Protecting the atmosphere and hydrosphere

Air is polluted by natural causes (volcanoes, dust), burning of fuel, industry and transport, and burning of waste; poisonous gases such as NO, NO₂, CO, SO₂, Cl₂, H₂S, HCl, HF and dust enter the air. Electrostatic precipitators, adsorbents and wetting the area (the wet method) are used to capture dust and aerosols. Acid rain forms like this: sulfur in fuel becomes SO₂ (S + O₂ → SO₂), which is oxidised to SO₃ and gives sulfuric acid with water (2SO₂ + O₂ → 2SO₃; SO₃ + H₂O → H₂SO₄); nitrogen oxides give nitric acid (4NO₂ + O₂ + 2H₂O → 4HNO₃). Such rain harms plants, soil, buildings and metals; to reduce it, fuel should be freed of sulfur and gases captured. Drinkable water is a very small part of the water on Earth, so we must save it and treat waste water: water is filtered, then lime (Ca(OH)₂) and Al₂(SO₄)₃ are added, and the Al(OH)₃ precipitate carries impurities down (Al₂(SO₄)₃ + 3Ca(OH)₂ → 2Al(OH)₃↓ + 3CaSO₄), and it is disinfected with chlorinated lime. Pesticides (insecticides, fungicides, herbicides) are used against pests, but they do not break down quickly and may accumulate in soil, water and food and poison, so only specialists work with them, following safety rules.