IGCSE Chemistry 0620: Comparing the Effects of Oxides of Nitrogen and Sulfur Dioxide

An environmental scientist compares air-quality readings from two monitoring stations: one beside a busy urban ring road, where oxides of nitrogen are the main pollutant of concern, and one near a coal-burning power station several kilometres outside the city, where sulfur dioxide from the combustion of sulfur-containing fuel is the main pollutant of concern.

(a) State the source of the oxides of nitrogen detected at the ring-road station. [1]

(b) Both oxides of nitrogen and sulfur dioxide contribute to the same adverse environmental effect. Name this shared effect. [1]

(c) State one further adverse effect of oxides of nitrogen, on people or the environment, that is not caused by sulfur dioxide. [1]

(d) Suggest one reason why fitting a catalytic converter to a car, which reduces the oxides of nitrogen (and carbon monoxide) in its exhaust, would NOT reduce the sulfur dioxide produced by the power station. [1]

Part (a): Source of oxides of nitrogen

Oxides of nitrogen (such as nitrogen monoxide) are produced inside car engines, where the high temperatures of combustion allow nitrogen and oxygen from the air to react together.

Part (b): The shared adverse effect

Both oxides of nitrogen and sulfur dioxide dissolve in atmospheric moisture and are converted into acidic compounds, so both gases contribute to acid rain.

Part (c): An effect specific to oxides of nitrogen

Both gases cause acid rain, and both can also irritate the lungs and airways, so respiratory problems are not unique to oxides of nitrogen. One further adverse effect that oxides of nitrogen cause but sulfur dioxide does not is:

Photochemical smog, oxides of nitrogen react in sunlight to contribute to the formation of photochemical smog.

Part (d): Why a catalytic converter cannot reduce the power station’s emissions

A catalytic converter is a small unit built into a car’s own exhaust system. It only reacts with the gases (such as oxides of nitrogen and carbon monoxide) that are formed inside that particular engine as it runs. The power station is an entirely separate, stationary source of pollution several kilometres away, so a catalytic converter fitted to a car has no way of treating gases released from the power station’s chimney at all.

Final answers

(a) Oxides of nitrogen come from car engines.
(b) Shared effect: acid rain.
(c) A further effect of oxides of nitrogen not caused by sulfur dioxide: photochemical smog.
(d) A catalytic converter only treats exhaust gases from the car it is fitted to; it cannot act on emissions from a separate, stationary source such as a power station.