Real-time monitoring of atmospheric ammonia based on modifier-enhanced vacuum ultraviolet photoionization ion mobility spectrometry.

Ammonia (NH) plays an important role in the atmospheric environment such as the formation of PM, the concentration monitoring of which could hence help in the air quality assessment. In this study, a method for quantitative monitoring of atmospheric NH was developed based on modifier-enhanced selectivity detection using a homemade vacuum ultraviolet photoionization ion mobility spectrometry (VUV-PI-IMS). To enhance the resolution and sensitivity of measuring NH, 2-butanone as the gas modifier was introduced into the drift tube with the drift gas. Atmospheric NH can be selectively detected, where the peak-to-peak resolution () of 7.69 was obtained. The product ions were identified to be [CHO]NH by using a homemade time-of-flight mass spectrometer. The calculated limit of detection (LOD) was 0.39 ppbv improving about 10 times. For the most common concentration variation of atmospheric NH in the range of 10-100 ppbv, the linear curve was obtained with of 0.997. Lastly, the VUV-PI-IMS was used to monitor the evolution of atmospheric NH near our laboratory and mounted on a car for monitoring the regional distribution of atmospheric NH in Dalian, China. The results also showed that VUV-PI-IMS has a promising application prospect in monitoring the concentration of atmospheric NH and supporting the air quality assessment.