ACTRIS - University of Helsinki Topical Centre units provide support for measurements of secondary aerosol formation

ACTRIS is a European distributed research infrastructure producing high-quality data on short-lived atmospheric constituents. ACTRIS facilitates free access to long-term atmospheric data and access to its world-class facilities and extends its resources to academia, the private sector, and the general public. The infrastructure comprises National Facilities, encompassing observational and exploratory platforms, and Central Facilities that support these units through training, guidelines, and standard operation procedures. University of Helsinki (UH) is hosting two specialized Topical Centre Units dedicated to standardizing measurements of secondary aerosol formation. The Cluster Calibration Centre (CCC) focuses on sub-10nm aerosol particle concentration and size distribution measurements, while CiGas-UHEL concentrates on condensable trace gases, which can serve as aerosol precursors. The main tasks of the UH Topical Centre Units are to 1) provide training and consultancy, 2) produce and provide measurement and data procedures and tools 3) improve the methods to calibrate the relevant instrumentation and provide instrument calibrations for ACTRIS National Facilities, 4) organize calibration and intercomparison workshops and 5) carry out measurement and calibration method and instrument development. Currently, both CCC and CiGas-UHEL are at the midpoint of their implementation, with full operative capacity anticipated by 2026. In the past year, significant strides were made with piloting ACTRIS intercomparison workshops. CiGas-UHEL hosted the 1st Chemical Ionization Mass Spectrometer intercomparison workshop in March 2023 (Leipzig), while CCC organized the 1st Neutral cluster and Air Ion Spectrometer (NAIS) intercomparison workshop in May 2023 (Helsinki) and the 1st Nanoparticle instrument intercomparison workshop in November 2023 (Helsinki). These workshops serve as critical platforms, providing essential insights into measurement techniques and instrument functionality .