Environmental Science
The gas that shows the most variation from place to place and from time to time in the lower atmosphere:

Methane (CH4)
Ozone (O3)
Water vapour (H2O)
Carbon dioxide (CO2)
Argon (Ar)

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Environmental Science
Low clouds retard surface cooling at night better than clear skies because:

The formation of the clouds releases latent heat energy
The clouds are better conductors of heat than is the clear night air
The water droplets in the clouds reflect infrared energy back to earth
The clouds start convection currents between them
The clouds absorb and radiate infrared energy back to earth

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