Research on air pumping effects over central Japanese Alps in summer

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Air pumping effects over mountain areas are caused by solar heating of the mountain slope. The air pumping effect may inject significant amount of polluted air into the free-troposphere over Japan. To characterize the air pumping effect over the central Japanese Alps, we conducted in-situ measurements on atmospheric aerosol particles, ozone, and radon concentrations with meteorological parameters at Mt.Norikura during the study period of 2001 and 2002. We observed column amount and vertical distribution of aerosols by using a sky-radiometer and a ceilometer. Size-segregated aerosol particles for chemical analysis were also sampled during intensive observation periods during summer and early fall.Under the clear sky conditions in summer, polluted air from mountain valley area is lifted up about 4km of altitude (1km above the mountain top) over Mt.Norikura. The ratio of aerosol volume concentration for daytime (polluted valley wind) to nighttime (clean free-tropospheric) conditions was about 10. The air pumping effects over central Japanese Alps carry about 10 time higher concentration of aerosols to the free-troposphere over Japan in summer. Under the high pressure system centered over the northwest Pacific in typical summer condition, backward air trajectories were originated from the northwest Pacific to Mt.Norikura and forward trajectories returned to the north Pacific with some deviations to east Russia and the Kurile Islands. The air pumping effects over mountain area provide a strong pollution source mechanism to the free-troposphere over the western Pacific region including east Asia.