Utility of ammonium salts for the calibration of NH₃ sensors

Abstract The calibration of NH 3 -sensing instruments has been an ongoing challenge to atmospheric chemists. Here, the potential utility of ammonium nitrate (NH 4 NO 3 ), -sulfate ((NH 4 ) 2 SO 4 ), -bisulfate (NH 4 HSO 4 ), -carbonate ((NH 4 ) 2 CO 3 ), and -bicarbonate (NH 4 HCO 3 ) to generate gas streams containing NH 3 or aerosol NH 4 + calibrated by measuring the co-emitted acids was investigated. Head space vapors and aerosols were analyzed using a commercial total nitrogen (N t ) instrument modified to quantify N t mixing ratios in both the gas- and particle phases, scanning mobility particle sizing, thermal-dissociation cavity ring-down spectroscopy, and Fourier transform infrared spectroscopy. The best results were obtained with NH 4 HCO 3 . Using a simple gas delivery setup consisting of two dilution stages and a line heater, the NH 3 output from NH 4 HCO 3 was calibrated by quantifying the stoichiometric co-emission of CO 2 with a relatively inexpensive non-dispersive infrared spectrometer. The new approach constitutes a viable alternative to conventional NH 3 cylinder calibration setups.