What are the two categories that Continuous Emission Monitoring Systems (CEMS) are classified into?

Continuous Emission Monitoring Systems (CEMS) are crucial for measuring the concentration of pollutants emitted from industrial processes. The correct classification of CEMS into two categories is based on how the sampling and measurement of emissions is conducted.

Extractive systems operate by capturing a sample of flue gas from the stack or duct and then transporting it to an analysis device. This allows for the measurement of various gas components in a controlled environment, often providing more accurate and precise results due to the ability to isolate the sample from environmental interferences.

On the other hand, in-situ systems perform the measurement directly in the flue gas stream without extracting a sample. This method allows for real-time monitoring and can provide instantaneous results, which can be advantageous for immediate emissions control adjustments.

This classification underscores the operational principles and technical capabilities of the monitoring systems, making it clear why "Extractive and In-Situ" is the correct answer. The other categorizations do not represent the standard terminology used in CEMS, thereby confirming the importance of understanding both methodologies in monitoring emissions effectively.