11-CS-3 Engineering Management · December 2019
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2019 — 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.
Ground-level (tropospheric) ozone: (i) formation—a secondary pollutant formed from NOₓ and VOCs reacting in sunlight; (ii) effects—harmful, a respiratory irritant damaging lungs and vegetation; (iii) human influence—humans increase it by emitting its precursors (vehicles, combustion). Stratospheric ozone: (i) formation—formed naturally by UV photolysis of O₂ high in the atmosphere; (ii) effects—beneficial, absorbing harmful solar UV; (iii) human influence—humans deplete it by releasing ozone-destroying substances (CFCs). Human activity worsens ozone in both places—adding it where harmful, removing it where beneficial.
Fine particulate matter, PM₂.₅ (particles 2.5 micrometres in diameter or smaller), is most harmful to health. Because they are so small, these particles evade the body's upper-airway defences and penetrate deep into the lungs (the alveoli), and can even enter the bloodstream, where they cause and aggravate respiratory and cardiovascular disease. Larger particles are mostly filtered out in the nose and throat, so the fine fraction poses the greatest health risk—which is why PM₂.₅ is regulated most stringently.
The two acids are sulfuric acid (H₂SO₄) from sulfur dioxide (SO₂)—mainly coal-fired power plants and smelters—and nitric acid (HNO₃) from nitrogen oxides (NOₓ)—mainly combustion in vehicles and power plants. Two effects: acidification of lakes/streams (killing fish and aquatic life) and damage to forests and soils (leaching nutrients), plus corrosion of structures.
Convert to CO₂e (CO₂ = 1, CH₄ = 25, N₂O = 298, SF₆ = 22,800); 9.3 t = 9,300 kg, 0.93 Mg = 930 kg:
Ranked by warming effect: N₂O (≈27,700) > CH₄ (23,250) > SF₆ (≈21,200) > CO₂ (9,300) kg CO₂e. Ranked by potency per unit mass (the GWP multipliers themselves) the order would instead be SF₆ (22,800) > N₂O (298) > CH₄ (25) > CO₂ (1); the CO₂e totals above measure each emission’s actual contribution to warming. Here the small masses of the high-GWP gases (N₂O, SF₆) outweigh the larger mass of CO₂—again showing that total impact depends on both mass and potency.
Incoming short-wave solar radiation (visible/UV) passes through the atmosphere and warms the surface, which re-radiates energy as long-wave infrared. CO₂ (and other greenhouse gases) is transparent to the incoming sunlight but absorbs and re-emits the outgoing infrared, trapping heat in the lower atmosphere. Adding CO₂ increases the infrared absorbed and returned to the surface, so the planet warms to restore radiative balance—the enhanced greenhouse effect.
