Patent ID: 7820028

Claim:
A method of calculating a total NOx concentration, comprising steps of: providing a gas stream having a NO concentration and a NO2 concentration, wherein a sum of the NO concentration and the NO2 concentration is a total NOx concentration; contacting the gas stream with a first zirconium oxide based oxygen sensor at a first temperature to measure a first oxygen concentration and then using the first oxygen concentration to predict a first ratio of NO:NO2 at equilibrium at the first temperature; contacting the gas stream with a second zirconium oxide based oxygen sensor at a second temperature to measure a second oxygen concentration and then using the second oxygen concentration to predict a second ratio of NO:NO2 at equilibrium at the second temperature, the second temperature being different than the first temperature; and calculating the total NOx concentration using the first ratio of NO:NO2 at equilibrium and the second ratio of NO:NO2 at equilibrium.