Single-particle characterization of aerosols collected at a remote site in the Amazonian rainforest and an urban site in Manaus, Brazil [post]

Chul-Un Ro
2019 unpublished
18 In this study, aerosol samples collected at a remote site in the Amazonian rainforest and an urban 19 site in Manaus, Brazil, were investigated on a single particle basis using a quantitative energy-20 dispersive electron probe X-ray microanalysis (ED-EPMA). Twenty-three aerosol samples were 21 collected in four size ranges (0.25-0.5, 0.5-1.0, 1.0-2.0, and 2.0-4.0 µm) during the wet season in 22 2012 at two Amazon basin sites: 10 samples in Manaus, an urban area; and 13 samples at an 80-m 23
more » ... high tower, located at the Amazon Tall Tower Observatory (ATTO) site in the middle of the 24 rainforest, 150 km northeast of Manaus. The aerosol particles were classified into nine particle 25 types based on the morphology on the secondary electron images (SEIs) together with the 26 elemental concentrations of 3,162 individual particles: (i) secondary organic aerosols (SOA), (ii) 27 ammonium sulfate (AS), (iii) SOA and AS mixtures, (iv) aged mineral dust, (v) reacted sea-salts, 28 (vi) primary biological aerosol (PBA), (vii) carbon-rich or elemental carbon (EC) particles, such 29 as soot, tar ball, and char, (viii) fly ash, and (ix) heavy metal (HM, such as Fe, Zn, Ni, and Ti)-30 containing particles. In submicron aerosols collected at the ATTO site, SOA and AS mixture 31 particles were predominant (50-94% in relative abundance) with SOA and ammonium sulfate 32 comprising 73-100%. In supermicron aerosols at the ATTO site, aged mineral dust and sea-salts 33 (37-70%) as well as SOA and ammonium sulfate (28-58%) were abundant. PBAs were observed 34 abundantly in the PM2-4 fraction (46%), and EC and fly ash particles were absent in all size 35 fractions. The analysis of a bulk PM0.25-0.5 aerosol sample from the ATTO site using Raman 36 microspectrometry and attenuated total reflection Fourier transform infrared spectroscopy showed 37 that ammonium sulfate, organics, and minerals are the major chemical species, which is consistent 38 with the ED-EPMA results. In the submicron aerosols collected in Manaus, either SOA and 39 ammonium sulfate (17-80%) or EC particles (6-78%) were dominant depending on the samples. 40 In contrast, aged mineral dust, reacted sea-salt, PBA, SOA, ammonium sulfate, and EC particles 41 comprised most of the supermicron aerosols collected in Manaus. The SOA, ammonium sulfate, 42 and PBAs were mostly of a biogenic origin from the rainforest, whereas the EC and HM-containing 43 particles were of an anthropogenic origin. Aged mineral dust and reacted sea-salt particles, 44 including mineral dust mixed with sea-salts probably during long-range transatlantic transport, 45 were abundant in the supermicron fractions at both sites. Among the aged mineral dust and reacted 46 sea-salt particles, sulfate-containing ones outnumbered those containing nitrates and 47 sulfate+nitrate in the ATTO samples. In contrast, particles containing sulfate+nitrate were 48 comparable in number to particles containing sulfate only in the Manaus samples, indicating the 49 different sources and formation mechanisms of secondary aerosols, i.e., the predominant presence 50 of sulfate at the ATTO site from mostly biogenic emissions and the elevated influences of nitrates 51 from anthropogenic activities at the Manaus site. 52 53 anthropogenic activities, particularly during the wet season (Andreae, 2007; Martin et al., 2010b; 57 Chen et al., 2015). The unique near-natural conditions during the wet season make it an ideal place 58 to understand the occurrence, nature, origin, and transport of aerosol particles, which can directly 59 scatter and absorb solar radiation and indirectly serve as cloud condensation nuclei (CCN) and/or 60 ice nuclei (IN), to better predict the additional anthropogenic effects on aerosol particles, and to 61 help determine their influences on the environment, climate, and human health (Artaxo et al., 62 2013). 63
doi:10.5194/acp-2018-1067-ac1 fatcat:e5d5ueviczgnzffo2ffl7tdj6m