Aerosol properties, in-canopy gradients, turbulent fluxes and VOC concentrations at a pristine forest site in Amazonia

Abstract

a b s t r a c tAerosol physical and chemical properties were measured in a forest site in central Amazonia (Cuieiras reservation, 2.61S; 60.21W) during the dry season of 2004 (AugeOct). Aerosol light scattering and absorption, mass concentration, elemental composition and size distributions were measured at three tower levels (Ground: 2 m; Canopy: 28 m, and Top: 40 m). For the first time, simultaneous eddy covariance fluxes of fine mode particles and volatile organic compounds (VOC) were measured above the Amazonian forest canopy. Aerosol fluxes were measured by eddy covariance using a Condensation Particle Counter (CPC) and a sonic anemometer. VOC fluxes were measured by disjunct eddy covariance using a Proton Transfer Reaction Mass Spectrometer (PTR-MS). At nighttime, a strong vertical gradient of phosphorus and potassium in the aerosol coarse mode was observed, with higher concentrations at Ground level. This suggests a source of primary biogenic particles below the canopy. Equivalent black carbon measurements indicate the presence of lightabsorbing aerosols from biogenic origin. Aerosol number size distributions typically consisted of superimposed Aitken (76 nm) and accumulation modes (144 nm), without clear events of new particle formation. Isoprene and monoterpene fluxes reached respectively 7.4 and 0.82 mg m À2 s À1 around noon. An average fine particle flux of 0.05 AE 0.10 10 6 m À2 s À1 was calculated, denoting an equilibrium between emission and deposition fluxes of fine mode particles at daytime. No significant correlations were found between VOC and fine mode aerosol concentrations or fluxes.

Multi-year statistical and modelling analysis of submicrometer aerosol number size distributions at a rain forest site in Amazonia

“…Median particle number concentration reaches 1254 (557-2928) cm −3 (Table 1). The values are compatible with previously reported values for dry season from another site in the same forest reservation (ZF2) (averages in the range of 1080 to 1400 cm −3 , according to 5 Rissler et al, 2004;Rizzo et al, 2010). In spite of the three fold increase from wet to dry season, observed particle number concentrations are well below the observations in the Amazonian state of Rondônia for example, a site heavily affected by biomass burning emissions where particle number concentration averages in the range of 5700 to 10440 cm To analyze dynamic variations of the particle number size distributions, one to three lognormal modes were fitted to each size spectra.…”

“…Observations have shown that sulfuric acid, amines and organic vapor play a key role in the activation and subsequent growth of particle clusters (Almeida et al, 2013;Ehn et al, 2014;Kulmala et al, 2013;Paasonen 5 et al, 2010). NPF have been observed worldwide and in different environments (Kulmala et al, 2004), but several intensive experiments have shown that in Amazonia nucleation and subsequent particle growth is rare inside the boundary layer (BL) (Rissler et al, 2004;Rizzo et al, 2010;Zhou et al, 2002). Since the occurrence of NPF may depend on season and location (i.e., may vary depending on atmospheric conditions), short duration experiments cannot be conclusive about its frequency in Amazonia.…”

Emission and dry deposition of accumulation mode particles in the Amazon Basin

“…However, upward particle fluxes often appeared in the morning. Rizzo et al (2010) also observed upward particle number fluxes in the morning simultaneously with increasing particle number concentration, during aerosol flux measurements in the dry season at another tower at the same site. These early morning upward fluxes may have been related to primary biogenic aerosol emission of particles that have been stored in the canopy throughout the night, similar to CO 2 (Goulden et al, 2006;Araújo et al, 2008;Tóta et al, 2008), and the fact that these upward fluxes were sometimes correlated with increasing number concentrations suggest that they cannot be explained only as a result of dilution caused by entrainment during mixed layer growth.…”

Análise Da Profundidade Ótica De Aerossóis E Coeficiente De Angstrom No Cerrado Mato-Grossense

“…Estudos confirmam a Amazônia como um potencial emissor de material particulado biogênico (GRAHAM et al, 2003;ANDREAE, 2007;RIZZO et al, 2010), mas há também a contribuição de partículas emitidas pela queima de biomassa que influenciam fortemente as taxas fotossintéticas que afetam o balanço regional de carbono (OLIVEIRA et al, 2007). Sendo também responsáveis por alterações no balanço radiativo da atmosfera (RAMANATHAN et al, 2001).…”