11-CS-3 Engineering Management · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
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. Photochemical smog (ground-level ozone). In the presence of sunlight and volatile organic compounds, nitrogen oxides drive the formation of ground-level ozone and other oxidants. The key photochemical step is the photolysis of nitrogen dioxide and the subsequent formation of ozone:
The NO produced by combustion is oxidized to NO₂, which then photolyzes; the freed atomic oxygen combines with molecular oxygen to make ozone. In a clean atmosphere ozone would be destroyed again by NO, but VOCs intercept that cycle, allowing ozone to accumulate as urban smog that irritates the respiratory system and damages vegetation.
2. Acid rain (acid deposition). Nitrogen oxides are oxidized in the atmosphere to nitric acid, which returns to the surface as acidic precipitation:
The nitric acid so formed acidifies rain, lakes, soils, and forests, harming aquatic life and vegetation and corroding structures. (Sulfur oxides contribute the other major share of acid deposition.)
Optimize the existing system: (1) fit three-way catalytic converters, which chemically reduce NOₓ in the exhaust back to nitrogen ($2\,\text{NO} \rightarrow \text{N}_2 + \text{O}_2$ over the catalyst); and (2) use exhaust-gas recirculation (EGR) and combustion tuning to lower peak flame temperature, since thermal NOₓ formation rises steeply with temperature. Re-engineer the system: (3) replace the internal-combustion drivetrain with electric or hybrid vehicles, or switch to cleaner fuels (natural gas, hydrogen), removing tailpipe NOₓ at source. Redefine the problem: (4) reduce the need to travel by private vehicle through public transit, higher-density and mixed-use urban planning, cycling infrastructure, and telecommuting—cutting emissions by cutting vehicle-kilometres rather than treating each vehicle. These four span the escalating degrees of design freedom from tweaking the current system to eliminating the underlying demand.
Lightning (which fixes atmospheric N₂ and O₂ into NO at high temperature) and microbial activity in soils (nitrification and denitrification by bacteria release NO); forest fires and volcanic activity are further natural sources.
NO is a primary pollutant because it is emitted directly from the source (combustion) into the atmosphere. Ground-level ozone is a secondary pollutant because it is not emitted directly; it is formed within the atmosphere by chemical/photochemical reactions among primary pollutants (NOₓ and VOCs) in sunlight.
The same molecule is harmful or beneficial depending on where it is. At ground level ozone is a pollutant: it is a strong oxidant that irritates and damages the respiratory tract, harms crops, and degrades materials, and humans are directly exposed to it. In the stratosphere ozone is beneficial because it absorbs harmful solar ultraviolet radiation, shielding life at the surface—"good up high, bad nearby."
The principal federal statute is the Canadian Environmental Protection Act (CEPA). Air pollution is a shared federal–provincial responsibility: the environment is not assigned exclusively to either order of government under the Constitution, so the federal government legislates through CEPA (and toxic-substance and interprovincial/international matters) while the provinces regulate local emissions and permitting.
