Single particle analysis of the accumulation mode aerosol over the northeast Amazonian tropical rain forest, Surinam, South America

[摘要] Single particle analysis of aerosols particles larger than 0.2 μmdiameter was performed on 24 samples collected over Surinam tropical rainforest and in the adjacent marine boundary layer (MBL) during theLBA-CLAIRE 98 campaign in March 1998. Elemental composition and morphology of2308 particles was determined using SEM-EDX. The aerosol particles were dividedinto seven groups according to their chemical composition: organicparticles, mineral dust, aged mineral dust, sea salt, aged sea salt,Ca-rich, and biogenic aerosol. However the organic material in aerosolparticles cannot be identified directly by SEM-EDX, we present indirectmethod of detection of organic material using this technique. Samples werefurther divided with respect to the distinct atmospheric layers present inthe tropical troposphere including MBL, continental mixed layer, cloudconvective layer, free troposphere and region of deep convection outflow.The organic and mineral dust particles are two major groups observed overthe rainforest. In the MBL also sea salt particles represented a largefraction between 15 and 27%. The organic particles control much of thechemical characteristic of the aerosol in the continental tropicaltroposphere. Their abundance ranged from less than 20% in the MBL tomore than 90% in the free troposphere between 4.5- and 12.6-km altitude.During the transport of the air masses from the MBL over the rain forest,fraction of organic aerosol particles more than doubled, reaching 40–60%in the continental boundary layer. This increase was attributed todirect emissions of biogenic aerosols from the tropical vegetation. The highfraction of the organic accumulation mode particles in the upper tropicaltroposphere could be a good indicator for the air masses originated over thetropical rain forest.

[学科分类] 大气科学