Gas Analysis for Determination of Dry Molecular Weight – USEPA Method 3

USEPA Method 3 is used for the determination of carbon dioxide (CO₂) and oxygen (O₂) concentrations and dry molecular weight of a sample from a source where it has been determined that compounds other than CO₂, O₂, carbon monoxide (CO), and nitrogen (N₂) are not present in concentrations sufficient to affect the results.
 
The gas sample is analyzed for percent CO₂ and percent O₂ using an Orsat gas analyzer.  A gas sample is extracted from a stack by one of the following methods:

• single-point, grab sampling;
• single-point, integrated sampling;
• multi-point, integrated sampling.

Other methods, as well as modifications to the procedure described in Method 1, are also applicable for all of the above determinations.  Examples include the use of continuous emissions analyzers to perform the gas analysis, calculation of either CO₂ or O₂ stoichiometrically, or assigning a value for dry molecular weight in lieu of actual measurements.  These methods and modifications are subject to the approval of the Administrator.