I’ve been trying to find out why methane is a more potent greenhouse gas than carbon dioxide. The best I can figure out is that methane’s structure means it absorbs infrared better than carbon dioxide, but why?
In: Chemistry
Almost every object has a set of frequencies that it likes to vibrate at. Swings, for example have a frequency they like to go back and forth. Swings will also swing side to side, and when they do they do it at a different frequency.
Molecules are the same: they have several different patterns they like to vibrate (called vibrational modes), each of which has a different frequency. Each of the different frequencies has a different energy level associated with it. Changing from one vibrational mode to another is a change in energy level, and will be accompanied be emitting or absorbing a photon with energy making up the difference.
It just happens, almost by coincidence, the the energy level differences in methane correspond very well to the energy level of the photons in infrared light.
Polutants are often given a ranked value for global warming, often comparing it to CO2. There are several reasons that a pollutant can have a larger effect:
1. Global warming is caused by the release of chemicals in the atmosphere that absorb/block the flow of heat out of earth’s atmosphere. Gasses like CO2 or methane, or suspended particles like ash or water clouds will absorb infrared light, which is a major way that earth sends heat out into space. The greenhouse chemicals in the atmosphere trap the infrared light from escaping, so it has to remain as heat on Earth’s surface.
2. Other greenhouse chemicals don’t directly cause warming, but can indirectly cause damage. For instance, some chemicals act as catalysts which destroy helpful chemicals, or help build up harmful chemicals. For instance, a group of chemicals known as CFCs are very good at destroying ozone gas, which is an important part of Earth’s natural protective shield from harmful solar radiation. Each CFC molecule can destroy thousands of ozone molecules and therefore have a very harmful indirect effect.
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