1. A parameter value estimator for a process primarily performed to control emission of a particular non-particulate pollutant into the air, the process having multiple process parameters (MPPs) including a parameter representing an amount of the particular non-particulate pollutant emitted, comprising: one of a neural network process model and a non-neural network process model representing a relationship between one of the MPPs, other than the parameter representing the amount of the emitted particular non-particulate pollutant, and one or more of the other MPPs; and a processor configured with the logic to estimate a value of the one MPP based on a value of each of the one or more other MPPs and the one model.