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 PM2.5. 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.