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Atmospheric Pollution Caused By Coal-fired Power Stations And Motor Vehicle Engines.

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Introduction

Atmospheric Pollution Caused By Coal-fired Power Stations And Motor Vehicle Engines Photochemical smog contains a mixture of primary and secondary pollutants. Primary pollutants are released directly into the atmosphere whereas secondary pollutants undergo further reactions (1). The main primary and secondary pollutants in the atmosphere are shown in table 1 below. Table 1 Primary Pollutants NOx (NO + NO2), VOCs, CO Secondary Pollutants O3, NO2, H2O2, PAN, Partially oxidised VOCs, HNO3 The two main types of primary pollutants are oxides of nitrogen and VOC's (Volatile organic compounds) mostly hydrocarbons. Both are naturally present in the atmosphere but human activity heavily adds to this. Oxides of nitrogen are always produced when fossils fuels are burnt at a high temperature e.g. in a motor vehicle internal combustion engine. 95% of this is NO, which is a primary pollutant, with only small amounts being NO2 which is a secondary pollutant. Unburnt fuel in motor vehicles also releases hydrocarbons into the atmosphere. ...read more.

Middle

The Null Cycle With No Hydrocarbons Present More hydrocarbons in the atmosphere will mean more NO2 will be available to produce more oxygen atoms and therefore more ozone. The following two reactions show the first two steps of breaking a hydrocarbon Reaction 4: RCH3 + OH ==> RCH2 + H2O Reaction 5: RCH2 + O2 ==> RCH2O2 The peroxy radical RCH2O2 then reacts with NO to form NO2 (5): Reaction 6: RCH2O2 + NO ==> RCH2O + NO2 These reactions provide a means of regenerating NO2 from NO which does not involve the destruction of ozone so the concentration of ozone rises. At Longannet, SOx emissions are reduced by a process called 'sea water scrubbing.' This involves passing the fuel gasses through the seawater allowing the SOx to dissolve producing sulphite ions in the water. The seawater is aerated (air is passed through the seawater) to oxidise the sulphite ions to sulphate ions, which are more suitable for disposal at sea. ...read more.

Conclusion

This is why the 'Gas Reburn,' system being used as the BPEO for reducing NOx emissions at Longannet. Chemists have used various techniques to research the formation of photochemical smog. These include the monitoring of tropospheric pollutants. This provides data for the concentrations of pollutants involved in the production photochemical smog, at different times in the day. Chemists can then use this data to deduce when photochemical smog is most likely to occur. By studying individual reactions in the laboratory, which are known to be involved with production photochemical smog, chemists can begin to make predictions about rates of reactions. The findings and predictions can be fed into a computer to produce an accurate computer model that can be used for simulating different scenarios/situations. Finally tests can be carried out on a grand scale in smog chamber simulations. All these techniques are very important as emissions of primary pollutants increase worldwide every year so any decisions made are based on firm scientific understanding of the processes involved. ...read more.

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