scholarly journals Size-resolved observations of refractory black carbon particles in cloud droplets at a marine boundary layer site

2015 ◽  
Vol 15 (3) ◽  
pp. 1367-1383 ◽  
Author(s):  
J. C. Schroder ◽  
S. J. Hanna ◽  
R. L. Modini ◽  
A. L. Corrigan ◽  
S. M. Kreidenwies ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Black Carbon ◽  
Marine Boundary Layer ◽  
Volume Fraction ◽  
Particle Diameter ◽  
Cloud Droplet ◽  
Cloud Droplets ◽  
Back Trajectories ◽  
Carbon Particles ◽  
La Jolla

Abstract. Size-resolved observations of aerosol particles and cloud droplet residuals were studied at a marine boundary layer site (251 m a.m.s.l.) in La Jolla, San Diego, California, during 2012. A counterflow virtual impactor (CVI) was used as the inlet to sample cloud residuals while a total inlet was used to sample both cloud residuals and interstitial particles. Two cloud events totaling 10 h of in-cloud sampling were analyzed. Based on bulk aerosol particle concentrations, mass concentrations of refractory black carbon (rBC), and back trajectories, the two air masses sampled were classified as polluted marine air. Since the fraction of cloud droplets sampled by the CVI was less than 100%, the measured activated fractions of rBC should be considered as lower limits to the total fraction of rBC activated during the two cloud events. Size distributions of rBC and a coating analysis showed that sub-100 nm rBC cores with relatively thick coatings were incorporated into the cloud droplets (i.e., 95 nm rBC cores with median coating thicknesses of at least 65 nm were incorporated into the cloud droplets). Measurements also show that the coating volume fraction of rBC cores is relatively large for sub-100 nm rBC cores. For example, the median coating volume fraction of 95 nm rBC cores incorporated into cloud droplets was at least 0.9, a result that is consistent with κ-Köhler theory. Measurements of the total diameter of the rBC-containing particles (rBC core and coating) suggest that the total diameter of rBC-containing particles needed to be at least 165 nm to be incorporated into cloud droplets when the core rBC diameter is ≥ 85 nm. This result is consistent with previous work that has shown that particle diameter is important for activation of non-rBC particles. The activated fractions of rBC determined from the measurements ranged from 0.01 to 0.1 for core rBC diameters ranging from 70 to 220 nm. This type of data is useful for constraining models used for predicting rBC concentrations in the atmosphere.

scholarly journals Size-resolved observations of refractory black carbon particles in cloud droplets at a marine boundary layer site

2014 ◽  
Vol 14 (8) ◽  
pp. 11447-11491 ◽  
Author(s):  
J. C. Schroder ◽  
S. J. Hanna ◽  
R. L. Modini ◽  
A. L. Corrigan ◽  
A. M. Macdonald ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Black Carbon ◽  
Marine Boundary Layer ◽  
Back Trajectory ◽  
Cloud Droplets ◽  
Back Trajectories ◽  
Air Masses ◽  
Carbon Particles ◽  
Back Trajectory Analysis ◽  
La Jolla

Abstract. Size resolved observations of aerosol particles (including black carbon particles) and cloud residuals were studied at a marine boundary layer site (251 m a.m.s.l.) in La Jolla, CA during 2012. A counterflow virtual impactor was used to sample cloud residuals while a total inlet was used to sample both cloud residuals and interstitial particles. Two cloud events totaling ten hours of in-cloud sampling were analyzed. Since the CVI only sampled cloud droplets larger than ≈11 μm, less than 100% of the cloud droplets were sampled during the two cloud events (≈38% of the cloud droplets for the first cloud event and ≈24% of the cloud droplets for the second cloud were sampled). Back trajectories showed that air masses for both cloud events spent at least 96 h over the Pacific Ocean and traveled near, or over populated regions just before sampling. Based on bulk aerosol particle concentrations measured from the total inlet the two air masses sampled were classified as polluted marine air, a classification that was consistent with back trajectory analysis and the mass concentrations of refractory black carbon (rBC) measured from the total inlet. The activated fraction of rBC, estimated from the measurements, ranged from 0.01 to 0.1 for core diameters ranging from 70 to 220 nm. Since the fraction of cloud droplets sampled by the CVI was less than 100%, the measured activated fractions of rBC should be considered as lower limits to the total fraction of rBC activated during the two cloud events. Size distributions of rBC sampled from the residual inlet show that sub-100 nm rBC cores were incorporated into the droplets in both clouds. The coating analysis shows that the rBC cores had average coating thicknesses of 75 nm for core diameters of 70 nm and 29 nm for core diameters of 220 nm. The presence of sub-100 nm rBC cores in the cloud residuals is consistent with kappa-Köhler theory and the measured coating thicknesses of the rBC cores.

scholarly journals Observations of high droplet number concentrations in Southern Ocean boundary layer clouds

2016 ◽  
Vol 16 (2) ◽  
pp. 971-987 ◽  
Author(s):  
T. Chubb ◽  
Y. Huang ◽  
J. Jensen ◽  
T. Campos ◽  
S. Siems ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Southern Ocean ◽  
Atmospheric Chemistry ◽  
High Performance ◽  
Cloud Droplet ◽  
Environmental Research ◽  
Cloud Droplets ◽  
Back Trajectories ◽  
Boundary Layer Clouds ◽  
Microphysical Properties

Abstract. Cloud physics data collected during the NSF/NCAR High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) Pole-to-Pole Observations (HIPPO) campaigns provide a snapshot of unusual wintertime microphysical conditions in the boundary layer over the Southern Ocean. On 29 June 2011, the HIAPER sampled the boundary layer in a region of pre-frontal warm air advection between 58 and 48° S to the south of Tasmania. Cloud droplet number concentrations were consistent with climatological values in the northernmost profiles but were exceptionally high for wintertime in the Southern Ocean at 100–200 cm−3 in the southernmost profiles. Sub-micron (0.06  < D <  1 µm) aerosol concentrations for the southern profiles were up to 400 cm−3. Analysis of back trajectories and atmospheric chemistry observations revealed that while conditions in the troposphere were more typical of a clean remote ocean airmass, there was some evidence of continental or anthropogenic influence. However, the hypothesis of long-range transport of continental aerosol fails to explain the magnitude of the aerosol and cloud droplet concentration in the boundary layer. Instead, the gale force surface winds in this case (wind speed at 167 m above sea level was  > 25 m s−1) were most likely responsible for production of sea spray aerosol which influenced the microphysical properties of the boundary layer clouds. The smaller size and higher number concentration of cloud droplets is inferred to increase the albedo of these clouds, and these conditions occur regularly, and are expected to increase in frequency, over windy parts of the Southern Ocean.

scholarly journals Ultraclean Layers and Optically Thin Clouds in the Stratocumulus-to-Cumulus Transition. Part II: Depletion of Cloud Droplets and Cloud Condensation Nuclei through Collision–Coalescence

2018 ◽  
Vol 75 (5) ◽  
pp. 1653-1673 ◽  
Author(s):  
Kuan-Ting O ◽  
Robert Wood ◽  
Christopher S. Bretherton
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Liquid Water Content ◽  
Cloud Base ◽  
Condensation Nuclei ◽  
Cloud Droplets ◽  
Droplet Concentration ◽  
Cloud Thickness

In Part I, aircraft observations are used to show that ultraclean layers (UCLs) in the marine boundary layer (MBL) are a common feature of the stratocumulus-to-cumulus transition (SCT) region over the northeast Pacific. The ultraclean layers are defined as layers of either cloud or clear air in which the concentration of particles with diameter larger than 0.1 μm is below 10 cm−3. Here, idealized microphysical parcel modeling shows that in the cumulus regime, collision–coalescence can strongly deplete cloud droplet concentration in cumulus (Cu) updrafts, thereby removing cloud condensation nuclei (CCN) from the atmosphere, suggesting that collision scavenging is likely the key process causing the low particle concentration in UCLs. Furthermore, the model results suggest that the stratocumulus regime is typically not favorable for UCL formation, because condensate amounts are generally not large enough to deplete drops in the time it takes to loft air to the upper planetary boundary layer (PBL). A bulk parameterization of the coalescence-scavenging rate is derived based on in situ measurements. The fractional coalescence-scavenging rate is found to be strongly dependent upon liquid water content (LWC) and, hence, the height above cloud base, indicating that a higher cloud top and thus a greater cloud thickness in a Cu updraft is an important factor accounting for the observed sharp rise of UCL coverage in the SCT region. An important implication is that PBL height, which controls maximum cloud thickness, and therefore LWC in updrafts, could be a crucial factor constraining coalescence scavenging and thus the formation of UCLs in the MBL.

scholarly journals Aerosol concentration and size distribution measured below, in, and above cloud from the DOE G-1 during VOCALS-REx

2012 ◽  
Vol 12 (1) ◽  
pp. 207-223 ◽  
Author(s):  
L. I. Kleinman ◽  
P. H. Daum ◽  
Y.-N. Lee ◽  
E. R. Lewis ◽  
A. J. Sedlacek III ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Cloud Droplet ◽  
Number Concentration ◽  
Dew Point ◽  
Cloud Droplets ◽  
High Frequency Signal ◽  
The North ◽  
Stratocumulus Clouds ◽  
Constant Altitude

Abstract. During the VOCALS Regional Experiment, the DOE G-1 aircraft was used to sample a varying aerosol environment pertinent to properties of stratocumulus clouds over a longitude band extending 800 km west from the Chilean coast at Arica. Trace gas and aerosol measurements are presented as a function of longitude, altitude, and dew point in this study. Spatial distributions are consistent with an upper atmospheric source for O3 and South American coastal sources for marine boundary layer (MBL) CO and aerosol, most of which is acidic sulfate. Pollutant layers in the free troposphere (FT) can be a result of emissions to the north in Peru or long range transport from the west. At a given altitude in the FT (up to 3 km), dew point varies by 40 °C with dry air descending from the upper atmospheric and moist air having a boundary layer (BL) contribution. Ascent of BL air to a cold high altitude results in the condensation and precipitation removal of all but a few percent of BL water along with aerosol that served as CCN. Thus, aerosol volume decreases with dew point in the FT. Aerosol size spectra have a bimodal structure in the MBL and an intermediate diameter unimodal distribution in the FT. Comparing cloud droplet number concentration (CDNC) and pre-cloud aerosol (Dp>100 nm) gives a linear relation up to a number concentration of ~150 cm−3, followed by a less than proportional increase in CDNC at higher aerosol number concentration. A number balance between below cloud aerosol and cloud droplets indicates that ~25 % of aerosol with Dp>100 nm are interstitial (not activated). A direct comparison of pre-cloud and in-cloud aerosol yields a higher estimate. Artifacts in the measurement of interstitial aerosol due to droplet shatter and evaporation are discussed. Within each of 102 constant altitude cloud transects, CDNC and interstitial aerosol were anti-correlated. An examination of one cloud as a case study shows that the interstitial aerosol appears to have a background, upon which is superimposed a high frequency signal that contains the anti-correlation. The anti-correlation is a possible source of information on particle activation or evaporation.

scholarly journals Modeling microphysical effects of entrainment in clouds observed during EUCAARI-IMPACT field campaign

2013 ◽  
Vol 13 (16) ◽  
pp. 8489-8503 ◽  
Author(s):  
D. Jarecka ◽  
H. Pawlowska ◽  
W. W. Grabowski ◽  
A. A. Wyszogrodzki
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Marine Boundary Layer ◽  
Cloud Droplet ◽  
Droplet Radius ◽  
Subgrid Scale ◽  
Microphysics Scheme ◽  
Local Conditions ◽  
Field Campaign ◽  
Les Model

Abstract. This paper discusses aircraft observations and large-eddy simulation (LES) modeling of 15 May 2008, North Sea boundary-layer clouds from the EUCAARI-IMPACT field campaign. These clouds are advected from the northeast by the prevailing lower-tropospheric winds and featured stratocumulus-over-cumulus cloud formations. An almost-solid stratocumulus deck in the upper part of the relatively deep, weakly decoupled marine boundary layer overlays a field of small cumuli. The two cloud formations have distinct microphysical characteristics that are in general agreement with numerous past observations of strongly diluted shallow cumuli on one hand and solid marine stratocumulus on the other. Based on the available observations, a LES model setup is developed and applied in simulations using a novel LES model. The model features a double-moment warm-rain bulk microphysics scheme combined with a sophisticated subgrid-scale scheme allowing local prediction of the homogeneity of the subgrid-scale turbulent mixing. The homogeneity depends on the characteristic time scales for the droplet evaporation and for the turbulent homogenization. In the model, these scales are derived locally based on the subgrid-scale turbulent kinetic energy, spatial scale of cloudy filaments, mean cloud droplet radius, and humidity of the cloud-free air entrained into a cloud, all predicted by the LES model. The model reproduces contrasting macrophysical and microphysical characteristics of the cumulus and stratocumulus cloud layers. Simulated subgrid-scale turbulent mixing within the cumulus layer and near the stratocumulus top is on average quite inhomogeneous, but varies significantly depending on the local conditions.

scholarly journals Global simulations of aerosol processing in clouds

2008 ◽  
Vol 8 (23) ◽  
pp. 6939-6963 ◽  
Author(s):  
C. Hoose ◽  
U. Lohmann ◽  
R. Bennartz ◽  
B. Croft ◽  
G. Lesins
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Climate Model ◽  
Cloud Droplet ◽  
Model Aerosol ◽  
Aerosol Processing ◽  
Stratiform Clouds ◽  
Sensitivity Studies ◽  
Cloud Scavenging ◽  
Aerosol Volume

Abstract. An explicit and detailed representation of in-droplet and in-crystal aerosol particles in stratiform clouds has been introduced in the global aerosol-climate model ECHAM5-HAM. The new scheme allows an evaluation of the cloud cycling of aerosols and an estimation of the relative contributions of nucleation and collision scavenging, as opposed to evaporation of hydrometeors in the global aerosol processing by clouds. On average an aerosol particle is cycled through stratiform clouds 0.5 times. The new scheme leads to important changes in the simulated fraction of aerosol scavenged in clouds, and consequently in the aerosol wet deposition. In general, less aerosol is scavenged into clouds with the new prognostic treatment than what is prescribed in standard ECHAM5-HAM. Aerosol concentrations, size distributions, scavenged fractions and cloud droplet concentrations are evaluated and compared to different observations. While the scavenged fraction and the aerosol number concentrations in the marine boundary layer are well represented in the new model, aerosol optical thickness, cloud droplet number concentrations in the marine boundary layer and the aerosol volume in the accumulation and coarse modes over the oceans are overestimated. Sensitivity studies suggest that a better representation of below-cloud scavenging, higher in-cloud collision coefficients, or a reduced water uptake by seasalt aerosols could reduce these biases.

scholarly journals The single-particle mixing state and cloud scavenging of black carbon: a case study at a high-altitude mountain site in southern China

2017 ◽  
Vol 17 (24) ◽  
pp. 14975-14985 ◽  
Author(s):  
Guohua Zhang ◽  
Qinhao Lin ◽  
Long Peng ◽  
Xinhui Bi ◽  
Duohong Chen ◽  
...  
Keyword(s):  
Black Carbon ◽  
Single Particle ◽  
Southern China ◽  
Cloud Droplet ◽  
Mixing State ◽  
Cloud Droplets ◽  
Aerosol Mass ◽  
Mountain Site ◽  
Cloud Scavenging ◽  
Scavenging Efficiency

Abstract. In the present study, a ground-based counterflow virtual impactor (GCVI) was used to sample cloud droplet residual (cloud RES) particles, while a parallel PM2.5 inlet was used to sample cloud-free or cloud interstitial (cloud INT) particles. The mixing state of black carbon (BC)-containing particles and the mass concentrations of BC in the cloud-free, RES and INT particles were investigated using a single-particle aerosol mass spectrometer (SPAMS) and two aethalometers, respectively, at a mountain site (1690 m a. s. l. ) in southern China. The measured BC-containing particles were extensively internally mixed with sulfate and were scavenged into cloud droplets (with number fractions of 0.05–0.45) to a similar (or slightly lower) extent as all the measured particles (0.07–0.6) over the measured size range of 0.1–1.6 µm. The results indicate the preferential activation of larger particles and/or that the production of secondary compositions shifts the BC-containing particles towards larger sizes. BC-containing particles with an abundance of both sulfate and organics were scavenged less than those with sulfate but limited organics, implying the importance of the mixing state on the incorporation of BC-containing particles into cloud droplets. The mass scavenging efficiency of BC with an average of 33 % was similar for different cloud events independent of the air mass. This is the first time that both the mixing state and cloud scavenging of BC in China have been reported. Our results would improve the knowledge on the concentration, mixing state, and cloud scavenging of BC in the free troposphere.

scholarly journals Airborne DOAS measurements in Arctic: vertical distributions of aerosol extinction coefficient and NO<sub>2</sub> concentration

2011 ◽  
Vol 11 (5) ◽  
pp. 13525-13574
Author(s):  
A. Merlaud ◽  
M. Van Roozendael ◽  
N. Theys ◽  
C. Fayt ◽  
C. Hermans ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Scattered Light ◽  
Optical Absorption Spectroscopy ◽  
North Coast ◽  
Aerosol Extinction ◽  
Back Trajectories ◽  
The North ◽  
Source Regions ◽  
Vertical Distributions

Abstract. We report airborne differential optical absorption spectroscopy (DOAS) measurements of aerosol extinction and NO2 tropospheric profiles performed off the North coast of Norway in April 2008. The DOAS instrument was installed on the Safire ATR-42 aircraft during the POLARCAT-France spring campaign and recorded scattered light spectra in near-limb geometry using a scanning telescope. We use O4 slant column measurements to derive the aerosol extinction at 360 nm. Regularization is based on the maximum a posteriori solution, for which we compare a linear and a logarithmic approach. The latter inherently constrains the solution to positive values and yields aerosol extinction profiles more consistent with independently measured size distributions. Two soundings are presented, performed on 8 April 2008 above 71° N, 22° E and on 9 April 2008 above 70° N, 17.8° E. The first profile shows aerosol extinction and NO2 in the marine boundary layer with respective values of 0.04±0.005 km−1 and 1.9±0.3 × 109 molec cm−3. A second extinction layer of 0.01±0.003 km−1 is found at 4 km altitude. During the second sounding, clouds prevented us to retrieve profile parts under 3 km altitude but a layer with enhanced extinction (0.025±0.005 km−1) and NO2 (1.95±0.2 × 109 molec cm−3) is clearly detected at 4 km altitude. From CO and ozone in-situ measurements complemented by back-trajectories, we interpret the measurements in the free troposphere as, for the first sounding, a mix between stratospheric and polluted air from Northern Europe and for the second sounding, polluted air from Central Europe containing NO2. Considering the boundary layer measurements of the first flight, modeled source regions indicate closer sources, especially the Kola Peninsula smelters, which can explain the NO2 enhancement not correlated with a CO increase at the same altitude.

scholarly journals Modeling the smoky troposphere of the southeast Atlantic: a comparison to ORACLES airborne observations from September of 2016

2020 ◽  
Vol 20 (19) ◽  
pp. 11491-11526 ◽  
Author(s):  
Yohei Shinozuka ◽  
Pablo E. Saide ◽  
Gonzalo A. Ferrada ◽  
Sharon P. Burton ◽  
Richard Ferrare ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Optical Properties ◽  
Black Carbon ◽  
Marine Boundary Layer ◽  
Organic Aerosol ◽  
Airborne Lidar ◽  
Aerosol Mass ◽  
Wide Range ◽  
Smoke Layer ◽  
Mass Concentrations

Abstract. In the southeast Atlantic, well-defined smoke plumes from Africa advect over marine boundary layer cloud decks; both are most extensive around September, when most of the smoke resides in the free troposphere. A framework is put forth for evaluating the performance of a range of global and regional atmospheric composition models against observations made during the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) airborne mission in September 2016. A strength of the comparison is a focus on the spatial distribution of a wider range of aerosol composition and optical properties than has been done previously. The sparse airborne observations are aggregated into approximately 2∘ grid boxes and into three vertical layers: 3–6 km, the layer from cloud top to 3 km, and the cloud-topped marine boundary layer. Simulated aerosol extensive properties suggest that the flight-day observations are reasonably representative of the regional monthly average, with systematic deviations of 30 % or less. Evaluation against observations indicates that all models have strengths and weaknesses, and there is no single model that is superior to all the others in all metrics evaluated. Whereas all six models typically place the top of the smoke layer within 0–500 m of the airborne lidar observations, the models tend to place the smoke layer bottom 300–1400 m lower than the observations. A spatial pattern emerges, in which most models underestimate the mean of most smoke quantities (black carbon, extinction, carbon monoxide) on the diagonal corridor between 16∘ S, 6∘ E, and 10∘ S, 0∘ E, in the 3–6 km layer, and overestimate them further south, closer to the coast, where less aerosol is present. Model representations of the above-cloud aerosol optical depth differ more widely. Most models overestimate the organic aerosol mass concentrations relative to those of black carbon, and with less skill, indicating model uncertainties in secondary organic aerosol processes. Regional-mean free-tropospheric model ambient single scattering albedos vary widely, between 0.83 and 0.93 compared with in situ dry measurements centered at 0.86, despite minimal impact of humidification on particulate scattering. The modeled ratios of the particulate extinction to the sum of the black carbon and organic aerosol mass concentrations (a mass extinction efficiency proxy) are typically too low and vary too little spatially, with significant inter-model differences. Most models overestimate the carbonaceous mass within the offshore boundary layer. Overall, the diversity in the model biases suggests that different model processes are responsible. The wide range of model optical properties requires further scrutiny because of their importance for radiative effect estimates.

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