Airtox: A Next-Generation PTR-Based Instrument for Autonomous Long-Term VOC Monitoring

Volatile organic compounds (VOCs) play a central role in atmospheric chemistry and air quality yet their long-term, high time resolution measurements remain challenging to deploy at scale due to instrument complexity, maintenance requirements, and the need for expert-driven data processing. As monitoring networks continue to expand their observational capability across Europe, new instrumentation strategies are required. Here, we introduce the Airtox monitor, a new proton-transfer-reaction (PTR)-based instrument specifically designed for autonomous, long-term VOC monitoring in both stationary and mobile applications. The system features a vacuum ultraviolet (VUV) ionization source coupled to a high-resolution time-of-flight mass spectrometer, delivering broad chemical coverage with unprecedent stability. Integrated automation - including real-time background correction, online mass calibration, and scheduled gas-phase calibrations, enables fully unattended operation while providing continuous stream of reliable quantitative concentration data. We evaluate Airtox performance during month-long deployments at two ACTRIS sites: the Deutscher Wetterdienst (DWD) station in Germany and the high-altitude Jungfraujoch (JFJ) observatory in Switzerland. In both campaigns, the instrument operated continuously without human intervention, demonstrating exceptional robustness under varying environmental and logistical constraints. Automated workflows maintained stable instrument response and calibration, while real-time quality control verified proper system operation and ensuring reliability of the delivered concentration data. We compare these real-time concentration outputs to post processed datasets to assess the accuracy, identify where postprocessing remains beneficial and outline the remaining challenges for true real- time VOC monitoring. We show how the same system also supports mobile monitoring with rapid time response, enabling spatially resolved VOC mapping during on-road or near-source surveys. This versatility allows the same system to be deployed at a monitoring station for long-term observations or to be transferred into a mobile laboratory for targeted field campaigns, extending its utility across diverse research and regulatory applications. We demonstrate that Airtox provides a robust, autonomous VOC monitoring solution that lowers operational barriers and supports reliable, decision-ready data delivery.