A method and apparatus for providing output emission data corresponding to output emissions from a source of emissions includes a sensing emission monitoring system that senses the output emissions directly from the source of emissions and a predictive emission monitoring system that predicts the output emissions from the source of emissions. The sensing emission monitoring system provides a first set of output values indicative of the output emissions, while the predictive emission monitoring system provides a second set of output values indicative of the output emissions. The system checks the operating state of the sensing emission monitoring system and generates output emission data from the first set of output values if the sensing emission monitoring system is operable and from the second set of the output values if the sensing emission monitoring system is inoperable.