1. Scope 1.1 This Standard applies to the measurement of the concentration of sulphur dioxide in air. 1.2 This Standard sets forth the Pararosaniline Colorimetric Procedure based on the West-Gaeke Method as the reference method for the measurement of sulphur dioxide in the range 25 to 1000 µg·m-3 at 25°C and 101.3 kPa. Note. All concentrations referred to throughout this Standard are based on a temperature of 25°C and an atmospheric pressure of 101.3 kPa unless otherwise stated. 1.3 This Standard recognizes that several instrumental methods are available for the continuous monitoring of sulphur dioxide. Brief outlines of some of the instrumental techniques are given as Appe ndices to this Standard. These methods may be preferred over the reference method for the routine analysis of this pollutant. However, any such method shall first be shown to be equivalent to the reference method, or shall be mutually acceptable to all interested parties. Note: For additional information on equivalence testing, refer to Item 1 of the Bibliography.