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Primary pollutants.

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Primary pollutants are polluting substances which are released directly into the atmosphere by combustion of fuels. Secondary pollutants are polluting substances which are produced by molecules of primary pollutants undergo series of photochemical reactions, when molecules absorb energy from sunlight. Primary pollutants are NOX (oxides of nitrogen, NO and NO2), SOX (oxides of sulphur, SO2 and SO3), volatile organic compounds (VOCs or hydrocarbons), CO (carbon monoxide) and CO2 (carbon dioxide). Secondary pollutants are O3 (ozone), NO2 (nitrogen dioxide), H2O2 (hydrogen peroxide), PAN (peroxyacetyl nitrate), partially oxidised VOCs and HNO3 (hydrogen nitrate). In a coal-fired power station, the following pollutants are formed when coal is combusted; Nitrogen oxides are formed by nitrogen compounds, from proteins, are oxidised and when atmospheric nitrogen and oxygen molecules react with each other: Sulphur oxides are formed by sulphur compounds reacting with oxygen molecule. Carbon dioxide is formed by complete combustion of hydrocarbons, RCH3: Carbon monoxide is formed by incomplete combustion of hydrocarbons: The most ...read more.


Then the RCH2 radical reacts with dioxygen molecule to form peroxy radical, RCH2O2 (reaction E): Then the peroxy radical reacts with nitrogen oxide radical to form nitrogen dioxide: This means that there are higher concentrations of nitrogen dioxide. Concentration of ozone will increase because via reaction B, more NO2 molecules are photo dissociated to form nitrogen oxide radicals and oxygen biradicals. Then the oxygen biradicals react with dioxygen molecule to form an ozone molecule (reaction A). In order for reactions D, E and F to take place, the hydroxyl radical is needed to react with hydrocarbon molecules, as stated in reaction D. The hydroxyl radical is formed by photodissociation of ozone molecules, which the oxygen bond is broken homolytically, to form an oxygen molecule and an oxygen biradical: Then the oxygen radical reacts with a water molecule to form two hydroxyl radicals: At Longannet, the following processes are chosen to reduce sulphur dioxide and nitrogen oxides emissions. ...read more.


They study individual reactions in the laboratory by measuring the rate at which each reaction takes place under a variety of controlled conditions. This means that the chemists can predict the rate of these reactions for any condition. They use computer simulation models and information on reaction rates to reproduce and predict the behaviour of pollutants during a photochemical smog episode. The more accurate the information used, the better predictions can be made and results the model provides. Finally, smog chamber simulations are used conduct large scale experiments. Primary pollutants are mixed in a smog chamber, which is a large clear plastic bag, and exposed to sunlight under carefully controlled conditions. Probes are used to monitor concentrations of pollutants as the photochemical smog builds up. The smog chamber has to be large to minimise reactions taking place on the container walls instead of in gaseous phase. The information collected by chemists meant that action has been taken by politicians to reduce emissions of primary pollutants. ...read more.

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