Abstract
Abstract. Here we describe the design and performance of a new water cluster chemical ionization–atmospheric pressure interface time-of-flight mass spectrometer (CI-APi-TOF). The instrument selectively measures trace gases with high proton affinity such as ammonia and dimethylamine, which are important for atmospheric new particle formation and growth. Following the instrument description and characterization, we demonstrate successful measurements at the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber where very low ammonia background levels of ∼4 pptv were achieved (at 278 K and 80 % RH). The limit of detection of the water cluster CI-APi-TOF is estimated to be ∼0.5 pptv for ammonia. Although no direct calibration was performed for dimethylamine (DMA), we estimate its detection limit is at least 3 times lower. Due to the short ion–molecule reaction time and high reagent ion concentrations, ammonia mixing ratios up to at least 10 ppbv can be measured with the instrument without significant reagent ion depletion. Besides the possibility to measure compounds like ammonia and amines (dimethylamine), we demonstrate that the ionization scheme is also suitable for the measurement of trace gases containing iodine. During CLOUD experiments to investigate the formation of new particles from I2, many different iodine-containing species were identified with the water cluster CI-APi-TOF. The compounds included iodic acid and neutral molecular clusters containing up to four iodine atoms. However, the molecular structures of the iodine-containing clusters are ambiguous due to the presence of an unknown number of water molecules. The quantification of iodic acid (HIO3) mixing ratios is performed from an intercomparison with a nitrate CI-APi-TOF. Using this method the detection limit for HIO3 can be estimated as 0.007 pptv. In addition to presenting our measurements obtained at the CLOUD chamber, we discuss the applicability of the water cluster Ci-APi-TOF for atmospheric measurements.
Highlights
Ammonia (NH3) is an important atmospheric trace gas that is mainly emitted by vehicles in urban environments and by agricultural activity due to animal husbandry and the use of fertilizers
Besides the measurement of basic compounds with high proton affinity, we find that the protonated water clusters are well-suited to measure iodine-containing species such as iodic acid (HIO3) and neutral molecular clusters containing up to four iodine atoms
Our findings indicate that the water cluster chemical ionization (CI)-APi-TOF can provide sensitive real-time measurements of several trace gases that are important for atmospheric new particle formation and growth: ammonia, amines and iodine species
Summary
Ammonia (NH3) is an important atmospheric trace gas that is mainly emitted by vehicles in urban environments and by agricultural activity due to animal husbandry and the use of fertilizers. Ammonia has a very strong effect on nucleation involving sulfuric acid and water; e.g., recent studies have shown that very low amounts of NH3 in the parts per trillion by volume range, or even below, can enhance nucleation rates by orders of magnitude compared with the pure binary system of sulfuric acid and water (Kirkby et al, 2011; Kürten et al, 2016a; Kürten, 2019). The experimental measurements are confirmed by quantum chemical calculations that compare the stabilizing effects of ammonia, amines and diamines (Kurtén et al, 2008; Elm et al, 2017; Yu et al, 2018). For these reasons improved gas-phase measurements of these compounds are required. Sensitive real-time measurements are needed, spanning mixing ratios over a broad atmospheric range between a few parts per trillion by volume to a few parts per billion by volume of ammonia in the boundary layer, as well as around a few parts per trillion by volume of amines (Ge et al, 2011; Hanson et al, 2011; You et al, 2014; Kürten et al, 2016b; Yao et al, 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
