A High-Resolution Multi-Pressure Chemical Ionization Platform for Comprehensive Monitoring of Atmospheric Organics

Comprehensive detection of atmospheric organic compounds remains a key analytical challenge, particularly for highly oxygenated organic molecules (HOMs), semi-volatile species, and amines. These compounds play central roles in secondary aerosol formation and atmospheric reactivity, yet are often underrepresented in long-term datasets due to limitations in sensitivity, resolution, or chemical coverage.We present a high-resolution multi-pressure chemical ionization mass spectrometry (HR-MPCIMS) system, integrating novel ionization schemes with a high resolution accurate mass analyzer (>120,000 resolving power). Ionization is carried out at both ambient and low pressures using interchangeable solid-state reagent sources (nitrate, urea, and fluoranthene), enabling detection of a wide range of organics without the need for pressurized gas cylinders or vapor delivery of toxic substances.The system allows rapid switching between ion chemistries and has demonstrated stable performance in both laboratory oxidation experiments and ambient air campaigns. Observations include VOCs, OVOCs, peroxides, HOMs, and amines, with sensitivities reaching the ppqv range. Time series of ambient amines highlight its applicability to nitrogen-containing organics. During a three-month deployment at the CLOUD experiment at CERN, the instrument achieved >99.9% uptime.These results demonstrate the potential of HR-MPCIMS for wide coverage, high-resolution monitoring of gas-phase organics in both laboratory and field settings.