The mechanism of nanoparticles processed in flame aerosol reactors involves vapor to solid reaction, nucleation, coalescence, agglomeration, diffusion and other processes. Determination of internal (e.g., particle size distribution (PSD), aggregate fractal dimension (AFD), and particle volume fraction (PVF)) and external (e.g., temperature and flow velocity) properties of nanoparticles through numerical simulations or experimental measurements is critical to understanding the underlying particle dynamics, which still remains a major challenge. Multiple key internal and external properties of nanoparticles in flame were measured and characterized simultaneously in this study by a simple and novel dual time-interval thermophoretic sampling (DTTS) method. A tailor-made fine-wire thermocouple was first used to measure flame temperature, with a sufficiently short residence time to reduce the effects of radiation losses and nanoparticles deposition as possible and thereby the thermocouple response met the first-order dynamic equation where only heat convection was considered. Two TEM grids were used for nanoparticle sampling at a position and were exposed to flame for two different time intervals. As the amount of particles deposited on the probe surface by the thermophoretic force is a function of gas temperature, flow velocity. PVF and the probe exposure time in the flame, we proposed an integrative solution for these multiple parameters using the two samples by accounting for the effects of the unsteady temperature gradient of the probe. The effects of flow velocity on convection heat transfer of flame and TEM grids were considered by analyzing the visible microscopic state of thermophoretic-deposited particles. A co-flow diffusion CH4 flame for TiO2 nanoparticle synthesis by feeding TiCl4 vapor was measured via the DTTS method. The experimental measurements of flame temperature, flow velocity and PVF at the different flame heights agree well with the simulation results by coupled computational fluid dynamics with population balance modeling (CFD-PBM). (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.