The advent of dry, low-emissions combustion systems for gas turbine applications and the trend towards requiring emissions monitoring and lower NOx limits by regulatory agencies, have created renewed interests in the uncertainty of NOx emissions measurements. This paper addresses the uncertainty of measuring NOx emissions from gas turbines in the field, including gas turbines equipped with conventional combustion systems, with or without water injection, with dry, low-emissions combustion systems and with exhaust clean-up systems.

The sources of errors, using current state-of-the-art instruments, in field emissions testing or continuous emission monitoring of gas turbines to meet specific emission (ppmvd @ 15% O2) as well as mass emission rate (kg/hr) limits are identified. The uncertainty of measuring NOx emissions from gas turbines is estimated and compared with Geld data. The effect of NOx emission levels on measurement uncertainty is also addressed. The minimus NOx measurement uncertainty is determined and is in good agreement with what is currently allowed by regulatory agencies.

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