In aviation terminology, what does "NAC" stand for?

In aviation terminology, "NAC" stands for Non-Absolute Concentration. This term relates to measurements and evaluations in the field of airborne particulate matter and other substances that may not conform to absolute values, particularly in the context of environmental assessments within the aviation industry. Understanding this concept is crucial as it influences how air quality and emissions are monitored and managed around airports and during flight operations.

The other terms do not accurately reflect standard aviation terminology or practices, which is essential for maintaining clarity in communications and understanding technical aspects relevant to aviation.