Heterogeneous chemistry of organic acids on soot surfaces.

We have investigated the heterogeneous interaction between a number of carboxylic acids and soot generated from different fuel sources and formation mechanisms. A low-pressure fast flow reactor in conjunction with ion drift-chemical ionization mass spectrometry detection was employed to study uptake of monocarboxylic (benzoic, oleic, and steric) and dicarboxylic (glutaric, maleic, oxalic, and phthalic) acids on deposited soot surfaces formed by combustion of methane, propane, and kerosene. Most acids exhibited irreversible uptake on the soot surfaces and the uptake coefficient was measured in the range of 9 x 10(-4) to 1 x 10(-1) estimated based on the geometric surface areas. Brunauer, Emmett, and Teller surface areas of the deposited soot surfaces were measured and the soot bulk and surface chemical compositions were evaluated with Fourier transform infrared spectroscopy and attenuated total reflection spectroscopy. Plausible uptake mechanisms were discussed on the basis of the measured soot physiochemical properties by comparing the mono and dicarboxylic acids.