The kinetics of thermal desorption of two four-ring polycyclic aromatic hydrocarbons, fluoranthene, and pyrene from well-characterized laboratory-generated kerosene soot surface was studied over the temperature range 260-320 K in a low-pressure flow reactor combined with an electron-impact mass spectrometer. Two methods were used to measure the desorption rate constants: monitoring of the surface-bound fluoranthene and pyrene decays due to desorption using off-line HPLC measurements of their concentrations in soot samples, and monitoring of the desorbed molecules in the gas phase using in situ mass spectrometric detection. Results obtained with the two methods were in good agreement and yielded the following Arrhenius expressions for the desorption rate constants: k(des) (fluoranthene) = 4 x 10(14) exp[-(93900 +/- 1700)/RT] and k(des) (pyrene) = 6 x 10(14) exp[-(95200 +/- 1800)/RT] (k(des) are in units of s(-1), and activation energies are in J mol(-1)). In addition, the combined uptake coefficient of fluoranthene and pyrene on soot (calculated using specific surface area) was estimated to be near 5 x 10(-3) at T = 310 K.

The kinetics of the thermal desorption of a set of three- to five-ring polycyclic aromatic hydrocarbons (PAHs) from a laboratory-generated kerosene soot surface was studied over the temperature range 250-355 K in a low-pressure flow reactor combined with an electron-impact mass spectrometer. Two methods were used to measure the desorption rate constants: monitoring of the surface-bound PAH decays due to desorption using off-line HPLC measurements of their concentrations in soot samples and monitoring of the desorbed molecules (anthracene and phenanthtrene) in the gas phase using in situ mass spectrometric detection. The Arrhenius parameters (A factors and activation energies) for the desorption rate constants of 10 soot-bound PAHs were determined. The PAH-soot binding energies were found to be similar for PAHs with the same number of carbon atoms and to increase with increasing number of PAH carbon atoms. The experimental data are discussed in the frame of the existing theoretical gas to particle partitioning model.