5.1 Most oxides of nitrogen are formed during high-temperature combustion. The U.S. Environmental Protection Agency (EPA) has set primary and secondary air quality standards for NO₂ that are designed to protect the public health and the public welfare (40 CFR, Part 50).

5.2 Oxides of nitrogen are generated by many industrial processes that can result in employee exposures. These are regulated by the Occupational Safety and Health Administration (OSHA), which has promulgated exposure limits for the industrial working environment (29 CFR, Part 1910).

5.3 These test methods have been found to be satisfactory for measuring oxides of nitrogen in ambient and workplace atmospheres over the ranges shown in 1.1.

1.1 These test methods cover procedures for the continuous determination of total nitrogen dioxide (NO₂) and nitric oxide (NO) as NO_x, or nitric oxide (NO) alone or nitrogen dioxide (NO₂) alone, in the ranges shown in the following table:

Approximate Range of Concentration
(25°C and 101.3 kPa (1 atm))

Gas

Ambient Atmosphere

Workplace Atmosphere

μg/m³ (ppm)

mg/m³ (ppm)

NO

10 to 600 (0.01 to 0.5)

0.6 to 30 (0.5 to 25)

(NO + NO₂) = NO_x

20 to 1000 (0.01 to 0.05)

1 to 50 (0.5 to 25) 

NO₂

20 to 1000 (0.01 to 0.5)

1 to 50 (0.5 to 25) 

1.2 The test methods are based on the chemiluminescent reaction between nitric oxide and ozone.

1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.

1.4 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 Section 9.

1.5 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.