Although the use of harmful CFCs is being phased out, suggest why these compounds are expected to remain in the atmosphere for the next 80–100 years.

Discuss one advantage and two disadvantages of using hydrocarbons as alternatives to CFCs.

Advantage:

Disadvantages:

CFCs have a low reactivity/strong bonds/are highly stable;

CFCs/radicals they produce/ Cl have high residual time in atmosphere;

some (developing) countries still producing/consuming CFCs / slower phase-out of CFCs;

harmful CFCs are still present in expanded polystyrene and old refrigerators and have yet to leak into the atmosphere;

slow mixing between lower atmosphere/troposphere and upper atmosphere/stratosphere;

Advantage:

do not damage the ozone layer;

decompose less readily (than CFCs);

cheaper than CFCs;

Disadvantages:

flammable;

both contribute to global warming/greenhouse gases/absorb IR radiation;

The equations required in the first part of this question were amongst the best known in the examination; the result of memorisation? A number of candidates incorrectly gave the reaction between two oxygen atoms as a significant process in ozone depletion and some discussed the way CFCs accelerate the depletion, rather than giving the natural processes asked for. Relatively few could give correct reasons for the persistence of CFCs in the atmosphere, but advantages and disadvantages of were relatively widely known.

The equations required in the first part of this question were amongst the best known in the examination; the result of memorisation? A number of candidates incorrectly gave the reaction between two oxygen atoms as a significant process in ozone depletion and some discussed the way CFCs accelerate the depletion, rather than giving the natural processes asked for. Relatively few could give correct reasons for the persistence of CFCs in the atmosphere, but advantages and disadvantages of were relatively widely known.