18-Env-A5 Air Quality and Pollution Control Engineering · December 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 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.
Benzene (from gasoline evaporation and exhaust). Regulatory strategy: Canada's Benzene in Gasoline Regulations (under CEPA) cap benzene content in gasoline at 1.5% by volume, cutting the toxic at its source in the fuel itself rather than relying solely on tailpipe aftertreatment. Relative cost: moderate — refiners must reformulate the gasoline blend (typically substituting other octane-boosting aromatics/oxygenates), a process-level cost absorbed across the whole fuel supply rather than a per-vehicle hardware cost.
Diesel particulate matter (from heavy-duty diesel exhaust). Regulatory strategy: Canadian on-road heavy-duty vehicle emission standards, harmonized with US EPA/California standards, require ultra-low-sulphur diesel (ULSD, ≤15 ppm S) together with a diesel particulate filter (DPF) and, for NOx, SCR aftertreatment on the vehicle. Relative cost: higher — DPF/SCR hardware adds significant per-vehicle capital cost plus an ongoing urea-reagent operating cost, and ULSD refining itself required substantial refinery capital investment, making this a costlier control path than the benzene fuel-specification approach.
A car coating or metal printing operation emits low-concentration, high-volume solvent-laden air (VOC-bearing odorous compounds from paints, thinners and inks) — the classic application for a regenerative thermal oxidizer (RTO). The fundamental principle is complete thermal destruction of the odorous organic compounds: process exhaust air is drawn through a bed of ceramic heat-exchange media pre-heated by the previous combustion cycle, raising the air to combustion temperature (typically 780–820 °C) with minimal supplemental fuel; at that temperature and with adequate residence time (≥0.5–1 s) in the combustion chamber, the VOC/odorous molecules are oxidized to CO2 and H2O, eliminating the odour rather than merely masking or diluting it. The hot, cleaned exhaust then passes through a second ceramic bed, transferring its heat back for the next incoming air charge (typically 95%+ thermal recovery), which is what makes an RTO economical to run continuously on a large, dilute exhaust stream compared with a simple non-regenerative afterburner.
A cap-and-trade programme sets a regulator-determined aggregate emission cap for a pollutant across all covered sources, then allocates or auctions tradeable emission allowances (each representing the right to emit one unit of the pollutant) totalling that cap. Sources whose control costs are low can reduce emissions below their allocation cheaply and sell the surplus allowances; sources whose control costs are high can instead buy allowances rather than install expensive controls immediately. Because trading concentrates the actual emission reductions at the sources where abatement is cheapest, the SAME aggregate reduction is achieved at lower total economic cost than a uniform, source-by-source technology mandate — and because the cap itself is fixed (and can be ratcheted down over successive compliance periods), the environmental outcome is guaranteed regardless of how the trading unfolds, unlike a pollution tax which fixes price but leaves the total emitted quantity uncertain.
