5.1 Sulfur dioxide is a major air pollutant, commonly formed by the combustion of sulfur-bearing fuels. The Environmental Protection Agency (EPA) has set primary and secondary air quality standards (7) that are designed to protect the public health and welfare.

5.2 The Occupational Safety and Health Administration (OSHA) has promulgated exposure limits for sulfur dioxide in workplace atmospheres (8).

5.3 These methods have been found satisfactory for measuring sulfur dioxide in ambient and workplace atmospheres over the ranges pertinent in 5.1 and 5.2.

5.4 Method A has been designed to correspond to the EPA-Designated Reference Method (7) for the determination of sulfur dioxide.

1.1 These test methods cover the bubbler collection and colorimetric determination of sulfur dioxide (SO₂) in the ambient or workplace atmosphere.

1.2 These test methods are applicable for determining SO₂ over the range from approximately 25 μg/m³ (0.01 ppm(v)) to 1000 μg/m³ (0.4 ppm(v)), corresponding to a solution concentration of 0.03 μg SO₂/mL to 1.3 μg SO₂/mL. Beer's law is followed through the working analytical range from 0.02 μg SO₂/mL to 1.4 μg SO₂/mL.

1.3 The lower limit of detection is 0.075 μg SO₂/mL (1),2 representing an air concentration of 25 μg SO₂/m³ (0.01 ppm(v)) in a 30-min sample, or 13 μg SO₂/m³ (0.005 ppm(v)) in a 24-h sample.

1.4 These test methods incorporate sampling for periods between 30 min and 24 h.

1.5 These test methods describe the determination of the collected (impinged) samples. A Method A and a Method B are described.

1.6 Method A is preferred over Method B, as it gives the higher sensitivity, but it has a higher blank. Manual Method B is pH-dependent, but is more suitable with spectrometers having a spectral band width greater than 20 nm.

Note 1: These test methods are applicable at concentrations below 25 μg/m³ by sampling larger volumes of air if the absorption efficiency of the particular system is first determined, as described in Annex A4.

Note 2: Concentrations higher than 1000 μg/m³ can be determined by using smaller gas volumes, larger collection volumes, or by suitable dilution of the collected sample with absorbing solution prior to analysis.

1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.8 Warning—Mercury has been designated by many regulatory agencies as a hazardous material that can cause serious medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to materials. Caution should be taken when handling mercury and mercury containing products. See the applicable product Safety Data Sheet (SDS) for additional information. Users should be aware that selling mercury and/or mercury containing products into your state or country may be prohibited by law.

1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For specific precautionary statements, see 8.3.1, Section 9, and A3.1.3.

1.10 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.