📚 Combustion of Fuels and Atmospheric Pollution | 燃料燃烧与大气污染
Burning fuels such as coal, petrol, diesel and natural gas releases energy for transport, electricity generation and heating, but it also emits a range of harmful substances into the air. Understanding the chemistry behind these emissions is crucial for IGCSE Science students, as it links everyday processes to major environmental challenges like acid rain, smog and global dimming.
燃烧煤炭、汽油、柴油和天然气等燃料为交通、发电和取暖释放能量，但同时也向空气中排放多种有害物质。理解这些排放背后的化学原理对IGCSE科学学生至关重要，因为它将日常过程与酸雨、烟雾和全球变暗等重大环境问题联系起来。
1. Complete Combustion of Hydrocarbons | 碳氢化合物的完全燃烧
When a hydrocarbon fuel burns in a plentiful supply of oxygen, complete combustion occurs. The only products are carbon dioxide (CO₂) and water vapour (H₂O). The general word equation is:
当碳氢燃料在充足的氧气中燃烧时，发生完全燃烧。唯一的产物是二氧化碳（CO₂）和水蒸气（H₂O）。通用文字方程式为：
Hydrocarbon + Oxygen → Carbon dioxide + Water
碳氢化合物 + 氧气 → 二氧化碳 + 水
For example, methane (CH₄) burns completely according to the equation:
例如，甲烷（CH₄）完全燃烧的方程式为：
CH₄ + 2O₂ → CO₂ + 2H₂O
This release of CO₂, a greenhouse gas, contributes to global warming even when combustion is efficient.
尽管燃烧效率高，二氧化碳作为一种温室气体的释放仍然会导致全球变暖。
2. Incomplete Combustion and Carbon Monoxide | 不完全燃烧与一氧化碳
In limited oxygen, fuels undergo incomplete combustion. This produces carbon monoxide (CO) instead of, or alongside, carbon dioxide. Carbon particles (soot) may also form. CO is a colourless, odourless, highly toxic gas that binds to haemoglobin in red blood cells more strongly than oxygen does, reducing the blood's ability to carry oxygen.
在氧气有限的情况下，燃料发生不完全燃烧。这会产生一氧化碳（CO），替代或伴随二氧化碳。碳颗粒（烟灰）也可能形成。一氧化碳是一种无色、无味、剧毒的气体，它与红细胞中的血红蛋白结合的能力比氧气更强，从而降低血液携带氧气的能力。
In road vehicles, catalytic converters help convert CO into CO₂ before exhaust gases leave the tailpipe. The equation for incomplete combustion of methane is one example:
在道路车辆中，催化转化器有助于在废气离开排气管之前将CO转化为CO₂。甲烷不完全燃烧的方程式就是一个例子：
2CH₄ + 3O₂ → 2CO + 4H₂O
Black soot from diesel engines, visible as fine particles, also contributes to respiratory problems.
来自柴油发动机的黑色烟灰（可见的细微颗粒）也会导致呼吸系统问题。
3. Sulfur Dioxide from Fuel Impurities | 燃料杂质产生的二氧化硫
Many fossil fuels, especially coal and some crude oils, contain sulfur compounds. When these fuels burn, the sulfur is oxidised to sulfur dioxide (SO₂). The reaction can be represented as:
许多化石燃料，尤其是煤炭和一些原油，含有硫化合物。当这些燃料燃烧时，硫被氧化为二氧化硫（SO₂）。反应可表示为：
S + O₂ → SO₂
Sulfur dioxide itself irritates the respiratory system and can trigger asthma attacks. More importantly, SO₂ dissolves in cloud droplets to form sulfurous acid (H₂SO₃) and eventually sulfuric acid (H₂SO₄), leading to acid rain.
二氧化硫本身会刺激呼吸系统，可能诱发哮喘发作。更重要的是，SO₂溶解在云滴中形成亚硫酸（H₂SO₃），并最终形成硫酸（H₂SO₄），导致酸雨。
Acid rain damages forests, acidifies lakes and rivers, and erodes limestone buildings and metal structures. To combat this, many power stations use flue gas desulfurisation, where SO₂ reacts with calcium carbonate or calcium oxide to form solid calcium sulfate.
酸雨损害森林，酸化湖泊和河流，并侵蚀石灰岩建筑和金属结构。为了应对这一问题，许多发电站采用烟气脱硫技术，使SO₂与碳酸钙或氧化钙反应，生成固体硫酸钙。
4. Oxides of Nitrogen from High-temperature Combustion | 高温燃烧产生的氮氧化物
In air, nitrogen (N₂) and oxygen (O₂) normally do not react. However, inside car engines and furnaces where temperatures exceed 1000 °C, nitrogen and oxygen combine to form nitrogen monoxide (NO), a colourless gas. This then oxidises further in the atmosphere to nitrogen dioxide (NO₂), a brown, pungent gas.
在空气中，氮气（N₂）和氧气（O₂）通常不反应。然而，在温度超过1000 °C的汽车发动机和熔炉中，氮气和氧气结合生成一氧化氮（NO），一种无色气体。然后它在空气中进一步氧化为二氧化氮（NO₂），一种棕色、有刺激性气味的气体。
N₂ + O₂ → 2NO
2NO + O₂ → 2NO₂
Collectively called NOx, these oxides of nitrogen contribute to acid rain and produce photochemical smog, a brown haze seen over large cities. NO₂ also irritates the lungs and can intensify bronchitis.
这些统称为NOx的氮氧化物会导致酸雨，并产生光化学烟雾，即大城市上空常见的棕色阴霾。NO₂还会刺激肺部，可能加重支气管炎。
Catalytic converters in petrol cars reduce NOx back to harmless N₂ and O₂ using a reduction catalyst (often rhodium).
汽油车中的催化转化器利用还原催化剂（通常为铑）将NOx还原为无害的氮气和氧气。
5. Particulate Matter from Combustion | 燃烧产生的颗粒物
Incomplete combustion of fuels, especially diesel, releases tiny solid particles of carbon (soot) and unburned hydrocarbons. These particulates, measured as PM₁₀ and PM₂.₅ (particles with diameter less than 10 or 2.5 micrometres), can penetrate deep into the lungs and even enter the bloodstream.
燃料的不完全燃烧，尤其是柴油，会释放出微小的碳颗粒（烟灰）和未燃烧的碳氢化合物。这些颗粒物，以PM₁₀和PM₂.₅（直径小于10或2.5微米的颗粒）来衡量，能够深入肺部，甚至进入血液。
Long-term exposure increases the risk of heart disease, stroke and lung cancer. Diesel particulate filters (DPFs) are fitted to modern vehicles to trap these solids, burning them off periodically through regeneration.
长期接触会增加患心脏病、中风和肺癌的风险。现代车辆配备柴油颗粒过滤器（DPF）以捕获这些固体，并通过再生过程定期将其烧掉。
6. Carbon Dioxide and the Greenhouse Effect | 二氧化碳与温室效应
Although non-toxic, CO₂ is the most significant long-term pollutant from fuel combustion. It acts as a greenhouse gas, trapping infrared radiation in the atmosphere and causing global warming. The more hydrocarbon fuels we burn, the more CO₂ accumulates, enhancing the natural greenhouse effect.
虽然无毒，但CO₂是燃料燃烧产生的最重要的长期污染物。它作为一种温室气体，将红外辐射截留在大气中，导致全球变暖。我们燃烧的碳氢燃料越多，积累的CO₂就越多，从而加剧自然的温室效应。
Reducing CO₂ emissions requires switching to renewable energy sources, improving energy efficiency, and developing carbon capture and storage (CCS) technologies.
减少CO₂排放需要用可再生能源替代化石燃料、提高能源效率以及发展碳捕获与储存（CCS）技术。
7. Role of Catalytic Converters | 催化转化器的作用
A three-way catalytic converter, used in petrol cars, simultaneously reduces NOx to N₂, oxidises CO to CO₂, and oxidises unburned hydrocarbons to CO₂ and H₂O. It uses a combination of platinum, palladium, and rhodium catalysts. The reactions take place on a honeycomb ceramic structure that provides a large surface area.
汽油车使用的三元催化转化器能同时将NOx还原为N₂，将CO氧化为CO₂，并将未燃烧的碳氢化合物氧化为CO₂和H₂O。它使用铂、钯和铑催化剂的组合。这些反应发生在提供大表面积的蜂窝陶瓷结构上。
Typical chemical equations inside the converter include:
转化器内典型的化学方程式包括：
2CO + O₂ → 2CO₂
2NO + 2CO → N₂ + 2CO₂
However, catalytic converters only work effectively when the engine is hot. They do not reduce CO₂ emissions directly, and in fact, the oxidation of CO produces CO₂.
然而，催化转化器只有在发动机达到工作温度时才有效。它们不能直接减少CO₂排放，事实上，CO的氧化会产生CO₂。
8. Flue Gas Desulfurisation (FGD) | 烟气脱硫
In coal-fired power stations, the flue gas is passed through a slurry of limestone (calcium carbonate) or lime (calcium oxide). The SO₂ reacts to form calcium sulfite, which is often oxidised further to calcium sulfate (gypsum), a useful by-product for plasterboard:
在燃煤发电站中，烟气通过石灰石（碳酸钙）或生石灰（氧化钙）浆液。SO₂反应生成亚硫酸钙，通常进一步氧化为硫酸钙（石膏），这是一种可用于石膏板的有用副产品：
CaCO₃ + SO₂ → CaSO₃ + CO₂
2CaSO₃ + O₂ → 2CaSO₄
This process can remove over 90% of the sulfur dioxide, dramatically reducing acid rain potential. It is one of the most widely used industrial methods for controlling SO₂ emissions.
此过程可以去除超过90%的二氧化硫，大幅降低形成酸雨的可能性。它是控制SO₂排放最广泛使用的工业方法之一。
9. Consequences of Acid Rain | 酸雨的后果
Acid rain caused by SO₂ and NOx has a pH typically between 4 and 5. It leaches vital nutrients like calcium and magnesium from the soil, damages the waxy cuticle of leaves, and releases toxic aluminium ions into freshwater, killing fish. It also accelerates the corrosion of limestone and marble buildings and statues.
由SO₂和NOx引起的酸雨pH值通常在4到5之间。它从土壤中淋洗掉钙和镁等重要的营养元素，损害叶片的蜡质角质层，并向淡水中释放有毒的铝离子，导致鱼类死亡。它还加速石灰石和大理石建筑及雕像的腐蚀。
Statues made of limestone (calcium carbonate) crumble because the acid reacts with the carbonate, forming soluble salts that wash away:
石灰石（碳酸钙）制成的雕像会碎裂，因为酸与碳酸盐反应，形成可溶性盐被冲刷掉：
CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂
International agreements such as the Gothenburg Protocol have helped reduce SO₂ and NOx emissions in many regions.
哥德堡议定书等国际协议帮助许多地区减少了SO₂和NOx的排放。
10. Photochemical Smog Formation | 光化学烟雾的形成
Nitrogen oxides and unburned hydrocarbons released from vehicle exhausts react in the presence of sunlight to form a mixture of secondary pollutants, including ozone (O₃) at ground level, peroxyacetyl nitrate (PAN), and other irritants. This brownish haze is called photochemical smog.
车辆尾气排放的氮氧化物和未燃烧碳氢化合物在阳光照射下反应，形成包括地面臭氧（O₃）、过氧乙酰硝酸酯（PAN）和其他刺激物在内的二次污染物混合物。这种淡棕色的雾霾被称为光化学烟雾。
Ground-level ozone damages crops, reduces lung function, and aggravates asthma. It is different from the protective ozone layer in the stratosphere.
地面臭氧损害农作物，降低肺功能，并加重哮喘。它与平流层中的保护性臭氧层不同。
Cities with heavy traffic and sunny climates, such as Los Angeles and Beijing, frequently experience photochemical smog episodes. Reducing NOx and hydrocarbon emissions is key to tackling this problem.
交通繁忙且阳光充足的城市，如洛杉矶和北京，经常出现光化学烟雾事件。减少NOx和碳氢化合物排放是解决这一问题的关键。
11. Exam-style Summary Table of Pollutants | 污染物考试型总结表
The following table summarises the main pollutants from fuel combustion, their sources, effects, and control measures, as frequently tested in IGCSE Edexcel Science examinations.
下表总结了燃料燃烧的主要污染物及其来源、影响和控制措施，这是IGCSE Edexcel科学考试中常见的考点。
| Pollutant 污染物 | Source 来源 | Effects 影响 | Control 控制措施 |
| CO₂ 二氧化碳 | Complete combustion of any hydrocarbon 任何碳氢化合物的完全燃烧 | Greenhouse gas; global warming 温室气体；全球变暖 | Renewable energy, CCS 可再生能源，碳捕获与储存 |
| CO 一氧化碳 | Incomplete combustion 不完全燃烧 | Toxic, binds to haemoglobin 有毒，与血红蛋白结合 | Catalytic converter 催化转化器 |
| SO₂ 二氧化硫 | Sulfur impurities in fuels 燃料中的硫杂质 | Acid rain, respiratory problems 酸雨，呼吸问题 | Flue gas desulfurisation 烟气脱硫 |
| NOx 氮氧化物 | High temperature in engines 发动机高温 | Acid rain, photochemical smog 酸雨，光化学烟雾 | Catalytic converter 催化转化器 |
| Particulates 颗粒物 | Incomplete combustion, diesel 不完全燃烧，柴油 | Lung damage, respiratory illness 肺部损伤，呼吸系统疾病 | Diesel particulate filter 柴油颗粒过滤器 |
12. Reducing Our Reliance on Fossil Fuels | 减少我们对化石燃料的依赖
Beyond emission control technologies, the ultimate solution to air pollution from combustion is to shift away from fossil fuels. Using hydrogen fuel cells (which only emit water), electric vehicles charged with renewable electricity, and biofuels that are carbon-neutral over their life cycle can dramatically cut pollutant emissions.
除了排放控制技术，解决燃烧造成的空气污染的最终方案是摆脱化石燃料。使用仅排放水的氢燃料电池、用可再生电力充电的电动汽车，以及在其生命周期内碳中和的生物燃料，可以大幅减少污染物排放。
At an individual level, reducing car journeys, insulating homes to lower heating fuel use, and supporting clean energy policies all contribute to cleaner air and a healthier planet.
在个人层面，减少汽车出行、给房屋做保温以降低取暖燃料用量，以及支持清洁能源政策，都有助于实现更清洁的空气和更健康的地球。
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