Photochemical Smog

Question 1

How many people die prematurely due to air pollution every year?

Answer 1

1 million

Question 2

How much urban air pollution in LEDCs comes from old motor vehicles which are poorly maintained?

Answer 2

Over 90%

Question 3

How much GDP is lost by air pollution?

Answer 3

2% in MEDCs

5% in LEDCs

Question 4

What are primary pollutants?

Answer 4

Emitted directly from a process eg. volcanic eruptions, car exhausts, fossil fuel combustion, building sites, forest fires

Question 5

Name a major source of anthropogenic air pollution

Answer 5

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

Question 6

What are secondary pollutants?

Answer 6

• Formed when primary pollutants undergo reactions w other chemicals present in atmosphere
• Sometimes this is a photochemical reaction in presence of sunlight

Question 7

Name 3 examples of secondary pollutants

Answer 7

• tropospheric ozone
• particulates produced from gaseous primary pollutants
• PAN

Question 8

How much of atmospheric ozone is in the troposphere?

Answer 8

Only 10%

Question 9

How does tropospheric ozone form?

Answer 9

• 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

Question 10

Why under normal conditions is there only a very slight build-up of ozone near ground level?

Answer 10

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

Question 11

Effects of tropospheric ozone

Answer 11

• 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

Question 12

How are particulates formed?

Answer 12

• 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

Question 13

What are the dangers of particulates?

Answer 13

• 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

Question 14

What was the result of forest fires in Kalimantan, Indonesia in 1997?

Answer 14

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

Question 15

What is photochemical smog?

Answer 15

• 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

Question 16

What process leads to a build up of ozone near ground level and smog formation?

Answer 16

• 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

Question 17

Why is photochemical smog at its maximum in the early afternoon?

Answer 17

When light intensity is at its highest

Question 18

Name 4 cities that frequently suffer from photochemical smog

Answer 18

• Beiing
• Athens
• Mexico City
• Los Angeles

Question 19

The occurence of photochemical smog is governed by a large no. of factors, including the:

Answer 19

• local topography (mountains take away most of the wind + on warm days, severe smog can occur)
• climate
• population density
• fossil fuel use

Question 20

How does thermal inversion make things worse?

Answer 20

• 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

Question 21

Why does weather play an important role in the disappearance of smog?

Answer 21

• Rain cleans the air of pollutants

- Winds disperse the smog

Question 22

Reducing urban air pollution // altering human activity producing pollution

Answer 22

• 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

Question 23

Reducing urban air pollution // regulating + reducing pollutants at point of emission

Answer 23

• Government regulation // taxation
• Catalytic converters to clean exhaust of primary pollutants from car exhaust
• Fuel quality regulated by government

Question 24

Reducing urban air pollution // clean up and restoration

Answer 24

• Afforestation in inc. carbon sinks + filter air (but does not reduce emissions)
• Re-greening of cities (more trees, parks) absorb co2