CARIBIC-AMS: a fully automated aerosol mass spectrometer for operation on routine passenger flights (IAGOS-CARIBIC) – instrument description and first flight application

In this study, we present a fully automated aerosol mass spectrometer (AMS) that is operated during regular passenger aircraft flights in the CARIBIC (Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container) module of the European Research Infrastructure IAGOS (In-service Aircraft for a Global Observing System - https://www.iagos.org/, last access: 20 September 2025). The instrument, termed CARIBIC-AMS, is able to measure the mass concentration of non-refractory aerosol species, namely sulfate, nitrate, ammonium, and organics, in a particle diameter range of approximately 50-800 nm. The main challenge was the mechanical and electrical redesign of a commercial instrument in order to comply with the operating and safety requirements in the IAGOS-CARIBIC container-laboratory before and during flight. In the container-laboratory, the instrument has to operate fully autonomously, typically during four consecutive long-haul flights of 10 h. The CARIBIC-AMS weighs 74 kg, has a volume of 0.16 m3, and consumes 360 W of electrical power during regular operation. Due to the short time for evacuation of the vacuum chamber to sufficiently low pressures before measurement, detection limits are higher during regular flights than during ground operation and were determined to be 0.035 mu gm-3 for sulfate, 0.055 mu gm-3 for nitrate, 0.69 mu gm-3 for organics, 0.38 mu gm-3 for ammonium, and 0.022 mu gm-3 for chloride (all at STP), for a time resolution of 30 s. ... mehrThese values represent typical averages under flight conditions and refer to a collection efficiency of 0.5. Since the IAGOS-CARIBIC project aims for climatological, regular, long-term data, longer data averaging times are possible, thereby lowering the detection limits by the square root of the number of averaged data points. Data validation, calibration, and instrument characterization were conducted by means of laboratory-based comparisons with existing established aerosol mass spectrometers. Here we report on the details of the automation and the instrument characterization, as well as first in-flight data measured in the upper troposphere and lower stratosphere during two IAGOS-CARIBIC flights and during the TPEx (Tropopause Composition Gradients and Small-scale Mixing Experiment) field campaign, conducted in 2024 using a Learjet as research aircraft over northern Europe.