18-Env-A5 Air Quality and Pollution Control Engineering · December 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
04-Env-A5 / 18-Env-A5, Air Quality and Pollution Control Engineering — National Exam, December 2016. 3 hours, open book. Question 1 is compulsory; any other four (4) of Questions 2–7 complete the 100-mark paper (only the first five (5) answers in the work book are marked). All seven Problems are answered below.
Reference texts
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.
Part (i) — particulate control for a tall stack servicing a coal-fired kiln. A coal kiln's emission is a wide, roughly log-normal particle-size distribution spanning coarse fly ash (tens of µm) down to sub-micron combustion aerosol. A single control device rarely handles the whole distribution efficiently, so the standard train is staged by size: a cyclone (or multiclone) first strips the coarse fraction cheaply (>90% efficient above ~10–15 µm but poor below ~5 µm), followed by a high-efficiency fabric filter (baghouse) or electrostatic precipitator (ESP) to capture the fine fraction the cyclone misses (fabric filters and ESPs both exceed 99% overall efficiency, including sub-micron particles). Particle size distribution matters because collection efficiency for every mechanism (impaction, interception, diffusion, electrostatic attraction) is a strong function of particle diameter; the distribution's shape sets both the overall mass-removal efficiency achievable and the number-weighted fraction of fine, more deeply-inhalable particles that will penetrate through to the stack if only coarse-oriented control (e.g. a cyclone alone) is installed.
Part (ii) — three particulate measurement methods.
| Method | Merits | Disadvantages |
|---|---|---|
| High-volume gravimetric sampler (filter + pump, weighed before/after) | Simple, low-cost, the reference/regulatory method; directly measures mass, size-selective inlets available (PM₂.₅, PM₁₀) | Only gives an integrated average over the sampling period (e.g. 24 h); no real-time data; labour-intensive filter handling |
| Tapered element oscillating microbalance (TEOM) | Near real-time mass concentration; automated, continuous record | Heated inlet can drive off semi-volatile PM components, biasing readings low; more expensive and maintenance-intensive than gravimetric |
| Opacity monitor / transmissometer (light attenuation across the stack) | True continuous, in-stack, real-time compliance signal; simple pass/fail against an opacity limit | Measures light attenuation, not mass directly — needs site calibration against gravimetric mass, and is insensitive to fine, weakly light-scattering particles |
Part (iii) — PM2.5 vs. PM10: health and aesthetics. (1) Health: PM10 (up to 10 µm) is largely filtered by the nose and upper airway, so its health effects concentrate on upper-respiratory irritation; PM2.5 penetrates past the upper airway into the alveoli and bloodstream, driving the more serious cardiovascular and deep-lung outcomes (heart attack, stroke, chronic bronchitis) that dominate air-quality mortality statistics. (2) Aesthetics: PM10 is dominated by mechanically generated dust (road dust, construction, wind-blown soil) that settles out quickly and causes visible soiling/dustfall on nearby surfaces; PM2.5 stays airborne far longer and, because its diameter is comparable to the wavelength of visible light, scatters light very efficiently — it is the primary cause of regional visibility-reducing haze even when surface dustfall is unnoticeable.
