What is the generally accepted technique for measuring attainments with the National Ambient Air Quality Standard for NOx?

What is the generally accepted technique for measuring attainments with the National Ambient Air Quality Standard for NOx?

• A. Pararosaniline
• B. Chemiluminescence
• C. Nondispersive infrared spectroscopy
• D. Transmissometer

Answer: (B)

Chemiluminescence is the standard approach for measuring NOx in ambient air because it directly detects nitric oxide through its reaction with ozone, which emits light. The light intensity is proportional to the NO concentration, and by converting NO2 to NO before detection, the method can quantify total NOx. This combination—high sensitivity, fast response, and suitability for continuous regulatory monitoring—makes it the preferred technique for assessing attainment with NOx air quality standards. Other methods aren’t used for this purpose: colorimetric pararosaniline is designed for different pollutants, nondispersive infrared spectroscopy doesn’t reliably quantify ambient NOx at regulatory levels due to interference and sensitivity issues, and a transmissometer measures visibility, not atmospheric chemistry.

Chemiluminescence is the standard approach for measuring NOx in ambient air because it directly detects nitric oxide through its reaction with ozone, which emits light. The light intensity is proportional to the NO concentration, and by converting NO2 to NO before detection, the method can quantify total NOx. This combination—high sensitivity, fast response, and suitability for continuous regulatory monitoring—makes it the preferred technique for assessing attainment with NOx air quality standards.

Other methods aren’t used for this purpose: colorimetric pararosaniline is designed for different pollutants, nondispersive infrared spectroscopy doesn’t reliably quantify ambient NOx at regulatory levels due to interference and sensitivity issues, and a transmissometer measures visibility, not atmospheric chemistry.