Seasonal Variations of Atmospheric Aerosol Particles Focused on Cloud Condensation Nuclei and Ice Nucleating Particles from Ground-Based Observations in Tsukuba, Japan

Abstract

Since March 2012, multi-year ground-based observation of atmospheric aerosol particles has been carried out in Tsukuba, Japan to characterize the aerosol particle number concentrations (NCs), air mass origin relevance, and specifically, their cloud condensation nuclei (CCN) and ice nucleating particle (INP) characteristics. The CCN NCs at any water supersaturation (SS) exhibit strong seasonality, being higher in winter and lower in summer; this pattern is similar in the polluted urban environment in East Asia and contrary to that in the Pacific coastal region. The hygroscopicity (κ) is generally high in early autumn and low in early summer, likely due to the seasonal difference of synoptic-scale systems. In contrast, the INP NCs and ice nucleation active surface site density (ns) at defined temperature (−15 to −35°C) and SS (0%–5%) lack clear seasonal influence. The average INP NCs and ns in this study were comparable at warmer temperatures and approximately one order of magnitude lower at colder temperatures, compared with those in other urban locations under limited dust impact. Moreover, the ns values were one to four orders of magnitude lower and exhibited weaker temperature dependence than previous parameterizations on mineral dust particles.