Chemical composition and sources of coastal marine aerosol particles during the 2008 VOCALS-REx campaign

Lee, Y.-N.; Springston, Stephen; Jayne, John T.; Wang, J.; Hubbe, J. M.; Senum, G.; Kleinman, Lawrence I.; Daum, P. H.

doi:10.5194/acp-14-5057-2014

Cited by 10 publications

(7 citation statements)

References 24 publications

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“…The sulfate consistently showed a higher loading near the surface within the MBL and decreased loadings with altitude for profiles of all air mass types. The AMS-derived ammonium and sulfate loadings (NH 4 and SO 4 ) had an equivalent ratio of 1.5-2 for most of the SLRs; highly acidic sulfate was also previously observed along the western coast of South America (Lee et al, 2014). There were some SLRs with relatively high sulfate and hematite loadings during SA + SD air masses.…”

Section: The Hematite Content Of Dust Aerosolsupporting

confidence: 61%

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

et al. 2018

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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 ExperimentDust (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 (D eff ) for supermicron SAL dust (d = 1-20 µm) was found to be 5-6 µm regardless of dust age, whereas submicron D eff (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 (F Hm ) 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, F Hm 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 ...

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Section: The Hematite Content Of Dust Aerosolsupporting

confidence: 61%

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

et al. 2018

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“…The transport is substantial during the dry season and thus, the aerosols very likely contain a large fraction of BC and organic carbon (OC) which is characteristic of biomass burning. Allen et al [2011] and Lee et al [2014] reported large amounts of organic aerosols simultaneously with increased CO concentration in the remote FT over the southeast Pacific Ocean and suggested that the aerosols were long-range transported from continental sources. In agreement with our findings, Freitag et al [2014] reported that air masses over the Pacific could be transported from 80 ∘ W to 120 ∘ W and also from the upper to the lower FT.…”

Section: Discussionmentioning

confidence: 99%

“…However, anthropogenic aerosols may also be present, in particular, during biomass burning periods [Clarke and Kapustin, 2010]. Lee et al [2014] found in their measurements near the South American coast in October and November 2008 that the MBL was dominated by sea salt, sulfate, and organic aerosols, where the sulfate and organics were mostly of continental origin.…”

Section: Introductionmentioning

confidence: 99%

Aerosol transport over the Andes from the Amazon Basin to the remote Pacific Ocean: A multiyear CALIOP assessment

2015

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Six years (2007Six years ( -2012 of data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite instrument were used to investigate the vertical distribution and transport of aerosols over the tropical South American continent and the southeast Pacific Ocean. The multiyear aerosol extinction assessment indicates that aerosols, mainly biomass burning particles emitted during the dry season in the Amazon Basin, are lifted in significant amounts over the Andes. The aerosols are mainly transported in the planetary boundary layer between the surface and 2 km altitude with an aerosol extinction maximum near the surface. During the transport toward the Andes, the aerosol extinction decreases at a rate of 0.02 km −1 per kilometer of altitude likely due to dilution and deposition processes. Aerosols reaching the top of the Andes, at altitudes typically between 4 and 5 km, are entrained into the free troposphere (FT) over the southeast Pacific Ocean. A comparison between CALIOP observations and ERA-Interim reanalysis data indicates that during their long-range transport over the tropical Pacific Ocean, these aerosols are slowly transported toward the marine boundary layer by the large-scale subsidence at a rate of 0.4 cm s −1 . The observed vertical/horizontal transport ratio is 0.7-0.8 m km −1 . Continental aerosols linked to transport over the Andes can be traced on average over 4000 km away from the continent indicating an aerosol residence time of 8-9 days in the FT over the Pacific Ocean. The FT aerosol optical depth (AOD) above the Pacific Ocean near South American coast accounts on average for 6% and 25% of the total AOD during the season of low and high biomass burning, respectively. This result shows that, during the biomass burning season, continental aerosols largely influence the AOD over the remote southeast Pacific Ocean. Overall, FT AOD decrease exponentially with the distance to continental sources at a rate of about 10% per degree of longitude over the Pacific Ocean.

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“…Aircraft observations of marine stratocumulus clouds showed that the vertical profile of LWC is essentially the same as the adiabatic profile; i.e., the cloud is almost adiabatic (Keil and Haywood, 2003). Furthermore, it remains unclear whether the subsequent entrainment-mixing mechanism is predominantly homogeneous, inhomogeneous, or in between (Andrejczuk et al, 2009;Lehmann et al, 2009). Some previous studies have shown that stratocumulus is generally dominated by the inhomogeneous mechanism (Pawlowska et al, 2000;Burnet and Brenguier, 2007;Haman et al, 2007;Lu et al, 2011;Yum et al, 2015).…”

Section: Entrainment In Stratocumulusmentioning

confidence: 99%

Responses to Referee #1’s comments

Jia¹

2019

Preprint

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In situ aircraft measurements obtained during the VAMOS (Variability of the American Monsoons) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) field campaign are analyzed to study the aerosol-cloud interactions in the stratocumulus clouds over the southeastern Pacific Ocean (SEP), with a focus on three understudied topics (separation of aerosol effects from dynamic effects, dispersion effects, and turbulent entrainmentmixing processes). Our analysis suggests that an increase in aerosol concentration tends to simultaneously increase both cloud droplet number concentration (N d) and relative dispersion (ε), while an increase in vertical velocity (w) often increases N d but decreases ε. After constraining the differences of cloud dynamics, the positive correlation between ε and N d becomes stronger, implying that perturbations of w could weaken the aerosol influence on ε and hence result in an underestimation of dispersion effect. A comparative analysis of the difference of cloud microphysical properties between the entrainment and non-entrainment zones suggests that the entrainment-mixing mechanism is predominantly extremely inhomogeneous in the stratocumulus that capped by a sharp inversion, whereby the variation in liquid water content (25 %) is similar to that of N d (29 %) and the droplet size remains approximately constant. In entrainment zone, drier air entrained from the top induces fewer cloud droplets with respect to total in-cloud particles (0.56 ± 0.22) than the case in the non-entrainment zone (0.73 ± 0.13) by promoting cloud droplet evaporation. This study is helpful in reducing uncertainties in dispersion effects and entrainment mixing for stratocumulus, and the results of this study may benefit cloud parameterizations in global climate models to more accurately assess aerosol indirect effects.

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Chemical composition and sources of coastal marine aerosol particles during the 2008 VOCALS-REx campaign

Cited by 10 publications

References 24 publications

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

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

Aerosol transport over the Andes from the Amazon Basin to the remote Pacific Ocean: A multiyear CALIOP assessment

Responses to Referee #1’s comments

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