Outline the conditions and processes that lead to the formation of photochemical smog.

Evaluate the use of biotic indices compared with direct methods of measuring pollution.

Pollution management strategies may be applied at any of the three levels identified in the diagram below:

With reference to acid deposition, evaluate the political and economic advantages of applying management strategies at the levels of production and impact of the pollutant.

Conditions for photochemical smog [2 max]:
local topography/valleys/lack of wind reducing dispersal of pollutants;
temperature inversion;
high population density/fossil fuel use/traffic density;
high amounts/intensity of solar radiation / sunny;

Processes forming photochemical smog [3 max]:
largely photochemical reactions / reactions increased by sunlight;
use of fossil fuels releases hydrocarbons through evaporation / nitrogen oxide/NO through combustion;
emission of suspended particles catalyse photochemical reactions;
NO reacts with oxygen to form NO₂;
Sunlight promotes the formation of O atoms from NO₂;
… that combine with O₂ to form ozone (the main secondary pollutant in photochemical smog);
hydrocarbons react with NO₂, O₂ and light to form aldehydes & PAN;

[4 max]

Award 1 max for distinguishing biotic indices and direct methods.
biotic indices measure the quality of ecosystem rather than quantity of pollutant / biotic indices are dependent on the tolerance/diversity/abundance of organisms, not concentration/toxicity/identity of pollutant;

They are advantageous in that:
they measure the widespread effects/impacts of pollutants on the system;
…which is more significant than the quantity/concentration/nature of the pollutant;
they are specific to the characteristics of a given habitat;
they will address the combined/integrated impact of many pollutants/human activities;
Avoids use of expensive instrumentation;

They are disadvantageous in that:
they do not identify the specific pollutants;
… leaving the possible source of pollution unclear;
the quality of a given community may vary for reasons other than pollution / initial quality may not be known;
may require counting/identification of organisms which are difficult to collect/identify (eg lichen, invertebrates) / prone to human error;

Award [4 max] for responses that give only advantages, or only disadvantages.

[6 max]

Level of “producing”. Award [1 max] for outlining such management: relevant to acid rain:
Eg management can be applied at level of producing by reducing use of fossil fuels/ switching to alternative energy sources;

political advantages/disadvantages:
it may not be popular to impose limits on use of fossil fuels in certain societies;
but it does address root cause of problem;
and political factors have the advantage of generating laws/incentives;
in democratic societies such management may have strong influence on voting/political support;
may gain international support for an issue that often crosses national boundaries;

economic advantages/disadvantages:
it may be very costly to switch to alternative energy sources;
could be long-term economic benefit in this for countries importing fuel;
would be economically beneficial in context of international C-trading;
may gain volunteer support from community/NGOs that make management more cost effective;

Level of “impact”. Award [1 max] for outlining such management:
Eg. management can be applied at level of impact by liming of water bodies/restoration of natural communities;

political advantages/disadvantages:
it may be popular because it allows use of fossil fuels to continue;
and restores aesthetic qualities of environment;
but may conflict with the increasing “green”/ecocentric sector of many societies;

economic advantages/disadvantages:
avoids cost of switching from fossil fuel technologies;
liming and restoration may be very costly;
could be mitigating benefits eg sustainable goods/services of restored systems;
provides for environmental projects attractive to local community/NGO voluntary support;

Alternative points of equivalent validity, significance and relevance to those given, should be credited.

Award [5 max] for responses that address only one level of management, or only political, or only economic, factors.

[8 max]

Expression of ideas: [2 max]

Generally mediocre. Most candidates were able to make one or two specific points, but rarely more.

Generally weak. While most candidates gave a thorough description of biotic indices with examples, few addressed the key focus of the question that was a comparative evaluation with direct methods.

Generally OK, but responses were very mixed in quality. Those candidates that clearly referred to a management strategy relevant to acid deposition at each of the required levels usually went on to give clear political/economic advantages. Those that floundered at this first step, however, often gained very little further credit.