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D3824-20 – Standard Test Method Technical Guide
📖 Scope and Principle of the Method
ASTM D3824-20 provides standard test methods for the continuous measurement of oxides of nitrogen in ambient and workplace atmospheres. The methods are based on the chemiluminescent reaction between nitric oxide (NO) and ozone (O₃). The homogeneous gas phase reaction produces excited nitrogen dioxide (NO₂*), which emits light (hv) upon returning to its ground state:
NO + O₃ → NO₂* + O₂
NO₂* → NO₂ + hv
In the presence of excess ozone, the intensity of the light emission is directly proportional to the nitric oxide concentration. These test methods cover procedures for the determination of total nitrogen dioxide (NO₂) and nitric oxide (NO) as NOx, or NO alone, or NO₂ alone. All values are stated in SI units, with values in parentheses provided for information only and not considered standard. These test methods are under the jurisdiction of ASTM Committee D22 on Air Quality, Subcommittee D22.03 on Ambient Atmospheres and Source Emissions.
⚙️ Measurement Ranges and Configurations
The standard defines the applicable concentration ranges at 25°C and 101.3 kPa (1 atm) for both ambient and workplace atmospheres. The ranges cover NO, NO₂, and total NOx as shown in the following table:
| 🟦 Gas Type | 📏 Ambient (µg/m³) | 🎯 Ambient (ppm) | ⚡ Workplace (mg/m³) | 📐 Workplace (ppm) |
|---|---|---|---|---|
| NO | 10 to 600 | 0.01 to 0.5 | 0.6 to 30 | 0.5 to 25 |
| (NO + NO₂) = NOx | 20 to 1000 | 0.01 to 0.5 | 1 to 50 | 0.5 to 25 |
| NO₂ | 20 to 1000 | 0.01 to 0.5 | 1 to 50 | 0.5 to 25 |
🔬 Unit Considerations: Ambient atmosphere ranges are expressed in µg/m³ with ppm in parentheses, while workplace atmosphere ranges are in mg/m³ with ppm in parentheses. The values in parentheses are provided for information only under the specific conditions of 25°C and 101.3 kPa (1 atm).
📚 Referenced Documents and Compliance
The execution of these test methods requires adherence to several key referenced ASTM standards. These ensure proper terminology, sampling practices, calibration, and operational procedures:
- D1356 – Terminology Relating to Sampling and Analysis of Atmospheres
- D1357 – Practice for Planning the Sampling of the Ambient Atmosphere
- D1914 – Practice for Conversion Units and Factors
- D3195/D3195M – Practice for Rotameter Calibration
- D3249 – Practice for General Ambient Air Analyzer Procedures
- D3609 – Practice for Calibration Techniques Using Permeation Tubes
- D3631 – Test Methods for Measuring Surface Atmospheric Pressure
Furthermore, users must be aware of regulatory compliance frameworks such as 29 CFR Part 1910 (Occupational Safety and Health Standards) and 40 CFR Parts 50 and 53 (EPA Regulations on Ambient Air Monitoring Reference and Equivalent Methods).
⚠️ Safety Notice: 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 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 of the full standard text.
❓ Frequently Asked Questions
🔍 What is the underlying principle of the D3824-20 test method?
The method is based on the chemiluminescence emitted from the homogeneous gas phase reaction of nitric oxide (NO) with ozone (O₃). The intensity of the light emitted is directly proportional to the nitric oxide concentration when excess ozone is used.
💡 What is the concentration range for measuring NO in a workplace atmosphere?
For workplace atmospheres at 25°C and 101.3 kPa, the standard specifies a range of 0.6 to 30 mg/m³ (0.5 to 25 ppm) for nitric oxide (NO).
⚡ Which ASTM practices are critical for proper calibration in this standard?
Key calibration practices include D3249 for general analyzer procedures, D3609 for calibration techniques using permeation tubes, and D3195/D3195M for rotameter calibration.
📌 What does the fixed designation D3824-20 signify?
The standard is issued under the fixed designation D3824. The number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. The ‘20’ indicates the year of last revision, with the original approval dating back to