11-CS-3 Engineering Management · May 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2017 — 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.
The slogan refers to ozone (O₃). It captures the fact that the same molecule is harmful or beneficial depending on where it is, which is best understood through hazard and exposure. Ozone is always intrinsically hazardous (a strong, reactive oxidant). "Bad nearby": at ground level, humans and plants are directly exposed to it, so its hazard is realized as harm—respiratory irritation and vegetation damage. "Good up high": in the stratosphere, ozone is out of reach of direct human exposure, and there its reactivity does beneficial work by absorbing harmful solar UV. So the risk (hazard × exposure) is high at ground level, where exposure is high, and effectively protective aloft, where humans are not exposed to it but benefit from its UV-blocking.
1. Ground-level ozone:
NOₓ photolyzes in sunlight to release atomic oxygen that forms ozone, which (with VOCs) accumulates as smog. 2. Nitric acid / acid deposition (or PAN):
NO₂ is oxidized to nitric acid in the atmosphere, forming acid rain—a secondary pollutant not emitted directly. (Peroxyacetyl nitrate, PAN, formed from NO₂ and organic radicals, is an equally valid second secondary pollutant.)
The Sun emits short-wave ultraviolet and visible radiation, which passes through the atmosphere and warms the surface. The warmed surface re-radiates energy as long-wave infrared. Greenhouse gases are transparent to the incoming UV/visible but absorb and re-emit the outgoing IR, returning heat to the surface. A higher greenhouse-gas concentration absorbs more outgoing IR, trapping more heat and forcing the surface to warm to restore radiative balance—hence a warmer planet.
Convert to CO₂e (CO₂ = 1, CH₄ = 25, PFC ≈ 10,000 representative, range 7,390–12,200):
Ranked from greatest to least: PFCs (≈1.7×10¹⁵) > CH₄ (1.25×10¹⁵) > CO₂ (1.20×10¹⁵). (The PFC result depends on the specific compound's GWP—using the low end 7,390 gives ≈1.28×10¹⁵, still above CH₄; using the high end it is clearly largest—so PFCs rank highest across the plausible range.)
Mitigation reduces the cause of climate change, by cutting greenhouse-gas emissions or enhancing carbon sinks, so that less future warming occurs. Example: replacing coal-fired generation with wind or solar power. Electricity is produced without burning fossil carbon, so the CO₂ that coal would have emitted (roughly 0.9–1 t CO₂ per MWh) never enters the atmosphere. A carbon price, such as Canada's federal fuel charge and output-based pricing system, pursues the same goal as a policy instrument: it makes emitting costly, so the low-carbon options win.
Adaptation reduces vulnerability to climate change that is already happening or is unavoidable. It accepts the changed climate and limits the damage. Example: raising dikes and adopting higher flood-construction levels in a low-lying coastal community such as those in the Fraser River delta. Higher, stronger dikes physically hold back the higher sea level and storm surge, protecting people and property. Other examples include drought-tolerant crops, larger storm sewers sized for more intense rainfall, and FireSmart vegetation management around communities.
The key difference is that mitigation attacks the driver and brings global benefits over decades, whereas adaptation manages the consequences and brings local benefits now. Both are needed, because the warming already committed cannot be avoided by mitigation alone.
