Chiang Mai Journal of Science

Cloud condensation nuclei (CCN) study is important for a better understanding of precipitation processes but CCN measurements are very rare in Southeast Asia region. Airborne measurements have been carried out to achieve CCN characteristics over the Northern Thailand during summertime 2012. This manuscript found the variation of  CCN and aerosol that influenced by biomass burning, especially in summer confirmed by satellite images. CCN concentrations were quite low, while the period of monsoon onset showed significantly high CCN concentration which contrary to those of accumulation mode aerosol. It is shown that washout by rain is the effective mechanism to reduce aerosols from the atmosphere. The Twomey’s fitted parameters from sequential supersaturation measurements(0.2%, 0.5%, and 0.8%), C and k, showed the considerably high value (C was 6,000-9,700 cm-3 and k was around 4) in summer while they decreased to the range of continental regime in monsoon onset. The case study of vertical distribution indicated that most CCN and aerosols were contained within the boundary layer which extended to 3000 meters in April and was capped by temperature inversions. The observation showed that accumulation mode aerosols size distribution was independent of altitude, while the concentration was not.