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D3162-21 – Standard Test Method Technical Guide
This test method, designated as ASTM D3162-21, details the procedure for the continuous measurement of carbon monoxide (CO) in the atmosphere using Nondispersive Infrared Spectrometry (NDIR). This standard is a critical component of ambient air quality monitoring programs focused on gaseous criteria pollutants, superseding the previous version D3162-12(2020).
🔬 Scope and Measurement Principle
The standard is specifically applicable to the determination of CO concentrations between 0.6 mg/m³ (0.5 ppm(v)) and 115 mg/m³ (100 ppm(v)). It achieves a limit of detection of approximately 0.6 mg/m³ (0.5 ppm(v)). The core measuring principle is based on the specific absorption of infrared radiation by CO molecules at its characteristic wavelength in the 4.7 µm region.
📝 Important Note on Units: The values stated in SI units (mg/m³) are regarded as the standard. The units in parentheses (ppm(v)) are provided for information only and are not considered standard.
⚙️ Instrument Configuration and Summary of Test Method
The atmospheric sample is introduced into a sample conditioning system and then into the NDIR spectrometer. The standard recognizes several optical configurations for detection, including:
- Single Path: A monitor capable of distinguishing between sample and reference gases.
- Dual Beam: Two parallel infrared beams passing through separate sample and reference cells to a selective detector.
- Gas Filter Correlation: Using a concentrated sample of CO as a filter for the IR beam to produce a reference beam that cannot be further attenuated by the CO in the sample cell.
| 🟦 Parameter | 🎯 Specification / Value |
|---|---|
| Concentration Range | 0.6 mg/m³ (0.5 ppm(v)) to 115 mg/m³ (100 ppm(v)) |
| Limit of Detection (LOD) | Approximately 0.6 mg/m³ (0.5 ppm(v)) |
| Analytical Wavelength | 4.7 µm (Infrared Region) |
| Detection Principle | Nondispersive Infrared Spectrometry (NDIR) |
📈 Key Performance Characteristics and Terminology
The standard defines specific performance metrics essential for data quality. A key term is Fall Time, which is critical for understanding the dynamic response of the analyzer to decreasing concentrations.
| 🟦 Term | ⚡ Definition (per Standard) |
|---|---|
| Fall Time | The time interval between the initial response and 90 % of the final response after a step decrease in input concentrations. |
⚠️ Regulatory and Safety Compliance: This standard does not purport to address all safety concerns. It is the responsibility of the user to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations. Refer to Section 9 of D3162-21 for specific precautions.
❓ Frequently Asked Questions
🔍 What is the applicable concentration range of ASTM D3162-21?
The test method is applicable to CO concentrations ranging from 0.6 mg/m³ (0.5 ppm(v)) to 115 mg/m³ (100 ppm(v)) in the atmosphere.
💡 At what wavelength does the NDIR detection occur for carbon monoxide?
The measuring principle is based on the specific absorption of infrared radiation by carbon monoxide at the 4.7 µm region of the spectrum.
⚡ How is the “fall time” defined in this standard?
Fall time is specifically defined as the time interval between the initial response and 90 % of the final response after a step decrease in the input concentrations.
📌 What are the primary detection configurations allowed by D3162-21?
The standard allows for several configurations including single-path monitors, dual-beam systems, and instruments using the gas filter correlation technique to compare the IR absorption spectrum.