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(Referência obtida automaticamente do Web of Science, por meio da informação sobre o financiamento pela FAPESP e o número do processo correspondente, incluída na publicação pelos autores.)

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

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Gacita, Madeleine Sanchez ; Longo, Karla M. ; Freire, Julliana L. M. ; Freitas, Saulo R. ; Martin, Scot T.
Número total de Autores: 5
Tipo de documento: Artigo Científico
Fonte: Atmospheric Chemistry and Physics; v. 17, n. 3, p. 2373-2392, FEB 15 2017.
Citações Web of Science: 10

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. Regardless of the large smoke aerosol loads in the region during the dry season, kinetic limitations are expected to be low. (AU)

Processo FAPESP: 13/02101-9 - Contribuição dos aerossóis orgânicos à deposição de nitrogênio reativo na América do Sul
Beneficiário:Madeleine Sánchez Gácita Casagrande
Modalidade de apoio: Bolsas no Exterior - Estágio de Pesquisa - Doutorado
Processo FAPESP: 12/13575-9 - Participação no experimento de campo SAMBBA, análise dos dados coletados e modelagem
Beneficiário:Karla Maria Longo de Freitas
Modalidade de apoio: Auxílio à Pesquisa - Regular
Processo FAPESP: 12/09934-3 - Deposição atmosférica de nitrogênio reativo na América do Sul
Beneficiário:Madeleine Sánchez Gácita Casagrande
Modalidade de apoio: Bolsas no Brasil - Doutorado
Processo FAPESP: 14/01564-8 - Modelagem do efeito indireto de aerossóis na atmosfera da Amazônia
Beneficiário:Karla Maria Longo de Freitas
Modalidade de apoio: Bolsas no Exterior - Pesquisa