What makes a gas greenhouse gas? able to absorb infrared light Must have molecular vibration(s) This excludes monoatomic gases as greenhouse gases (That is why argon, the third most abundant atmospheric constituents is transparent to infrared irradiation) The molecular vibrations must be non symmetric, i.e. infrared active Homonuclear diatomic molecules only have symmetric vibrations. That's why n2, 02 are not greenhouse gases
What makes a gas greenhouse gas? Able to absorb infrared light • Must have molecular vibration(s) – This excludes monoatomic gases as greenhouse gases. (That is why argon, the third most abundant atmospheric constituents is transparent to infrared irradiation) • The molecular vibrations must be nonsymmetric, i.e. infrared active – Homonuclear diatomic molecules only have symmetric vibrations. That’s why N2, O2 are not greenhouse gases
What are the major greenhouse gases? H20 CO2 CH4 N2O ·O3 CFCS SF6
What are the major greenhouse gases? • H2O • CO2 • CH4 • N2O • O3 • CFCs • SF6
Absorption of terrestrial radiation by H20 and CO2 Infrared radiation emitted from Earth's surface atmosphe Absorbed in window (unabsorbed atmosphere by H,O or cO, H,O absorption spectrum CO, absorption spectrum 4.000 8.000 12,000 16,000 20,00 Wavelength(nm Atmospheric window: 8000-12000nm
Absorption of terrestrial radiation by H2O and CO2 Atmospheric window: 8000-12000nm
What determines the contribution of a greenhouse gas to global warming? Concentrations H20 and Co2 are the two biggest contributors to the atmospheric warming because of their higher concentrations Lifetime The longer-live a gas is, the higher the contribution e g N20 contribution> CH4 Effectiveness as an infrared absorber For example, cFc-11 and CFC-12
What determines the contribution of a greenhouse gas to global warming? • Concentrations – H2O and CO2 are the two biggest contributors to the atmospheric warming because of their higher concentrations. • Lifetime – The longer-live a gas is, the higher the contribution. e.g. N2O contribution > CH4 • Effectiveness as an infrared absorber – For example, CFC-11 and CFC-12
Radiation emitted from Earth's surface CFC-11 and CFC-12 Region unabsorbed are effective by natural atmospheric gases infrared absorber CF CL absorption The absorption spectra of CFC-11 and CFC-12 coincides with the atmospheric window CFCL, absorption 8,000 10,00012,000 Wavelength(nm)
CFC-11 and CFC-12 are effective infrared absorber The absorption spectra of CFC-11 and CFC-12 coincides with the atmospheric window