11-CS-3 Engineering Management · December 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 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.
NO is formed in high-temperature combustion (vehicle engines, boilers) and is oxidized to NO₂; in the presence of VOCs, peroxy radicals (RO₂) convert NO back to NO₂ without consuming ozone, so the cycle regenerates NO₂ and ozone builds up through a sunny day. NO₂ photolyzes in sunlight to release atomic oxygen that forms ozone (accumulating with VOCs as smog). Ground-level ozone is a pollutant—a strong oxidant harming lungs and vegetation where people are exposed—whereas stratospheric ozone is beneficial, absorbing harmful solar UV. CFCs (chlorofluorocarbons) are inert synthetic compounds (former refrigerants and propellants); released to the atmosphere, they drift to the stratosphere where UV frees chlorine atoms that catalytically destroy ozone ($\text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2$; $\text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2$), each chlorine atom destroying thousands of ozone molecules—thinning the protective ozone layer.
Two natural sources: windblown dust/soil and sea-salt spray; volcanic ash, wildfire smoke, and pollen are others. Two anthropogenic sources: combustion of fossil fuels (vehicle exhaust, coal-burning power plants) and industrial processes/construction (dust, grinding, and—secondarily—particles formed from SO₂ and NOₓ emissions). PM₂.₅ means fine particulate matter 2.5 micrometres or less in diameter; it is a health concern because these fine particles penetrate deep into the lungs (and can enter the bloodstream), causing respiratory and cardiovascular disease.
Sulfur dioxide (SO₂) and nitrogen oxides (NOₓ)—which are oxidized in the atmosphere to sulfuric and nitric acids, respectively.
Convert to CO₂-equivalents (N₂O = 298, CH₄ = 25, SF₆ = 22,800; note 605 g = 0.605 kg):
Ranked by warming effect: N₂O (≈14,000) > SF₆ (≈13,800) > CH₄ (13,500). The three are strikingly close despite vastly different masses (47 kg, 0.605 kg, and 540 kg)—their differing GWPs nearly offset their differing masses, a neat illustration of the CO₂-equivalent concept.
Mitigation: (1) renewable electricity replacing fossil generation; (2) energy efficiency and electrified transport (heat pumps, EVs)—both cut emissions. Adaptation: (1) sea walls/dykes against rising seas; (2) drought-resistant crops and improved water storage against changing rainfall. Mitigation limits future warming; adaptation reduces vulnerability to warming already occurring.
