Performance evaluation of a newly developed portable FAIMS instrument for atmospheric trace gas detection

This study aims to evaluate a newly developed portable field asymmetric ion mobility spectrometry (FAIMS) instrument for the detection of atmospheric trace gases. This instrument has a custom atmospheric pressure chemical ionization source and an interdigitated comb structure using a silicon-on-insulator micro-electro-mechanical system for miniaturization. The performance of the FAIMS instrument has been tested with several key atmospheric trace gases, including ammonia (NH 3 ), nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 ), hydrogen sulfide (H 2 S), α-pinene, carbon monoxide (CO), and carbon dioxide (CO 2 ). The changes in the FAIMS spectra in a positive corona discharge were successfully observed for different concentrations of NH 3 and α -pinene, whereas those in a negative corona discharge were observed for different concentrations of NO 2 , SO 2 , α -pinene, CO, and CO 2 . The detection limits for NH 3 , NO 2 , SO 2 , H 2 S, and α -pinene were estimated to be 0.1, 0.2, 0.2, 200, and 4 ppb, respectively. Although humidity was found to influence the signal intensities for the detections of NH 3 and SO 2 , these influences can be removed by normalizing these signals with the reactant ion signals under moderate and high humidity conditions above 8.5 g/m 3 , which corresponds to a relative humidity of 41.5 % at 25C. Reasonable temporal variations in ambient NH 3 concentrations, ranging from sub-ppb to a few ppb, were successfully obtained during a 17-day preliminary field test at an industrial site in Japan. This research demonstrates that the FAIMS instrument is applicable for the real-time and mobile measurements of multiple gases, particularly NH 3 , NO 2 , and SO 2 , under typical ambient concentrations and is promising for a variety of air quality monitoring applications. • Newly developed portable FAIMS instrument using APCI ion source for trace gases are evaluated. • FAIMS spectra for NH 3 , NO 2 , SO 2 , H 2 S, α-pinene, CO, and CO 2 were analyzed. • High sensitivities for NH 3 , NO 2 , and SO 2 with detection limits of 0.1, 0.2, and 0.2 ppb, respectively, were obtained. • Influence of humidity to the sensitivity was minimum under humidity conditions above 8.5 g/m 3 .