Sulphur dioxide
Also called: SO2 · Topic: Geographical Issues: Pollution, Urban Waste, Slums and Land Degradation · NCERT: Beyond NCERT
Meaning
Sulphur dioxide (SO₂) is a colourless gas with a sharp smell. It forms when fuels that contain sulphur, mainly coal and oil, are burnt in power plants, refineries and factories. In the air, SO₂ turns into sulphuric acid. This makes acid rain, which is rain with a pH below about 5.6, meaning it is more acidic than normal rain. SO₂ also hurts the lungs, and it changes into tiny sulphate particles that add to PM2.5, the fine dust that goes deep into the lungs. SO₂ is one of the eight pollutants in India's National Air Quality Index. In December 2015, MoEFCC set SO₂ limits for coal power plants and gave them until December 2017 to meet them. That deadline has since been pushed back four times. Fewer than 8% of coal plants have fitted FGD units, which are scrubbers that remove SO₂ from chimney smoke.
Example
The Taj Mahal in Agra, Uttar Pradesh, was threatened by SO₂ from the nearby Mathura refinery. The gas formed acid that damaged and yellowed the white marble. In 1996, in the M.C. Mehta case, the Supreme Court created the Taj Trapezium Zone to control pollution around the monument.
Don't confuse with
- Nitrogen dioxide (NO₂): it also causes acid rain, but it comes mostly from vehicle engines and very hot burning, not from sulphur in the fuel.
- Carbon dioxide (CO₂): it is a greenhouse gas that warms the climate. It is not a main cause of acid rain.