Oxygen (O₂) Measurement in CARB Source Testing

As part of CARB-compliant source testing, REM incorporates continuous oxygen (O₂) measurement to ensure accurate normalization of emission data and proper characterization of combustion conditions. Oxygen concentration is a critical reference parameter used to correct pollutant concentrations to standardized conditions (e.g., % O₂ correction), enabling valid comparison against regulatory limits.

Why O₂ Measurement Matters

Oxygen levels in the exhaust stream directly reflect combustion efficiency and dilution. Because many emission standards are expressed at a reference oxygen concentration (commonly 3%, 7%, or 15% O₂ depending on the source type), precise O₂ measurement is required to:

• Normalize pollutant concentrations to regulatory reference conditions

• Verify combustion performance and excess air levels

• Ensure data integrity for compliance reporting

• Support calculation of emission rates and correction factors

Without accurate O₂ data, emission results cannot be properly interpreted or accepted under CARB protocols.

REM’s O₂ Testing Methodology

REM measures oxygen using extractive gas analysis systems that comply with CARB-approved methodologies (typically aligned with U.S. EPA Methods 3A or equivalent).

1. Sample Extraction

A representative sample of flue gas is extracted from the stack or duct using a heated probe system. This ensures that the sample remains above dew point temperature, preventing condensation and preserving gas composition integrity.

2. Sample Conditioning

The extracted gas passes through a conditioning system designed to:

• Remove moisture (via condensers or permeation dryers)

• Filter particulate matter

• Maintain stable pressure and flow to the analyzer

This step is essential to protect instrumentation and ensure accurate readings.

3. Oxygen Analysis

O₂ concentration is measured using a paramagnetic oxygen analyzer, the industry standard for regulatory testing. This technology leverages the paramagnetic properties of oxygen molecules, providing:

• High specificity to O₂ (minimal cross-interference)

• Fast response time

• Excellent accuracy and repeatability

Typical measurement ranges are selected based on the source but commonly span 0–25% O₂.

4. Calibration and Quality Assurance

To meet CARB and EPA QA/QC requirements, REM performs:

• Pre-test calibration using certified zero and span gases

• Mid-run drift checks (when required by method)

• Post-test calibration to verify analyzer stability

• Calibration error and drift assessments within allowable limits

All calibration gases are NIST-traceable, and calibration procedures follow strict protocol to ensure defensible data.

5. Data Acquisition and Integration

O₂ measurements are continuously recorded using a digital data acquisition system (DAS). These data are time-aligned with pollutant measurements (e.g., NOx, CO, CO₂) to enable:

• Real-time monitoring of test conditions

• Post-test correction of emission concentrations to reference O₂ levels

• Comprehensive reporting consistent with CARB requirements

Reporting and Use of O₂ Data

Measured oxygen concentrations are used to correct pollutant concentrations using standard reference formulas specified by CARB and EPA methods. Final reports include:

• Raw and corrected O₂ values

• Calibration records and QA/QC checks

• Time-resolved data logs

• Documentation of compliance with applicable test methods

Summary

REM’s O₂ testing approach ensures that all emission data are accurate, properly normalized, and fully compliant with CARB standards. By combining robust sampling techniques, high-precision analyzers, and rigorous QA/QC procedures, we deliver reliable oxygen measurements that underpin defensible compliance results.