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Primary and Secondary Pollutants:When fuels are burnt in both car exhausts and power stations primary pollutants are released into the atmosphere.

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Primary and Secondary Pollutants: When fuels are burnt in both car exhausts and power stations primary pollutants are released into the atmosphere. Secondary pollutants are formed when primary pollutants undergo further reactions. For example Ozone is a secondary pollutant formed when sunlight shines on nitrogen oxides and hydrocarbons. Ozone is a major component of photochemical smog. Primary Pollutants Secondary Pollutants Nitrogen oxides (NOx) Carbon Monoxide (CO) Hydrocarbons (CxHy) Ozone (O3) Peroxyacetyl nitrate (PAN) HNO3 NO2 H2O2 There are 2 main types of primary pollutants responsible for photochemical smog. 1. Oxides of nitrogen formed when nitrogen in the air reacts with oxygen, under high temperatures and pressure. 2. Hydrocarbons emitted from car exhausts as unburnt fuel. Photochemical smog is formed by the action of the suns rays on these primary pollutants. How are Primary Pollutants formed ? Primary pollutants are formed during the combustion of fuel in coal fired power stations. Carbon dioxide, sulphur oxides and nitrogen oxides are all primary pollutants produced when coal is burnt. ...read more.


CxHyO2 + NO --> CxHyO +NO2 Ozone concentrations are increased during smog formation. One ozone molecule leads to the production of two OH radicals. Each OH radical can then lead to the production of one ozone molecule. In sunnier conditions there is more light energy to react with the Nitrogen dioxide, this increased light intensity results in a quicker rate of reaction. On sunny days there is more light energy, so there will be more ozone produced. Also in sunny conditions there is enough sunlight to react with all or most of the oxides of nitrogen produced by car exhausts, whereas in cloudy conditions there is less sunlight available so fewer reactions will occur, and so less oxygen atoms will be broken away from the Nitrogen dioxide. Formation of ozone is one of the most important photochemical reactions in the lower atmosphere. So increasing amount of ozone will increase the amount of photochemical smog. The most favourable conditions for photochemical smog are warm sunny conditions so that h? ...read more.


In the primary combustion zone powdered coal is oxidised in low air concentration, so the combustion rate is lowered and less NOx produced. Natural gas is then injected into the boiler just above the reburning zone. The NOx reacts with these alkanes to produce N2, CO2 and H2O. CH4 + 4NO ==> 2N2 + CO2 + 2H2O This process chemically removes all NOx by reacting the NOx with natural gas to produce less harmful gases. This method is cheap and environmentally friendly because it does not put unwanted NOx's into the atmosphere. Chemists research: A lot of research is being conducted by chemists into the formation of photochemical smog. 1. Monitoring of tropospheric pollutants. Chemists have set up several monitoring stations to record pollutants present in the troposphere and their concentrations. 2. Studying individual reactions in a laboratory enables chemists to make predictions about pollution. 3. Modelling studies. Computer simulators are used to reproduce and predict behaviour of the pollutants during a smog episode. 4. Smog chamber simulations. Chemists create photochemical smog conditions so that concentrations of various species can be monitored as the smog builds up. ...read more.

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