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Photochemical smog is made up of primary and secondary pollutants.

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AS CHEMISTRY OPEN BOOK PAPER 2003 Photochemical smog is made up of primary and secondary pollutants Primary pollutants are pollutants released directly into the atmosphere from the combustion of fuels in motor vehicles. Primary pollutants 1 * NOx (a mixture of NO2 and NO), from atmospheric Nitrogen and Oxygen reacting in the heat of car exhausts. * Carbon Monoxide (CO) from incomplete combustion in the engine. * VOC's (volatile organic compounds, mainly hydrocarbons), which are emitted from exhausts as unburnt fuel. When these primary pollutants undergo chemical reactions with each other, and chemicals already present in the atmosphere, they form secondary pollutants. Secondary pollutants 1 * Ozone (O3) * NO2 * Hydrogen peroxide (H2O2) * Peroxy nitrates * Partially oxidised VOC's * Nitric acid (HNO3) Coal-fired power stations and their pollutants Coal-fired power stations also emit primary pollutants: NOx emissions Coal contains nitrogen compounds, from the proteins in the living organisms it was made from. ...read more.


RCH2 + O2 --> RCH2O2 1 The Peroxy radical then reacts with NO: 6. RCH2O2 + NO --> RCH2O + NO2 1 This reaction converts NO back to NO2, as in the third equation (above), where ozone is used up & re-generated at the same rate. But this reaction does not use up ozone to create the NO2, thus the concentration of ozone rises. The OH radical is formed from ozone: hv O3 --> O2 + O 1 The O atom has high energy, and reacts with water: O + H2O --> 2OH 1 Each Ozone atom creates 2 OH radicals. One OH radical will lead to the production of one O3 molecule through reactions 1,2,4,5, and 6. So the ozone concentration at least doubles. Controlling pollution from coal-fired power stations SOx emissions Sea water scrubbing This is when the flue gases are passed through seawater. Seawater is slightly alkaline and the sulphur dioxide dissolves in it to produce sulphite ions. ...read more.


CH4 --> CO + H2O The alkanes and CO are then reacted with air to combust them completely. This oxidation is exothermic and so produces heat that contributes to the generation of electricity. 4 Gas reburn is a means of achieving NOx reductions and is not an energy saving process in the conventional sense. It is expected that with 19% gas reburn, reductions in NOx emissions of at least 45% from the levels achieved with low NOx burners. 5 Photochemical smog - current research Monitoring Chemists monitor the concentrations of tropospheric pollutants, to study patterns and learn about the rate at which certain reactions will take place in certain conditions. Modelling studies They can put the data into computers, which then simulate the predicted behaviour in specific given photochemical scenarios. The more accurate the information, the better the predictions will be. Smog chamber simulations Primary pollutants are mixed together in a huge clear plastic bag (smog chamber), and exposed to direct sunlight, under carefully controlled conditions. Probes monitor the concentrations of the various components of photochemical smog. ...read more.

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