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 (NH3) 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 63Ni ion source. The selective detection of NH3 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 NH3. The time resolution of the IMS was less than 0.1s 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 NH3 in the range of 10–60ppb and 60–400ppb were obtained. The relative standard deviations (RSD), the confidence level and the errors were 1.06%, 95% and ± 0.21ppb by measuring 100ppb NH3 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 NH3 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 NH3 at an unprecedented accuracy and sensitivity with long-term stability.