18-Env-A5 Air Quality and Pollution Control Engineering · December 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2017 — 04-Env-A5 / Air Quality and Pollution Control Engineering. 3 hours duration; open book; Casio or Sharp approved calculator only. Four (4) of the five (5) questions constitute a complete paper (the first four answers as they appear are marked, maximum 100 marks); all five are solved below for completeness. Each question is worth 25 marks with section marks shown in brackets per the paper's own printed Marking Scheme.
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.
Mobile sources are non-stationary emitters — engines and equipment that move, or that are portable, rather than a fixed stack. Four examples: (1) light-duty on-road vehicles (cars, light trucks); (2) heavy-duty diesel trucks and buses; (3) marine vessels (harbour tugs, cargo ships); (4) non-road/off-road equipment (construction and agricultural machinery). Commonly associated substances: carbon monoxide and unburned hydrocarbons/VOCs (from gasoline-engine incomplete combustion), NOx and particulate matter (diesel-engine combustion), and SOx (from higher-sulfur marine bunker fuel).
Emission reduction/elimination. After-treatment technology — three-way catalytic converters on gasoline engines and diesel particulate filters/selective catalytic reduction on diesel engines; cleaner fuel specification — ultra-low-sulfur diesel and reformulated gasoline, and IMO-mandated low-sulfur marine fuel; engine-design improvements — direct injection, exhaust gas recirculation and turbocharging for more complete, lower-temperature combustion; progressively tighter emission standards (e.g. Tier 3 light-duty, EPA/CARB heavy-duty standards) forcing the above technologies into the fleet; and electrification/hybridization, which eliminates tailpipe emissions entirely for the electrified duty cycle. Inspection-and-maintenance programs (periodic emissions testing) catch and correct in-service deterioration of these controls.
Odour is the sensory perception produced when volatile chemical compounds stimulate olfactory receptors; it is characterized by four attributes — detectability (threshold concentration), intensity, character/quality, and hedonic tone (how pleasant or unpleasant it is perceived to be). Perceived intensity follows a roughly logarithmic (Weber–Fechner) relationship with chemical concentration, so a simple ppm/ppb reading does not correlate linearly with how strong an odour is perceived to be.
Units. Odour is quantified in odour units per cubic metre (OU/m3), determined by dynamic dilution olfactometry: a sample is progressively diluted with odour-free air and presented to a trained human panel until it is just detectable (the "dilutions-to-threshold," D/T, value), and that dilution factor is the odour concentration in OU/m3.
Industrial sources. Wastewater treatment plants (H2S and organic sulfur compounds from anaerobic zones, sludge handling); kraft pulp mills (total reduced sulfur compounds — H2S, methyl mercaptan, dimethyl sulfide — from the pulping and recovery process); rendering plants and composting/biosolids operations (organic decomposition odours).
Program: British Columbia's Environmental Management Act (EMA), through its Waste Discharge Regulation, requires a facility with the potential for significant air emissions to hold a valid discharge permit issued by the Ministry of Environment (or to operate under an approved industry-specific Code of Practice), setting facility-specific emission limits, monitoring and reporting conditions before the discharge is authorized.
Substance: sulfur dioxide (SO2). Source: a kraft pulp mill's recovery boiler, where sulfur-bearing black liquor is combusted to recover pulping chemicals, generating SO2 that would otherwise be released uncontrolled to the airshed. The permit sets a facility-specific stack SO2 limit and continuous emission monitoring/reporting obligations, with non-compliance enforceable under the EMA through orders and administrative penalties — a provincial complement to the federal air-toxics standard-setting and enforcement discussed generally in the preceding papers of this subject.
