Refrigerant Gases and Global Warming

In the early use of refrigeration, the process used ammonia and sulfur dioxide, for compression and decompression to obtain cooling. These gases were somewhat obnoxious and were subsequently replaced by chlorofluorocarbons (CFCs). However, someone later developed the theory that CFCs were reacting with ozone in the upper stratosphere and it was necessary to preserve the ozone as a protective barrier to damaging radiation from the sun at the Earth's surface. We will not now discuss the merits of this theory, but it led to modification of the CFCs, with the intention of using gases less reactive to ozone. These modified gases are now being criticized as contributing to global warming. See Cheryl Hogue's article in the December 5 issue of C&E News.

As is usual with most problems, a mathematical analysis usually brings the problem into perspective, with respect to its significance. Let's do this with refrigerants to determine whether their contribution to global warming is significant.

The weight of the Earth's atmosphere, which is mostly nitrogen and oxygen, is estimated to be 5.5x10 E 21 grams. The "E 21" means there are 21 zeros following the 5.5. The molecular weight of air is approximately 30 g per mole. Therefore, the number of moles of air in the atmosphere is 5.5x10 E 21 divided by 30, or about 2x10 E 20.

A mole of any substance is made up of 6x10 E 23 molecules. Therefore, the number of molecules of air in the atmosphere is 2x10 E 30 times 6x10 E 23, or about 1x10 E 44.

In 1991, usage of CFCs for refrigeration and blowing agents was 6.8x10 E 11 grams. Assume the worst-case for the atmosphere, which is that all the CFCs entered the atmosphere. The molecular weight of the most common CFC (dichlorodifluoromethane) is 120. Therefore, the number of moles of CFC entering the atmosphere was 6.8x10 E 11 divided by 120, or about 6x10 E 9. Again converting to numbers of molecules, 6x10 E9 times 6x10 E 23 gives 36x10 E 32, or 3.6x10 E 33.

We now divide the number of air molecules in the atmosphere by the number of CFC molecules entering the atmosphere in 1991. 1x10 E 44 divided by 3.6x10 E. 33 gives about 1x10 E 11. In other words, there were 100 trillion times more air molecules then CFC molecules in the atmosphere in 1991.

The theory of global warming is that some molecules are greater reflectors of heat than others. The global warming effect is said to occur by those molecules not allowing heat to escape from the Earth's surface.

Assume the worst-case scenario. That is, molecules of nitrogen and oxygen in the atmosphere allow complete passage of heat from the earth's surface to interstellar space, while molecules of CFC completely block this passage of heat.

Let us now also make an analogy that we have a net containing 100 trillion holes (pretty big net!). One of the holes is completely blocked. Is that enough to have any significant effect on what passes through all the remaining holes?