Elemental carbon and soot

In Table 2.34, the total BC emission was given between 11 and 17Tg C yr where about 50 % is contributed by biomass and fossil fuel burning. Other more recent data suggest a lower emission of 5.8-8.0 Tg C yr i (Haywood and Boucher 2000, Bond et al. 2004). Bond et al. (2004) estimated 8.0 Tg for black carbon and 33.9 Tg for organic carbon where the contributions of fossil fuel, biofuel and open burning are estimated as 38%, 20% and 42%, respectively, for BC and 7%, 19% and 74%, respectively. The uncertainty ranges of 4.3-22 Tg yr i for BC and 17-77 Tg yr-i for OC. 

Without doubt, the large OC fraction in soot will undergo aging by oxidation. Decesari et al. (2002) showed that the WSOC produced from the oxidation of soot particles increased rapidly with ozone exposure and consisted primarily of aromatic polyacids found widely in atmospheric aerosols and which are frequently referred to as macromolecular humic-like substances (HULIS). 

However, we only can speculate that reactive oxygen species such as O3 and OH can react with carbon similar to CO  

This process is extremely slow and can result in the chemical lifetime of hundreds or more years under climate system conditions. It is known that surfaces covered with photocatalytic active Ti02 obviously remain clean with respect to soot pollution, whereas reference surfaces become black. As discussed in Chapter 5.3.5, under such photocatalytic conditions large OH concentrations might locally produced. 

The fate of the about 8 Tg BC yr widely dispersed on the globe is deposited into oceans and soils. It is known that coal can survive in soils for hundreds of years and can improve soil structure and water budget. The survival of atmospherie coal combustion soot from the Middle Ages can still be seen at old ehurehes and it is cultural question to regard it as patina with respect or unwanted pollution. 

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