Source apportionment of SMPS-CPC measurement biases and its impact on aerosol hygroscopicity retrievals in an indoor environment

¹ Sanya Oceanographic Institution (OUC), Key Laboratory of Marine Environment and Ecology (MoE), and Frontiers Science Center for Deep Ocean Multispheres and Earth System, Ministry of Education, Ocean University of China, Qingdao, 266100, China
² Laboratory for Marine Ecology and Environmental Sciences, Laoshan Laboratory, Qingdao, 266237, China

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Accurate quantification of new particle formation (NPF) events relies on precise aerosol number concentration measurements, which are frequently hindered by systematic measurement biases between instruments. In this study, one-month synchronous observations were conducted in a stable indoor environment using a Scanning Mobility Particle Sizer (SMPS) and a Condensation Particle Counter (CPC). An average 23% systematic underestimation by the SMPS relative to the CPC was observed. By applying Positive Matrix Factorization (PMF) to resolve the modes of instrument disagreement, we identified that the variance in this negative bias was predominantly driven by low transmission efficiency and diffusion losses within the nucleation and Aitken modes. However, a closure analysis of aerosol hygroscopicity demonstrated that the chemistry-derived parameter (κ_chem, 0.31 ± 0.06) exhibited excellent agreement with the SMPS-CCN derived parameter at 0.28% supersaturation (κ_0.28%SS, 0.30 ± 0.10). These findings suggest that while absolute numerical biases exist in ultrafine particle counting, the relative size distribution remains robust for mass-dominant larger particles, ensuring reliable physicochemical retrievals in this regime, though caution is strictly required when interpreting data at higher supersaturations.