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39 Cards in this Set
- Front
- Back
What are the two types of smog?
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photochemical and reducing Smog
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The term smog comes from the words...
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smoke and fog
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What are the characteristic of contaminated air
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Yellow/brown color
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What does photochemical smog consists of
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mixture of secondary pollutant chemicals, air and water
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Where is reducing smog found?
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In coal burning cities with cold, wet winters, where thermal inversion can trap cold, still air close to the Earth's surface.
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Where do the primary pollutants for smog come from?
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internal combustion engines-automobiles
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What are the prefect conditions for smog to form
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bowl shaped cities (lack of wind) and high density of population (lot's of combustion engines)
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What is thermal inversion
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The abnormal temperature arrangement of air masses
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What are the primary sources of smog?
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VOCs, NOx (especially NO)
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How many types of smog exist? Name them.
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2, reducing smog and photochemical smog
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Desribe photochemical smog
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When a layer of warm air acts like a lid on the cold air which traps pollutants
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is photochemical smog oxidizing or reducing?
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oxidizing
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What effect does wind have on smog?
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under normal circumstance wind disperses the smog forming chemicals and smoke. without wind these pollutants collect and begin to form smog with the help of thermal inversion
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Which conditions are optimal for thermal inversion?
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windlessness, bowl-shaped cities, warm, dry and cloudless skies, as the UV light can easily reach the Earth
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What is necesary for the reactions in photochemical smog???
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UV light from the sun
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Where does smog occur?
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Smog typically occurs where there is temperature inversion
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When do pariculates, VOCs and NO peak and why?
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In the morning rush hours because they come from the car's engine
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Name one environmental condition that can promote photochemical smog
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Therma/temperature inversion
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Termination of proxide and nitrogen dioxide free radicals
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ROO• + •NO2 --> ROONO2
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What is thermal inversion?
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Thermal inversion is the increase in temperature in a layer of warm, still air, between the cold/clean air (higher altitudes) and the cold/polluted air (lower altitudes)
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Free radical produced when photochemical oxidants oxidise VOCs
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ROO• , a peroxide free radical
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What is it called when a layer of warmer air is trapped between two layers of colder air?
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Thermal inversion
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Stages of smog during the day
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1. release of VOC's, NOx 2.Increase in NO concentration and its oxidation to brown NO2 3. this dissociates with sun radiation into NO+•O 4. free radical O initiates reactions to form secondary pollutants 5. Photochemical oxidants oxidize VOC's to form secondary pollutants.
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What are PAN's?
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Peroaxyacyl nitrates
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What happens during early morning hours with with hydrocarbons and NOx
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N2+O2 --> NO2+N NO2+UV -->NO+N
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What is the propagation of free radicals?
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One free radical is used up but another is formed
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Oxidisation of NO
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Either 2NO+O2-->2NO2 or NO+O3-->NO2+O2
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What is the role of VOCs and particulates during formation of secondary pollutants?
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They act as catalysts and reactants in the formation of secondary pollutants.
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When does termination of free radicals take place?
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When two free radicals combine
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What are some secondary pollutants formed in photochemical smog?
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ozone, hydroxyl free radicals, aldehydes, peroxacyl nitrates (PANs)
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equation for formation of nitrogen oxide, from N2 and oxygen
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N2 + O2 --> 2NO
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Formation of hydroxide radicals
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O• + H2O --> 2OH•
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Formation of low altitude ozone
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O• + O2 --> O3
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Formation of nitric acid is the atmosphere
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OH• + NO2 --> HNO3
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What can ozone and hydroxyl free radicals do?
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act as photochemical oxidants
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Reaction to form brown NO2
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2NO+O2--->2NO2 or NO+O3--->NO2+O2
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Formation of peroxide radical
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ROO•
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Formation of PANs
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ROO• + NO2 --> ROONO2
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Formation of peroxides, aldehydes and ketones.
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OH• + RH --> R• + H2O
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