Gas turbines frequently have automatic sampling systems or continuous emissions monitors (CEMs), although Subpart GG does not require CEMs. Figure 1 illustrates the major components of an automatic sampling system for a gas turbine. Emissions are initially drawn into the system through the probe which is mounted into the stack so it is exposed to the exhaust. A pump is used to acquire a sample from the stack. The sample is conditioned to protect the analyzers. After the stack gas passes through the analyzer, it goes into an exhaust manifold and out to the atmosphere. The system also uses calibration gases to confirm the accuracy of the analyzers. When calibrations are performed, the valve to the desired calibration gas is opened, while no exhaust is allowed to flow from the stack. Since the concentration of the pollutant in the calibration gas is known, the operation of the analyzers can be checked.