8.3 Urban air pollutionIB Environmental Systems and Societies HL: Subtopic test

1. 1
   On a hot, sunny summer day in Los Angeles, morning rush-hour traffic releases nitrogen oxides and unburned hydrocarbons (volatile organic compounds) into the air. By early afternoon, ozone concentrations in the east of the Los Angeles basin have risen above health guidelines, and a brown haze hangs over the city. On cool, cloudy days with the same amount of traffic, ozone concentrations are much lower.

   (a)

   Which statement best describes how photochemical smog forms?

   [1 mark]

   • ASulfur dioxide dissolves in water droplets to form acid
   • BParticulate matter from burning fuel blocks sunlight
   • CNitrogen oxides are released by lightning only
   • DSunlight acts on primary pollutants such as nitrogen oxides and hydrocarbons, producing secondary pollutants such as ozone

   (b)

   Which of the following is a secondary pollutant in photochemical smog?

   [1 mark]

   • ACarbon monoxide
   • BTropospheric ozone
   • CSoot particles
   • DSulfur dioxide

   (c)

   Explain why ozone concentrations are higher on hot, sunny days than on cool, cloudy days even when traffic is the same.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Eastern North America has been affected by acid rain since the mid-twentieth century. Lakes in the Adirondack Mountains of New York became acidic and lost many fish populations, and forests of red spruce at high altitude declined. The United States Clean Air Act Amendments of 1990 introduced a cap-and-trade system for sulfur dioxide from power stations, in which the total allowed emissions were reduced over time and plants could buy and sell allowances. Sulfur dioxide emissions from power plants have since fallen by around 90%.

   (a)

   Which pair of gases are the main cause of acid rain?

   [1 mark]

   • ACarbon dioxide and methane
   • BCarbon monoxide and ozone
   • CSulfur dioxide and nitrogen oxides
   • DAmmonia and oxygen

   (b)

   The cap-and-trade system for sulfur dioxide is an example of which type of strategy?

   [1 mark]

   • AReducing production at source by setting a limit on total emissions
   • BTreating the effects of pollution on a lake
   • CIncreasing the output of power stations
   • DRemoving all vehicles from the roads

   (c)

   Explain two ecological effects of acid deposition shown in the scenario.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In field trials, wheat was grown in chambers with different average concentrations of tropospheric ozone. At 30 parts per billion (ppb), the yield was 6.0 tonnes per hectare. At 60 ppb, the yield was 5.1 tonnes per hectare. At 90 ppb, the yield was 4.2 tonnes per hectare. Ozone enters leaves through the stomata (pores) and reacts with cell tissues. Rubber materials such as car tyres and seals also become brittle and crack when exposed to ozone over time.

   (a)

   Calculate the percentage fall in wheat yield between 30 ppb and 90 ppb of ozone, and explain how ozone directly harms the crop.

   [3 marks]

   (b)

   Explain the indirect impacts of tropospheric ozone on society and the economy.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Mexico City lies in a high basin, about 2,240 m above sea level, almost completely ringed by mountains. It has about 9 million residents in the city and more than 20 million in the wider urban area, and millions of vehicles. Intense sunlight, light winds and frequent temperature inversions in the dry season trap pollution in the basin, and ozone concentrations regularly exceed health guidelines. Since 1989 the 'Hoy No Circula' (No Driving Today) programme has banned most cars from the road on one weekday each week, according to their number plates. Some households responded by buying a second, often older, car.

   (a)

   Evaluate the strategies used in Mexico City to reduce air pollution.

   [6 marks]

   (b)

   Discuss how meteorological and topographical factors intensify photochemical smog in Mexico City.

   [6 marks]

   Total for question 4: 12 marks

End of questions