Gas Analysis with TDLAS: Pros and Cons of Extracted/Sampled Gas Analysis Compared to In-Situ and Cross-Stack Measurements

Gas analysis plays a vital role in monitoring and measuring gas emissions in various industries and environments. There are different methods and techniques for gas analysis, including TDLAS (Tunable Diode Laser Absorption Spectroscopy). In this blog post, we will explore the use of TDLAS for gas analysis with extracted/sampled gas and compare it to in-situ and cross-stack measurements. We will also discuss the advantages and disadvantages of each method.

Extracted/Sampled Gas Analysis:

When using TDLAS for gas analysis, a common method is to extract or sample the gas from the source and transport it to the analysis instrument. This allows for accurate measurements in controlled conditions. The advantages of extracted/sampled gas analysis include:


  • Improved measurement accuracy: By extracting or sampling the gas and analyzing it in a controlled laboratory or measurement space, TDLAS can offer high measurement accuracy.
  • Ability to analyze multiple gases: Extracted/sampled gas analysis with TDLAS enables the measurement and analysis of multiple gases simultaneously, which is particularly useful in complex environments.
  • Flexibility in measuring inaccessible locations: By sampling the gas from inaccessible locations or pipelines, TDLAS can be used to monitor emissions or gas flows in places where in-situ or cross-stack measurements are challenging to perform.


  • Time-consuming: Extracting or sampling the gas and transporting it to the analysis instrument can be a time-consuming process, which can extend the measurement time.
  • Potential loss of representativeness: There is a risk that the extracted or sampled gas may not be entirely representative of the overall gas flow or emission, which can affect the reliability of the measurement results.

Comparison with In-Situ and Cross-Stack Measurements:

In-situ measurements are performed directly at the source, while cross-stack measurements are conducted by analyzing the gas across a path between an emitter and a receiver. Here are some comparisons with extracted/sampled gas analysis:

  • In-situ measurements can provide real-time data and the ability to monitor changes over time. On the other hand, extracted/sampled gas analysis offers better accuracy and the ability to analyze multiple gases simultaneously.
  • Cross-stack measurements can be useful for monitoring large emission sources. However, extracted/sampled gas analysis can be more flexible and applicable to inaccessible locations or smaller emissions.


Extracted/sampled gas analysis with TDLAS offers advantages such as high accuracy and the ability to analyze multiple gases simultaneously. It is a useful method for monitoring emissions or gas flows in inaccessible environments. However, there are drawbacks such as time-consuming processes and potential loss of representativeness. The choice of method depends on specific needs and conditions to achieve accurate and reliable gas analysis results.