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Subunit 7 Urban Air Pollution Source and Impact of Troposphere Ozone In the troposphere which is the lower layer in the atmosphere, ozone is considered a pollutant. It is different from the protective layer of ozone in the upper atmosphere or stratosphere. In the upper atmosphere, ozone is formed by sunlight splitting oxygen molecules into atoms that regroup to form ozone. In the lower atmosphere, ozone is formed as the result of pollution by volatile organic compounds which are VOCs, hydrocarbons and oxides of nitrogen (NOx). In the burning of fossil fuels Hydrocarbon and Nitric Oxides are released. Nitrogen monoxide reacts with oxygen creating Nitrogen Dioxide which can react with sunlight to break oxygen molecules and create ozone. VOCs are organic chemical compounds that are able to evaporate into gases. Examples of VOCs are methane, ethane and alcohol. The main source of VOCs is road transport. Nitric oxide and nitrogen dioxide are formed in combustion processes. Then nitrogen dioxide can absorb sunlight and break up to release oxygen atoms that combine with oxygen in the air to form ozone. The photochemical reactions between the nitrogen oxides and VOCs in sunlight may take hours or days to produce ozone. Because the reactions are photochemical, ozone concentrations are greatest during the day, especially during warm conditions. Impacts Ozone damages crops and forests; in humans it irritates eyes, susceptibility to infection and can cause breathing difficulties. It has effects on forests and crops. Troposphere ozone pollution is a cause of the dieback in German forests and has also caused poor air quality in the UK. Ozone is not directly emitted from human made sources in large quantities. Ozone occurs naturally in the upper atmosphere, but the chemical reactions between VOCs, nitrogen oxides and sunlight cause ground-level ozone. Pollution Monitoring

Photosynthesis and growth may significantly reduce crop yields and affect extensive areas of arable farming. Effects on humans can be harming lung tissues, impair the body’s defense mechanism, increase respiratory infections, and aggravate asthma, bronchitis and pneumonia. The long-term effects include premature ageing of the lungs. Children born and raised in areas where there are high levels of ozone can experience up to a 15 per cent reduction in their lung capacity. The risk of death is similar for adults of all ages but slightly higher for people with respiratory or cardiovascular problems. An increase of 10ppb in the daily ozone levels for the previous week was associated with a 0.52 per cent increase in daily mortality. This corresponds to 3767 additional deaths annually in the 95 urban areas studied. According to the study, if ozone levels in the USA were reduced by about a third, about 4000 lives each year would be saved. The formation of photochemical smog Photochemical smog talks about poor air quality caused by a mixture of pollutants like: nitrogen oxides and VOCs, ozone being the main pollutant. Photochemical smog is associated with high air pressure. Poor air quality often stays for many days because stable high pressure conditions generally prevail for a few days. In some climates, notably Mediterranean climates, stable high pressure conditions persist all season, hence poor air quality can remain for months. In monsoonal areas, smog occurs in the dry season. This means that the regularity and severity of photochemical smog depends on topography including climate, population density, and the use of fossil fuels. Winds can disperse the smog and it accumulates in valleys because there is more heat there, for example: Rio de Janeiro, Santiago de Chile, Los Angeles, Beijing, Mexico City and Sao Paulo.

Here is one way to put it:

And another way to put it:

Summer and Winter smog Summer smog occurs on calm sunny days when photochemical activity leads to ozone formation. Ozone is formed because VOCs react in the sunlight.

Winter smog occurs with temperature inversions and high levels of sulfur dioxide and other pollutants, because of increasing heating of homes, offices and industries. Also vehicles work less efficiently until they have warmed up. This inefficient operation releases larger amounts of carbon monoxide and hydrocarbons. Management Strategies -Reduction of fossil fuels: Switching to renewable energy like the use of Solar or Hydroelectric power, improving public transport to reduce the use of private cars, educate industries and individuals about the importance of reducing the burning of fossil fuels. -Catalytic converters: A catalytic converter uses a catalyst or substance to hydrocarbons, carbon monoxide and nitrogen oxides in car exhaust into inoffensive compounds. In a catalytic converter, the catalyst (platinum and palladium) is covered with a ceramic honeycomb that is stored in a type of package connected to the exhaust pipe. Carbon monoxide converted into carbon dioxide with the help of the catalyst. The hydrocarbons are transformed into carbon dioxide and water and the nitrogen oxides into nitrogen and oxygen.

Can you think of any other management strategies? Create a PMM with other strategies that you can think of! Complete the Word Search below which includes important concepts! Subunit 7- Urban Air Pollution

U N O Z O N E P O L L U T I O N N M B S G V D T R O P O S P H E R E A I L W A K G O M S R E T N I W S Y S E S U N L I G H T N E G Y X O Q T U P S T S Y E L L A V A J W X J O F J S L L A X B K G N A H N P B W L S Q I S N R S J U J Z E W G Z O I Q M I D Y H P A R G O P O T A T S W T U P J H S T Z U A R F H U Z S Q S S U M M E R S M O G J L B C O O N A P V H M G C K M B I B L Z F D T B D S A K L T K K D R F W A Y T E Q I R E V H R M U V V O V K V B I Q H L J C P J E U U N M P H O T O C H E M I C A L S M O G H T C H P P T W B B H A Y Y W P O D U S E C W U U W Y B R Y D H V U Fossil Fuels






Photochemical Smog



Winter Smog

Summer Smog


Work Cited:

"Instant Online Word Search Maker." N.p., 2011. Web. 08 Jan. 2013. <>. "Urban Air Pollution." Pollution Managment. N.p., n.d. Web. 27 Dec. 2012.

< nvi onmentalSystemsandSocietiesChapter5.pdf>. "What Is a Catalytic Converter and How Does It Work?" HowStuffWorks. N.p., n.d. Web. 04 Jan. 2013. <>.