11-CS-3 Engineering Management · May 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2015 — 11-CS-3 Sustainability, Engineering and the Environment. Closed book; approved calculator permitted. Any four questions constitute a complete paper; all questions are of equal value (25 marks each).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Nitrogen fixation: N₂ → NH₃ or NO (reactants N₂ + H₂ or N₂ + O₂). Nitrification: NH₄⁺ + O₂ → NO₂⁻ → NO₃⁻ (bacterial oxidation of ammonium to nitrate). Denitrification: NO₃⁻ → N₂ (+ N₂O) under anaerobic conditions, returning nitrogen to the atmosphere. The ratio of human to natural nitrogen fixation is now roughly 1:1—human activity (chiefly the Haber–Bosch process for fertilizer, plus combustion and legume cultivation) fixes approximately as much reactive nitrogen as all natural processes combined, so to the nearest integer the ratio is about 1. This doubling of the global nitrogen-fixation rate is a profound human alteration of a natural biogeochemical cycle.
Combustion NO oxidizes to NO₂, which photolyzes in sunlight to release atomic oxygen that forms ozone (VOCs let it accumulate). Ground-level ozone is a pollutant—a strong oxidant that harms lungs and vegetation where people are exposed—whereas stratospheric ozone is beneficial, absorbing harmful solar UV. "Good up high, bad nearby."
The Sun emits short-wave visible and ultraviolet radiation, which passes through the atmosphere and warms the surface; the surface re-radiates long-wave infrared. Greenhouse gases are transparent to the incoming visible/UV but absorb and re-emit the outgoing infrared, trapping heat; adding greenhouse gases enhances this effect and warms the planet.
Mitigation reduces the cause—cutting emissions or enhancing sinks (e.g. renewable energy). Adaptation adjusts to effects already occurring (e.g. sea walls, drought-resistant crops). Mitigation attacks the source; adaptation manages the consequences.
CO₂e expresses a greenhouse gas's warming effect as the mass of CO₂ causing the same warming (mass × global warming potential). Ranked by GWP: SF₆ (≈23,500) > N₂O (≈265) > CH₄ (≈28) > CO₂ (1). Despite the lowest GWP, CO₂ adds the most CO₂e from human activity because it is emitted in vastly greater quantities.
