The invention relates to the field of air quality control. More specifically, the invention relates to a system for identifying the presence of gaseous chemical pollutants, preferably volatile organic compounds, in a closed environment, said system comprising: a support (1), a gaseous chemical pollutant sensor (2), and at least one colorimetric reference mark (5A, 5B, 5C, 5D, 5E) of a given colour, located on the support.