Ion-mobility spectrometry sensor for NOx detection

A sensor and detection methods are provided for detecting nitric oxides (NOx) in an exhaust gas based upon ion mobility spectrometry (IMS) technique. An ionization chamber having an interior electrically conductive shell receives exhaust gas. A spark electrode having a needle tip extends into the ionization chamber. A shutter grid is coupled between the ionization chamber and an ion drift tube. A substantially continuous spark discharge is established between the electrically conductive shell and the needle tip of the spark electrode for ionization of the exhaust gas. Negative NO₂ ions are kept inside the chamber by biasing the electrically conductive shell and the shutter grid at a negative voltage. Then a positive pulse is applied to the shutter grid to cause the shutter to open for negative NO₂ ions to exit into the ion drift tube. The IMS sensor is small-sized, low-cost, robust, and reliable.