See linked PDF for a discussion about ozone starvation (usually caused by diminishing UV output and therefore lessoning O3 production from the ozone lamp). CLD_NOx_ozone_starvation_response_graph_discussion.pdf
Possible symptoms of ozone starvation (O3): poor linearity; bad CGA results; failed RATA; poor raw counts on span gas (and low signal delta).
Other key words: plateau, knee in the response curve, excessive gain, high gain, chemiluminescence
Applicable to: Rosemount NGA-2000 CLD, 951A, 951C, 951E, and any other NO/NOX analyzer relying on an ozone – NO (nitric oxide) reaction