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@Article{SánchezGácitaLonFreFreMar:2017:ImMiSt,
               author = "S{\'a}nchez G{\'a}cita, Madeleine and Longo, Karla Maria and 
                         Freire, Juliana Larise Mendon{\c{c}}a and Freitas, Saulo Ribeiro 
                         de and Martin, Scot T.",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)} and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)} and {Instituto Nacional de Pesquisas 
                         Espaciais (INPE)} and {Harvard University}",
                title = "Impact of mixing state and hygroscopicity on CCN activity of 
                         biomass burning aerosol in Amazonia",
              journal = "Atmospheric Chemistry and Physics",
                 year = "2017",
               volume = "17",
               number = "3",
                pages = "2373--2392",
                month = "Feb.",
             abstract = "Smoke aerosols prevail throughout Amazonia because of widespread 
                         biomass burning during the dry season, and external mixing, low 
                         variability in the particle size distribution and low particle 
                         hygroscopicity are typical. There can be profound effects on cloud 
                         properties. This study uses an adiabatic cloud model to simulate 
                         the activation of smoke particles as cloud condensation nuclei 
                         (CCN) for three hypothetical case studies, chosen as to resemble 
                         biomass burning aerosol observations in Amazonia. The relative 
                         importance of variability in hygroscopicity, mixing state, and 
                         activation kinetics for the activated fraction and maximum 
                         supersaturation is assessed. For a population with kappa(p) = 0.04 
                         an overestimation of the cloud droplet number concentration N d 
                         for the three selected case studies between 22.4 +/- 1.4 and 54.3 
                         +/- 3.7% was obtained when assuming a hygroscopicity parameter 
                         kappa(p) = 0.20. Assuming internal mixing of the aerosol 
                         population led to overestimations of up to 20% of N d when a group 
                         of particles with medium hygroscopicity was present in the 
                         externally mixed population cases. However, the overestimations 
                         were below 10% for external mixtures between very low and 
                         low-hygroscopicity particles, as seems to be the case for Amazon 
                         smoke particles. Kinetic limitations were significant for 
                         medium-and high-hygroscopicity particles, and much lower for very 
                         low and low-hygroscopicity particles. When particles were assumed 
                         to be at equilibrium and to respond instantly to changes in the 
                         air parcel supersaturation, the overestimation of the droplet 
                         concentration was up to similar to 100% in internally mixed 
                         populations, and up to similar to 250% in externally mixed ones, 
                         being larger for the higher values of hygroscopicity. In addition, 
                         a perceptible delay between the times when maximum supersaturation 
                         and maximum aerosol activated fraction are reached was noticed 
                         and, for aerosol populations with effective hygroscopicity 
                         kappa(Peff) higher than a certain threshold value, the delay in 
                         particle activation was such that no particles were activated at 
                         the time of maximum supersaturation. Considering internally mixed 
                         populations, for an updraft velocity W = 0.5 m s(-1) this 
                         threshold of no activation varied between kappa(Peff) = 0.35 and 
                         kappa(Peff) = 0.5 for the different case studies. However, for low 
                         hygroscopicity, kinetic limitations played a weaker role for CCN 
                         activation of particles, even when taking into account the large 
                         aerosol mass and number concentrations. For the very low range of 
                         hygroscopicities, the overestimation of the droplet concentration 
                         due to the equilibrium assumption was lowest and the delay between 
                         the times when maximum supersaturation and maximum activated 
                         fraction were reached was greatly reduced or no longer observed 
                         (depending on the case study). These findings on uncertainties and 
                         sensitivities provide guidance on appropriate simplifications that 
                         can be used for modeling of smoke aerosols within general 
                         circulation models. The use of medium values of hygroscopicity 
                         representative of smoke aerosols for other biomass burning regions 
                         on Earth can lead to significant errors compared to the use of low 
                         hygroscopicity for Amazonia (between 0.05 and 0.13, according to 
                         available observations). Also in this region, consideration of the 
                         biomass burning population as internally mixed will lead to small 
                         errors in the droplet concentration, while significantly 
                         increasing the computational burden.",
                  doi = "10.5194/acp-17-2373-2017",
                  url = "http://dx.doi.org/10.5194/acp-17-2373-2017",
                 issn = "1680-7316 and 1680-7324",
             language = "en",
           targetfile = "sanchez_impact.pdf",
        urlaccessdate = "29 nov. 2020"
}


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