The kinetics of thermal desorption of two four-ring polycyclic aromatic hydrocarbons, fluoranthene, and pyrene from we I I-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 Z 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 C C, 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)). III 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.