11-CS-3 Engineering Management · May 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2014 — 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.
Nitrogen fixation is the conversion of inert atmospheric nitrogen gas (N₂), which most organisms cannot use, into reactive nitrogen compounds (such as ammonia or nitrogen oxides) that are biologically or chemically available. Two technological ways: the Haber–Bosch process, which combines nitrogen and hydrogen under high temperature and pressure to make ammonia for fertilizer, $\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3$; and high-temperature combustion (in engines and furnaces), which fixes nitrogen as nitric oxide, $\text{N}_2 + \text{O}_2 \rightarrow 2\text{NO}$. Two natural ways: lightning, whose intense energy fixes atmospheric nitrogen, $\text{N}_2 + \text{O}_2 \rightarrow 2\text{NO}$; and biological fixation by nitrogen-fixing bacteria (e.g. Rhizobium in legume root nodules), which enzymatically reduce nitrogen to ammonia, $\text{N}_2 + 8\text{H}^+ + 8e^- \rightarrow 2\text{NH}_3 + \text{H}_2$.
1. Photochemical smog (ground-level ozone):
Combustion NO oxidizes to NO₂, which photolyzes in sunlight to release atomic oxygen that forms ozone; with VOCs present, ozone accumulates as a respiratory-irritant smog. 2. Acid rain:
NOₓ oxidizes to nitric acid, which acidifies rain, lakes, and soils, harming aquatic life and forests.
Incoming short-wave solar radiation warms the Earth's surface, which re-radiates long-wave infrared. Greenhouse gases such as CO₂ are transparent to the incoming sunlight but absorb and re-emit the outgoing infrared, trapping heat in the lower atmosphere and warming the surface. Adding CO₂ enhances this natural greenhouse effect, driving global warming.
Humans perturb the carbon cycle mainly through fossil-fuel combustion (releasing geologically stored carbon as CO₂) and land-use change, chiefly deforestation (releasing carbon stored in vegetation and reducing uptake). Of these, fossil-fuel combustion currently adds far more CO₂—roughly 30–35 Gt CO₂/yr versus a few Gt from land-use change.
Methane (CH₄)—from livestock, rice paddies, landfills, and natural-gas leakage; and nitrous oxide (N₂O)—from nitrogen fertilizers and combustion.
Mitigation means acting to reduce the cause of climate change—cutting greenhouse-gas emissions or enhancing sinks—so as to limit the eventual warming. Example: replacing fossil-fuel generation with renewable energy, or capturing and storing carbon. Adaptation means adjusting to the effects of climate change that are already occurring or unavoidable, to reduce harm. Example: building sea walls and flood defences against rising sea levels, or planting drought-resistant crops. In short, mitigation attacks the problem's source while adaptation manages its consequences; a sound climate strategy uses both.
