The pre-industrial level of carbon dioxide remained constant over the past 10,000 years, but has increased from 250 ppm in 1900 to about 350 ppm today. Since 1970, atmospheric CO 2 levels have been increasing at an exponential rate. Elevated levels of atmospheric carbon dioxide may have a profound impact on the earth's climate, and an international agreement that was formulated in December 1997 in Kyoto Japan, attempts to reduce carbon emissions to pre-1990 levels. Chlorine Chlorine is an interesting atmospheric pollutant. The most common atmospheric form of chlorine, however, is as chloride, where a chlorine atom has acquired an eighth electron from some unsuspecting atom with less electronegativity.
Chloride is water-soluble and washes out of the atmosphere quickly.
Inorganic chlorides, therefore, have very short lifetimes and do not constitute an environmental threat. Ultraviolet radiation can cause covalent bonds to separate into individual atoms containing unpaired electrons. Any covalent bond can be broken if sufficient energy is applied, and the ambient energy available in the stratosphere breaks up larger molecules into individual atoms as if they had been placed on an anvil and struck with a hammer. Molecules that contain chlorine produce chlorine atoms in the stratosphere, and having an odd number of electrons, the chlorine atom results in a stable free radical. The reactions of stratospheric chlorine atoms are discussed in detail in lecture 39.