Impact of mixing state and hygroscopicity on CCN activity of biomass burning aerosol in Amazonia

摘要: Abstract. Smoke aerosols prevail throughout Amazonia because of widespread biomass burning during the dry season, and external mixing, low variability in particle size distribution hygroscopicity are typical. There can be profound effects on cloud properties. This study uses an adiabatic model to simulate activation smoke particles as condensation nuclei (CCN) for three hypothetical case studies, chosen resemble aerosol observations Amazonia. The relative importance hygroscopicity, mixing state, kinetics activated fraction maximum supersaturation is assessed. For a population with κp = 0.04, overestimation droplet number concentration Nd selected studies between 22.4 ± 1.4 54.3 ± 3.7 % was obtained when assuming parameter κp = 0.20. Assuming internal led overestimations up 20 % group medium present externally mixed cases. However, were below 10 % mixtures very low-hygroscopicity particles, seems Amazon particles. Kinetic limitations significant medium- high-hygroscopicity much lower When assumed at equilibrium respond instantly changes air parcel supersaturation,  ∼  100 % internally populations,  ∼  250 % ones, being larger higher values hygroscopicity. In addition, perceptible delay times reached noticed and, populations effective κpeff than certain threshold value, such that no time supersaturation. Considering updraft velocity W = 0.5 m s−1 this varied κpeff = 0.35 κpeff = 0.5 different studies. kinetic played weaker role CCN even taking into account large mass concentrations. range hygroscopicities, due assumption lowest greatly reduced or longer observed (depending study). These findings uncertainties sensitivities provide guidance appropriate simplifications used modeling within general circulation models. use representative other regions Earth lead errors compared (between 0.05 0.13, according available observations). Also region, consideration will small concentration, while significantly increasing computational burden. Regardless loads region expected low.