11-CS-3 Engineering Management · December 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 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.
1) Acid rain: NO oxidizes to NO₂, which forms nitric acid:
The nitric acid acidifies precipitation, harming lakes, soils, and forests. 2) Ground-level ozone:
NO₂ photolyzes in sunlight, releasing atomic oxygen that forms ozone; with VOCs present the ozone accumulates as photochemical smog.
Precursors: ground-level ozone is a secondary pollutant formed from NOₓ and VOCs in sunlight, whereas stratospheric ozone forms naturally from the photolysis of O₂ by high-energy solar UV. Duration/location: ground-level ozone is transient, forming in the lower atmosphere on sunny days near sources, while stratospheric ozone is a persistent layer high in the atmosphere. Effects on humans: ground-level ozone is harmful—a respiratory irritant that damages lungs and vegetation—whereas stratospheric ozone is beneficial, shielding people from harmful UV radiation. The same molecule is a pollutant at ground level and a protector aloft.
The Montreal Protocol controls ozone-depleting substances: chlorofluorocarbons (CFCs), halons, hydrochlorofluorocarbons (HCFCs), carbon tetrachloride, and methyl bromide.
Mitigation example: generating electricity from wind or solar instead of fossil fuels, reducing greenhouse-gas emissions. Adaptation example: building sea walls or dykes to cope with rising sea levels and storm surge. A technology achieving both: urban trees / green roofs. They mitigate by sequestering carbon and reducing building energy use (cutting emissions), and they adapt by providing shade and evaporative cooling against heat waves and by absorbing stormwater to reduce urban flooding—so a single measure both lessens the cause of climate change and reduces vulnerability to its effects. (Reforestation similarly sequesters carbon while controlling flooding and erosion.)
Convert each mass to CO₂-equivalents (mass × GWP; GWP: CO₂ = 1, CH₄ ≈ 25, SF₆ ≈ 22,800). Using Pg = 10¹⁵ g, Tg = 10¹² g, Gg = 10⁹ g:
Ranked from greatest to least warming effect: CH₄ (2.70×10¹⁵) > CO₂ (1.75×10¹⁵) > SF₆ (2.74×10¹⁴). Although SF₆ is by far the most potent per gram, its tiny emitted mass gives it the smallest total effect here—illustrating that total impact depends on both potency and quantity.
