In biomass gasification processes, the formation and handling of tars are of major concern. Robust and versatile analytical tools are needed to on-line monitor tar compound concentrations in process gases from lab- to industrial scale. This study addresses the development and application of an on-line UV-Vis method, based on a liquid quench sampling system. The high sensitivity of this method allows to detect UV-Vis active tar compounds in the low ppmv region. Recorded spectra from the liquid phase were analyzed for their tar composition by means of a classical least squares (CLS) and partial least squares (PLS) approach. The developed method was applied to two case studies, involving a lab-scale tar reformer and a pilot-scale gas scrubber. Quantification results in gases with limited complexity in tar composition showed good agreement with off-line reference methods (GC-FID). The case studies show that the developed method is a rapid, sensitive tool that can be applied for qualitative process monitoring with the added benefit of quantification in gases with a limited number of tar compounds. (C) 2016 Elsevier Ltd. All rights reserved.