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dc.contributor.authorThalman, Ryan
dc.contributor.authorde Sá, Suzane S.
dc.contributor.authorPalm, Brett B.
dc.contributor.authorBarbosa, Henrique M. J.
dc.contributor.authorPöhlker, Mira L.
dc.contributor.authorAlexander, M. Lizabeth
dc.contributor.authorBrito, Joel
dc.contributor.authorCarbone, Samara
dc.contributor.authorCastillo, Paulo
dc.contributor.authorDay, Douglas A.
dc.contributor.authorKuang, Chongai
dc.contributor.authorManzi, Antonio
dc.contributor.authorNg, Nga Lee
dc.contributor.authorSedlacek, Arthur J. III
dc.contributor.authorSouza, Rodrigo
dc.contributor.authorSpringston, Stephen
dc.contributor.authorWatson, Thomas
dc.contributor.authorPöhlker, Christopher
dc.contributor.authorPöschl, Ulrich
dc.contributor.authorAndreae, Meinrat O.
dc.contributor.authorArtaxo, Paulo
dc.contributor.authorJimenez, Jose L.
dc.contributor.authorMartin, Scot T.
dc.contributor.authorWang, Jian
dc.date.accessioned2018-10-02T20:10:06Z
dc.date.available2018-10-02T20:10:06Z
dc.date.issued2017-10-05
dc.identifier.issn1680-7324
dc.identifier.otherhttps://doi.org/10.5194/acp-17-11779-2017
dc.identifier.urihttp://hdl.handle.net/1951/70468
dc.description© Author(s) 2017. This work is distributed under the Creative Commons Attribution 3.0 License.en_US
dc.description.abstractDuring the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign, size-resolved cloud condensation nuclei (CCN) spectra were characterized at a research site (T3) 60km downwind of the city of Manaus, Brazil, in central Amazonia for 1 year (12 March 2014 to 3 March 2015). Particle hygroscopicity (κCCN) and mixing state were derived from the size-resolved CCN spectra, and the hygroscopicity of the organic component of the aerosol (κorg) was then calculated from κCCN and concurrent chemical composition measurements. The annual average κCCN increased from 0.13 at 75nm to 0.17 at 171nm, and the increase was largely due to an increase in sulfate volume fraction. During both wet and dry seasons, κCCN, κorg, and particle composition under background conditions exhibited essentially no diel variations. The constant κorg of ∼ 0. 15 is consistent with the largely uniform and high O:C value (∼ 0. 8), indicating that the aerosols under background conditions are dominated by the aged regional aerosol particles consisting of highly oxygenated organic compounds. For air masses strongly influenced by urban pollution and/or local biomass burning, lower values of κorg and organic O:C atomic ratio were observed during night, due to accumulation of freshly emitted particles, dominated by primary organic aerosol (POA) with low hygroscopicity, within a shallow nocturnal boundary layer. The O:C, κorg, and κCCN increased from the early morning hours and peaked around noon, driven by the formation and aging of secondary organic aerosol (SOA) and dilution of POA emissions into a deeper boundary layer, while the development of the boundary layer, which leads to mixing with aged particles from the residual layer aloft, likely also contributed to the increases. The hygroscopicities associated with individual organic factors, derived from PMF (positive matrix factorization) analysis of AMS (aerosol mass spectrometry) spectra, were estimated through multivariable linear regression. For the SOA factors, the variation of the κ value with O:C agrees well with the linear relationship reported from earlier laboratory studies of SOA hygroscopicity. On the other hand, the variation in O:C of ambient aerosol organics is largely driven by the variation in the volume fractions of POA and SOA factors, which have very different O:C values. As POA factors have hygroscopicity values well below the linear relationship between SOA hygroscopicity and O:C, mixtures with different POA and SOA fractions exhibit a steeper slope for the increase in κorg with O:C, as observed during this and earlier field studies. This finding helps better understand and reconcile the differences in the relationships between κorg and O:C observed in laboratory and field studies, therefore providing a basis for improved parameterization in global models, especially in a tropical context.en_US
dc.language.isoen_USen_US
dc.publisherAtmospheric Chemistry and Physicsen_US
dc.titleCCN activity and organic hygroscopicity of aerosols downwind of an urban region in central Amazonia: Seasonal and diel variations and impact of anthropogenic emissionsen_US


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