18-Env-A5 Air Quality and Pollution Control Engineering · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2013 — 04-Env-A5 / Air Quality and Pollution Control Engineering. 3 hours duration; closed book with a candidate-prepared 8.5×11 in double-sided aid sheet; Casio or Sharp approved calculator only. Any five (5) questions constitute a complete paper (the first five answers as they appear are marked); all seven are solved below for completeness. Each question is worth 20 marks with section marks shown in brackets.
Reference texts. Cooper & Alley, Air Pollution Control: A Design Approach (4th ed.); Wark, Warner & Davis, Air Pollution: Its Origin and Control (3rd ed.); Davis & Cornwell, Introduction to Environmental Engineering (6th ed.); Canadian Environmental Protection Act, 1999 (CEPA) and the Canadian Ambient Air Quality Standards (CAAQS) administered by Environment and Climate Change Canada.
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.
Strategy 1 — fuel reformulation. Reducing the aromatic (benzene precursor) content of gasoline and blending in oxygenates promotes more complete, cleaner combustion and directly lowers unburned benzene and polycyclic organic matter (products of incomplete combustion/pyrolysis of aromatics) in the tailpipe exhaust, independent of any after-treatment hardware.
Strategy 2 — exhaust after-treatment (three-way catalytic converter / diesel particulate filter). A properly functioning three-way catalyst oxidizes unburned hydrocarbons (including benzene and POM precursors) to CO2 and H2O over a platinum-group-metal catalyst bed at typical exhaust temperatures, while a diesel particulate filter physically traps POM-laden soot particles; both are supported by an inspection-and-maintenance program to catch degraded catalysts/filters before their removal efficiency falls off, since a poorly maintained fleet can emit disproportionately more air toxics than its numbers suggest.
A widely used physical-chemical technology is a packed-bed wet chemical scrubber using an oxidizing solution (e.g., dilute sodium hypochlorite or potassium permanganate) — commonly applied to rendering, meat-processing or brewery odour streams dominated by reduced-sulfur compounds (H2S, mercaptans) and amines. The fundamental principle is two-stage: (1) physical mass transfer — the odorous gas stream is contacted with a large gas–liquid interfacial area in the packing, driving the odorous compounds from the gas into the liquid film by concentration-gradient-driven absorption; (2) chemical oxidation — once dissolved, the oxidant chemically converts the malodorous, volatile reduced-sulfur/amine species into non-volatile, non-odorous oxidized products (e.g., sulfate) that stay in the recirculating liquor rather than re-volatilizing, which is what distinguishes this from a purely physical water scrubber (which would only transfer the odour problem from air to a smelly effluent).
The Western Climate Initiative (WCI) cap-and-trade system linking California and Québec is a clear example operating at the international level: each government sets a declining annual cap on total covered greenhouse-gas emissions, issues (via auction or free allocation) a matching number of tradeable emission allowances (carbon credits, one per tonne CO2e), and requires covered emitters to hold enough allowances to cover their actual emissions. A facility that reduces its emissions below its allocation can sell its surplus allowances to a facility elsewhere in the linked market that finds abatement more expensive, so the market finds the least-cost combination of reductions across both jurisdictions while the total emissions ceiling (the cap) still declines year over year — the same underlying mechanism used internationally by systems such as the EU Emissions Trading System.
