From AMS Glossary
(Symbol C.) The 12th element in the periodic table, mass 12.000. Carbon is one of the most versatile elements and combines with itself and many other elements to form a huge variety of organic compounds, for example, hydrocarbons and their derivatives, some of which are found in the atmosphere.
Elemental carbon occurs in the atmosphere, mostly in the form of soot from incomplete combustion of organic matter. Smoke particles also have a large proportion of carbonaceous material in them. Together, soot and smoke account for a large part of the reduction in visibility occurring over continental and polluted regions, due to light scattering and light absorption.