Many of us probably remember learning about greenhouse gases in middle school. The one that first comes to mind is likely carbon dioxide. But it is only one of several primary greenhouse gases. Water vapor, methane, nitrous oxide, and ozone are all on the list as well.
But what is the determining factor of whether a gas is a greenhouse gas? A greenhouse gas is a gas in the atmosphere that absorbs and emits radiation within the thermal infrared range. In other words, first it must be able to absorb radiation. Traditionally, to absorb radiation a molecule must have a dipole moment; this means that the positive and negative charges are not equally balanced in the molecule. For example, water consists of a negatively charged oxygen and two positively charged hydrogens, and like a magnet, it has a negative end and a positive end. As a counter example, hydrogen gas, H2, has no dipole moment because the charge distribution is symmetric, with an equal number of positive and negative charges between the two identical atoms. (more…)