{"id":"AIBD-0845","title":"EPA finds that SmartCEM-75 models matched NOx analyzers on all eight T.H. Wharton turbines, and NRG has reported emissions with them since 2009","summary":"EPA found that SmartCEM-75 models trained on eight NRG turbines in Houston matched NOx analyzers over 720 hours each. NRG has reported NOx with them since 2009 for six units and 2011 for two.","date_observed":"2010-09-27","date_basis":"source publication","date_precision":"day","benefit_status":"reported","source_collection":null,"source_entry":null,"account":"NRG Texas Power runs eight gas turbines at its T.H. Wharton Generating Station in Houston. In October 2007 it asked EPA to let it monitor their NOx with CMC Solutions' SmartCEM-75 predictive emission monitoring system (PEMS). EPA describes the PEMS as statistical hybrid software, with a model of each turbine developed from training data. Temporary certified analyzers gave hourly reference data, and each PEMS ran beside them for 720 operating hours in the third quarter of 2007. EPA also ran the tests itself on the startup and shutdown hours. It found that the output on each unit passed all three statistical tests, with correlations from 0.936 to 0.999. EPA approved the systems on 30 December 2008 and restated the terms on 27 September 2010. In May 2025 EPA wrote that NRG had used the PEMS since 2009 for six units and since 2011 for the other two. Citing a very high passing rate among all units with approved PEMS, it cut the required audits from monthly to quarterly. 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