Oxides of nitrogen and pollution
Introduced| English | Meaning |
|---|---|
| oxides of nitrogen/ˈɒksaɪdz ɒv ˈnaɪtrədʒn/ | oxides of nitrogen |
| acid rain/ˈæsɪd reɪn/ | Precipitation made unusually acidic mainly by atmospheric reactions involving sulfur dioxide and nitrogen oxides. |
| catalytic converter/ˌkætəˈlɪtɪk kənˈvɜːtə/ | A device that uses catalysts to convert harmful vehicle exhaust gases into less harmful substances. |
| photochemical smog/ˌfəʊtəʊˈkemɪkl smɒɡ/ | Air pollution formed when sunlight drives reactions involving nitrogen oxides and volatile organic compounds, producing pollutants such as ozone. |
| nitric acid/ˈnaɪtrɪk ˈæsɪd/ | The acid HNO3, which forms nitrate ions when it donates protons. |
Pollution from the engine
- Oxides of nitrogen 氮氧化物 ($\text{NO}$ and $\text{NO}_2$, together NOₓ) pollute the air.
- They come from lightning and from engines.
- They cause smog and acid rain 酸雨 — but we can remove some.
NOx pollution route
Trace nitrogen oxides from hot engines to environmental harm.
Oxides of nitrogen from car engines contribute to acid rain and photochemical smog.
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NOₓ are atmospheric pollutants.
Where NOₓ comes from
- natural: lightning gives enough energy for $\text{N}_2$ and $\text{O}_2$ in the air to combine.
- man-made: the high temperature in a car engine makes them react: $\text{N}_2 + \text{O}_2 \rightarrow 2\text{NO}$.
Oxides of nitrogen contribute to smog and air pollution
Oxides of nitrogen (NOₓ) are produced by:
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Lightning (natural) and the heat of internal combustion engines both make N₂ and O₂ combine into NO.
Match each NOₓ fact.
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Each item links the term to its correct meaning.
Catalytic converters 催化转化器
- A catalytic converter cleans the exhaust by letting harmful gases react to harmless ones:
$$2\text{NO} + 2\text{CO} \rightarrow \text{N}_2 + 2\text{CO}_2$$
A catalytic converter turns harmful NO and CO into harmless N2 and CO2
In a catalytic converter, NO and CO react to form:
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2NO + 2CO → N₂ + 2CO₂; the harmful gases become harmless ones.
Smog and acid rain
- In sunlight, NOₓ reacts with unburned hydrocarbons to form PAN, part of brown photochemical smog 光化学烟雾.
- NOₓ makes acid rain two ways: $\text{NO}_2$ forms nitric acid 硝酸 directly, and it also catalyses the oxidation of $\text{SO}_2$ to $\text{SO}_3$ (→ sulfuric acid).
Nitrogen and sulfur oxides form nitric and sulfuric acid in rain
How does NO₂ contribute to acid rain?
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NO₂ dissolves to form nitric acid, and it also speeds up SO₂ → SO₃, which forms sulfuric acid.
Photochemical smog forms when NOₓ reacts in sunlight with unburned hydrocarbons to make:
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In sunlight NOₓ and hydrocarbons form PAN, a harmful part of the brown photochemical smog.
You've got it
- NOₓ comes from lightning (natural) and the high temperature in engines ($\text{N}_2 + \text{O}_2 \rightarrow 2\text{NO}$)
- a catalytic converter: $2\text{NO} + 2\text{CO} \rightarrow \text{N}_2 + 2\text{CO}_2$
- NOₓ → photochemical smog (PAN) and acid rain (nitric acid + catalysing $\text{SO}_2 \rightarrow \text{SO}_3$)