Flame-wall-interaction (FWI) is investigated numerically using a premixed stoichiometric Side-Wall Quenching configuration. Within the 2D fully resolving laminar simulation, detailed chemistry is used to study the stationary quenching of a methane-air (CH4) flame at an isothermal inert wall of 300 K. The investigation is related to a recent experimental study that revealed that the carbon-monoxide distribution substantially differs in the near-wall region when compared to an undisturbed flame. Simulations are carried out using different reaction mechanisms (GRI and Smooke) as well as diffusion treatments (unity Lewis and mixture averaged transport) and the results are compared to the measured temperature and CO concentrations. Specifically regarding the latter, being an important pollutant, recent attempts based on tabulated chemistry failed in predicting its near-wall accumulation. Accordingly, within this work the detailed chemistry simulations are used to investigate the origin of CO near the wall. Therefore, a Lagrangian analysis is applied to quantify the contribution of chemical production and consumption as well as diffusion to understand the root mechanism of the high CO concentrations measured. The analysis revealed that the high CO concentrations near the wall results from a transport originating from CO produced at larger wall distances. In that region being not submitted to large heat losses, a high chemical activity and corresponding CO production is found. Accordingly, a diffusion process is initiated towards the wall where the chemical sources itself were actually found to be negative. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.