5.1 Nitrogen dioxide plays an important role in photochemical smog-forming reactions and, in sufficient concentrations, is deleterious to health, agriculture, materials, and visibility.

5.2 In combustion processes, significant amounts of nitric oxide (NO) may be produced by combination of atmospheric nitrogen and oxygen; at ambient temperatures NO can be converted to NO₂ by oxygen and other atmospheric oxidants. Nitrogen dioxide may also be generated from processes involving nitric acid, nitrates, the use of explosives, and welding.

1.1 This test method2 covers the manual determination of nitrogen dioxide (NO₂) in the atmosphere in the range from 4 to 10 000 μg/m³ (0.002 to 5 ppm(v)) when sampling is conducted in fritted-tip bubblers.

1.2 For concentrations of NO₂ in excess of 10 mg/m³ (5 ppm(v)), as occur in industrial atmospheres, gas burner stacks, or automotive exhaust, or for samples relatively high in sulfur dioxide content, other methods should be applied. See for example Test Method D1608.

1.3 The maximum sampling period is 60 min at a flow rate of 0.4 L/min.

1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions to inch-pound units that are provided for information only and are not considered standard.

1.5 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. See also 7.2.2 for other precautions.

1.6 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.