Aerosol Composition, Mixing State, and Phase State of Free Tropospheric Particles and Their Role in Ice Cloud Formation

Abstract. Aerosol composition and mixing state near anthropogenic sources can be highly variable and can challenge predictions of cloud condensation nuclei (CCN). The impacts of chemical composition on CCN activation kinetics is also an important, but largely unknown, aspect of cloud droplet formation. Towards this, we present in-situ size-resolved CCN measurements carried out during the 2008 summertime August Mini Intensive Gas and Aerosol Study (AMIGAS) campaign in Atlanta, GA. Aerosol chemical composition was measured by two particle-into-liquid samplers measuring water-soluble inorganic ions and total water-soluble organic carbon. Size-resolved CCN data were collected using the Scanning Mobility CCN Analysis (SMCA) method and were used to obtain characteristic aerosol hygroscopicity distributions, whose breadth reflects the aerosol compositional variability and mixing state. Knowledge of aerosol mixing state is important for accurate predictions of CCN concentrations and that the influence of an externally-mixed, CCN-active aerosol fraction varies with size from 31% for particle diameters less than 40 nm to 93% for accumulation mode aerosol during the day. Assuming size-dependent aerosol mixing state and size-invariant chemical composition decreases the average CCN concentration overprediction (for all but one mixing state and chemical composition scenario considered) from over 190–240% to less than 20%. CCN activity is parameterized using a single hygroscopicity parameter, κ, which averages to 0.16 ± 0.07 for 80 nm particles and exhibits considerable variability (from 0.03 to 0.48) throughout the study period. Particles in the 60–100 nm range exhibited similar hygroscopicity, with a κ range for 60 nm between 0.06–0.076 (mean of 0.18 ± 0.09). Smaller particles (40 nm) had on average greater κ, with a range of 0.20–0.92 (mean of 0.3 ± 0.12). Analysis of the droplet activation kinetics of the aerosol sampled suggests that most of the CCN activate as rapidly as calibration aerosol, suggesting that aerosol composition exhibits a minor (if any) impact on CCN activation kinetics.

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A simplified empirical method for determination of aerosol hygroscopicity and composition

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-23627-2010 ◽

2010 ◽

Vol 10 (10) ◽

pp. 23627-23656

Author(s):

C. H. Chan ◽

A. Y. S. Cheng ◽

A. Viseu

Keyword(s):

Atmospheric Aerosols ◽

Climate Model ◽

Empirical Method ◽

Radiation Budget ◽

Cloud Formation ◽

Monthly Variation ◽

Aerosol Composition ◽

Remote System ◽

Aerosol Hygroscopicity

Abstract. Atmospheric aerosols have substantial influence on the Earth's radiation budget, visibility, cloud formation and precipitation. The aerosol hygroscopicity and the composition of aerosols are of vital importance for solar radiation budget calculation, cloud formation mechanism, and measurement of aerosol spatiotemporal distribution through remote sensing, such as Lidar, MODIS and sun/star photometer. In this paper, hourly averaged records of humidity, visibility and aerosol concentration, conducted in Macao, P.R.C. from 1 February 2006 to 31 December 2008 (LT), are used to estimate aerosol hygroscopicity and composition with a simplified empirical method. The result of monthly variation of aerosol hygroscopicity indicates the important role of aerosol composition on optical properties, which is in agreement with the previous study. This aerosol composition pattern is also consistent with the Asiatic Monsoon pattern and vicinity, such as Hong Kong. The monthly variation of aerosol hygroscopicity and composition also shows the necessity to consider such a factor for the aerosols monitoring by remote system and aerosols forcing simulated by climate model.

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An adsorption theory of heterogeneous nucleation of water vapour on nanoparticles

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-21883-2015 ◽

2015 ◽

Vol 15 (15) ◽

pp. 21883-21906

Author(s):

A. Laaksonen ◽

J. Malila

Keyword(s):

Water Vapour ◽

Heterogeneous Nucleation ◽

Large Scale ◽

Laboratory Data ◽

Theoretical Description ◽

Nucleation Theory ◽

Cloud Formation ◽

Scale Model ◽

Adsorption Theory ◽

Ice Cloud

Abstract. Heterogeneous nucleation of water vapour on insoluble nuclei is a phenomenon that can induce atmospheric water and ice cloud formation. However, modelling of the phenomenon is hampered by the fact that the predictive capability of the classical heterogeneous nucleation theory is rather poor. A reliable theoretical description of the influence of different types of water-insoluble nuclei in triggering the water condensation or ice deposition would help to decrease uncertainty in large scale model simulations. In this paper we extend a recently formulated adsorption theory of heterogeneous nucleation to be applicable to highly curved surfaces, and test the theory against laboratory data for water vapour nucleation on silica, titanium dioxide and silver oxide nanoparticles. We show that unlike the classical heterogeneous nucleation theory, the new theory is able to quantitatively predict the experimental results.

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The roles of dynamical variability and aerosols in cirrus cloud formation

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-3-1415-2003 ◽

2003 ◽

Vol 3 (2) ◽

pp. 1415-1451 ◽

Cited By ~ 4

Author(s):

B. Kärcher ◽

J. Ström

Keyword(s):

Probability Distributions ◽

Cirrus Clouds ◽

Cloud Formation ◽

Cirrus Cloud ◽

Ice Crystal ◽

Mesoscale Variability ◽

Aerosol Composition ◽

Airborne Measurements ◽

Cloud Properties

Abstract. The probability of occurrence of ice crystal number densities in young cirrus clouds is examined based on airborne measurements. The observations have been carried out at midlatitudes in both hemispheres at equivalent latitudes (~52–55° N/S) during the same season (local autumn in 2000). The in situ measurements considered in the present study include temperatures, vertical velocities, and ice crystal concentrations, the latter determined with high precision and accuracy using a counterflow virtual impactor. Most young cirrus clouds typically contain high number densities (1–10 cm−3) of small (diameter <20 μm) ice crystals. This mode dominates the probability distributions in both hemispheres and is shown to be caused by rapid cooling rates associated with updraft speeds in the range 10–100 cm s-1. A second mode containing larger crystals extends from ~1 cm−3 to low concentrations close to the detection threshold (~3×104cm−3) and is associated with lower updraft speeds. Results of a statistical analysis provide compelling evidence that the dynamical variability of vertical air motions on the mesoscale is the key factor determining the observed probability distributions of pristine ice crystal concentrations in cirrus. Other factors considered are variations of temperature as well as size, number, and ice nucleation thresholds of the freezing aerosol particles. The variability in vertical velocities is likely caused by atmospheric waves. Inasmuch as gravity waves are widespread, mesoscale variability in vertical velocities can be viewed as a universa feature of young cirrus clouds. Large-scale models that do not account for this subgrid-scale variability yield erroneous predictions of the variability of basic cirrus cloud properties. Climate change may bring about changes in the global distribution of updraft speeds, mean air temperatures, and aerosol properties. As shown in this work, these changes could significantly modify the probability distribution of cirrus ice crystal concentrations. This study emphasizes the key role of vertical velocities and mesoscale variability in vertical velocities in controlling cirrus properties. The results suggest that, in any effort to ascribe cause to trends of cirrus cloud properties, a careful evaluation of dynamical changes in cloud formation should be done before conclusions regarding the role of other anthropogenic factors, such as changes in aerosol composition, are made.

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On the origin of subvisible cirrus clouds in the tropical upper troposphere

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-14875-2012 ◽

2012 ◽

Vol 12 (6) ◽

pp. 14875-14926 ◽

Cited By ~ 1

Author(s):

M. Reverdy ◽

V. Noel ◽

H. Chepfer ◽

B. Legras

Keyword(s):

Cloud Formation ◽

Formation Processes ◽

Ice Clouds ◽

Back Trajectories ◽

Air Masses ◽

Ice Cloud ◽

And Behavior ◽

Atmospheric Phenomena ◽

Mean Variance ◽

Lidar Observations

Abstract. Spaceborne lidar observations have recently revealed a previously undetected significant population of SubVisible Cirrus (SVC). We show them to be colder than −74 °C, with an optical depth below 0.0015 on average. The formation and persistence over time of this new cloud population could be related to several atmospheric phenomena. In this paper, we investigate the importance of external processes in the creation of this cloud population, vs. the traditional ice cloud formation theory through convection. The importance of three scenarios in the formation of the global SVC population is investigated through different approaches that include comparisons with data imaging from several spaceborne instruments and back-trajectories that document the history and behavior of air masses leading to a point in time and space where subvisible cirrus were detected. In order simplify the study of cloud formation processes, we singled out SVC with coherent temperature histories (mean variance lower than 4 K) according to back-trajectories along 5, 10 or 15 days (respectively 58, 25 and 11% of SVC). Our results suggest that external processes, including local increases in liquid and hygroscopic aerosol concentration (either through biomass burning or volcanic injection forming sulfate-based aerosols in the troposphere or the stratosphere) have no noticeable short-term or mid-term impact on the SVC population. On the other hand, we find that ~60% of air masses interacted with convective activity in the days before they led to cloud formation and detection, which correspond to 37 to 65% of SVC. These results put forward the important influence of classical cloud formation processes compared to external influences in forming SVC. They support the view that the SVC population observed by CALIOP is an extension of the general upper tropospheric ice clouds population with its extreme thinness as its only differentiating factor.

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Suspendable macromolecules are responsible for ice nucleation activity of birch and conifer pollen

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-2541-2012 ◽

2012 ◽

Vol 12 (5) ◽

pp. 2541-2550 ◽

Cited By ~ 150

Author(s):

B. G. Pummer ◽

H. Bauer ◽

J. Bernardi ◽

S. Bleicher ◽

H. Grothe

Keyword(s):

Radiative Forcing ◽

Pollen Grains ◽

Ice Nucleation ◽

Cloud Formation ◽

Distribution Area ◽

Ice Cloud ◽

Ice Nuclei ◽

Nucleation Activity ◽

Ice Nucleation Activity ◽

The Impact

Abstract. The ice nucleation of bioaerosols (bacteria, pollen, spores, etc.) is a topic of growing interest, since their impact on ice cloud formation and thus on radiative forcing, an important parameter in global climate, is not yet fully understood. Here we show that pollen of different species strongly differ in their ice nucleation behaviour. The average freezing temperatures in laboratory experiments range from 240 to 255 K. As the most efficient nuclei (silver birch, Scots pine and common juniper pollen) have a distribution area up to the Northern timberline, their ice nucleation activity might be a cryoprotective mechanism. Far more intriguingly, it has turned out that water, which has been in contact with pollen and then been separated from the bodies, nucleates as good as the pollen grains themselves. The ice nuclei have to be easily-suspendable macromolecules located on the pollen. Once extracted, they can be distributed further through the atmosphere than the heavy pollen grains and so presumably augment the impact of pollen on ice cloud formation even in the upper troposphere. Our experiments lead to the conclusion that pollen ice nuclei, in contrast to bacterial and fungal ice nucleating proteins, are non-proteinaceous compounds.

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Transport of pollution to a remote coastal site during gap flow from California's interior: impacts on aerosol composition, clouds, and radiative balance

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-1491-2017 ◽

2017 ◽

Vol 17 (2) ◽

pp. 1491-1509 ◽

Cited By ~ 12

Author(s):

Andrew C. Martin ◽

Gavin C. Cornwell ◽

Samuel A. Atwood ◽

Kathryn A. Moore ◽

Nicholas E. Rothfuss ◽

...

Keyword(s):

Regional Climate ◽

Central Valley ◽

Ground Level ◽

Weather Conditions ◽

Cloud Formation ◽

Aerosol Composition ◽

Radiative Balance ◽

Gap Flow ◽

Climate Simulations ◽

Bodega Bay

Abstract. During the CalWater 2015 field campaign, ground-level observations of aerosol size, concentration, chemical composition, and cloud activity were made at Bodega Bay, CA, on the remote California coast. A strong anthropogenic influence on air quality, aerosol physicochemical properties, and cloud activity was observed at Bodega Bay during periods with special weather conditions, known as Petaluma Gap flow, in which air from California's interior is transported to the coast. This study applies a diverse set of chemical, cloud microphysical, and meteorological measurements to the Petaluma Gap flow phenomenon for the first time. It is demonstrated that the sudden and often dramatic change in aerosol properties is strongly related to regional meteorology and anthropogenically influenced chemical processes in California's Central Valley. In addition, it is demonstrated that the change in air mass properties from those typical of a remote marine environment to properties of a continental regime has the potential to impact atmospheric radiative balance and cloud formation in ways that must be accounted for in regional climate simulations.

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An adsorption theory of heterogeneous nucleation of water vapour on nanoparticles

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-135-2016 ◽

2016 ◽

Vol 16 (1) ◽

pp. 135-143 ◽

Cited By ~ 8

Author(s):

A. Laaksonen ◽

J. Malila

Keyword(s):

Water Vapour ◽

Heterogeneous Nucleation ◽

Large Scale ◽

Laboratory Data ◽

Theoretical Description ◽

Nucleation Theory ◽

Cloud Formation ◽

Scale Model ◽

Adsorption Theory ◽

Ice Cloud

Abstract. Heterogeneous nucleation of water vapour on insoluble nuclei is a phenomenon that can induce atmospheric water and ice cloud formation. However, modelling of the phenomenon is hampered by the fact that the predictive capability of the classical heterogeneous nucleation theory is rather poor. A reliable theoretical description of the influence of different types of water-insoluble nuclei in triggering the water condensation or ice deposition would help to decrease uncertainty in large-scale model simulations. In this paper we extend a recently formulated adsorption theory of heterogeneous nucleation to be applicable to highly curved surfaces, and test the theory against laboratory data for water vapour nucleation on silica, titanium dioxide and silver oxide nanoparticles. We show that unlike the classical heterogeneous nucleation theory, the new theory is able to quantitatively predict the experimental results.

Download Full-text