Measurement of ammonia, amines and iodine species using protonated water cluster chemical ionization mass spectrometry

Abstract. A new water cluster Chemical Ionization-Atmospheric Pressure interface-Time Of Flight mass spectrometer (CI-APi-TOF) is introduced. The instrument is designed for the selective measurement of trace gases with high proton affinity, such as ammonia, amines, and diamines that are, for example, relevant for atmospheric new particle formation. Following the instrument description and characterization, we demonstrate successful measurements at the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber where very low ammonia background levels of ~ 4 pptv were achieved (at 278 K and 80 % RH). The estimated level of detection of the water cluster CI-APi-TOF can be estimated as ~ 0.5 pptv for ammonia and it is significantly lower for amines. Due to a short reaction time (