As noted in Chapter 12, the substitutes for CFCs have been hydrogen-containing chloro fluorocarbons (HCFCs). fluorocarbons (HFCs), and some volatile hydrocar hydrogen-containing bon formulations. The presence of hydrogen in an H-C bond in these compounds provides a point of attack for hydroxyl radical to initiate compound decomposition in te troposphere. The first class of substitutes to be widely used was the Cs, which generally have only about 5% of the ozone depleting potential of CFCs. One of the most popular of these has been HCFC-22, chemical formula CHCF2, that was widely used in air conditioners, refrigerators, and as a foam blowing agent. Other popular HCFCs have included HCFC-142b CF3CHCF (CH3CCF2, used as a refrigerant, often in a blend with HCFC-22), CHCl2CF3 (HCFC-123), (HCFC-124), and CH3CCl2F (HCFC-141b)