Methane CH₄

Methane is a potent greenhouse gas that has significant impact on the earth’s climate. It is produced by both natural and human activities, including microbial digestion, fossil fuel production, transportation and waste management.

To effectively understand the sources and magnitude of methane emissions and develop strategies to mitigate them, it is crucial to have accurate, real-time, ambient methane measurements

The CH₄ module uses a Gas Sensitive Semiconductor (GSS) sensor.

The module contains a proprietary flow design that minimizes baseline drift and the sample air is filtered using a proprietary scrubber to reduce interferences. The sensor output is determined under both baseline and sample conditions, and a proprietary algorithm is used to calculate the methane concentration. The flow rate is controlled by a flow control orifice on the exhaust side of the sensor module (expected to be approximately 60 mL min^-1).

The CH₄ module performance specifications are given in the table below.

An Aeroqual AQS containing a methane module was co-located in November 2022 with a Picarro methane analyzer. The CH₄ module produced a R² of 0.87 and a mean absolute error (MAE) of 0.2 ppm. The low MAE value is indicative that the module has low zero and span drift. Performance in an Aeroqual AQM 65 would exceed this.

The sensor based methane system can be field calibrated using standard calibration equipment and reference gases. This ensures the module calibration is fully traceable to NIST primary standards.

The CH₄ module factory calibration is achieved using a zero-air source, certified calibration gas standards and a certified gas dilution calibrator. The Aeroqual AirCal 1000 or 8000 systems can be used to calibrate the CH₄ module in the field.

Calibration frequency will be dependent on the user’s data quality objectives and Quality Assurance Project Plan (QAPP), but based on the low rate of field drift the recommended calibration frequency is 1-3 months.

The Aeroqual methane module is specific towards CH₄ but other gases in the environment may also cause a response from the CH₄ sensor. These do not indicate a fault. These effects are part of the module behavior and should be considered when examining data.

The CH₄ module response to other ambient air pollutants is documented in the table below.

The methane module contains several components that are consumed during use. The chemical scrubber has an expected life of 2 to 3 years. The GSS sensor has an expected life of 2 to 3 years.

The Aeroqual methane sensor head uses a Gas Sensitive Semiconductor (GSS) sensor. The sensing material for the sensor head is a n-type semiconductor, whose resistance decreases when the sensing layer is exposed to CH₄. The sensor resistance is used to calculate concentration using a proprietary algorithm.

The table below contains the methane sensor head specifications. It is designed for industrial health and safety monitoring and can be used on our Ranger, S Series and Series 900 products.