Transcript Atmosphere
26.12.2014 Overview The Structure of the Atmosphere Major Greenhouse Gases Global Warming Kyoto Protocol Atmospheric Pollution Air Pollutants Smog Acid Deposition Ozone Depletion Atmospheric gas composition Gas Nitrogen (N) Oxygen (O) Water (HO) Argon (Ar) Carbon Dioxide (CO2) Neon (Ne) Ozone (O3) Helium (He) Methane (CH4) Krypton (Kr) Hydrogen (H) Nitrous Oxide (N2O) Carbon Monoxide (CO) Chlorofluorocarbons Carbonyl Sulfide (COS) Mole fraction 0.78 0.21 0.04 to < 5∙10–3; 4∙10–6 – strat 0.0093 370∙10–6 (date: 2000) 18.2∙10–6 0.02∙10–6 to 10∙10–6 5.2∙10–6 1.7∙10–6 1.1∙10–6 0.55∙10–6 0.32∙10–6 0.03∙10–6 to 0.3∙10–6 3.0∙10–9 0.1∙10–9 The Structure of the Atmosphere Earth's atmosphere extends more than 560 km above the planet's surface and is divided into 4 layers. The troposphere extends from the Earth's surface up to 8 to 16 km. Temperatures decrease by about 6.5°C with each km of altitude. The stratosphere extends from the tropopause to 50 km. Temperatures increase with altitude because of absorption of sunlight by stratospheric ozone. 90 % of the ozone in the atmosphere is found in the stratosphere. In the mesosphere temperatures fall with increasing altitude, to a low of about –93 °C at an altitude of 85 km. In the thermosphere temperatures again warm with altitude, rising higher than 1700 °C. Major Greenhouse Gases (GHGs) Water vapor, ozone, carbon dioxide, methane, and nitrous oxide are naturally present in the atmosphere. Carbon dioxide (CO2) is the product of the oxidation of carbon in organic matter (through combustion of carbon-based fuels or the decay of biomass). Major Greenhouse Gases (GHGs) Methane (CH4) is produced by anaerobic decay of organic material in landfills, wetlands, and rice fields; enteric fermentation in the digestive tracts of animals such as cattle, goats, and sheep; wastewater treatment; fossil fuel combustion; and leaks from natural gas transportation and distribution systems and abandoned coal mines. Nitrous oxide (N2O) is produced by fertilizer use, animal waste management, fossil fuel combustion, and industrial activities. Hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) are synthetic chemicals that are used in a variety of industrial production processes such as semiconductor manufacturing. PFCs are also produced as a by-product of aluminum smelting. Both groups of chemicals are finding increasing use as substitutes for ozonedepleting chlorofluorocarbons (CFCs). HFCs and PFCs are replacing CFCs in applications such as refrigeration and foam-blowing for insulation. Important human activities that are raising atmospheric GHG concentrations fossil fuel combustion (CO and small quantities of methane and NO); deforestation (CO releases from forest burning, plus lower forest carbon uptake); landfills (methane) and wastewater treatment (methane, NO); livestock production (methane, NO); rice cultivation (methane); fertilizer use (NO); industrial processes (HFCs, PFCs, SF). Global warming and greenhouse effect GHGs are trapping infrared radiation emitted from the planet's surface and warming the Earth. Global average surface temperatures have risen, increasing by 0.6 °C +/– 0.2 °C during the 20th century. Kyoto Protocol The Kyoto Protocol was developed by the United Nations Framework Convention on Climate Change (UNFCCC) as an international agreement to reduce greenhouse gas emissions worldwide. The Kyoto Protocol commits industrialized countries to binding GHG emission reductions of at least 5 % below their 1990 levels by the period of 2008–2012. The Kyoto Protocol entered into force in 2005 and has been ratified to date by 163 countries, representing 61.6 % of developed countries' GHG emissions. The United States signed the Protocol but has not ratified it. Atmospheric Pollution Sulfur dioxide (SO2) is a gas formed when sulfur is exposed to oxygen at high temperatures during fossil fuel combustion, oil refining, or metal smelting. SO2 is toxic at high concentrations, but its principal air pollution effects are associated with the formation of acid rain and aerosols. SO2 dissolves in cloud droplets and oxidizes to form sulfuric acid (H2SO4), which can fall to Earth as acid rain. Nitrogen oxides (NO and NO2, referred together as NOx) are highly reactive gases formed when oxygen and nitrogen react at high temperatures during combustion or lightning strikes. Nitrogen present in fuel can also be emitted as NOx during combustion. Emissions are dominated by fossil fuel combustion and by biomass burning. In the atmosphere NOx reacts with volatile organic compounds (VOCs) and CO to produce ground-level ozone through a complicated chain reaction mechanism. Like sulfuric acid, nitric acid contributes to acid deposition and to aerosol formation. Atmospheric Pollution Carbon monoxide (CO) is an odorless, colorless gas formed by incomplete combustion of carbon in fuel. The main source is motor vehicle exhaust, along with industrial processes and biomass burning. CO binds to hemoglobin in red blood cells, reducing their ability to transport and release oxygen throughout the body. Volatile organic compounds (VOCs), including hydrocarbons (CxHy) but also other organic chemicals are emitted from a very wide range of sources, including fossil fuel combustion, industrial activities, and natural emissions from vegetation and fires. Some anthropogenic VOCs such as benzene are known carcinogens. Aerosols - The atmosphere contains solid and liquid particles that are suspended in the air. Aerosols in the atmosphere typically measure between 0.01 and 10 mcm in diameter, a fraction of the width of a human hair. Aerosols are removed the lower troposphere when rain or snow carries them out of the atmosphere or when larger particles settle out of suspension due to gravity. Smog Two types: industrial smog and photochemical smog. Industrial smog – also called gray or black smog – forms due to SO2 emissions from burning coal. Industrial smog develops under cold and humid conditions. Cold temperatures are often associated with inversions that trap the pollution near the surface. High humidity allows for rapid oxidation of SO2 to form sulfuric acid and sulfate particles. Today coal combustion is a major contributor to urban air pollution in China. Photochemical smog forms when NOx and VOCs react in the presence of solar radiation to form ozone. The solar radiation also promotes formation of secondary aerosol particles from oxidation of NOx, VOCs, and SO2. Photochemical smog typically develops in summer in stagnant conditions promoted by temperature inversions and weak winds. Acid Rain Acid rain refers to precipitation with pH values below 5, which generally happens only when large amounts of manmade pollution are added to the atmosphere. CO2 alone at natural levels would result in a rain pH of 5.7. The main components of acid rain worldwide are sulfuric acid and nitric acid. These acids form when SO2 and NOx are oxidized in the atmosphere. Damage Acid rain causes serious damage to plants, soils, streams, and lakes. Ozone Depletion Earth's stratospheric ozone layer absorbs 99 % of incoming solar UV radiation. UV radiation damages cells and causes sunburn and premature skin aging in low doses. At higher levels, it can cause skin cancer and immune system suppression. Catalytic Ozone Destruction Caused by Man-made Compounds A major threat to the ozone layer: rising atmospheric concentrations of manmade industrial chemicals called chlorofluorocarbons (CFCs), which were widely used as refrigerants, in aerosol sprays, and in manufacturing plastic foams. CFC molecules are inert in the troposphere, so they are transported to the stratosphere, where they photolyze and release chlorine (Cl) atoms. Chlorine atoms cause catalytic ozone loss by cycling with ClO. Montreal Protocol on Substances That Deplete the Ozone Layer The first international treaty to protect the ozone layer was signed in 1987, subsequently amended in 1990, 1992, 1995, and 1997. It establishes in participating countries a schedule for the phaseout of chloroflourocarbons and other substances with an excessive ozone-depleting potential. It has been ratified by 190 countries. Cyclones 1 – dirty gas 2 – dust 3 – clean gas A cyclone is centrifugal separator where the particles are swung as a result of their mass by the centrifugal force to the outside. Gas scrubber Gas scrubber are cleanings installations in which the gas flow is brought in intensive contact with a fluid which as aim to remove gaseous components from the gas to the fluid. Air filtration Two types of filtration processes - depth and surface filtration. Fabric and membrane filters are considered surface filters, while fibrous and granular filters fall under the depth filtration category. http://www.climatecontrolme.com/en/2011/03/air-filtration-change-approach/ Electrostatic precipitator The solids are separated from the flue gas by the impact of an electric field. The electrically neutral dust particles are charged by emission electrodes. The impact of the electrical forces transports the particles towards the precipitation electrode and thereby discharges them from the gas flow.