18-Env-A5 Air Quality and Pollution Control Engineering · December 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2015 — 04-Env-A5 / Air Quality and Pollution Control Engineering. 3 hours duration; closed book with a candidate-prepared 8½×11 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 the CCME and 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.
Two examples: benzene (present in gasoline vapour and combustion exhaust, a known human carcinogen) and mercury (emitted from coal-fired power generation, a persistent, bioaccumulative neurotoxin).
Determining the standard. For a non-threshold carcinogen such as benzene, the ambient standard is typically risk-based: a cancer unit-risk (slope) factor derived from toxicological/epidemiological dose–response data is applied to a target acceptable lifetime excess-cancer-risk level (commonly in the range of 1-in-100,000 to 1-in-1,000,000), then back-calculated to an allowable ambient concentration. For a threshold toxicant such as mercury, the standard is derived from a reference concentration (RfC) — the dose below which no appreciable adverse effect is expected in toxicological studies, with uncertainty/safety factors applied. In Canada these become Canadian Ambient Air Quality Standards (CAAQS), set jointly by federal, provincial and territorial governments through the CCME and informed by Health Canada risk assessment; hazardous air pollutants of this kind are also listed as toxic substances under Schedule 1 of the Canadian Environmental Protection Act, 1999 (CEPA).
Enforcement. Regulators require permitted facilities to install continuous emission monitoring systems (CEMS) or undergo periodic stack testing, and to report releases (e.g. to the National Pollutant Release Inventory); operating permits carry enforceable emission limits, and an independent ambient monitoring network confirms real-world air quality against the CAAQS. Non-compliance triggers escalating enforcement — compliance orders, administrative monetary penalties, and prosecution under CEPA or the applicable provincial Environmental Management Act.
Example technology: a biotrickling filter/biofilter — the foul air stream is passed through a packed bed of organic media (compost, wood chips or an inert structured packing) that supports a colony of sulfur-oxidizing bacteria. H2S in the air stream absorbs into the moist biofilm coating the media and is biologically oxidized to sulfate, permanently removing the odour compound rather than merely diluting or masking it.
Key design strategy. Size the bed for an adequate empty-bed residence time (EBRT, typically 15–60 seconds depending on H2S loading), so the contaminated air is in contact with the biofilm long enough for the biological oxidation reaction to reach completion before the treated air exits — and maintain the bed's moisture content (via a recirculating trickle or humidification system), since the biofilm loses activity and the microbial population declines if the bed is allowed to dry out. Under-sizing EBRT and letting the bed dry are the two most common causes of odour breakthrough in the field.
A cap-and-trade system sets an overall regulatory cap on total emissions of a pollutant across a jurisdiction or sector, then allocates or auctions tradeable emission allowances summing to that cap. Sources that can reduce emissions cheaply do so and sell their surplus allowances; sources facing high abatement costs buy allowances to cover the emissions they cannot economically eliminate. This lets the market find the least-cost combination of reductions across all sources to hit the aggregate cap, rather than mandating an identical percentage cut from every source regardless of its abatement cost.
Applied to Canada–U.S. transborder pollution: sulfur and nitrogen oxides (acid-rain precursors) and greenhouse gases routinely cross the border on prevailing westerly winds, so a purely domestic Canadian cap has limited effect if U.S. border-state emissions continue unabated (and, symmetrically, Canadian emissions reaching the U.S. Northeast are outside U.S. domestic control). Linking cap-and-trade systems across the border — as was done historically for SO2 under the 1991 Canada–U.S. Air Quality Agreement, and more recently for greenhouse gases through the linkage between Quebec's cap-and-trade system and California/other Western Climate Initiative jurisdictions — lets reductions happen wherever they are cheapest on either side of the border, while still lowering the total transboundary pollutant load reaching the other country: a facility in a U.S. border state can transact allowances with a linked Canadian program, so total North American emissions fall even though the two countries' individual caps and programs differ.
