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.
Air pollution is the presence, in outdoor (ambient) or indoor air, of one or more substances — gaseous, liquid-aerosol or particulate — in a concentration and duration sufficient to be injurious to human health, to damage vegetation, ecosystems or materials, to reduce visibility, or to alter climate, where the loading exceeds the atmosphere's natural capacity to disperse or assimilate it. Common examples: sulfur dioxide (SO2), oxides of nitrogen (NOx), carbon monoxide (CO), ground-level ozone (O3, a secondary pollutant), particulate matter (PM10/PM2.5), volatile organic compounds (VOCs) and lead (Pb).
Specific sources are usefully grouped by geometry: point sources — a single identifiable stack, e.g. a coal-fired power plant, base-metal smelter or kraft pulp mill (SO2, NOx, PM); mobile/line sources — vehicle exhaust along a highway corridor (CO, NOx, VOCs, PM); area sources — many small, diffuse emitters aggregated over a region, e.g. residential wood heating or agricultural operations (PM, NH3); and natural sources — wildfires, volcanic eruptions and biogenic VOC emissions from vegetation, which contribute background loading independent of human activity.
Radon (Rn-222). A naturally occurring, radioactive, odourless noble gas that infiltrates buildings from uranium-bearing soil and rock through foundation cracks and sumps, accumulating in poorly ventilated basements. Health impacts: (1) its short-lived alpha-emitting decay progeny (Po-218, Po-214) lodge in lung tissue when inhaled, making radon the leading cause of lung cancer among non-smokers; (2) a strong synergistic effect with tobacco smoke multiplies lung cancer risk well beyond the sum of the two exposures alone. Ecological impacts: (1) alpha-emitting decay progeny plate out on indoor surfaces and building materials, creating a low-level radiological legacy that must be accounted for if the material is later recycled or demolished (construction-waste handling); (2) the mechanical sub-slab depressurization fans commonly installed as mitigation run continuously, adding a small but permanent increment to the building's energy demand and associated greenhouse-gas footprint.
Formaldehyde / off-gassed VOCs. Emitted from pressed-wood products, urea-formaldehyde insulation, adhesives, paints and new furnishings. Health impacts: (1) eye, nose and throat irritation at typical indoor concentrations; (2) classified as a probable human carcinogen under chronic higher-level exposure. Ecological impacts: (1) once purged by mechanical ventilation, VOCs are exhausted to the outdoor atmosphere where they act as ozone/photochemical-smog precursors, contributing to regional outdoor air quality degradation downwind of a dense urban building stock; (2) the engineered-wood supply chain that is the dominant formaldehyde source is itself linked to forestry practices, so specifying low-emission (e.g. ULEF-rated) products has a lifecycle ecological benefit beyond the indoor air-quality one.
Indoor pollution is the accumulation of contaminants within an enclosed, occupied space at concentrations that are often higher than in the outdoor ambient air, because the building envelope limits the air-exchange rate available to dilute pollutants generated by combustion appliances, off-gassing materials, biological growth or infiltration. Example: environmental tobacco smoke (ETS, "second-hand smoke"). Specific substance: ETS is a complex mixture of fine particulate matter and thousands of gas-phase compounds, including known carcinogens such as benzo(a)pyrene and formaldehyde. Health impact: chronic exposure elevates the risk of respiratory illness (asthma exacerbation, reduced lung function) and lung cancer among non-smoking occupants, with children in a smoking household at particularly elevated risk of respiratory infections and impaired lung development.
Atmospheric pollutants are classified along several complementary axes. By origin: primary pollutants are emitted directly from a source in the form found in ambient air (SO2, CO, primary PM); secondary pollutants form afterward in the atmosphere through chemical/photochemical reaction among primary pollutants (O3, sulfate/nitrate aerosol, PAN). By physical state: gaseous pollutants (SO2, NOx, CO, VOCs) versus particulate pollutants (solid or liquid aerosol, further split by aerodynamic diameter into PM10 and PM2.5). By source geometry: point, mobile/line, area and natural, as in part (i). By regulatory category: the "criteria air contaminants" with established ambient standards (CO, SO2, NOx, O3, PM, Pb) versus air toxics/hazardous air pollutants, which are regulated individually because even trace exposure carries meaningful health risk (e.g. benzene, mercury).
