AEROSOL VARIABILITY IN THE VERTICAL IN THE SOUTHWEST PACIFIC

Vertical variations of the tropospheric aerosol concentration and size distribution, for sizes between 0. 12-mum and 8-mum diameter, in the Southwest Pacific have been examined. The data were obtained from flig hts by an instrumented aircraft over a period of more than 3 years. Th e data show that 44% of the variance in the concentration of the accum ulation mode aerosol (0. 12 mum to 0.5 mum) can be accounted for when it is modeled by an exponential decrease with height to 2400 m and a c onstant concentration above. The coarse mode aerosol concentration (gr eater than 0.5 mum) also decreases exponentially with height to 2400 m (46% of the variance accounted for) at a rate only slightly greater t han for the accumulation mode aerosol. More of the variance can be acc ounted for by fitting the exponential decrease multiplied by a differe nt constant term to each vertical profile separately. This implies an improvement in the predictability of the aerosol concentration in the vertical if the column amount or the concentration at some height is k nown. Examination of the shape of the size distributions in the free t roposphere shows no coarse mode, although the tail of the accumulation mode distribution extends to sizes greater than 0.5 mum At low altitu des the concentration of accumulation mode particles is greater and a coarse mode is apparent. The shapes of the distributions, particularly above the boundary layer, are similar and independent of the particle concentration.