--- title: "Sources and effects of SO2, NOx and CO" subject: "Environment and Pollution Control" chapter: 1 key: "semester_7/environment_and_pollution_control:gaseous-pollutants-so2-nox-co" source: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/gaseous-pollutants-so2-nox-co site: BCT Engineering --- # Sources and effects of SO2, NOx and CO Environment and Pollution Control · Chapter 1: Air pollution - Asked in: year not given, 6 marks - Video: [E.1.1 Describe the main sources of CO, NOx, SOx, particlulates and VOCs in the atmosphere](https://www.youtube.com/watch?v=hhN9Ux_SPFs) — Mike Sugiyama Jones (MSJ Chem) - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/environment_and_pollution_control/gaseous-pollutants-so2-nox-co - Whole chapter: https://www.bctengineer.com/md/semester_7/environment_and_pollution_control/chapter-1 ## Question Describe the major sources and the harmful effects of the gaseous pollutants sulphur dioxide, oxides of nitrogen and carbon monoxide. ## Short answer SO2 from coal/oil burning and ore smelting irritates the respiratory tract and causes acid rain damaging forests, lakes and buildings. NOx from vehicle and power plant combustion causes lung damage, photochemical smog and acid rain. CO from incomplete combustion binds haemoglobin 200–250 times more strongly than oxygen, causing headache, dizziness and potentially death. ## Answer #### Sulphur dioxide ($\text{SO}_2$) **Sources:** burning of coal and fuel oil containing sulphur ($\text{S} + \text{O}_2 \rightarrow \text{SO}_2$), smelting of sulphide ores, oil refineries, and volcanoes. **Effects:** - A colourless gas with a sharp smell that irritates the eyes and respiratory tract and aggravates asthma and bronchitis. - Oxidises to $\text{SO}_3$ and then to sulphuric acid, causing **acid rain** that damages lakes, forests and buildings. - Bleaches and damages leaves (chlorosis); corrodes metals and attacks limestone and marble. #### Oxides of nitrogen ($\text{NO}_x$ = NO + $\text{NO}_2$) **Sources:** high-temperature combustion in vehicle engines and power plants, where atmospheric $\text{N}_2$ and $\text{O}_2$ combine ($\text{N}_2 + \text{O}_2 \rightarrow 2\text{NO}$); also fertiliser plants and lightning. **Effects:** - $\text{NO}_2$ is a reddish-brown toxic gas that damages lung tissue and lowers resistance to infection. - Takes part in photochemical smog and ozone formation. - Forms nitric acid, which adds to acid rain. - Damages plants and fades fabrics. #### Carbon monoxide (CO) **Sources:** incomplete combustion of carbon fuels, mainly petrol vehicles, also biomass burning, forest fires and industries. **Effects:** - Colourless and odourless. It combines with haemoglobin about 200-250 times more strongly than oxygen, forming carboxyhaemoglobin (COHb) and reducing oxygen transport. - Causes headache, dizziness, drowsiness, and at high levels unconsciousness and death. - It is especially dangerous in closed garages and poorly ventilated kitchens. In the open atmosphere it is slowly oxidised to $\text{CO}_2$. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why do vehicle engines and power plants produce NOx? A. Fuel nitrogen compounds burn at low temperature B. At high temperature atmospheric N2 and O2 combine to form NO C. Incomplete combustion of carbon D. Sulphur in fuel reacts with air Answer: B. High-temperature combustion makes atmospheric N2 and O2 combine: N2 + O2 -> 2NO. (Key point: Source of NOx) 2. Why is carbon monoxide poisonous? A. It corrodes lung tissue like acid B. It binds to haemoglobin about 200-250 times more strongly than O2, forming COHb C. It displaces CO2 from blood D. It forms acid rain in the lungs Answer: B. CO forms carboxyhaemoglobin, reducing the oxygen carried by blood. (Key point: CO toxicity mechanism) 3. How does SO2 lead to acid rain? A. It reacts with N2 to form nitric acid B. It oxidises to SO3 and then to sulphuric acid C. It dissolves directly as CO2 D. It is reduced to H2S Answer: B. SO2 oxidises to SO3 and then forms sulphuric acid, which falls as acid rain. (Key point: SO2 and acid rain) 4. Carbon monoxide is mainly produced by: A. Complete combustion of coal B. Incomplete combustion of carbon fuels, mainly petrol vehicles C. Smelting of sulphide ores D. Fertiliser plants Answer: B. CO arises from incomplete combustion, especially of petrol in vehicles. 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