Question

Gases that absorb radiation outside the region 500 – 2500 cm-1 do not contribute significantly to the greenhouse effect. Which of the following gases would make a contribution to the greenhouse effect. (give reasons for your answers): HCl, N2, CH4, H2O.

Answer 1

A large amount of CO2 gets introduced into the atm from fossil fuel burning , furnaces & breathing of animals. In dense concentration it can act as a serious pollutant. The temp at the surface of the earth has been maintained by the energy balance of the sun's rays strike on the planet & the heat that gets radiated back into the space. Some of the sun's rays that penetrate the thick layer of CO2 are able to strike the earth & get converted into heat. The heated earth is able to reradiate this absorbed energy as radiations of longer wavelengths. Much of this does not pass through CO2 layer to outer space but gets absorbed by the CO2 & H2O in the atm & adds to the heat that has been already present. By this process earths atm heats up. This phenomenon is known as green house effect.

Increase in the CO2 concentration means more IR radiation is trapped & re- emitted back to the earth , producing a build up of IR radiation in the atm & a mean global temp rise. Gases like CH4 have strong infrared absorptions , could influence the mean global temp.