Cloud Condensation Nuclei Properties Research Articles

CCN activation in homogeneous isotropic turbulence: Response to particle characteristics and environmental conditions

Direct Numerical Simulation (DNS) of turbulent cloud parcels are presented where particles evolve in response to the local values in supersaturation (s) led by turbulent fluctuations. A pseudo-spectral DNS is modified to incorporate aerosol particles and Cloud Condensation Nuclei (CCN) activation applying a droplet growth equation based on κ-Köhler theory that works for the whole range of warm cloud particles, from un-activated deliquesced aerosol particles to activated cloud droplets, that grow by condensation. The Lagrangian microphysics applied ensures that each particle experiences a supersaturation (fluctuations added to the mean) corresponding to its near-particle gas phase surroundings, which differs from the uniform parcel view where an average value of supersaturation, s¯, is applied to every particle in the domain. A non-turbulent Lagrangian parcel model with similar mean thermodynamics and CCN properties is compared with turbulent DNS parcels of varying fluctuation intensities to distinguish the impact of turbulence on CCN activation. It is shown that, in a given distribution, a subset of aerosols respond to fluctuations rather than the mean thermodynamics allowing particles of similar dry size to co-exist as un-activated haze particles as well as cloud droplets. The cloud microphysical properties are analysed in a series of DNS experiments with contrasting thermodynamic and aerosol properties. DNS results agrees with the general understanding of aerosol activation and cloud droplets evolution in response to various background conditions such as pristine and polluted aerosol distributions, composition of CCN with respect to organic - inorganic components and magnitude of vertical velocity. DNS considers turbulence-microphysics interactions in such problems providing additional knowledge on the role of turbulence in clouds. It is argued that incorporating turbulent fluctuations in simulating the CCN activation and droplet growth is well reasoned and a constructive way forward.

Rapid growth and high cloud-forming potential of anthropogenic sulfate aerosol in a thermal power plant plume during COVID lockdown in India

The COVID lockdown presented an interesting opportunity to study the anthropogenic emissions from different sectors under relatively cleaner conditions in India. The complex interplays of power production, industry, and transport could be dissected due to the significantly reduced influence of the latter two emission sources. Here, based on measurements of cloud condensation nuclei (CCN) activity and chemical composition of atmospheric aerosols during the lockdown, we report an episodic event resulting from distinct meteorological conditions. This event was marked by rapid growth and high hygroscopicity of new aerosol particles formed in the SO2 plume from a large coal-fired power plant in Southern India. These sulfate-rich particles had high CCN activity and number concentration, indicating high cloud-forming potential. Examining the sensitivity of CCN properties under relatively clean conditions provides important new clues to delineate the contributions of different anthropogenic emission sectors and further to understand their perturbations of past and future climate forcing.

Investigating the Applicability of a Global Average Calibration Line for Ambient Size-Resolved Cloud Condensation Nuclei (CCN) Measurements: A Technical Note

Abstract Aerosol–cloud–precipitation interaction represents the largest uncertainty in climate change’s current and future understanding. Therefore, aerosol properties affecting the cloud and precipitation formation and their accurate estimation is a first step in developing improved parameterizations for the prognostic climate models. Over the last couple of decades, a commercially available Cloud Condensation Nuclei Counter (CCNC) has been deployed in the field and laboratory for characterizing CCN properties of ambient or atmospherically relevant laboratory-generated aerosols. However, most of the CCN measurements performed in the field are often compounded with the erroneous estimation of CCN concentration and other parameters due to a lack of robust and accurate CCNC calibration. CCNC is not a plug-and-play instrument and requires prudent calibration and operation, to avoid erroneous data and added parameterization uncertainties. In this work, we propose and demonstrate the usability of a global calibration equation derived from CCNC calibration experiments from 8 contrasting global environments. Significant correlation was observed between the global calibration and each of the 16 individual experiments. A significant improvement in the correlation was observed when the calibration experiments were separated for high-altitude measurements. Using these equations, we further derived the effective hygroscopicity parameter and found lower relative uncertainty in the hygroscopicity parameter at higher effective supersaturation. Our results signify that altitude-based pressure change could be of importance for accurate calibration at high-altitude locations. Our results are consistent with previous studies emphasizing the criticality of the accurate CCN calibration for the lower supersaturations.

A study of the effect of open biomass burning aerosol on rainfall event over Malaysia by using EOF analysis

Significant biomass burning aerosols resulted from biomass burning activities from Sumatra and Kalimantan Island transported to Malaysia every year from August to October by the southeast monsoon. These transboundary haze changes the precipitation pattern by aerosol interaction with radiation and cloud which affects the solar radiation budget and cloud condensation nuclei properties. In this work, empirical orthogonal function (EOF) was used to assess the effect of biomass burning aerosol on rainfall pattern over Malaysia from both a spatial and a temporal perspective. Over Peninsular Malaysia, regional rainfall activities tend to be suppressed by concentrated biomass burning aerosols and produce another heavy rain over the downwind areas after 30-60 days (60 days) under highly (less) populated condition. Similar precipitation pattern has been indicated over Sarawak and Sabah where biomass burning aerosols suppress rainfall in the southwestern area while leads to a more intensified rainfall event in the northeast area with 30-60 days (60 days) interval under highly (less) populated condition.

Impact of urban aerosols on the cloud condensation activity using a clustering model

The indirect effect of aerosols on climate through aerosol-cloud-interactions is still highly uncertain and limits our ability to assess anthropogenic climate change. The foundation of this uncertainty is in the number of cloud condensation nuclei (CCN), which itself mainly stems from uncertainty in aerosol sources and how particles evolve to become effective CCN. We analyze particle number size distribution (PNSD) and CCN measurements from an urban site in a two-step method: (1) we use an unsupervised clustering model to classify the main aerosol categories and processes occurring in the urban atmosphere and (2) we explore the influence of the identified aerosol populations on the CCN properties. According to the physical properties of each cluster, its diurnal timing, and additional air quality parameters, the clusters are grouped into five main aerosol categories: nucleation, growth, traffic, aged traffic, and urban background. The results show that, despite aged traffic and urban background categories are those with lower total particle number concentrations (Ntot) these categories are the most efficient sources in terms of contribution to the overall CCN budget with activation fractions (AF) around 0.5 at 0.75 % supersaturation (SS). By contrast, road traffic is an important aerosol source with the highest frequency of occurrence (32 %) and relatively high Ntot, however, its impact in the CCN activity is very limited likely due to lower particle mean diameter and hydrophobic chemical composition. Similarly, nucleation and growth categories, associated to new particle formation (NPF) events, present large Ntot with large frequency of occurrence (22 % and 28 %, respectively) but the CCN concentration for these categories is about half of the CCN concentration observed for the aged traffic category, which is associated with their small size. Overall, our results show that direct influence of traffic emissions on the CCN budget is limited, however, when these particles undergo ageing processes, they have a significant influence on the CCN concentrations and may be an important CCN source. Thus, aged traffic particles could be transported to other environments where clouds form, triggering a plausible indirect effect of traffic emissions on aerosol-cloud interactions and consequently contributing to climate change.

Circum-Antarctic abundance and properties of CCN and INPs

Abstract. Aerosol particles acting as cloud condensation nuclei (CCN) or ice-nucleating particles (INPs) play a major role in the formation and glaciation of clouds. Thereby they exert a strong impact on the radiation budget of the Earth. Data on abundance and properties of both types of particles are sparse, especially for remote areas of the world, such as the Southern Ocean (SO). In this work, we present unique results from ship-borne aerosol-particle-related in situ measurements and filter sampling in the SO region, carried out during the Antarctic Circumnavigation Expedition (ACE) in the austral summer of 2016–2017. An overview of CCN and INP concentrations over the Southern Ocean is provided and, using additional quantities, insights regarding possible CCN and INP sources and origins are presented. CCN number concentrations spanned 2 orders of magnitude, e.g. for a supersaturation of 0.3 % values ranged roughly from 3 to 590 cm−3. CCN showed variable contributions of organic and inorganic material (inter-quartile range of hygroscopicity parameter κ from 0.2 to 0.9). No distinct size dependence of κ was apparent, indicating homogeneous composition across sizes (critical dry diameter on average between 30 and 110 nm). The contribution of sea spray aerosol (SSA) to the CCN number concentration was on average small. Ambient INP number concentrations were measured in the temperature range from −5 to −27 ∘C using an immersion freezing method. Concentrations spanned up to 3 orders of magnitude, e.g. at −16 ∘C from 0.2 to 100 m−3. Elevated values (above 10 m−3 at −16 ∘C) were measured when the research vessel was in the vicinity of land (excluding Antarctica), with lower and more constant concentrations when at sea. This, along with results of backward-trajectory analyses, hints towards terrestrial and/or coastal INP sources being dominant close to ice-free (non-Antarctic) land. In pristine marine areas INPs may originate from both oceanic sources and/or long-range transport. Sampled aerosol particles (PM10) were analysed for sodium and methanesulfonic acid (MSA). Resulting mass concentrations were used as tracers for primary marine and secondary aerosol particles, respectively. Sodium, with an average mass concentration around 2.8 µg m−3, was found to dominate the sampled, identified particle mass. MSA was highly variable over the SO, with mass concentrations up to 0.5 µg m−3 near the sea ice edge. A correlation analysis yielded strong correlations between sodium mass concentration and particle number concentration in the coarse mode, unsurprisingly indicating a significant contribution of SSA to that mode. CCN number concentration was highly correlated with the number concentration of Aitken and accumulation mode particles. This, together with a lack of correlation between sodium mass and Aitken and accumulation mode number concentrations, underlines the important contribution of non-SSA, probably secondarily formed particles, to the CCN population. INP number concentrations did not significantly correlate with any other measured aerosol physico-chemical parameter.

Physical and Chemical Properties of Cloud Droplet Residuals and Aerosol Particles During the Arctic Ocean 2018 Expedition.

Detailed knowledge of the physical and chemical properties and sources of particles that form clouds is especially important in pristine areas like the Arctic, where particle concentrations are often low and observations are sparse. Here, we present in situ cloud and aerosol measurements from the central Arctic Ocean in August–September 2018 combined with air parcel source analysis. We provide direct experimental evidence that Aitken mode particles (particles with diameters ≲70 nm) significantly contribute to cloud condensation nuclei (CCN) or cloud droplet residuals, especially after the freeze‐up of the sea ice in the transition toward fall. These Aitken mode particles were associated with air that spent more time over the pack ice, while size distributions dominated by accumulation mode particles (particles with diameters ≳70 nm) showed a stronger contribution of oceanic air and slightly different source regions. This was accompanied by changes in the average chemical composition of the accumulation mode aerosol with an increased relative contribution of organic material toward fall. Addition of aerosol mass due to aqueous‐phase chemistry during in‐cloud processing was probably small over the pack ice given the fact that we observed very similar particle size distributions in both the whole‐air and cloud droplet residual data. These aerosol–cloud interaction observations provide valuable insight into the origin and physical and chemical properties of CCN over the pristine central Arctic Ocean.

Aerodynamic size-resolved composition and cloud condensation nuclei properties of aerosols in a Beijing suburban region

Abstract. The size-resolved physiochemical properties of aerosols determine their atmospheric lifetime, cloud interactions and the deposition rate on the human respiratory system; however most atmospheric composition studies tend to evaluate these properties in bulk. This study investigated size-resolved constituents of aerosols on mass and number basis, and their droplet activation properties, by coupling a suite of online measurements with an aerosol aerodynamic classifier (AAC) based on aerodynamic diameter (Da) in Pinggu, a suburb of Beijing. While organic matter accounted for a large fraction of mass, a higher contribution of particulate nitrate at larger sizes (Da>300 nm) was found under polluted cases. By considering the mixing state of refractory-black-carbon-containing particles (rBCc) and composition-dependent densities, aerosols including rBCc were confirmed to be nearly spherical at Da>300 nm. Importantly, the number fraction of rBCc was found to increase with Da at all pollution levels. The number fraction of refractory black carbon (rBC) is found to increase from ∼3 % at ∼90 nm to ∼15 % at ∼1000 nm, and this increasing rBC number fraction may be caused by the coagulation during atmospheric ageing. The droplet activation diameter at a water supersaturation of 0.2 % was 112±6 and 193±41 nm for all particles with Da smaller than 1 µm (PM1) and rBCc respectively. As high as 52±6 % of rBCc and 50±4 % of all PM1 particles in number could be activated under heavy pollution due to enlarged particle size, which could be predicted by applying the volume mixing of substance hygroscopicity within rBCc. As rBCc contribute to the quantity of aerosols at larger particle size, these thickly coated rBCc may contribute to the radiation absorption significantly or act as an important source of cloud condensation nuclei (CCN). This size regime may also exert important health effects due to their higher deposition rate.

Tropical and Boreal Forest – Atmosphere Interactions: A Review

This review presents how the boreal and the tropical forests affect the atmosphere, its chemical composition, its function, and further how that affects the climate and, in return, the ecosystems through feedback processes. Observations from key tower sites standing out due to their long-term comprehensive observations: The Amazon Tall Tower Observatory in Central Amazonia, the Zotino Tall Tower Observatory in Siberia, and the Station to Measure Ecosystem-Atmosphere Relations at Hyytiäla in Finland. The review is complemented by short-term observations from networks and large experiments. The review discusses atmospheric chemistry observations, aerosol formation and processing, physiochemical aerosol, and cloud condensation nuclei properties and finds surprising similarities and important differences in the two ecosystems. The aerosol concentrations and chemistry are similar, particularly concerning the main chemical components, both dominated by an organic fraction, while the boreal ecosystem has generally higher concentrations of inorganics, due to higher influence of long-range transported air pollution. The emissions of biogenic volatile organic compounds are dominated by isoprene and monoterpene in the tropical and boreal regions, respectively, being the main precursors of the organic aerosol fraction. Observations and modeling studies show that climate change and deforestation affect the ecosystems such that the carbon and hydrological cycles in Amazonia are changing to carbon neutrality and affect precipitation downwind. In Africa, the tropical forests are so far maintaining their carbon sink. It is urgent to better understand the interaction between these major ecosystems, the atmosphere, and climate, which calls for more observation sites, providing long-term data on water, carbon, and other biogeochemical cycles. This is essential in finding a sustainable balance between forest preservation and reforestation versus a potential increase in food production and biofuels, which are critical in maintaining ecosystem services and global climate stability. Reducing global warming and deforestation is vital for tropical forests.

Technical note: Real-time diagnosis of the hygroscopic growth micro-dynamics of nanoparticles with Fourier transform infrared spectroscopy

Abstract. Nanoparticles can absorb water to grow, and this process will affect the light-scattering behavior, cloud condensation nuclei properties, lifetime, and chemical reactivity of these particles. Current techniques for calculation of aerosol liquid water content (ALWC) usually restrict the size of particles to be within a certain range, which may result in a large uncertainty when the particle size is beyond the specified range. Furthermore, current techniques are difficult to use to identify the intermolecular interactions of phase transition micro-dynamics during particles' hygroscopic growth process because their limited temporal resolutions are unable to capture complex intermediate states. In this study, the hygroscopic growth properties of nanoparticles with electrical mobility diameters (Dem) of ∼ 100 nm and their phase transition micro-dynamics at the molecular level are characterized in real time by using the Fourier transform infrared (FTIR) spectroscopic technique. We develop a novel real-time method for ALWC calculation by reconstructing the absorption spectra of liquid water and realize real-time measurements of water content and dry nanoparticle mass to characterize hygroscopic growth factors (GFs). The calculated GFs are generally in good agreement with the Extended Aerosol Inorganics Model (E-AIM) predictions. We also explore the phenomenon that the deliquescence points of the ammonium sulfate / sodium nitrate (AS/SN) mixed nanoparticles and the AS / oxalic acid (AS/OA) mixed nanoparticles are lower than that of the pure AS. We further normalize the FTIR spectra of nanoparticles into 2D IR spectra and identify in real time the hydration interactions and the dynamic hygroscopic growth process of the functional groups for AS, AS/SN, and AS/OA nanoparticles. The results show that both SN and OA compounds can lower the deliquescence point of AS, but they affect AS differently. The SN can change but OA cannot change the hydrolysis reaction mechanism of AS during the hygroscopic growth process. Compared with previous studies, we captured more complex processes and the intermediate state of the hygroscopic growth of nanoparticles. This study not only can provide important information with respect to the difference in the phase transition point under different conditions but also can improve current understanding of the chemical interaction mechanism between nanoparticles (particularly for organic particles) and the surrounding medium, which is of great significance for investigation of haze formation in the atmosphere.

Equal abundance of summertime natural and wintertime anthropogenic Arctic organic aerosols

Aerosols play an important yet uncertain role in modulating the radiation balance of the sensitive Arctic atmosphere. Organic aerosol is one of the most abundant, yet least understood, fractions of the Arctic aerosol mass. Here we use data from eight observatories that represent the entire Arctic to reveal the annual cycles in anthropogenic and biogenic sources of organic aerosol. We show that during winter, the organic aerosol in the Arctic is dominated by anthropogenic emissions, mainly from Eurasia, which consist of both direct combustion emissions and long-range transported, aged pollution. In summer, the decreasing anthropogenic pollution is replaced by natural emissions. These include marine secondary, biogenic secondary and primary biological emissions, which have the potential to be important to Arctic climate by modifying the cloud condensation nuclei properties and acting as ice-nucleating particles. Their source strength or atmospheric processing is sensitive to nutrient availability, solar radiation, temperature and snow cover. Our results provide a comprehensive understanding of the current pan-Arctic organic aerosol, which can be used to support modelling efforts that aim to quantify the climate impacts of emissions in this sensitive region.

Influence of aerosol physico-chemical properties on cloud microphysical parameters perceived using in-situ high altitude observations

Variability in cloud microphysical parameters, aerosol physicochemical properties and their relationship were studied using in-situ ground observations from a high altitude site in Western Ghats, India, during monsoon season. Cloud microphysical parameters, such as cloud droplet number concentration (CDNC), liquid water content (LWC), and effective diameter (ED), have been analyzed. Aerosol–CCN (cloud condensation nuclei) number concentration and mass concentration of non-refractory particulate matter (NR-PM1) during summer monsoon also showed day to day and monthly variation. Cloud droplet size distribution (CDSD) showed a bimodal spectrum with two prominent peaks i.e. in 3–10 μm and 12–22 μm size ranges. The estimated spectral width of CDSD (σ) broadly varied from 0 to 4 μm and the effective radius ratio (β) from 0.6–1.8. Further, the effect of aerosol on cloud microphysical parameters and CDSD has been investigated. There was an apparent variation in CCN super saturation spectrum, aerosol chemical composition, and cloud microphysics during high and low aerosol loading daysThe aerosol chemical composition showed a higher sulphate and ammonium (organics) contribution during low (high) aerosol loading days. CCN concentration and CDNC (ED) were higher (less) during high aerosol days and vice versa during low aerosol days. A review of microphysical characteristics of monsoon clouds over various locations of the Indian region has shown that this is the first such report that provides observational evidence of how variation in aerosol physical and chemical properties affects the CCN and cloud properties derived explicitly from long-term ground-based observations.

Planetary Boundary Layer Height Modulates Aerosol—Water Vapor Interactions During Winter in the Megacity of Delhi

AbstractThe Indo‐Gangetic Plain (IGP) is one of the dominant sources of air pollution worldwide. During winter, the variations in planetary boundary layer (PBL) height, driven by a strong radiative thermal inversion, affect the regional air pollution dispersion. To date, measurements of aerosol‐water vapor interactions, especially cloud condensation nuclei (CCN) activity, are limited in the Indian subcontinent, causing large uncertainties in radiative forcing estimates of aerosol‐cloud interactions. We present the results of a one‐month field campaign (February‐March 2018) in the megacity, Delhi, a significant polluter in the IGP. We measured the composition of fine particulate matter (PM1) and size‐resolved CCN properties over a wide range of water vapor supersaturations. The analysis includes PBL modeling, backward trajectories, receptor models and fire spots to elucidate the influence of PBL and air mass origins on aerosols. The aerosol properties depended strongly on PBL height and a simple power‐law fit could parameterize the observed correlations of PM1 mass, aerosol particle number and CCN number with PBL height, indicating PBL induced changes in aerosol accumulation. The low inorganic mass fractions, low aerosol hygroscopicity and high externally mixed weakly CCN‐active particles under low PBL height (100 m) indicated the influence of PBL on aerosol aging processes. In contrast, aerosol properties did not depend strongly on air mass origins or wind direction, implying that the observed aerosol and CCN are from local emissions. An error function could parameterize the relationship between CCN number and supersaturation throughout the campaign.

Properties and emission factors of cloud condensation nuclei from biomass cookstoves – observations of a strong dependency on potassium content in the fuel

Abstract. Residential biomass combustion is a significant source of aerosol particles on regional and global scales influencing climate and human health. The main objective of the current study was to investigate the properties of cloud condensation nuclei (CCN) emitted from biomass burning of solid fuels in different cookstoves mostly of relevance to sub-Saharan east Africa. The traditional three-stone fire and a rocket stove were used for combustion of wood logs of Sesbania and Casuarina with birch used as a reference. A natural draft and a forced-draft pellet stove were used for combustion of pelletised Sesbania and pelletised Swedish softwood alone or in mixtures with pelletised coffee husk, rice husk or water hyacinth. The CCN activity and the effective density were measured for particles with mobility diameters of ∽65, ∽100 and ∽200 nm, respectively, and occasionally for 350 nm particles. Particle number size distributions were measured online with a fast particle analyser. The chemical composition of the fuel ash was measured by application of standard protocols. The average particle number size distributions were by number typically dominated by an ultrafine mode, and in most cases a soot mode was centred around a mobility diameter of ∽150 nm. The CCN activities decreased with increasing particle size for all experiments and ranged in terms of the hygroscopicity parameter, κ, from ∽0.1 to ∽0.8 for the ultrafine mode and from ∽0.001 to ∽0.15 for the soot mode. The CCN activity (κ) of the ultrafine mode increased (i) with increasing combustion temperature for a given fuel, and (ii) it typically increased with increasing potassium concentration in the investigated fuels. The primary CCN and the estimated particulate matter (PM) emission factors were typically found to increase significantly with increasing potassium concentration in the fuel for a given stove. In order to link CCN emission factors to PM emission factors, knowledge about stove technology, stove operation and the inorganic fuel ash composition is needed. This complicates the use of ambient PM levels alone for estimation of CCN concentrations in regions dominated by biomass combustion aerosol, with the relation turning even more complex when accounting for atmospheric ageing of the aerosol.

Satellite Retrieval of Cloud Condensation Nuclei Concentrations in Marine Stratocumulus by Using Clouds as CCN Chambers

AbstractA new methodology for the satellite retrieval of cloud condensation nuclei (CCN) in shallow marine boundary layer clouds is developed and validated in this study. The methodology is based on retrieving cloud base drop concentrations (Nd) and updrafts (Wb), which are used for calculating the supersaturation (S). The Nd is then defined as the CCN at that S. The accuracy of the satellite retrievals was validated against ship‐borne measurements of CCN done in recent campaigns in the Southern Oceans (ACE‐SPACE, MARCUS, & PEGASO [2015–2018]) and in the subtropics (MAGIC [2012–2013]). The satellite‐retrieved Nd and S at cloud base were validated against the measured CCN at sea surface. The main findings show that (a) coupled clouds have good agreement between satellite retrievals and ship measurements of CCN; (b) the best agreement is achieved when using the brightest 10% of the clouds and accounting for their adiabatic fraction; (c) most of the decoupled clouds had much lower CCN than were present at the underlying surface. This means that most CCN in the coupled clouds originate from the surface and not from the free troposphere. This study validates the satellite retrievals of CCN and allows us to further quantify the relationships between CCN and cloud microphysical properties.

Cloud condensation nuclei properties of South Asian outflow over the northern Indian Ocean during winter

Abstract. Extensive measurements of cloud condensation nuclei (CCN) and condensation nuclei (CN) concentrations in the South Asian outflow to the northern Indian Ocean were carried out on board an instrumented research vessel, as part of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) during the winter season (January–February 2018). Measurements include a north–south transect across the South Asian plume over the northern Indian Ocean and an east–west transect over the equatorial Indian Ocean (∼2∘ S), which is far away from the continental sources. South Asian outflow over the northern Indian Ocean is characterized by the high values of CCN number concentration (∼5000 cm−3), low CCN activation efficiency (∼25 %) and a steep increase in CCN concentration with the increase in supersaturation. In contrast, low CCN concentration (∼1000 cm−3) with flat supersaturation spectra was found over the equatorial Indian Ocean. The CCN properties exhibited significant dependence on the geometric mean diameter (GMD) of the aerosol number size distribution, and CCN activation efficiency decreased to low values (<20 %) at the time of new-particle formation events over near-coastal and remote oceanic regions. The analysis of the activation efficiencies for the “similar” aerosol size distributions over the northern Indian Ocean indicated the primary role of aerosol number size distribution on CCN activation efficiency. The dependence of CCN properties and activation efficiency on size-segregated aerosol number concentration, especially during the ultrafine (<100 nm) particle events, is investigated in detail for the first time over the region.

Observations of Aerosol‐Cloud Interactions During the North Atlantic Aerosol and Marine Ecosystem Study

AbstractClouds and their response to aerosols constitute the largest uncertainty in our understanding of 20th‐century climate change. We present an investigation that determines linkages between remotely sensed marine cloud properties with in situ measurements of cloud condensation nuclei (CCN) and meteorological properties obtained during the North Atlantic Aerosols and Marine Ecosystems Study. The first two deployments of this campaign have geographically similar domains but occur in different seasons allowing the response of clouds to a range of CCN concentrations and meteorological conditions to be investigated. Well‐defined connections between CCN and cloud microphysical properties consistent with the indirect effect are observed, as well as complex, nonlinear secondary effects that are partially supported by previously proposed mechanisms. Using the Research Scanning Polarimeter's remotely sensed effective variance parameter, correlation is found with liquid water path. In general, cloud macrophysical properties are found to better correlate with atmospheric state parameters than changes in CCN concentrations.

Study on CCN activity of fission product aerosols (CsI and CsOH) and their effect on size and other properties

Abstract This paper discusses the size resolved cloud condensation nuclei (CCN) properties of two cesium bound compounds viz. CsI and CsOH. These properties are important in context of risk analysis and management of probable environmental releases during postulated nuclear reactor accident conditions. If released as fission product aerosols, these particles have potential to act as CCN, when exposed to humid environment. On activation, their evolution-deposition dynamics and consequently fate is expected to be affected in closed and/or open atmosphere. Size resolved CCN efficiency spectra (20–300 nm) are obtained for 0.2–1% supersaturation (SS) for pure CsI and CsOH particles employing a DMT-CCN counter. The essential parameters estimated from these measurements are activation diameter and size-averaged hygroscopicity (κ) at targeted SS levels. Experimental results were also compared with the standard theories available in the literature. Accuracy of the deposition rates for these particles (if released) in reactor component systems estimated by nuclear reactor accident analyses codes will improve when CCN properties are also taken into account. CCN efficiency spectra and activation diameters at specific SS for CsI and CsOH particles are being reported for the first time. Information on these properties strengthen the database which is vital for simulating behavioral characteristics of these particles. This in turn has capability to improve environmental source term estimations in the most unlikely scenario of containment breach during severe reactor accident conditions.

Large Summer Contribution of Organic Biogenic Aerosols to Arctic Cloud Condensation Nuclei

AbstractA k‐means cluster analysis of a 5‐year aerosol particle size distribution data set from northeast Greenland is combined with measurements of coincident shorter field studies of aerosol equivalent black carbon (eBC) content, hygroscopic growth factor (HGF), and cloud condensation nuclei (CCN) concentrations. This led to five clusters strongly controlled by natural emissions (eBC 8–15 ng/m3) and three anthropogenic clusters with larger particle concentrations in the accumulation mode (eBC 29–77 ng/m3). The HGF and CCN properties of the eight aerosol clusters differ drastically. Anthropogenic clusters feature high growth factors (1.62–1.81) and low CCN κ values (0.10–0.46), while natural clusters show lower HGF (1.38–1.70) but remarkably higher κ values (0.35–0.51). Extrapolating the CCN properties on the basis of the cluster analysis to annual timescales suggests that biogenic organic aerosol may drive Arctic aerosol production during summer.

Subpollen particles as atmospheric cloud condensation nuclei

Bioparticles represent a significant fraction of the total atmospheric aerosol. Their size range varies from nanometers (macromolecules) to hundreds of micrometers (plant pollen, vegetation residues) and like other atmospheric aerosol particles, the degree of involvement of bioaerosols in atmospheric processes largely de- pends on their hygroscopic and cloud condensation nuclei properties. In this paper the ability of the pine, birch and rape subpollen particles to act as cloud condensation nuclei are considered. Submicron particles were obtained by aqueous extraction of biological material from pollen grains and subsequent solidification of the atomized liquid droplets. The parameters of cloud activation are determined in the size range of 20-270 nm in the range of water vapor supersaturations 0.1-1.1%. Based on experimental results, the hygroscopicity parameter, characterizing the effect of the chemical composition of the subparticles on their con- densation properties, is determined. The range of the hygroscopic parameter changes was 0.12-0.13. In general, the results of measurements showed that the condensation activity of the subpollen particles is comparable with the condensation activity of secondary organic aerosols and weakly depends on the type of the primary pollen.