An aircraft-based Ion Trap Mass Spectrometer Instrument ITCIMS for measurements of atmospheric trace gases and ions aboard HALO - Phase 2: Extensions of ITCIMS capabilities, flight tests on the FALCON, and deployment on HALO

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The second phase of project HALO-ITCIMS aims for an extension of the capabilities and the deployment aboard the research aircraft HALO of a novel and highly versatile aircraft-based ion trap mass spectrometer-instrument ITCIMS (Ion Trap Chemical Ionization Mass Spectrometer). The ITCIMS has the capability to make fast and very sensitive in-situ measurements of atmospheric trace gases, including also ultra-trace gases, and gas-phase ions. The ITCIMS instrument can be operated in various modes including active and passive CIMS (chemical ionization mass spectrometry) for trace substance detection using negative and positive reagent ions. The active CIMS mode involves reagent ions generated by an onboard ion source. The passive CIMS-mode (PACIMS) involves ambient atmospheric ions as reagent ions and is extremely sensitive (smallest detectable atmospheric trace gas mole fraction: about 0.0001 pptv). In addition, the ITCIMS can be operated in an ion fragmentation mode, which allows collisional fragmentation studies of mass selected ions. This mode is extremely helpful for the identification of ions and thereby also of neutral species to be detected by CIMS. Major advantages of the ITMS are its excellent duty cycle and its ability to offer simultaneous and very fast measurements of a very large mass spectral range (20- 4000 atomic mass units). For the planned active CIMS-measurements the ITCIMS instrument will be operated preferably in the negative reagent ion mode while planned PACIMS measurements will involve ambient negative and positive ions as reagent ions. The focus of the trace gas measurements by ITCIMS aboard HALO will be on species having major roles in atmospheric photochemistry and aerosol formation. Important gases to be measured include among others: PAN, PPN, M-PAN, N2O5, HNO3, HCN, HCl, SO2, ClNO2, Br2, BrO, organic acids, H2SO4, NH3, (CH3)2CO, and additional organics. Phase 2 of the HALO-ITCIMS project has 5 major parts: (1) Extensions of the ITCIMS capabilities focussing on novel ion-molecule reaction schemes for neutral trace gas detection and focussing also on improvements of atmospheric gas-phase ion measurements (2) Tests of ITCIMS and novel ion reaction schemes in the laboratory, which will be also by a novel very powerful laboratory mass spectrometer recently set up at DLRIPA (triple quadrupole mass spectrometer with hyperbolic rods offering a very high mass resolution and mass precision. The TQMS also offers an alternative mass selected ion fragmentation mode) (3) Tests of ITCIMS on the research aircraft FALCON and on the research aircraft HALO (4) Conversion of a second ITCIMS instrument for the deployment aboard HALO (5) Deployment of the ITCIMS instrument within the framework of large scientific measurement campaigns using HALO.