Even though the mass ratio of soot

Even though the mass ratio of soot in aerosol is small, its surface area ratio is much larger than the mass ratio since soot has an amorphous and fractal structure, and it has the similar importance for the heterogeneous reactions in the atmosphere as other aerosols. The uptake coefficients of soot obtained so far has an uncertainty of a few orders of magnitude, and the causes are thought to be largely ascribed to the difference in the type and amount of surface functional groups due to the difference in formation methods, and the estimate of surface area. It has been known that there are at least two reactive sites on soot, and the fresh soot near the emission source has sites with large reaction rates, but changes to less reactive site for the aged soot in the atmosphere. The actual values of uptake coefficients of soot in the atmosphere is thus thought to be affected by the difference in the gas-solid contact time resulting in the chemical transformation of the soot surface.