Question 1 of 7: Sources, Classification and Health/Ecological Impacts of Atmospheric Pollutants

Problem 1: Sources, Classification and Health/Ecological Impacts of Atmospheric Pollutants (20 marks)

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) — source types and classification schemes. Two source types: stationary (point) sources — fixed-location combustion or process stacks such as coal-fired power plants, smelters and refineries, which emit SO₂, NOₓ, particulate matter (PM) and CO from a well-defined discharge point that dispersion models can treat directly; and mobile sources — highway vehicles, marine vessels and off-road engines, which emit CO, NOₓ, volatile organic compounds (VOCs) and diesel PM from a distributed, moving line/area source that is far harder to control at a single point.

Two classification schemes, each with four example chemicals per category: (1) Primary vs. secondary pollutants — primary pollutants are emitted directly from the source (CO, SO₂, PM, Pb), while secondary pollutants form in the atmosphere from primary precursors (O₃, peroxyacetyl nitrate/PAN, HNO₃ aerosol, H₂SO₄ aerosol). (2) Criteria pollutants vs. hazardous air pollutants (air toxics) — criteria pollutants are regulated against national ambient air quality standards (SO₂, NO₂, O₃, PM₂.₅/PM₁₀), while air toxics are typically regulated by source-specific emission limits owing to their carcinogenic/chronic toxicity (benzene, formaldehyde, mercury (Hg), polycyclic aromatic hydrocarbons (PAHs)).

Part (ii) — an indoor air pollutant. Radon (₂₂₂Rn) is a naturally occurring, colourless, odourless radioactive gas produced by the decay of uranium/radium in soil and bedrock; it enters buildings through foundation cracks, sump pits and utility penetrations, drawn in by the slight negative pressure ("stack effect") a heated building exerts on the soil gas beneath it. Health impact: radon and its short-lived decay products emit alpha radiation that damages lung epithelial tissue on inhalation, making radon the second-leading cause of lung cancer after smoking (and the leading cause among non-smokers). Two engineering strategies: (1) active soil depressurization (ASD) — a vent pipe and fan drawing soil gas from beneath the slab and exhausting it above the roofline, before it can enter the living space; (2) sealing entry pathways (foundation cracks, sump lids, pipe penetrations) combined with mechanical ventilation (e.g. a heat-recovery ventilator) to dilute any residual indoor concentration.

Part (iii) — lead (Pb) from highway traffic. Two health impacts: (1) neurotoxicity in children — lead crosses the blood-brain barrier and interferes with neurodevelopment even at low blood-lead levels, producing measurable IQ deficits and behavioural effects, with no known safe threshold; (2) haematological/renal impairment in adults — lead inhibits enzymes in the heme-synthesis pathway (e.g. ALA dehydratase), causing anaemia, and accumulates in the kidney, impairing renal function on chronic exposure. Two ecological impacts: (1) soil and roadside vegetation contamination — lead particulate deposits and accumulates in soils adjacent to highways, is taken up by roadside vegetation and can biomagnify through grazing animals into the food chain; (2) aquatic contamination via stormwater runoff — lead-laden road dust washes into receiving waters during storm events, where it accumulates in sediment and impairs reproduction and growth in benthic invertebrates and fish.