乗鞍岳における大気エアロゾルの観測－粒子数粒径分布の変化とその要因

抄録

Mt. Norikura (36.1 °N, 137.5 °E, summit 3,026 m a.s.l.) is a high elevation site that has been utilized for atmospheric observations since the 1960s. This paper highlights the observation on number-size distributions of atmospheric aerosol particles performed at Mt. Norikura (2,770 m a.s.l.) in September 2001 and August-September 2002. First, we present the number-size distributions of the aerosol particles observed during nighttime (free tropospheric aerosol) , which was analyzed in terms of the relation to the air-mass transportation pathway, the cumulative precipitation amount in the air mass for the last 24 h, and the local precipitation rate. Results of the analysis suggest that the precipitation scavenging is an important process to modify the particle size distribution by decreasing the particle concentration. Considering the data for the air masses without the experience of precipitation scavenging before the arrival, the data suggests that air-mass transportation pathway is an important controlling factor especially for Aitken mode particle concentration. Next, we describe the relationship between occurrence of nucleation mode in particle number-size distributions and air-mass exchange associated with the diurnal variation of local wind system. The nucleation mode particles were observed in the mixed layer air transported by upslope valley wind but never observed in the free tropospheric air transported by down slope mountain wind, which suggest that new particle formation occurred in the mixed layer but never did in the free troposphere just above the mixed layer.