AEROSOL CONCENTRATIONS OBSERVED AT MT. HARUNA, JAPAN, IN RELATION TO LONG-RANGE TRANSPORT OF ASIAN MINERAL DUST AEROSOLS

摘要

As a part of the effort to understand thestructure of long-range transported aerosolplumes and local pollution, aerosol observationsmonitored the mass concentrations andnumber-size distributions during the periodAugust 2006 to July 2009 near the top of Mt.Haruna (1365 m), an isolated mountain in theKanto Plain in Japan. The mass concentrationsobserved at Mt. Haruna and plain sites showed aseasonal variation with a maximum in spring andsummer, respectively. The spring peaks inaerosols at Mt. Haruna were probably caused bylong-range transport of mineral dust andanthropogenic particles from the Asian continent.The summer peaks at the plain sites wasattributed to local pollution from the Tokyometropolitan area. Three examples of 2007Asian dust events were investigated to show thataerosols may be dispersed in a complicatedthree-dimensional structure and that delayedarrivals of the dust plumes at plain sitescompared to Mt. Haruna were not a rare case.Because of the boundary layer being stable atnight, the dust layer was advected eastwardwithout the vertical mixing before sunrise. Thisstudy suggests that after thermal convectionactivated by sunlight during daytime Asian dusttransported in the free troposphere may bebrought down into the atmospheric boundarylayer, increasing the dust concentration there.