Composition and Stratification of the Atmosphere - Assignment Example

Composition and Stratification of the Atmosphere A1. Which three gases constitute most of the earth's atmosphere? Nitrogen Oxygen Carbon dioxide A2. What range of altitudes constitute the troposphere? the stratosphere? Troposphere: 0 to 16 km above the sea level Stratosphere: 16 to 50 km A3. Describe the stratification of the atmosphere. Consider the basis on which stratification is achieved, and the names, features, and predominant chemical species and chemical process which occur in each of the strata. a. Troposphere Lowest atmospheric layers Has a thickness ranging from 8km to at the poles to 16km at the equator Experiences declining temperatures with rising altitude Contains about 75% of the atmospheric mass, it supports life, and weather elements b. Stratosphere Second layer and distinct from troposphere by tropopause It runs from 16 to 50km and experiences rising temperatures with increasing altitude It has ozone layer that absorbs the harmful ultraviolet rays It is almost completely free from weather elements Advantageous for long distant flights since it does not experience stormy conditions c. Mesosphere Distinct from stratosphere by stratopause Little it is in the middle and the third layer It occupies 50 to 80 km above the earth’s surface Experiences dropping temperatures with increasing altitude Considered the coldest of all the layers Layer in which most of the meteors burn up while trying to get into the atmosphere d. Thermosphere Literally referred to as heat sphere Mesopause separates it from mesosphere Its temperatures increases gradually above 10000C depending on the solar energy Its altitude ranges from 80 to 550km High temperatures are due to absorption of the solar radiation by the oxygen molecules e. Ionosphere Layer containing ionized air molecules extending from almost 80km to above 600km Technically it occupies similar region as the upper part of the thermosphere Solar energy is great at this point that it breaks apart air molecules and atoms, hence, leaving them as free floating electrons Ionization process is the role of ultraviolet radiations and cosmic rays from the sun It is the layer that enables transmission of radio waves A4. What phenomenon is responsible for the temperature maximum at the boundary of the stratosphere and the mesosphere? Temperature maximum is due to the availability of the ozone layer and heating effect resulting from absorption of the ultraviolet rays preceded by radiations and relaxation. Energy and Mass Transfer in the Atmosphere B1. Outline how the interactive effects of the circulation of air masses, the evaporation and condensation of water, and the redistribution of solar energy results in the weather pattern of a particular area During solar radiation, heat from the sun fall on various surfaces of the earth including lakes, rivers, oceans, and plants Exposure to elevated temperatures results in evaporation of water moisture, which forms the air masses due to their uniform characteristics, and similar direction of movement. Warm air rises due to lower density compared to colder air Upon reaching the atmosphere, due to lower temperatures, these moisture condenses to form water droplets This often results in the formation of rainfall B2. Discuss the causes and effects of the El-Nino Southern Oscillation (ENSO). a. Causes It results from cycling warm and cool temperatures on the ocean surfaces bordering central and eastern Pacific Ocean. Such regions are often colder than equatorial areas due to the effects of northeasterly trade winds, which is cold and originating from the coast of Chile and upwelling cold water from coastal Peru. Consequently, these cold surfaces results in warming up of the eastern and central pacific due to heat from tropical sun. This result in EL-Nino event causing heavy downpour in South America, but droughts in areas bordering eastern Australia On the contrary, if the injection of water becomes so intense, the phenomenon causes eastern surface of pacific to cool. This phenomenon is LA-NINA that causes droughts in Southern America but eastern Australia that initially experienced drought, experiences heavy floods. b. Effects El-Nino cause devastating effects on the fishing activities since it affects fish movement. Offshore warming causes flooding and related effects Warm air favours development of storms which greatly affects coastal activities ENSO often disrupts normal patterns relating to tropical precipitation and atmospheric circulation Abnormal warming of water within equatorial central leads to increased cloudiness and rainfall patterns within the region Carbon Dioxide and Global Climate C1. Explain in terms of the mechanism involved what is meant by the greenhouse effect. It is a circumstance in which the short wavelengths from the sun pass through the atmospheric window, which is a transparent medium and absorbed while the longer wavelengths are unable to pass through Through these absorptions, global temperatures tend to increase C2. Is water vapour a greenhouse gas? If so, why is it not usually present on lists of such substances? Yes: because its residence time within the atmosphere is less compared to other gases C3. What is meant by the term "window" as applied to the emission of IR from the Earth's surface? What is the range of wavelengths of this window? Window is an area within the atmosphere that allows some components of electromagnetic spectrum to pass through due to its transparency and low absorptive power. It allows infrared radiation to pass through the atmosphere to the surface of the earth. 3.0 – 4.0 microns is the wavelength range for light C4. Why are CFCs such as CF2Cl2 and CFCl3 such effective greenhouse gases? They are more powerful than other greenhouse gases and can remain in the atmosphere for a long duration (45 to 100 years) C5. What are the four important trace gases that contribute to the greenhouse effect? Water vapour Carbon dioxide Methane Nitrous oxide C6. What characteristics molecular properties of H2O and CO2cause their absorption of IR radiation? They both exhibit rotational and vibration transition which allow their molecules to acquire a quantum rotational and vibration energy. C7. Describe the two opposing effects on climate resulting from combustion of coal with high sulphur content. Sulphur compounds contribute to increasing greenhouse gases leading to absorption of radiations from the sun. As a result, it contributes to global rising temperatures. Sulphur dioxide reflects solar energy back into the atmosphere thus increasing the albedo of the earth, hence causing decline in global temperatures. C8. The amount of CH4 emitted annually is estimated to be 25 to 50 times greater than the amount of N2O emitted annually, yet the atmospheric concentration of CH4 is estimated to be only 6 times higher. Explain. Its concentration is higher due to the impact it has on climate change and ability to trap more heat per mass unit than N2O. Chemical and Photochemical Reactions in the Atmosphere D1. The enthalpy change for the decomposition of ozone into O2 and atomic oxygen is +105 kJ/mol. What is the longest wavelength of light that could dissociate ozone in this manner? Calculate the longest wavelength of light that decomposes ozone to O2 and O*, given that the excited state of atomic oxygen lies 190 kJ/mol above the ground state? Enthalpy = (h*c) ÷ l, therefore l = (h*c) ÷ E L = (6.626 x 10-34 Js x 3.00 x 108m/s) ÷ (1.05 x 105 x 6.022 x 1023) = (1.988 x 10-25) ÷ (6.323 x 1028) = 3.14 x 102 = 314 nm D2. What is (a) an excited state (b) a quanta of light (c) a Dobson unit (d) a free radical (e) steady state concentration (f) a tropospheric sink? Excited state is when molecules absorb photons from ultraviolet radiations and then it moves to a higher electronic state of energy Quanta of light are several photons that make up the particles of light Dobson unit is 0.01mm thickness of the ozone layer at standard temperature and pressure (STP) Free radicals are groups of atoms with odd number of unpaired electrons especially formed when oxygen reacts with other molecules. Steady state concentration is a situation in which the concentration of the intermediate is constant since formation rate is equivalent to destruction rate in two distinct reactions. Tropospheric sink are reactions or factors that remove gases from the troposphere D3. What is the two-step mechanism by which the hydroxyl free radical is produced in clean air? Photolysis Adsorption D4. What two chemical species are most generally responsible for the removal of hydroxyl radical from the unpolluted troposphere? Methane Carbon dioxide D5. By what mechanism is formaldehyde, H2CO, decomposed in air? Thermal or chemical decomposition D6. What function does a third body play in an atmospheric chemical reaction? To stabilize the excited product from the reaction through collision D7. Discuss, in general terms, the reactivity and stability of free radicals and electronically excited species in the upper atmosphere. Many factors are responsible for controlling the reactivity of radicals thus providing strategies of converting species considered highly reactive to ones that are more persistent. These reactions proceed due to adequate mobility and thermodynamic factors. Violation of these factors might lead to stable condition of relative radicals. Whenever free radical shares extra electrons instead of stealing, there is formation of new bond that results in reduction of energy This formation is exothermic, thus the resulting energy is lower in relation to that of separate free radical and the excited species. Stratospheric Ozone E1. Which atmospheric gas is primarily responsible for filtering sunlight in the 120-220 nm region? Oxygen Which gas absorbs most of the sun's rays in the 220-320 region? Carbon dioxide E2. Write the equation for the chemical reaction by which ozone is formed in the stratosphere. What are the sources of the different forms of oxygen used here as reactants? O + O2 --- O2 + heat O2 is naturaly available in the atmosphere while O (oxygen atom) forms from photochemical decomposition of O2 E3. Write the two reactions that, aside from the catalysed reactions, contribute most significantly to ozone destruction in the stratosphere. Cl + O3 ---- ClO + O2 O3 + O ---- 2O2 E4. Explain why the density of ozone peaks at 25 - 30 km altitude, yet the maximum temperature occurs at about 50 km. Because it has several absorption bands which are strong and also due to adiabatic processes occurring in the atmosphere E5. What are the two steps and the overall reaction by which species X such as Cl. catalytically destroy ozone in the middle and upper stratosphere? a. Step 1: O + O3 + XO + X b. Step 2: X + O2 + XO + O2 c. Overall reaction: O + O3 ----- 2O2 E6. What is the current estimate of the loss in stratospheric ozone per decade? 3.0% per decade E7. What is the principal four step mechanism by which chlorine destroys ozone in the spring over Antarctica? Step 1: Cl + O3ClO + O2 Step 2: 2ClOCl-O-O-Cl Step 3: ClOOCl + light (UV) + ClOO + Cl Step 4: ClOO O2 + Cl Simplified general process: 2ClO --- ClOOCl ---- light ---- 2ClO2 E8. Describe the process by which chlorine becomes activated in the Antarctic ozone-hole phenomenon. There is formation of ozone hole annually whenever there id reduction in total ozone in Antarctic. In dark cold winters, polar stratospheric clouds form when temperatures decline below -780C. These clouds play a crucial role in chemical changes thus promoting production of chemically active chlorine. If sunlight returns to Antarctic, the activated chlorine leads to depletion of ozone layer, which in turn leads to formation of Antarctic ozone hole. E9. Explain why ozone holes have not yet been observed over the Arctic. Within Arctic, there is sufficient ozone to filter UV-C and UV-B from sunlight radiation. E10. Explain why ozone destruction via the reaction of O3 with atomic oxygen does not occur to a significant extent in the lower atmosphere. Since there id scarce atomic oxygen within the lower stratosphere, this condition is helpful in inducing collision that aims at formation of ozone. Moreover, the scarcity is due to insufficient penetration of UV to dissociate the ozone. E11. Deduce the formulae for the compounds with the following code numbers: (a) 12 (b)113 (c)123 (d) 134. a. 12 + 90 = 102 CClF b. 113 + 90 = 203 C2Cl3F3 c. 123 + 90 = 213 C2HCl2F3 d. 134 + 90 = 224 C2H2Cl2F E12. Deduce the code numbers for each of the following compounds: (a) CH3CCl3 (b) CCl4 (c) CH3CFCl2 a. CFC-140 b. CFC-10 c. CFC-141 E13. What are the effects to human health that scientists believe will result from ozone depletion? Reduction in child growth Skin related diseases Highly carcinogenic Reduced lung and heart functionality Nauseas and chest tightness Particulates in the Atmosphere F1. Suppose a cubic particle with sides of length 3k is split up into 27 particles with sides of length k. Calculate the relative increase in surface area. Initial area = (3k x 3k) 6 = 54k2 Particulate area = (k x k) 6 = 6k2 x 27 = 162k2 Relative increase = 162 – 54 = 108k2 F2. Per unit mass, why are smaller particles more effective catalysts for atmospheric chemical reactions? Because they have increase surface area to volume ratio F3. Define the term "aerosol" and differentiate between "coarse" and "fine" particulates. What are the usual origins of these types of atmospheric particles. Why are coarse particles usually of less danger to human health than fine particles? Aerosols are fine or coarse colloidal particles usually solid or liquid in air or any other gas enclosed in a container and experiencing a high pressure. Fine particulates have an aerodynamic diameter of PM 2.5 or smaller. On the other hand, coarse particles’ aerodynamic diameter ranges from 2.5 to 10 µm (PM 10-2.5). Fine particles originate from conversion of precursor gases including sulphur oxides, nitrogen oxides and other organics into fine particles are nitrates, sulphates and organics. On the other hand, coarse particles are primary particles from the sources such as road dust and fly ash from coal burning. The particles embed around other surfaces in the atmosphere forming aerosols. Coarse particles are less dangerous since they are heavy and, therefore, settle over a short distance. In turn, it affects a few people within its coverage. In addition, due to their large size they cannot easily penetrate into the internal body organs unlike the fine particles, which penetrate and clog special organs such as the lungs. F4. What would the designation PM25 mean? PM 2.5 is the standard reference monitor for the quality of air. The indicator is the optimum requirement of quality of air efficient for breathing. Any value of quality of air beyond the designation is inefficient for breathing F5. Why are aerosols in the 0.1 to 1 µm size range especially effective in scattering light? Aerosols of smaller diameter especially 0.1 to 1 µm sized particles are efficient scatters of light due to their irregular structures as well their continuous spread in the atmosphere always forming zones of absorption of radiations. F6. Name and define two types of particulates found in the atmosphere, and indicate the sort of physical or chemical processes from which they may be formed. Aerosols from sprays and other human activities CFC from industrial processes F7. What are some of the environmental effects of atmospheric particulates? Particulate matter especially the fine particles are associated with health risks such as chronic bronchitis, decreased lung function and breathing diseases among other health effects. Fine particles especially from oil refinery emissions form smog in the nearby region minimising visibility. This reduces the visual range over some days. Some of these particles deposit into water bodies causing acidic water bodies through oxidation of sulphur oxide and nitrogen oxide. Consumption of such substances limits life expectancy. In some cases, the particles break the ozone layer exposing individuals in the affected area to dangerous ultraviolet rays from the sun. This eventually causes skin cancer. F8. Discuss the control of particulate emissions. Fuel choice and cleaning: Production industries need to seek alternative sources of energy other than coal for generating energy. For instance, replacement of coal with natural gas reduces such emissions by 10%. Moreover, oil fuels emit less particulate emissions. Fuel cleaning is one of the ways of minimising atmospheric particles. Washing and beneficiation of coal reduces emissions of ash and sulphur. Co-firing also provides a better alternative that reduces emission of ash. Efficient technologies and processes: most industries should be encouraged to adopt environmentally efficient technologies and processes such as gasification and fluidized-bed combustion. In addition, enclosed coal grinders and crushers also minimises emission of the particles. Equipment selection: Selection of efficient equipment with ambient air quality and large volumetric production at low pressure to reduce spread of the gases into the atmosphere. Use of filters and dust collectors reduces the dust emitted to the surrounding. Electrostatic precipitators also trap dust-reducing emission to the environment. Air Pollution: Acid rain G1. Calculate the pH of rain water in equilibrium with SO2 in a polluted air mass for which the sulfur dioxide concentration is 1 ppm (ie., 1 x 10-6atm), given that KH = 1 M atm-1 and Ka(H2SO3) = 1.7 x 10-2 M. PSo2 = (1 atm) x (1x10-6) = 1 x 10-6 atm (H2SO4) = Ka x PSo2 = (1.7 x 10-2) (1 x 10-6) = 1.7 x 10-8 Ph = -log (1.7 x 10-8) = 7.8 G2. What are the names and main sources of the primary pollutants that produce acid rain? Names of pollutants: sulphur dioxide, carbon dioxide and nitrogen oxides Sources of pollutants: human activities, volcanic eruptions, automobiles, industrial processes, and combustion of fossil fuels G3. What is the rationale for classifying most acid rain as secondary pollution? Because they are not the actual pollutant but they result from interaction with various components of the atmosphere and primary pollutants. G4. Outline a general mechanism for the formation of acid rain. a. Emission of pollutant oxides b. Depending on the oxide, there is oxidation in the atmosphere to form sulphate, carbonate, and nitrous oxides c. Atmospheric fixation in the presence of lightning d. Interaction with rainfall to form acid rain G5. Describe the environmental effects of acid precipitation. Ecological imbalance due to its hazardous effects on organisms It reduces the buffering ability of water, thus resulting in increased water acidity Acidity reduces nutrient levels in soils and water It causes subtle effects on the forests through influencing vegetation and soils Excess deposition of nitrates from acid rains cause eutrophication, as a result leading to growth of unwanted algae G6. How may acid rain be controlled? Curbing the release of pollutants that causes it Encouraging industries to use electronic precipitation to prevent release of pollutants into the atmospheres Promoting alternative sources of fuel Energy conservation Using roadworthy vehicles that do not pollute the environment G7. What are the main anthropogenic sources of sulfur dioxide? Describe the strategies by which these emissions can be reduced, providing chemical equations where appropriate. Anthropogenic sources: processing of sour gases, processing and combustion of fossil fuels, and production of sands oil Strategies to reduce emissions Using coals that contain less sulphur Developing scrubbers which chemically remove oxides of sulphur Switching of fuels by the power plants to employ combustion of natural gases that creates less sulphur dioxide Catalytic converter in vehicles also reduce sulphur dioxides G8. Using chemical equations, describe how acid rain can be neutralised by limestone. When an acid reacts with limestone (CaCO3) which is a base, there is neutralization reaction. After the reaction, limestone decay and becomes coated with gypsum which is the product of the reaction. This reduces the negative impacts of the acid rain. CaCO3 (s) + H2SO4 (l) CaSO4 (s) + CO2 (g) + H2O (l) Photochemical Smog H1. What are the names and main sources of the primary pollutants that produce photochemical smog? Names of pollutants a. Nitrogen dioxide (NO2) b. nitric oxide (NO) c. carbon dioxide (CO2) Sources of the pollutants a. exhaust from motor vehicles b. volatile organic compounds c. industrial processes H2. Outline a general mechanism for the formation of photochemical smog. a. Generation of oxygen atoms (O) from NOX b. O forms OH radicals (hydroxyl) c. OH radicals generate CH radicals (hydrocarbon) d. CH radicals generate CH peroxides e. Aldehydes forms from CH peroxides f. Aldehydes lead to formation of aldehyde peroxides g. Peroxyacylnitrate forms from aldehyde peroxides (Jeffries and Atmospheric Sciences Research Laboratory, 121, 2003) H3. What is the main species responsible for the oxidation of NO to NO2 in a smoggy atmosphere? a. Oxygen b. Ozone layer H4. Why does the production of high concentrations of NO2 lead to an increase in ozone levels in air? Ozone is more reactive than NO2 thus; it reduces it leading to formation of more ozone gases. Why does this not occur if much NO is present? NO is reducing agent that destroys the ozone layer at the rate at which it forms H5. What is the fate of NO2 molecules that photodissociate? that react with RC(O)OO.radicals? NO2 dissociates into NO and O (oxygen molecule). O reacts with O2 to form O3 while NO balances the level of concentration of the O3. NO2 reacts with RO3 radicals to form peroxylacetyl nitrate H6. What may be said about the time and place of the occurrence of maximum ozone levels from smog in respect to the origin of the primary pollutants that result in smog formation? Photochemical smog can only occur during the day since the volatile organic compounds must react with the sunlight. NO reduces ozone concentration to O2. H7. What are the environmental effects of photochemical smog? Reduced visibility due to formation of NO2 and increased cases of heart and lung complications. NO2 suppresses the growth of plants besides reduction in resistance to infection Eye irritation and toxicity in plants H8. How may photochemical smog be controlled? a. Through controlling traffics in order to reduce pollution index b. Using catalytic converters in vehicles c. Limiting the amount of exposure between volatile organic compounds and sunlight H9. Why are two catalytic reactors necessary to control all major automotive exhaust pollutants? They ensure complete combustion of CO in the presence of platinum catalyst They also reduce oxides of nitrogen to O2 and N2 Reference Jeffries, H. E., & Atmospheric Sciences Research Laboratory. (2003). Outdoor smog chamber experiments to test photochemical models: Phase II. Research Triangle Park, NC: U.S. Environmental Protection Agency, Atmospheric Sciences Research Laboratory. Read More