Intercomparison study of six HTDMAs : results and general recommendations for HTDMA operation

Abstract

We report on an intercomparison of six different hygroscopicity tandem differential mo-bility analysers (HTDMAs). These HTDMAs are used worldwide in laboratory experi-ments and field campaigns to measure the water uptake of aerosol particles and were never intercompared. After an investigation of the different design of the instruments 5 with their advantages and inconveniencies, the methods for calibration, validation and data analysis are presented. Measurements of nebulised ammonium sulphate as well as of secondary organic aerosol generated from a smog chamber were performed. Agreement and discrepancies between the instrument and to the theory are discussed, and final recommendations for a standard instrument are given, as a benchmark for 10 laboratory or field experiments to ensure a high quality of HTDMA data.