Carbon dioxide is necessary for plants. Why do we then consider it as a pollutant?

CBSE Class 9 CBSE Class 9 Science
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  1. Carbon dioxide is necessary for plants. Why do we then consider it as a pollutant?
  2. How is smog formed?
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  1. Carbon dioxide gas is necessary for plants to perform photosynthesis. It is also a greenhouse gas. Upto a certain concentration (approximately 350 ppm) in atmosphere, it is both a good raw material for photosynthesis as well as essential for keeping the Earth warm.
    But, when concentration of CO2 from its specified level rises, it starts acting like a pollutant and causes air pollution and global warming. Due to which temperature of the Earth will increase and polar ice and glaciers will start melting.
  2. Smog is formed by combination of suspended dust particles with water vapour.