Characterization of Ambient Aerosols from Amazonian Rainforest and City of Manaus, Brazil

초록

Aerosols and their effects in the pristine Amazonian rainforest, one of the few continental regions which are not dominated by anthropogenic sources, have been of great interest recently [1], [2]. Twenty-three aerosol particle samples were collected in four size ranges (0.25-0.5, 0.5-1.0, 1.0-2.0 and 2.0-4.0 μm) during a wet season at two Amazonian sites: 10 samples at LBA Manaus, an urban area; and 13 samples at Amazon Tall Tower Observatory (ATTO), located in the rainforest 150 km northeast of Manaus. Individual particles were analysed mainly by low-Z particle electron probe X-ray microanalysis (EPMA). Based on morphology and elemental compositions, particles observed at both sites were classified into seven major types: (i) (NH4)2SO4 (AS) particles, appearing thin and relatively bright with typical X-ray beam damage, sometimes with organic coating and K; (ii) water-soluble organics, appearing dark and round-shaped with aqueous foot-print; (iii) organic/misc. particles or secondary organic species condensing on other species like mineral, marine-derived, and biogenic particles, with core-shell-like structure; (iv) mineral dust particles, appearing irregular and bright, such as aluminosilicate, SiO2, and reacted (Ca,Mg)CO3 particles; (v) primary biogenic particles (2.0?4.0 ?m size) with typical morphologies and containing C, O, S, N, P, and K; (vi) marine-derived particles; and (vii) C-rich particles observed only at Manaus like soot and tar balls. AS (with K) particles of < 2.0 μm were encountered frequently by 30-50 % at ATTO, probably indicating emission of NH3 and SO42- along with biogenic species in the rainforest, as biomass burning events were not reported during the sampling period [2]. Organic/misc. particles were observed at both sites in relative abundances of 20~90 % at ATTO and 20~70 % at Manaus. Minerals mixed with sea-salts were observed at both sites, probably due to long-range transport of Saharan dust over the Atlantic Ocean. Further analysis o