The Hygroscopic Tandem Differential Mobility Analyser (HTDMA) became operational for the HygrA-CD campaign on May 29th. We specially thank the N.C.S.R. DEMOKRITOS researchers, Maria Gkini, Dr. Stergios Vratolis and Dr. Prodromos Fetfatzis, who devoted themselves on the set-up and calibration of the instrument.