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. In this study, aerosol samples collected at a remote site in the Amazonianrainforest and an urban site in Manaus, Brazil, were investigated on asingle-particle basis using a quantitative energy-dispersive electron probe X-raymicroanalysis (ED-EPMA). A total of 23 aerosol samples were collected in foursize ranges (0.25–0.5, 0.5–1.0, 1.0–2.0, and 2.0–4.0  µ m) duringthe wet season in 2012 at two Amazon basin sites: 10 samples in Manaus, anurban area; and 13 samples at an 80 m high tower, located at the Amazon TallTower Observatory (ATTO) site in the middle of the rainforest, 150 kmnortheast of Manaus. The aerosol particles were classified into nine particletypes based on the morphology on the secondary electron images (SEIs)together with the elemental concentrations of 3162 individual particles:(i) secondary organic aerosols (SOA); (ii) ammonium sulfate (AS); (iii) SOAand AS mixtures; (iv) aged mineral dust; (v) reacted sea salts; (vi) primarybiological aerosol (PBA); (vii) carbon-rich or elemental carbon (EC)particles, such as soot, tarball, and char; (viii) fly ash; and (ix) heavymetal (HM, such as Fe, Zn, Ni, and Ti)-containing particles. In submicronaerosols collected at the ATTO site, SOA and AS mixture particles werepredominant (50 %–94 % in relative abundance) with SOA and ammoniumsulfate comprising 73 %–100 %. In supermicron aerosols at the ATTO site,aged mineral dust and sea salts (37 %–70 %) as well as SOA and ammoniumsulfate (28 %–58 %) were abundant. PBAs were observed abundantly in thePM 2−4 fraction (46 %), and EC and fly ash particles were absent inall size fractions. The analysis of a bulk PM 0.25−0.5 aerosol samplefrom the ATTO site using Raman microspectrometry and attenuated totalreflection Fourier-transform infrared spectroscopy (ATR-FTIR) showed that ammoniumsulfate, organics, and minerals are the major chemical species, which isconsistent with the ED-EPMA results. In the submicron aerosols collected inManaus, either SOA and ammonium sulfate (17 %–80 %) or EC particles(6 %–78 %) were dominant depending on the samples. In contrast, agedmineral dust, reacted sea salt, PBA, SOA, ammonium sulfate, and EC particlescomprised most of the supermicron aerosols collected in Manaus. The SOA,ammonium sulfate, and PBAs were mostly of a biogenic origin from therainforest, whereas the EC and HM-containing particles were of ananthropogenic origin. Based on the different contents of SOA, ammoniumsulfate, and EC particles among the samples collected in Manaus, aconsiderable influence of the rainforest over the city was observed. Agedmineral dust and reacted sea-salt particles, including mineral dust mixedwith sea salts probably during long-range transatlantic transport, wereabundant in the supermicron fractions at both sites. Among the aged mineraldust and reacted sea-salt particles, sulfate-containing ones outnumberedthose containing nitrates and sulfate  +  nitrate in the ATTO samples. Incontrast, particles containing sulfate  +  nitrate were comparable innumber to particles containing sulfate only in the Manaus samples, indicatingthe different sources and formation mechanisms of secondary aerosols, i.e.,the predominant presence of sulfate at the ATTO site from mostly biogenicemissions and the elevated influences of nitrates from anthropogenicactivities at the Manaus site.

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