Cloud condensation nuclei (CCN5) concentrations and critical diameters (Dc5) at 0.5% supersaturation were continuously measured and corresponding hygroscopicity parameter (κ5) were calculated at Tsukuba during between January and March, 2016. The κ5 values were representative of particles in Aitken size ranges (approximately 50–100 nm diameter). In the periods just after the occurrence of new particle formation events, the κ5 values were widely ranged (0.01–0.6), however, they tended to concentrate into a narrow range of 0.05–0.15 as the particles grew larger. This tendency was explained partly with increasing mixing ratios of HOC and Char-EC, and decrease of SO₄ in PM_2.5. Internal mixing of many organic compounds and oxidation of SOA were also possibly effective to the concentrating tendency of κ values. According to examinations using electron microscope, extraordinary high values of κ were caused by high concentrations of ammonium sulfate concentrations (κ～0.4) or influences of biomass burnings (κ～0.2).

Gaseous compounds (NH₃ and HNO₃) and size-segregated aerosol particles (NH₄^＋ and NO₃^-) were measured at Chikushi Campus, Kyusyu University from July 31, 2014 to October 19, 2015. NH₃ and fine NH₄^＋ concentrations were semi-continuously (34 min interval) measured by using a micro flow analytical system. HNO₃ and size-segregated aerosol particles were collected for 1 to 3 days intervals by using an annular denuder with a multiple filter set (Nuclepore, PTFE, and Nylon). Intensive sampling (ca. 8 hours interval) was conducted twice from September 24 to October 9, 2014 and from January 7 to 17, 2015. NH₃ and HNO₃ concentrations were high in warm season, whereas NH₄^＋ and NO₃^- concentrations in fine particles were high in cold season. NH₃ concentrations were low after rain in the ensuing days and were higher after days without rain. HNO₃ concentration during fall experiment was periodically high in daytime under sunny and sea breeze wind conditions, suggesting contribution of local NO₂ oxidation to high HNO₃ during daytime. Seasonal variations of gas-particle phase relationships of NH₃ and HNO₃ were discussed in terms of temperature dependence of NH₄NO₃ equilibrium. Concentration products between NH₃ and HNO₃ were mostly below equilibrium of NH₄NO₃ estimated from air temperature during sample collection, suggesting that formation of NH₄NO₃ was limited during late winter to early spring.