Long-term sub second-response monitoring of gaseous ammonia in ambient air by positive inhaling ion mobility spectrometry

Abstract A real-time dynamic measurements of ammonia (NH 3 ) is crucial for understanding the atmospheric nucleation process. A novel method was developed for on line monitoring at the sub-second time scale for the gaseous ammonia in ambient air for months, based on a positive inhaling ion mobility spectrometry (IMS) with a 63 Ni ion source. The selective detection of NH 3 was achieved using a high resolution IMS with an optimization of the drift tube temperature above 150 °C. This method improved the peak-to-peak resolution significantly, thus avoided the interferences of the adjacent peaks to the quantitative analysis of NH 3 . The time resolution of the IMS was less than 0.1 s at a data averaging of 10 times. The limit of detection (LOD) achieved at sub-ppb level while a linear response of peak intensity versus concentration of NH 3 in the range of 10–60 ppb and 60–400 ppb were obtained. The relative standard deviations (RSD), the confidence level and the errors were 1.06%, 95% and ± 0.21 ppb by measuring 100 ppb NH 3 for 100 times. The effect of ambient humidity could be greatly reduced by using the drift temperature of over 150 °C. At last, the application of measuring the NH 3 concentration evolutions of Dalian city was performed from June 19 to December 3 in 2015. The results illustrated a potential method of using IMS for a real-time measuring atmospheric NH 3 at an unprecedented accuracy and sensitivity with long-term stability.