This International Standard specifies a modified Griess-Saltzman method for the determination of the mass concentration of nitrogen dioxide present in ambient air. The method is applicable to the determination of the mass concentration of nitrogen dioxide present in ambient and confined air within the range 0,003 mg/m^(3) to 2 mg/m^(3) and for sampling times between 10 min and 2 h. Substances present in the air mass under investigation, and thus in the air sample, and known to have an effect on the instrument reading, are given in 7.4. Information on the performance characteristics is given in 8.2. The method is not suitable for personal breathing-zone sampling. The Griess-Saltzman method is suitable for the analytical check of calibration gas mixtures which are used to calibrate chemiluminescence analysers (see ISO 7996).