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Aircraft and ground measurements of dust aerosols over the west African coast in summer 2015 during ICE-D and AER-D

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Aircraft and ground measurements of dust aerosols over the west African coast in summer 2015 during ICE-D and AER-D

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dc.contributor.author	Liu, Dantong
dc.contributor.author	Taylor, Jonathan W.
dc.contributor.author	Crosier, Jonathan
dc.contributor.author	Marsden, Nicholas
dc.contributor.author	Bower, Keith N.
dc.contributor.author	Lloyd, Gary
dc.contributor.author	Ryder, Claire
dc.contributor.author	Brooke, Jennifer
dc.contributor.author	Cotton, Richard
dc.contributor.author	Marenco, Franco
dc.contributor.author	Blyth, Alan
dc.contributor.author	Cui, Zhiqiang
dc.contributor.author	Estellés Leal, Víctor
dc.contributor.author	Gallagher, Martin
dc.contributor.author	Coe, Hugh
dc.contributor.author	Choularton, Tom W.
dc.date.accessioned	2019-04-10T14:13:27Z
dc.date.available	2019-04-10T14:13:27Z
dc.date.issued	2018
dc.identifier.citation	Liu, Dantong Taylor, Jonathan W. Crosier, Jonathan Marsden, Nicholas Bower, Keith N. Lloyd, Gary Ryder, Claire Brooke, Jennifer Cotton, Richard Marenco, Franco Blyth, Alan Cui, Zhiqiang Estellés Leal, Víctor Gallagher, Martin Coe, Hugh Choularton, Tom W. 2018 Aircraft and ground measurements of dust aerosols over the west African coast in summer 2015 during ICE-D and AER-D Atmospheric Chemistry and Physics 18 3817 3838
dc.identifier.uri	http://hdl.handle.net/10550/69838
dc.description.abstract	During the summertime, dust from the Sahara can be efficiently transported westwards within the Saharan air layer (SAL). This can lead to high aerosol loadings being observed above a relatively clean marine boundary layer (MBL) in the tropical Atlantic Ocean. These dust layers can impart significant radiative effects through strong visible and IR light absorption and scattering, and can also have indirect impacts by altering cloud properties. The processing of the dust aerosol can result in changes in both direct and indirect radiative effects, leading to significant uncertainty in climate prediction in this region. During August 2015, measurements of aerosol and cloud properties were conducted off the coast of west Africa as part of the Ice in Cloud Experiment - Dust (ICE-D) and AERosol properties - Dust (AER-D) campaigns. Observations were obtained over a 4-week period using the UK Facility for Atmospheric Airborne Measurements (FAAM) BAe 146 aircraft based on Santiago Island, Cabo Verde. Ground-based observations were collected from Praia (14∘57′ N, 23∘29′ W; 100 m a.s.l.), also located on Santiago Island. The dust in the SAL was mostly sampled in situ at altitudes of 2-4 km, and the potential dust age was estimated by backward trajectory analysis. The particle mass concentration (at diameter d = 0.1-20 µm) decreased with transport time. Mean effective diameter (Deff) for supermicron SAL dust (d = 1-20 µm) was found to be 5-6 µm regardless of dust age, whereas submicron Deff (d = 0.1-1 µm) showed a decreasing trend with longer transport. For the first time, an airborne laser-induced incandescence instrument (the single particle soot photometer - SP2) was deployed to measure the hematite content of dust. For the Sahel-influenced dust in the SAL, the observed hematite mass fraction of dust (FHm) was found to be anti-correlated with the single scattering albedo (SSA, λ = 550 nm, for particles d < 2.5 µm); as potential dust age increased from 2 to 7 days, FHm increased from 2.5 to 4.5 %, SSA decreased from 0.97 to 0.93 and the derived imaginary part (k) of the refractive index at 550 nm increased from 0.0015 to 0.0035. However, the optical properties of Sahara-influenced plumes (not influenced by the Sahel) were independent of dust age and hematite content with SSA ∼ 0.95 and k ∼ 0.0028. This indicates that the absorbing component of dust may be source dependent, or that gravitational settling of larger particles may lead to a higher fraction of more absorbing clay-iron aggregates at smaller sizes. Mie calculation using the measured size distribution and size-resolved refractive indices of the absorbing components (black carbon and hematite) reproduces the measured SSA to within ±0.02 for SAL dust by assuming a goethite ∕ hematite mass ratio of 2. Overall, hematite and goethite constituted 40-80 % of the absorption for particles d < 2.5 µm, and black carbon (BC) contributed 10-37 %. This highlights the importance of size-dependent composition in determining the optical properties of dust and also the contribution from BC within dust plumes.
dc.language.iso	eng
dc.relation.ispartof	Atmospheric Chemistry and Physics, 2018, num. 18, p. 3817-3838
dc.subject	Aerosols
dc.subject	Termodinàmica atmosfèrica
dc.title	Aircraft and ground measurements of dust aerosols over the west African coast in summer 2015 during ICE-D and AER-D
dc.type	journal article	es_ES
dc.date.updated	2019-04-10T14:13:27Z
dc.identifier.doi	10.5194/acp-18-3817-2018
dc.identifier.idgrec	131058
dc.rights.accessRights	open access	es_ES