Question 1 of 5: Sources and Classification of Atmospheric Pollutants

Problem 1: Sources and Classification of Atmospheric Pollutants (25 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) — what is air pollution, and two sources with their contaminants. Air pollution is the presence of one or more substances in the ambient atmosphere, at a concentration and duration sufficient to be injurious to human health, damage ecosystems or property, or interfere with the enjoyment of life, arising from either anthropogenic activity or natural processes (volcanic emissions, wildfire, wind-blown dust). Two representative sources:

Stationary combustion — a coal-fired power plant. Burning coal at high flame temperature generates SO₂ from oxidation of fuel-bound sulphur; NOₓ from two mechanisms — thermal NOₓ, formed when N₂ and O₂ in the combustion air dissociate and recombine at flame temperatures above roughly 1,300 °C (the Zeldovich mechanism), and fuel NOₓ, from oxidation of nitrogen chemically bound in the coal itself; and fly-ash particulate matter, the incombustible mineral fraction of the coal plus a small amount of unburned carbon, entrained in the flue gas.

Mobile source — a gasoline or diesel highway vehicle. Incomplete combustion under locally fuel-rich conditions in the cylinder (cold start, acceleration, rich idle) generates carbon monoxide and unburned/partially-oxidised hydrocarbons (VOCs); the same high in-cylinder temperature and pressure that improve engine efficiency also drive thermal NOₓ formation; and, in compression-ignition (diesel) engines specifically, incomplete combustion of the heavier fuel droplets produces elemental-carbon soot (diesel particulate matter). Both examples show the same generating logic — a fuel is oxidised at high temperature, and the contaminant is either an oxidation by-product of an element present in the fuel/air (S→SO₂, N₂→NOₓ) or a product of incomplete oxidation (CO, VOC, soot) where local combustion conditions fell short of full conversion to CO₂ and H₂O.

Part (ii) — two indoor pollutants: radon and carbon monoxide. Radon (²²²Rn) originates naturally from the radioactive decay chain of uranium-238 in soil and bedrock (elevated in granitic and uranium-bearing geology); as an inert gas it migrates through soil pores and enters a building through foundation cracks, sump pits, and floor–wall joints, drawn indoors by the small negative pressure a heated building exerts on the soil beneath it (the stack effect). Health impact: radon itself is chemically inert, but its short-lived decay progeny (²²&sup9;⁠Po, ²¹&sup4;⁠Pb, ²¹&sup4;⁠Bi, ²¹&sup4;⁠Po) attach to airborne dust and are inhaled, lodging in bronchial tissue where their alpha emissions damage epithelial DNA; radon is the second-leading cause of lung cancer after smoking (Health Canada's guideline is 200 Bq/m³). Carbon monoxide (CO) indoors originates from incomplete combustion in unvented or poorly maintained fuel-burning appliances — gas furnaces and water heaters, wood stoves, and vehicles idling in an attached garage. Health impact: CO binds haemoglobin with roughly 200× the affinity of oxygen, forming carboxyhaemoglobin and reducing the blood's oxygen-carrying capacity; symptoms progress from headache and dizziness at moderate exposure to confusion, unconsciousness, and death at high exposure, and the hazard is compounded by CO being colourless and odourless.

Part (iii) — indoor pollution, with an example. Indoor air pollution is the degradation of air quality inside buildings by off-gassing, combustion, biological, or infiltrated contaminants, which frequently reach higher concentrations indoors than outdoors because building ventilation dilutes and exchanges air far more slowly than the open atmosphere. A representative substance is formaldehyde, off-gassed from the urea-formaldehyde resin adhesives used in pressed-wood products (particleboard, plywood, medium-density fibreboard) and some furnishings; it is a respiratory and eye irritant at typical indoor concentrations and is classified by IARC as a human carcinogen at chronic elevated exposure, making source control (low-formaldehyde products) and adequate ventilation the standard mitigation measures.