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Since the industrial revolution, large amounts of pollutants have been released into the atmosphere.

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OPEN BOOK PAPER Since the industrial revolution, large amounts of pollutants have been released into the atmosphere. Consequently, photochemical oxidants are causing smog, acid rain is being formed, the greenhouse effect is increasing and ozone (O3) is being depleted from the stratosphere. Releasing large quantities of harmful pollutants, fuel-burning vehicles and coal-fired power stations are major sources of pollution. A direct effect of pollutants is photochemical smog containing primary and secondary pollutants, which is usually seen as a haze in summer. 'Primary pollutants are released directly into the atmosphere by various processes such as combustion of fuels in cars and power stations.'(1) Secondary pollutants form when primary pollutants react with each other or with other compounds in the air. The major component of photochemical smog is ozone, a secondary pollutant. The main primary and secondary pollutants are listed in Table 1. Table 1: Primary & secondary pollutants formed as a result of motor vehicles (2) Coal combustion occurring in coal-fired power plants also produces harmful pollutants including oxides of carbon, nitrogen and sulphur. These are primary pollutants contributing to the greenhouse effect. (Fig 1) ...read more.


O3 hv O2 + O Reaction 8: Ozone absorbs light & breaks down forming O2 and O radical. O + H2O 2OH Reaction 9: The O radical reacts with H2O to form 2 hydroxyl radicals. Pollution is not the only cause of high rates of photochemical smog and tropospheric ozone (Table 2), weather is also an important factor. 'High temperatures, low winds, intense radiation and low precipitation' (6) all cause levels to rise. FACTORS ENCOURAGING SMOG FORMATION & TROPOSPHERIC OZONE LEVELS. 1. Numerous sources of primary pollutants. 2. Inversions inhibiting turbulent mixing of air. 3. Little cloud cover permitting high UV intensity. 4. Light winds unable to disperse pollutants. 5. Terrain that allows accumulation of pollutants. Table 2: Main factors encouraging smog formation & high levels of tropospheric ozone. (6) Since coal-fired power stations are major contributors to pollution, stations such as Longannet try to minimise harmful emissions, such as SO2 and NOx to lessen environmental damage. Although coal used by Longannet contains less than 1% sulphur, a considerable quantity of SO2 gases will be produced since a lot of coal is being used. SO2 gas is harmful since it leads to acid rain, is dangerous to our health, and causes visibility degradation. ...read more.


low NOx burners in which air was controlled to give lower temperature flames resulting in a significant reduction of thermal and fuel NOx. Gas reburn is better since not only less NOx is produced but any NOx that is formed is chemically removed making it the BPEO for Longannet. Additionally, extra heat is produced (oxidation of gas is exothermic) which can generate electricity. To prevent harmful photochemical smogs chemists need to study the reactions involved in the formation of photochemical smog and their speeds. Chemical reactions are investigated in laboratories and their speeds measured under different conditions. These rates are inputted into computers which reproduce and predict behaviour of pollutants in smog. Experiments on a much larger scale, such as smog chamber simulations, are also being conducted in which primary pollutants are mixed in a smog chamber (a huge plastic bag) and exposed to sunlight under controlled conditions. (5C) As* photochemical smog develops, concentrations of various species are monitored by analytical probes. More recently though, 'bench-top gas chromatography and mass spectrometry systems coupled to smog chambers provide realistic photochemical experiments' (7) enabling chemists to carry out their studies in conditions more like the atmosphere thus acquiring more reliable data. Total Word Count: 1048 Fatema Jessa - 1 - ...read more.

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