Trace atmospheric reactions and evaluate pollutant-control evidence.
Method and worked examples
High engine temperature enables N2+O2→2NO. Oxygen then oxidises NO: 2NO+O2→2NO2. Sunlight can split NO2 into NO and O, followed by O+O2→O3. Volatile-organic-compound reactions can enable ozone accumulation. Nitrogen oxides and ground-level ozone contribute to photochemical smog.
Tropospheric ozone harms respiratory tissues and vegetation; stratospheric ozone absorbs harmful ultraviolet radiation. A catalytic converter accelerates reactions such as 2NO+2CO →N2+2CO2. It reduces NO and CO but still produces CO2. Calculate removal as (inlet − outlet)/inlet ×100 when concentrations are compared at equal flow and matched conditions.
Example 1
Balance the reduction of NO by CO to N2 and CO2.
2NO+2CO →N2+2CO2. Both sides contain two N atoms, two C atoms and four O atoms. NO is reduced while CO is oxidised.
Example 2
A converter lowers NO from 500 ppm to 100 ppm under the same conditions. Find percentage removal.
Removal =500500−100×100=80%. This measures NO reduction only; other pollutants and operating conditions need separate evidence.
Watch out:Stratospheric ozone is protective; tropospheric ozone is a reactive pollutant harmful to health and vegetation.
Nitrogen oxides, ozone and catalytic converters | Year 12 Chemistry | Ascent Arcade