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Describe, in terms of the production of photochemical smog, what is meant by primary pollutants, and secondary pollutants in the atmosphere, and list the main primary and secondary pollutants produced as a result of motor vehicles.

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Introduction

Describe, in terms of the production of photochemical smog, what is meant by primary pollutants, and secondary pollutants in the atmosphere, and list the main primary and secondary pollutants produced as a result of motor vehicles. (3) * 3 Paragraphs - One about photochemical smog, leading to PP, and SP. - One about PP and SP - List about the PP's and SP's produced by cars Photochemical smog is a combination of many chemical substances called primary and secondary pollutants. This smog is not very visible, but it's very oxidizing. It forms during high pressure conditions in the lowest part of the atmosphere, the troposphere. There is usually still air which doesn't mix with altitude air, trapping the pollutants. [1] Primary pollutants are pollutants that have been directly released into the atmosphere, for example in the combustion of fuels. When primary pollutants undergo further reactions, secondary pollutants are formed. [1] Primary pollutants: Nitrogen Oxides (NOx), Volatile Organic Compounds (VOC) and Carbon Monoxide (CO) [1] Secondary Pollutants: Ozone (O3), Nitrogen Dioxide (NO2), Hydrogen Peroxide (H2O2) and Peroxyacetyl Nitrate (PAN). [1] Describe how Primary pollutants are formed in the Combustion of the fuel in a coal fired power station. ...read more.

Middle

The reason why this helps is explained by the particle theory. [1] Photochemical smog creates a higher concentration of ozone. Two reactions taking place to destroy and produce happen at the same time, and eventually, it reaches a steady state. [1] (2) O2 + OO3 (Forms ozone) (3) O3 + NOO2 + NO2 (Destroys ozone) Therefore in photochemical smog, where there is more NO2 present, more oxygen atoms will be formed by photodissociation of NO2, therefore there will be more oxygen atoms to react with dioxygen molecules to form ozone in reaction (2). [1] This works as a positive feedback, because when ozone is broken down by Nitrogen Monoxide (like in reaction 3) nitrogen dioxide is produced. So the original NO2 that helped form the ozone, is now recycled, so it joins the extra NO2 that is already there. [1] Also when hydrocarbons are broken down, they form a peroxy radical, which reacts with NO to produce even more NO2. So now there is the NO2 from the exhaust fumes, the recycled NO2 from reaction (3) and now also from this reaction of the peroxy radical. ...read more.

Conclusion

Also the oxidation of these gases are exothermic, therefore it gives out energy, which can by used to generate electricity by Longannet. [2] & [3] The advantages of this process are that all the NOx is removed, and that extra energy is generated by the combustion of the gases. Outline the parts played by Chemists in the research on Photochemical smog Chemists monitor pollutants to find out exactly what pollutants are involved in smog formation, and how they vary in concentration. These changes in concentration can show changes in the atmosphere, for example the presence of sunlight. Chemists study reactions to see which pollutants react with which. Most importantly, to see which radicals are formed where, because they are very reactive, and cause a lot of atmospheric reactions. The speed of these reactions need to be measured to understand how fast substances are being made and destroyed. Chemists can makes models of situations, to predict what will happen in the future. One such model is smog chamber simulations. These are huge plastic bags which are exposed to sunlight under controlled conditions. Analytical probes monitor the concentrations of different gases as the photochemical smog forms. Stephanus Bernardus Jansen van Vuuren Candidate Number: 7166 ...read more.

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