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.
The reference automatic method for continuous SO2 monitoring is pulsed UV fluorescence. A pulsed UV lamp excites SO2 molecules in a sample cell at a wavelength (~214 nm) that promotes them to an excited electronic state; the molecules relax by emitting fluorescent light at a longer wavelength (~330 nm), and a photomultiplier tube measures that fluorescent intensity, which is linearly proportional to SO2 concentration over the instrument's calibrated range. Advantages: continuous, real-time (sub-minute) readings suitable for regulatory compliance and for tracking short-term exceedances; high sensitivity (ppb-level detection) and good specificity, since few other common flue-gas species fluoresce at the same wavelength. Limitations: aromatic hydrocarbons can cause a positive interference by also fluorescing in the same band, requiring an upstream hydrocarbon "kicker" scrubber in dirty industrial applications; the instrument also needs regular zero/span calibration with certified gas standards and periodic maintenance of the UV lamp and optics to maintain accuracy.
(1) Particle size distribution (PSD). Because collection-device efficiency curves are strongly size-dependent (the cyclone/ESP efficiency calculations in Questions 6–7 below), knowing the mass or number distribution across size fractions (PM10, PM2.5, and finer) is the single most important input to sizing and selecting a control device.
(2) Chemical composition. Whether the particulate is primarily inorganic (fly ash, metal oxides, sulfate/nitrate salts) or organic (soot, unburned hydrocarbon condensate) governs both its health toxicity profile and its physical behaviour in a control device — e.g., hygroscopic sulfate/nitrate particles swell and change effective diameter in humid flue gas, shifting their collection efficiency, and combustible organic particulate changes the fire/explosion-safety design of a fabric filter.
(3) Electrical resistivity. For electrostatic precipitator design specifically (Question 6(ii)), particle resistivity governs how readily the collected dust re-entrains by "back corona" if resistivity is too high, or fails to retain its charge and re-entrains if resistivity is too low — an ESP sized without checking the specific ash's resistivity against its optimal 104–1010 Ω·cm range can under-perform badly even with an otherwise correct plate area.
| Aspect | Similarity |
|---|---|
| Respiratory irritation | Both categories are respiratory irritants that can aggravate asthma and COPD and are linked to increased hospital admissions during high-PM episodes, differing mainly in HOW FAR into the respiratory tract each penetrates rather than whether irritation occurs at all. |
| Regulatory framework | Both are criteria pollutants regulated under the Canadian Ambient Air Quality Standards (CAAQS) with their own annual and 24-hour averaging-period objectives, reflecting that both are recognized as requiring independent regulatory attention. |
| Visibility/aesthetic reduction | Both scatter and absorb visible light and contribute to regional haze and reduced visibility, and both cause visible soiling of building surfaces and vegetation, even though the fine (PM2.5) fraction dominates the light-scattering share. |
| Common combustion source signature | Both categories are emitted by the same major source classes — fossil-fuel combustion, vehicle exhaust, and industrial process emissions — so a single combustion-source control measure (e.g., an ESP or baghouse) typically reduces both size fractions simultaneously, even at different removal efficiencies. |
