical decomposition of oxygen molecules occurs. (Science Fun, 2011) As diatomic oxygen absorbs ultra violet radiation with wavelengths of less than 240 nm it tends to disintegrate as: O2 ? 2O* (reaction 1) The resulting free oxygen atoms combine with more oxygen molecules to generate ozone as below: O + O2 ? O3 Another mechanism is when ozone molecules decompose when treated with ultraviolet radiation with a wavelength of less than 290 nm. The reaction is as under: O3 ? O2 + O* (reaction 2) b. Explain the link that is believed to exist between pollution and ozone layer depletion. [10 marks] Myriad chemicals released into the air are known to react with ozone causing its depletion. The greatest danger stems from chlorofluorocarbons (CFCs) which are disintegrated by the action of ultraviolet light as below: CFCl3 + hv ? CFCl2 + Cl* (reaction 1) The activated chlorine atom now reacts with an ozone molecule to give off oxygen and chlorine oxide as under: Cl + O3 ? ClO + O2 (reaction 2) The chlorine oxide further promotes disintegration of ozone as under: ClO + O3 ? Cl* + 2O2 (reaction 3) This reaction tends to persist as reactions 2 and 3 proliferate and cause further ozone molecules to disintegrate into oxygen molecules. The net reaction for reactions 1, 2 and 3 becomes:

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