Four air pollutants — source and effect
Carbon monoxide () — incomplete combustion; toxic, binds to haemoglobin, blocking oxygen transport. Sulfur dioxide () — burning sulfur fuels (and volcanoes); acid rain and lung damage. Oxides of nitrogen () — nitrogen and oxygen react at high temperatures in engines; acid rain and respiratory irritation. Particulates (soot) — diesel and solid fuels; damage the lungs.
(Extended) Catalytic converters — what they remove
(Extended) A catalytic converter uses a Pt/Rh/Pd catalyst on a honeycomb (large area) to treat three pollutants. CO oxidised to : . Hydrocarbons oxidised to and water. reduced to nitrogen: . It does not remove (it makes it) or . The catalyst is unchanged.
Greenhouse gases and climate change
Carbon dioxide () and methane () are the main greenhouse gases. Earth absorbs solar radiation, re-emitting infrared (IR); greenhouse-gas molecules absorb it and re-emit it, warming Earth. Human activity raises (fossil fuels, deforestation) and (livestock, landfill). Photosynthesis removes . Consequences: rising seas, extreme weather, ecosystem disruption.
Drawn from real examiner reports.
NOx source is hot engines, not "factories"
"Factories" or "burning fuels" score nothing for the source — CO and do too. What is specific to is high temperature: in a car engine, nitrogen and oxygen react, . Name the reactants (N and O from air) and the engine's high temperature.
Sources of oxides of nitrogen given too vaguely ('factories'); high-temperature combustion in car engines required. (W22 P31 Q5(d)(i); W22 P32 Q5(b)(i); S23 P31 Q8(b)(i))
Do not swap the pollutants' effects
Each pollutant needs its own effect. Only carbon monoxide binds to haemoglobin, stopping oxygen transport — not or . Acid rain comes from and (which form acids), not . Particulates damage the lungs and can carry carcinogens. Vague "affects health" earns nothing — name the specific harm.
Adverse effects of NOx confused with those of other pollutants; vague 'affects health' penalised. (W22 P31 Q5(d)(ii); W22 P32 Q5(b)(ii); S23 P31 Q8(b)(ii))
(Extended) Converter makes CO2, not removes it
(Extended) Saying a catalytic converter "reduces emissions" is wrong — it does the opposite. It oxidises CO to and burns hydrocarbons to and water, so it produces . It removes CO, unburned hydrocarbons and ; (a greenhouse gas) and pass through unchanged.
Carbon monoxide vs carbon dioxide
and differ. Carbon monoxide () — toxic, from incomplete combustion; binds to haemoglobin, can be fatal. Carbon dioxide () — from complete combustion; not toxic normally but a greenhouse gas driving climate change. Swapping and changes the answer.
SO2 comes from sulfur in fuel, not N2 + O2
Sulfur dioxide forms when sulfur impurities in a fuel (coal, crude-oil fractions) are burned: ; volcanoes too. It does not come from nitrogen and oxygen reacting (that gives ), nor from incomplete combustion (that gives ). Because sulfur is an impurity, low-sulfur fuel cuts at source.
CO2 absorbs IR — it does not block sunlight
does not "trap heat" by blocking sunlight. Solar radiation passes through and is absorbed by Earth, re-emitted as infrared (IR). Greenhouse-gas molecules absorb this IR and re-emit it, some back to the surface. An answer needs IR absorbed and re-emitted; " blocks the Sun's rays" is wrong.
Give the paired source and effect
Source/effect: — incomplete combustion / haemoglobin; — sulfur fuels / acid rain, lungs; — high-temp combustion / acid rain, respiratory; particulates — diesel/soot / lungs. Avoid "factories"/"affects health".
(Extended) Answering catalytic-converter questions
(Extended) Four points: removes three pollutants (CO, unburned hydrocarbons, ); large surface speeds the reactions; CO and hydrocarbons oxidised, reduced; catalyst unchanged. Never write "reduces " — it produces it.
(Extended) Explaining the greenhouse effect
(Extended) Chain: solar radiation absorbed by Earth → re-emitted as infrared → absorbed by / → re-emitted back → surface warms. Human link: fossil fuels/deforestation raise ; photosynthesis removes it.
Air pollutant — a substance in the air at a concentration that causes harm to living organisms or the environment.
Greenhouse gas — a gas that absorbs infrared (IR) radiation emitted by the Earth's surface and re-emits it, warming the lower atmosphere. The principal greenhouse gases are carbon dioxide () and methane ().
Greenhouse effect — the natural process by which greenhouse gases in the atmosphere retain heat energy from the Sun, keeping the Earth's surface warmer than it would otherwise be.
Enhanced greenhouse effect — the increase in the greenhouse effect caused by human activities that raise concentrations of and , leading to global warming and climate change.
Catalyst — a substance that increases the rate of a chemical reaction and is chemically unchanged at the end of the reaction. In a catalytic converter the catalyst is a platinum/rhodium/palladium metal alloy.
Name the FOUR air pollutants that students must know for Cambridge 0620.
Coal contains sulfur as an impurity. When coal burns in excess oxygen, the sulfur reacts to form sulfur dioxide.
Write a balanced symbol equation for this reaction. Include state symbols.
