Characterizing Long-Term Multimodal Condensational Growth of Atmospheric Aerosols with the Synchronous Monitor of Aerosol Size and Hygroscopicity (SMASH)

Ultrafine particles (diameters <100 nm) dominate atmospheric particle number concentrations, exerting substantial health and climatic impacts. Condensational growth significantly modifies their size and chemical composition, yet the long-term dominant condensing species remain poorly characterized, largely due to the lack of suitable instruments. Here, we developed the Synchronous Monitor of Aerosol Size and Hygroscopicity (SMASH) for condensing species characterization, integrating a rapid modal diameter identification strategy and the data transmissions between size distribution and size-resolved hygroscopicity measurements. This system thereby enables high-time-resolution (6 min) tracing of growing modal diameter and concurrent hygroscopicity measurements. The hygroscopicity parameter of condensing species, κ c, can be subsequently derived, which is indicative of its chemical compositions. This system also enabled characterization of multimodal simultaneous growth events, which yield unique insights into the size-dependence of condensations. The measured κ c exhibits high sensitivity to condensing species variations, offering a potential standardized method for growth episode classification and growth rate calculations. Moreover, the highly time-resolved measurements can discern the occurrence of nonideal mixing and thereby constraining associated uncertainties. Considering the dynamic mode-tracking capability, the high time resolution, low cost, and easy maintenance, this system is a promising new tool for large-scale long-term measurements to investigate general characteristics of condensing species.