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Atmospheric Concentrations
Recent trends in atmospheric concentration are shown in Figure 3, and
current values are given by the Carbon Dioxide
Information Analysis Center
Note that concentrations are given in parts per trillion per year (ppt/yr). The most recent data reveal that the concentrations are still increasing but less rapidly than in the past (Figure 4).
Concentrations will likely increase for some time for several reasons. Although the CFCs are not manufactured in the US, they are manufactured in some countries and are even the substance of a developing black market for international trade. Also, CFCs used before the manufacturing ban remain in air conditioners, in automobiles, homes and commercial and industrial buildings as well as in junkyards and landfills. As equipment containing CFCs deteriorate, seals age and containers rupture releasing CFCs to the atmosphere for some time. CFCs have been used in the past for manufacturing foams that are used for insulating materials. These foams have millions of tiny bubbles containing CFCs, which do not readily diffuse through the foam, to help retain their insulating property. Eventually, however, they will be released to the atmosphere, creating a source of atmospheric CFCs long after they are no longer manufactured.
There is some encouraging news however, on atmospheric CFC concentrations: even though measurements are consistent in showing continued increases in CFC concentrations, they are increasing at a decreasing rate, as shown in Figure 5 for Alaska, Colorado, Hawaii, Samoa, and the South Pole.
For example CFC 11 presently is increasing at only about four parts per trillion per year as compared with about 10 to 12 ppt just a few years ago. The 1989 Montreal Protocol to Reduce Substances that Deplete the Ozone Layer (and subsequent amendments) called for the elimination of CFC-11, -12, -113, -114, and -115 and methyl chloroform (CH3Cl3), carbon tetrachloride (CCl4) and the halons (H-1211, - -1301, -2402) by the end of the 20thcentury. This is widely regarded as the stimulating motivation for major international agreement on a significant environmental issue. The CFC numbering scheme was devised to label these molecules without revealing their molecular structure. See also the "numbers game."
NEXT: Stratospheric Ozone and Human Health
