11-CS-3 Engineering Management · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2018 — 11-CS-3 Sustainability, Engineering and the Environment. Open book; non-communicating 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.
Formation: ground-level ozone is a secondary pollutant formed from NOₓ and VOCs in sunlight near the surface; stratospheric ozone forms naturally from the photolysis of O₂ by high-energy solar UV. Effects: ground-level ozone is harmful—a respiratory irritant that damages lungs and vegetation; stratospheric ozone is beneficial, absorbing harmful UV. Human influence: humans increase ground-level ozone by emitting its NOₓ and VOC precursors (combustion, vehicles), whereas humans deplete stratospheric ozone by emitting ozone-destroying substances (CFCs). So human activity worsens ozone in both places—adding it where it is harmful and removing it where it is beneficial: "bad nearby, good up high."
NOₓ denotes the nitrogen oxides NO and NO₂ collectively. The nitrogen in combustion NOₓ comes chiefly from the atmospheric nitrogen (N₂) in the combustion air: at the high flame temperatures, atmospheric N₂ and O₂ combine to form NO ("thermal NOₓ"); a smaller contribution ("fuel NOₓ") comes from nitrogen chemically bound in the fuel. Two natural sources: lightning (which fixes atmospheric nitrogen) and soil microbial activity (nitrifying/denitrifying bacteria); wildfires are a further natural source.
The Sun emits short-wave ultraviolet and visible radiation that passes through the atmosphere and warms the surface; the surface re-radiates long-wave infrared. Greenhouse gases are transparent to the incoming UV/visible but absorb and re-emit the outgoing IR, trapping heat. A higher greenhouse-gas concentration absorbs more outgoing IR, so the surface warms to restore radiative balance—warming the planet.
Convert each to CO₂-equivalents (CO₂e = mass × GWP; CH₄ = 25, N₂O = 298, SF₆ = 22,800). Note 0.040 Mg = 40 kg:
Ranked by warming effect: SF₆ (≈1.0×10⁶ kg CO₂e) ≫ N₂O (1,001 kg) ≈ CH₄ (1,000 kg). The SF₆, though a modest mass, dwarfs the others because of its extreme GWP; the methane and nitrous-oxide contributions are nearly equal here (their differing masses offset by their differing GWPs). Ranked by the gases' own GWP per unit mass, the order is the same: SF₆ (22,800) > N₂O (298) > CH₄ (25).
Mitigation (reduce the cause): (1) renewable electricity (wind/solar) replacing fossil generation; (2) energy efficiency and electrified transport (heat pumps, EVs) cutting fuel use—both reduce greenhouse-gas emissions. Adaptation (manage the effects): (1) sea walls, dykes, and flood defences against rising seas and storm surge; (2) drought-resistant crops and improved water storage/irrigation to cope with changing rainfall. Mitigation limits future warming; adaptation reduces vulnerability to warming already underway.
