11-CS-3 Engineering Management · May 2019
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2019 — 11-CS-3 Sustainability, Engineering and the Environment. Closed book; approved Casio or Sharp 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 — "bad nearby": formation—it is not emitted directly but is a secondary pollutant formed when nitrogen oxides (NOₓ) and volatile organic compounds (VOCs) react in sunlight ($\text{NO}_2 + h\nu \rightarrow \text{NO} + \text{O}$, then $\text{O} + \text{O}_2 \rightarrow \text{O}_3$), so it peaks on hot, sunny afternoons; effects—harmful: a strong oxidant that inflames airways, aggravates asthma, reduces lung function, and damages crops and forests (the main ingredient of summer smog); human influence—humans increase it by emitting the precursors (vehicle and combustion NOₓ, VOCs from fuels and solvents).
Stratospheric ozone — "good up high": formation—formed naturally 15–35 km up when short-wave UV splits O₂ into oxygen atoms that combine with O₂; effects—beneficial: it absorbs UV-B and UV-C that would otherwise cause skin cancer, cataracts, and damage to crops and ecosystems; human influence—humans have depleted it by releasing CFCs, halons and other ozone-depleting substances whose chlorine and bromine destroy ozone catalytically (the "ozone hole"); the Montreal Protocol is now allowing slow recovery. Human activity thus worsens ozone in both places—adding it where it harms and removing it where it protects.
A primary pollutant is emitted directly into the air from a source in the form in which it causes harm—example: sulfur dioxide (SO₂) from a coal-fired power plant (others: CO, NO, primary particulates). A secondary pollutant is not emitted directly but forms in the atmosphere by chemical reactions among primary pollutants and natural constituents—example: ground-level ozone, formed from NOₓ and VOCs in sunlight (others: sulfuric/nitric acid aerosol, secondary PM₂.₅). The distinction matters for control: secondary pollutants must be controlled by limiting their precursors, often far from where the pollutant appears.
The two main acids are sulfuric acid (H₂SO₄), formed from sulfur dioxide (SO₂) whose main source is burning sulfur-bearing coal (power plants) and smelting sulfide ores, and nitric acid (HNO₃), formed from nitrogen oxides (NOₓ) whose main source is high-temperature combustion in vehicles and power plants. Two effects: (1) acidification of lakes and streams, mobilizing aluminum and killing fish and aquatic life (notably on the poorly buffered Canadian Shield); (2) damage to forests and soils, leaching calcium and magnesium and stressing trees. Corrosion of buildings, monuments and metal structures is a third.
The question says "three emissions" but lists four; all four are evaluated. Convert to kilograms (23.4 t = 23,400 kg, 0.932 Mg = 932 kg, 932 g = 0.932 kg) and multiply by the Table 2.3 GWP:
Ranked by warming effect: N₂O (≈23,480) > CO₂ (23,400) > CH₄ (23,300) > SF₆ (≈21,250) 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). Remarkably, the four emissions are within about 10% of one another despite masses ranging from under 1 kg to over 23 tonnes—their very different GWPs nearly offset their very different masses.
Mitigation (reducing the cause): replacing fossil-fuel generation with renewable electricity such as wind or solar, which cuts CO₂ emissions. Adaptation (coping with the effects): raising dykes and sea walls, or upsizing storm sewers and culverts for more intense rainfall, to protect communities from flooding that climate change is making more frequent.
