Acid Rain

Acid rain formation mechanism and ecological impact

Causes and chemical processes

Definition: Atmospheric precipitation with pH < 5.6 (natural rainwater pH = 5.6)

Human sources (accounting for ＞70%):

Coal combustion releases: SO₂ → H₂SO₄ (contribution rate 60%)

Automobile exhaust: NOx → HNO₃ (contribution rate 30%)

Natural Sources:

Volcanic eruptions: SO₂/H₂S contributes 12% of global sulfur deposition

Biological decomposition: NH₃ is oxidized to form nitrates

Cross-border transfer characteristics

Pollutant Migration distance Sedimentation rate Typical cases

SO₄²⁻ 500-1000km 0.5-2cm/s UK emissions cause acid rain in Northern Europe

NO₃⁻ 300-800km 0.3-1.2cm/s North China affects South Korea and Japan

Quantification of ecological environmental damage

■ Water acidification:

When pH < 5.0: fish gill mucus hyperplasia (mortality > 90%)

Aluminum dissolution toxicity: concentration > 0.2 mg/L causes nerve paralysis in aquatic organisms

■ Soil degradation:

| Soil Type | Effect of a 1 unit drop in pH |

|------------|----------------------------------|

| Ash soil | Cation exchange capacity (CEC) decreases by 40% |

| Red soil | Active aluminum concentration increased by 300% |

■ Vegetation damage:

Coniferous forest: Damage to the wax layer on the leaves (visible spots > 30% of the leaf area)

Crops: Inhibition of root Ca²⁺/Mg²⁺ absorption (yield reduction of 15-40%)

Building Corrosion and Economic Losses

Material pH=4.0 Annual corrosion amount Repair cost (100 million yuan/year)

Concrete 0.8-1.5mm China＞120

Marble Sculpture 3-5mm Europe＞25

Metal pipe 1.2-2.0mm Global＞80

Human health risks

Respiratory diseases:

PM2.5 adsorption of acid mist increases asthma incidence by 25%

When SO₂ concentration is ＞150μg/m³, children’s lung function decreases by 8%

Drinking water risks:

Lead pipe dissolution is accelerated (Pb²⁺＞15μg/L when pH＜6.5)

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