Reprint of: Number concentrations and elemental compositions of aerosol particles observed at Mt. Kiso-Komagatake in central Japan, 2010-2013

摘要

Aerosols in the lower troposphere over Japan are considered being influenced by those transported from Asian continent by westerly winds. In this study, we investigated the seasonal variation of aerosol number concentrations measured by means of optical particle counters at Mt. Kiso-Komagatake (2610 m altitude) in central Japan during the period from January 2010 to May 2013. We also collected aerosol samples in different seasons during part of the observation period and investigated their elemental compositions using transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDX). The seasonal variation of the number concentrations suggested that accumulation-mode particles (particle diameter ＞ 0.3 μm) increased during late spring perhaps owing to gas-to-particle conversion by means of photochemical reactions. The number concentrations of supermicron particles (＞1 μm) were highest in spring, during which Asian dust events were frequent. Short-duration spikes in aerosol number concentrations, which were attributed to long-range transport from the Asian continent, were frequently observed in all seasons except summer. TEM analysis indicated that sulfate was the predominant component of accumulation-mode particles throughout the year. The number fraction of carbonaceous particles was also considerable, especially in samples in fall. The predominant components of supermicron particles collected during winter, spring and fall, and summer were sulfate, minerals, and sea salt, respectively. Our results suggest that the lower tropospheric air over central Japan is strongly influenced by long-range transport of aerosols in all seasons except summer.