Photochemical Smog Flashcards
How many people die prematurely due to air pollution every year?
1 million
How much urban air pollution in LEDCs comes from old motor vehicles which are poorly maintained?
Over 90%
How much GDP is lost by air pollution?
2% in MEDCs
5% in LEDCs
What are primary pollutants?
Emitted directly from a process eg. volcanic eruptions, car exhausts, fossil fuel combustion, building sites, forest fires
Name a major source of anthropogenic air pollution
Major source of anthropogenic air pollution is from combustion of fossil fuels, producing:
- carbon monoxide
- carbon dioxide
- unburned hydrocarbons
- nitrogen oxides
- sulphur dioxide (from coal)
- particulates e.g. black carbon // soot suspended in air + cause lung diseases
What are secondary pollutants?
- Formed when primary pollutants undergo reactions w other chemicals present in atmosphere
- Sometimes this is a photochemical reaction in presence of sunlight
Name 3 examples of secondary pollutants
- tropospheric ozone
- particulates produced from gaseous primary pollutants
- PAN
How much of atmospheric ozone is in the troposphere?
Only 10%
How does tropospheric ozone form?
- Fossil fuel combustion emits nitrogen oxides (formed when oxygen + nitrogen react as a result of the high temp during combustion reactions)
- Nitrogen oxide reacts w oxygen to form nitrogen dioxide (a brown gas contributing to urban haze)
- Hydrocarbons + carbon monoxide accelerate formation of nitrogen dioxide
- When this absorbs light, it breaks up into nitric oxide + oxygen atoms
- Oxygen atoms react w oxygen molecules, forming ozone
Why under normal conditions is there only a very slight build-up of ozone near ground level?
Under normal conditions, most ozone molecules oxidise nitric oxide back into nitrogen dioxide, creating a virtual cycle that leads to only a very slight build-up of ozone near ground level
Effects of tropospheric ozone
- ozone = toxic gas + oxidising agent
- tropospheric ozone is absorbed by plant leaves where is degrades chlorophyll so photosynthesis + productivity are reduced
- At low concentrations, photochemical smog can reduce actions of the lungs
- Ozone reduces lifetime of car tyres
- Bleaches fabrics
How are particulates formed?
- Burning organic material // fossil fuels releases small particles of carbon called particulates
- Poorly maintained diesel engines esp. release large amounts of particulates in exhaust fumes
What are the dangers of particulates?
- Our respiratory filters cannot filter them out, so they enter out bodies + stay there causing asthma, lung cancer etc..
- Many particulates are carcinogenic
- Crops become covered w particulates, reducing their productivity as less sunlight reaches the leaf
What was the result of forest fires in Kalimantan, Indonesia in 1997?
Forest fires caused smog over much of SE Asia
Fires burned 8 million hectares
Cost government US$5 billion
Released a huge amount of co2 into atmosphere
What is photochemical smog?
- Mainly nitrogen dioxide + ozone
- Biggest contribution to photochemical smog is vehicle exhausts in cities
- It is formed when ozone, nitrogen oxides + gaseous hydrocarbons interact w strong sunlight
What process leads to a build up of ozone near ground level and smog formation?
- complex reactions create many chemicals in photochemical smog (inc. VOCs, ozone, nitrous oxides)
- highly reactive VOCs oxidise nitrogen oxide into nitrogen dioxide w/o breaking down any ozone molecules in process
- leads to build up of ozone near ground level + smog formation
Why is photochemical smog at its maximum in the early afternoon?
When light intensity is at its highest
Name 4 cities that frequently suffer from photochemical smog
- Beiing
- Athens
- Mexico City
- Los Angeles
The occurence of photochemical smog is governed by a large no. of factors, including the:
- local topography (mountains take away most of the wind + on warm days, severe smog can occur)
- climate
- population density
- fossil fuel use
How does thermal inversion make things worse?
- Normally air over cities is relatively warm + has tendency to rise
- On warm days, an even warmer layer of air on top of the warm polluted air can prevent air rising, trapping pollution at ground level
- This occurs most often in warm, dry climates
Why does weather play an important role in the disappearance of smog?
- Rain cleans the air of pollutants
- Winds disperse the smog
Reducing urban air pollution // altering human activity producing pollution
- Consume less fossil fuels
- Act as informed consumers for purchase of energy efficient technologies
- Use public transport
- Walking + cycling paths
- Lobby governments to increase renewable energy use
Reducing urban air pollution // regulating + reducing pollutants at point of emission
- Government regulation // taxation
- Catalytic converters to clean exhaust of primary pollutants from car exhaust
- Fuel quality regulated by government
Reducing urban air pollution // clean up and restoration
- Afforestation in inc. carbon sinks + filter air (but does not reduce emissions)
- Re-greening of cities (more trees, parks) absorb co2
