18-Env-A5 Air Quality and Pollution Control Engineering · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2014 — 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 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.
Given. A fuel is burnt with the stoichiometric amount of oxygen (supplied as air):
| Quantity | Symbol | Value |
|---|---|---|
| Fuel quantity | $n_{fuel}$ | 100 mol, formula C8H17 (as printed) |
| Sulphur content of fuel | — | 3% by mass |
| Oxidant | — | Stoichiometric O2, supplied as air (21% O2, 79% N2 by volume) |
Find. The SO2 concentration in the flue gas (ppmv and % by volume).
Approach. Find the moles of sulphur from the 3%-by-mass fuel composition, balance the stoichiometric combustion equation for the hydrocarbon, add the O2 consumed oxidizing S to SO2, bring in N2 from the air, then divide moles SO2 by total moles of flue gas.
| Quantity | Value |
|---|---|
| Moles of sulphur, $n_S$ | 10.59 mol |
| Total O2 required (stoichiometric) | 1236 mol |
| Total flue gas produced | 6309 mol |
| SO2 concentration | ≈ 1679 ppmv (0.168% v/v) |
Secondary air pollutants are not emitted directly from the stack; they form in the atmosphere when primary combustion products react further, usually driven by sunlight. SO2 oxidizes slowly to SO3 and, with atmospheric moisture, to sulfate aerosol (H2SO4 mist) — a major contributor to acid deposition and fine-particle haze. NOx and volatile organic compounds released alongside SO2 undergo photochemical reactions catalyzed by sunlight and hydroxyl radicals to form ground-level ozone (O3) and peroxyacetyl nitrate (PAN), the defining pollutants of photochemical smog. Because secondary pollutant formation depends on residence time, sunlight intensity and the presence of co-pollutants, its severity is often worse tens to hundreds of kilometres downwind of the source rather than at the stack itself.
Radon (222Rn) is a naturally occurring radioactive noble gas that seeps from soil and rock (particularly uranium-bearing bedrock, common across parts of Canada) through foundation cracks and sumps. Its short-lived decay progeny attach to airborne dust and, once inhaled, irradiate lung tissue; long-term exposure is the second leading cause of lung cancer after smoking. Formaldehyde and other VOCs off-gas continuously from pressed-wood products, adhesives, paints and new furnishings; they cause eye/respiratory irritation, headaches, and some (formaldehyde itself) are classified as human carcinogens at elevated chronic exposure.
Two engineering controls: (1) mechanical ventilation with heat recovery (HRV/ERV) continuously dilutes indoor air with outdoor air while recovering the energy penalty, directly lowering both radon and VOC concentrations; for radon specifically, sub-slab depressurization (a fan-driven vent pipe drawing soil gas from beneath the foundation before it enters the building) is the standard mitigation. (2) Source control — specifying low-VOC/no-added-urea-formaldehyde materials and allowing off-gassing (bake-out) before occupancy — reduces the emission rate itself rather than diluting after the fact.
Selecting formaldehyde released from an industrial operation (e.g., a resin or wood-products plant): Health impacts — (1) it is a potent respiratory and eye irritant even at low ppm concentrations, aggravating asthma and causing upper-airway inflammation in nearby residents; (2) IARC classifies formaldehyde as a human carcinogen (nasopharyngeal cancer) under chronic exposure. Ecological impacts — (1) as a highly reactive VOC it is an efficient ozone precursor, contributing disproportionately to downwind photochemical smog formation relative to its emission mass; (2) it is phytotoxic at elevated concentrations, damaging leaf tissue and reducing photosynthetic productivity in vegetation near the release point.
