Transport and stability of negative ions generated by negative corona discharge in air studied using ion mobility-oaTOF spectrometry

Abstract Negative corona discharge in wire to plane geometry was investigated by ion mobility-orthogonal acceleration TOF mass spectrometry (IMS-oaTOF). The formation of the ions in CD in synthetic air was studied under different gas flow, temperature and discharge current conditions. In standard flow mode we have detected formation of NO 2 − ·(HNO 3 ), NO 3 − ·(HNO 3 ) and NO 3 − ·(HNO 3 ) 2 ions even at relatively low water concentration (5 ppm) and determined their reduced ion mobilities of 2.11, 2.02 and 1.75 cm 2  V −1  s −1 . We have determined the lifetime of the NO 3 − ·(HNO 3 ) 2 ion at 295 and 308 K of 7.0(±1.0) ms and 2.5(±1.0) ms respectively. In the reverse flow the CD in wire to plane geometry different negative ions were detected, dominated by O 2 − (H 2 O) n ( n  = 0,1,2) with reduced ion mobility of 2.27 cm 2  V −1  s −1 and additional ions NO 3 − (2.29 cm 2  V −1  s −1 ) and N 2 O 2 − (2.37 cm 2  V −1  s −1 ) present in the spectrum.