scholarly journals A synthesis of cloud condensation nuclei counter (CCNC) measurements within the EUCAARI network

2015 ◽  
Vol 15 (21) ◽  
pp. 12211-12229 ◽  
Author(s):  
M. Paramonov ◽  
V.-M. Kerminen ◽  
M. Gysel ◽  
P. P. Aalto ◽  
M. O. Andreae ◽  
...  
Keyword(s):  
Size Distribution ◽  
Cloud Condensation Nuclei ◽  
Number Concentration ◽  
West Germany ◽  
Aerosol Size Distribution ◽  
Spatial And Temporal Variability ◽  
Condensation Nuclei ◽  
Aerosol Cloud ◽  
Hygroscopic Properties ◽  
South West

Abstract. Cloud condensation nuclei counter (CCNC) measurements performed at 14 locations around the world within the European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) framework have been analysed and discussed with respect to the cloud condensation nuclei (CCN) activation and hygroscopic properties of the atmospheric aerosol. The annual mean ratio of activated cloud condensation nuclei (NCCN) to the total number concentration of particles (NCN), known as the activated fraction A, shows a similar functional dependence on supersaturation S at many locations – exceptions to this being certain marine locations, a free troposphere site and background sites in south-west Germany and northern Finland. The use of total number concentration of particles above 50 and 100 nm diameter when calculating the activated fractions (A50 and A100, respectively) renders a much more stable dependence of A on S; A50 and A100 also reveal the effect of the size distribution on CCN activation. With respect to chemical composition, it was found that the hygroscopicity of aerosol particles as a function of size differs among locations. The hygroscopicity parameter κ decreased with an increasing size at a continental site in south-west Germany and fluctuated without any particular size dependence across the observed size range in the remote tropical North Atlantic and rural central Hungary. At all other locations κ increased with size. In fact, in Hyytiälä, Vavihill, Jungfraujoch and Pallas the difference in hygroscopicity between Aitken and accumulation mode aerosol was statistically significant at the 5 % significance level. In a boreal environment the assumption of a size-independent κ can lead to a potentially substantial overestimation of NCCN at S levels above 0.6 %. The same is true for other locations where κ was found to increase with size. While detailed information about aerosol hygroscopicity can significantly improve the prediction of NCCN, total aerosol number concentration and aerosol size distribution remain more important parameters. The seasonal and diurnal patterns of CCN activation and hygroscopic properties vary among three long-term locations, highlighting the spatial and temporal variability of potential aerosol–cloud interactions in various environments.

scholarly journals A synthesis of cloud condensation nuclei counter (CCNC) measurements within the EUCAARI network

2015 ◽  
Vol 15 (11) ◽  
pp. 15039-15086
Author(s):  
M. Paramonov ◽  
V.-M. Kerminen ◽  
M. Gysel ◽  
P. P. Aalto ◽  
M. O. Andreae ◽  
...  
Keyword(s):  
Size Distribution ◽  
Functional Dependence ◽  
Cloud Condensation Nuclei ◽  
Number Concentration ◽  
West Germany ◽  
Aerosol Size Distribution ◽  
Spatial And Temporal Variability ◽  
Condensation Nuclei ◽  
Hygroscopic Properties ◽  
South West

Abstract. Cloud Condensation Nuclei Counter (CCNC) measurements performed at 14 locations around the world within the EUCAARI framework have been analysed and discussed with respect to the cloud condensation nuclei (CCN) activation and hygroscopic properties of the atmospheric aerosol. The annual mean ratio of activated cloud condensation nuclei (NCCN) to the total number concentration of particles (NCN), known as the activated fraction A, shows a similar functional dependence on supersaturation S at many locations; exceptions to this being certain marine locations, a free troposphere site and background sites in south-west Germany and northern Finland. The use of total number concentration of particles above 50 and 100 nm diameter when calculating the activated fractions (A50 and A100, respectively) renders a much more stable dependence of A on S; A50 and A100 also reveal the effect of the size distribution on CCN activation. With respect to chemical composition, it was found that the hygroscopicity of aerosol particles as a function of size differs among locations. The hygroscopicity parameter κ decreased with an increasing size at a continental site in south-west Germany and fluctuated without any particular size dependence across the observed size range in the remote tropical North Atlantic and rural central Hungary. At all other locations κ increased with size. In fact, in Hyytiälä, Vavihill, Jungfraujoch and Pallas the difference in hygroscopicity between Aitken and accumulation mode aerosol was statistically significant at the 5% significance level. In a boreal environment the assumption of a size-independent κ can lead to a potentially substantial overestimation of NCCN at S levels above 0.6%; similar is true for other locations where κ was found to increase with size. While detailed information about aerosol hygroscopicity can significantly improve the prediction of NCCN, total aerosol number concentration and aerosol size distribution remain more important parameters. The seasonal and diurnal patterns of CCN activation and hygroscopic properties vary among three long-term locations, highlighting the spatial and temporal variability of potential aerosol-cloud interactions in various environments.

scholarly journals Long-term observations of cloud condensation nuclei in the Amazon rain forest – Part 1: Aerosol size distribution, hygroscopicity, and new model parametrizations for CCN prediction

2016 ◽  
Vol 16 (24) ◽  
pp. 15709-15740 ◽  
Author(s):  
Mira L. Pöhlker ◽  
Christopher Pöhlker ◽  
Florian Ditas ◽  
Thomas Klimach ◽  
Isabella Hrabe de Angelis ◽  
...  
Keyword(s):  
Size Distribution ◽  
Aerosol Particle ◽  
Rain Forest ◽  
Seasonal Cycle ◽  
Cloud Condensation Nuclei ◽  
Number Concentration ◽  
Aerosol Size Distribution ◽  
Condensation Nuclei ◽  
Central Amazon

Abstract. Size-resolved long-term measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted at the remote Amazon Tall Tower Observatory (ATTO) in the central Amazon Basin over a 1-year period and full seasonal cycle (March 2014–February 2015). The measurements provide a climatology of CCN properties characteristic of a remote central Amazonian rain forest site.The CCN measurements were continuously cycled through 10 levels of supersaturation (S  =  0.11 to 1.10 %) and span the aerosol particle size range from 20 to 245 nm. The mean critical diameters of CCN activation range from 43 nm at S  =  1.10 % to 172 nm at S  =  0.11 %. The particle hygroscopicity exhibits a pronounced size dependence with lower values for the Aitken mode (κAit  =  0.14 ± 0.03), higher values for the accumulation mode (κAcc  =  0.22 ± 0.05), and an overall mean value of κmean  =  0.17 ± 0.06, consistent with high fractions of organic aerosol.The hygroscopicity parameter, κ, exhibits remarkably little temporal variability: no pronounced diurnal cycles, only weak seasonal trends, and few short-term variations during long-range transport events. In contrast, the CCN number concentrations exhibit a pronounced seasonal cycle, tracking the pollution-related seasonality in total aerosol concentration. We find that the variability in the CCN concentrations in the central Amazon is mostly driven by aerosol particle number concentration and size distribution, while variations in aerosol hygroscopicity and chemical composition matter only during a few episodes.For modeling purposes, we compare different approaches of predicting CCN number concentration and present a novel parametrization, which allows accurate CCN predictions based on a small set of input data.

scholarly journals Hygroscopic properties and cloud condensation nuclei activity of atmospheric aerosols under the influences of Asian continental outflow and new particle formation at a coastal site in eastern Asia

2020 ◽  
Vol 20 (10) ◽  
pp. 5911-5922 ◽  
Author(s):  
Hing Cho Cheung ◽  
Charles Chung-Kuang Chou ◽  
Celine Siu Lan Lee ◽  
Wei-Chen Kuo ◽  
Shuenn-Chin Chang
Keyword(s):  
Chemical Composition ◽  
Cloud Condensation Nuclei ◽  
Particle Formation ◽  
Number Concentration ◽  
Pollution Sources ◽  
New Particle Formation ◽  
Condensation Nuclei ◽  
Air Masses ◽  
Hygroscopic Properties ◽  
Aerosol Hygroscopicity

Abstract. The chemical composition of fine particulate matter (PM2.5), the size distribution and number concentration of aerosol particles (NCN), and the number concentration of cloud condensation nuclei (NCCN) were measured at the northern tip of Taiwan during an intensive observation experiment from April 2017 to March 2018. The parameters of aerosol hygroscopicity (i.e., activation ratio, activation diameter and kappa of CCN) were retrieved from the measurements. Significant variations were found in the hygroscopicity of aerosols (kappa – κ – of 0.18–0.56, for water vapor supersaturation – SS – of 0.12 %–0.80 %), which were subject to various pollution sources, including aged air pollutants originating in eastern and northern China and transported by the Asian continental outflows and fresh particles emitted from local sources and distributed by land–sea breeze circulations as well as produced by processes of new particle formation (NPF). Cluster analysis was applied to the back trajectories of air masses to investigate their respective source regions. The results showed that aerosols associated with Asian continental outflows were characterized by lower NCN and NCCN values and by higher kappa values of CCN, whereas higher NCN and NCCN values with lower kappa values of CCN were observed in the aerosols associated with local air masses. Besides, it was revealed that the kappa value of CCN exhibited a decrease during the early stage of an event of new particle formation, which turned to an increasing trend over the later period. The distinct features in the hygroscopicity of aerosols were found to be consistent with the characteristics in the chemical composition of PM2.5. This study has depicted a clear seasonal characteristic of hygroscopicity and CCN activity under the influence of a complex mixture of pollutants from different regional and/or local pollution sources. Nevertheless, the mixing state and chemical composition of the aerosols critically influence the aerosol hygroscopicity, and further investigations are necessary to elucidate the atmospheric processing involved in the CCN activation in coastal areas.

scholarly journals Nucleation-mode particle pool and large increases in <i>N</i><sub>cn</sub> and <i>N</i><sub>ccn</sub> observed over the northwestern Pacific Ocean in the spring of 2014

2019 ◽  
Vol 19 (13) ◽  
pp. 8845-8861 ◽  
Author(s):  
Juntao Wang ◽  
Yanjie Shen ◽  
Kai Li ◽  
Yang Gao ◽  
Huiwang Gao ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Size Distribution ◽  
Cloud Condensation Nuclei ◽  
Number Concentration ◽  
Atmospheric Particles ◽  
Northwestern Pacific ◽  
Condensation Nuclei ◽  
Northwestern Pacific Ocean ◽  
Mean Values ◽  
Nucleation Mode

Abstract. Determination of the updated concentrations of atmospheric particles (Ncn) and the concentrations of cloud condensation nuclei (Nccn) over the northwestern Pacific Ocean (NWPO) are important to accurately evaluate the influence of aerosol outflow from the Asian continent on the climate by considering the rapid changes in emissions of air pollutants therein. However, field observations in the last two decades are scarce. We conducted a cruise campaign over the NWPO to simultaneously measure Ncn, Nccn and the size distribution of aerosol particles from day of year (DOY) 81 to DOY 108 of 2014. The mean values of Nccn at supersaturation (SS) of levels 0.2 % and 0.4 % were 0.68±0.38×103 and 1.1±0.67×103 cm−3, respectively, with an average of 2.8±1.0×103 cm−3 for Ncn during the cruise over the NWPO. All are approximately 1 order of magnitude larger than spring observations made during the preceding two decades in the remote marine atmosphere. The larger values, against the marine natural background reported in the literature, imply an overwhelming contribution from continental inputs. The calculated activity ratios (ARs) of the cloud condensation nuclei (CCN) were 0.30±0.11 and 0.46±0.19 at SS levels of 0.2 % and 0.4 %, respectively, which are almost the same as those of upwind semi-urban sites. High Nccn and CCN activities were observed from DOY 98 to DOY 102, when the oceanic zone received even stronger continental input. Excluding biomass burning (BB) and dust aerosols, good correlation between Nccn at 0.4 % SS and the number concentrations of > 60 nm particles (N>60 nm) was obtained during the entire cruise period, with a slope of 0.98 and R2=0.94, and the corresponding effective hygroscopicity parameter (κ) was estimated to be 0.40. A bimodal size distribution pattern of the particle number concentration was generally observed during the entire campaign when the N>90 nm varied largely. However, the N<30 nm, accounting for approximately one-third of the total number concentration, varied narrowly, and two NPF events associated with vertical transport were observed. This implies that a pool of nucleation-mode atmospheric particles is aloft. BB and dust events were observed over the NWPO, but their aerosol contributions to Ncn and Nccn were minor (i.e., 10 % or less) on a monthly timescale.

scholarly journals Quantifying the aerosol effect on droplet size distribution at cloud top

2019 ◽  
Vol 19 (11) ◽  
pp. 7839-7857
Author(s):  
Lianet Hernández Pardo ◽  
Luiz Augusto Toledo Machado ◽  
Micael Amore Cecchini ◽  
Madeleine Sánchez Gácita
Keyword(s):  
Size Distribution ◽  
Droplet Size ◽  
Initial Conditions ◽  
Cloud Condensation Nuclei ◽  
Droplet Size Distribution ◽  
Number Concentration ◽  
Population Characteristics ◽  
Aerosol Size Distribution ◽  
Effective Diameter ◽  
Distribution Sensitivity

Abstract. This work uses the number concentration-effective diameter phase-space to test cloud sensitivity to variations in the aerosol population characteristics, such as the aerosol size distribution, number concentration and hygroscopicity. It is based on the information from the top of a cloud simulated by a bin-microphysics single-column model, for initial conditions typical of the Amazon, using different assumptions regarding the entrainment and the aerosol size distribution. It is shown that the cloud-top evolution can be very sensitive to aerosol properties, but the relative importance of each parameter is variable. The sensitivity to each aerosol characteristic varies as a function of the parameter tested and is conditioned by the base values of the other parameters, showing a specific dependence for each configuration of the model. When both the entrainment and the bin treatment of the aerosol are allowed, the largest influence on the droplet size distribution sensitivity was obtained for the median radius of the aerosols and not for the total number concentration of aerosols. Our results reinforce that the cloud condensation nuclei activity can not be predicted solely on the basis of the w∕Na supersaturation-based regimes.

scholarly journals Cloud condensation nuclei measurements in the marine boundary layer of the Eastern Mediterranean: CCN closure and droplet growth kinetics

2009 ◽  
Vol 9 (18) ◽  
pp. 7053-7066 ◽  
Author(s):  
A. Bougiatioti ◽  
C. Fountoukis ◽  
N. Kalivitis ◽  
S. N. Pandis ◽  
A. Nenes ◽  
...  
Keyword(s):  
Size Distribution ◽  
Growth Kinetics ◽  
Eastern Mediterranean ◽  
Cloud Condensation Nuclei ◽  
Bulk Composition ◽  
Organic Content ◽  
Water Soluble ◽  
Aerosol Size Distribution ◽  
Droplet Growth ◽  
Condensation Nuclei

Abstract. Measurements of cloud condensation nuclei (CCN) concentrations (cm−3) between 0.2 and 1.0% supersaturation, aerosol size distribution and chemical composition were performed at a remote marine site in the eastern Mediterranean, from September to October 2007 during the FAME07 campaign. Most of the particles activate at ~0.6% supersaturation, characteristic of the aged nature of the aerosol sampled. Application of Köhler theory, using measurements of bulk composition, size distribution, and assuming that organics are insoluble resulted in agreement between predicted and measured CCN concentrations within 7±11% for all supersaturations, with a tendency for CCN underprediction (16±6%; r2=0.88) at the lowest supersaturations (0.21%). Including the effects of the water-soluble organic fraction (which represent around 70% of the total organic content) reduces the average underprediction bias at the low supersaturations, resulting in a total closure error of 0.6±6%. Using threshold droplet growth analysis, the growth kinetics of ambient CCN is consistent with NaCl calibration experiments; hence the presence of aged organics does not suppress the rate of water uptake in this environment. The knowledge of the soluble salt fraction is sufficient for the description of the CCN activity in this area.

scholarly journals On aerosol hygroscopicity, cloud condensation nuclei (CCN) spectra and critical supersaturation measured at two remote islands of Korea between 2006 and 2009

2011 ◽  
Vol 11 (7) ◽  
pp. 19683-19727 ◽  
Author(s):  
J. H. Kim ◽  
S. S. Yum ◽  
S. Shim ◽  
S.-C. Yoon ◽  
J. G. Hudson ◽  
...  
Keyword(s):  
Size Distribution ◽  
Total Concentration ◽  
Cloud Condensation Nuclei ◽  
Geometric Mean ◽  
Aerosol Size Distribution ◽  
Monitoring Site ◽  
Hygroscopic Growth ◽  
Condensation Nuclei ◽  
Critical Supersaturation ◽  
Aerosol Hygroscopicity

Abstract. Aerosol size distribution, total concentration (i.e., condensation nuclei (CN) concentration, NCN), cloud condensation nuclei (CCN) concentration (NCCN), hygroscopicity at ~90 % relative humidity (RH) were measured at a background monitoring site at Gosan, Jeju Island, south of the Korea Peninsula in August 2006, April to May 2007 and August to October 2008. Similar measurement took place in August 2009 at another background site (Baengnyeongdo Comprehensive Monitoring Observatory, BCMO) on the island of Baengnyeongdo, off the west coast of the Korean Peninsula. Both islands were found to be influenced by continental sources regardless of season and year. Average values for all of the measured NCCN at 0.2, 0.6 and 1.0 % supersaturations (S), NCN, and geometric mean diameter (Dg) from both islands were in the range of 1043–3051 cm−3, 2076–4360 cm−3, 2713–4694 cm−3, 3890–5117 cm−3 and 81–98 nm, respectively. Although the differences in Dg and NCN were small between Gosan and BCMO, NCCN at various S was much higher at the latter, which is closer to China. Most of the aerosols were internally mixed and no notable differences in hygroscopicity were found between the days of strong pollution influence and the non-pollution days for both islands. During the 2008 and 2009 campaigns, critical supersaturation for cloud nucleation (Sc) for selected particle sizes was measured. Particles of 100 nm diameters had mean Sc of 0.19 ± 0.02 % during 2008 and those of 81 and 110 nm diameters had mean Sc of 0.26 ± 0.07 % and 0.17 ± 0.04 %, respectively, during 2009. Hygroscopicity parameters estimated from the measured Sc were mostly higher than the ones from the measured hygroscopic growth at ~90 % RH. For the 2008 campaign, NCCN at 0.2, 0.6 and 1.0 % S were predicted based on the measured dry particle size distribution and various ways of representing aerosol hygroscopicity. The best closure was obtained when temporally varying and size-resolved hygroscopicity information from HTDMA was used, for which the average relative deviations from the measured values were 19 % for 1.0 % S and 28 % for 0.2 % S. Prescribing a constant hygroscopicity parameter suggested in literature (κ = 0.3) for all sizes and time resulted in the average relative deviations, 25–40 %. When constant hygroscopicity was assumed, the relative deviation tended to increase with decreasing NCCN, which was accompanied by increase of sub-100 nm fraction. These results suggest that hygroscopicity information for aerosols of diameters smaller than 100 nm is crucial for more accurate prediction of NCCN.

scholarly journals The challenge of simulating the sensitivity of the Amazonian clouds microstructure to cloud condensation nuclei number concentrations

2019 ◽  
Author(s):  
Pascal Polonik ◽  
Christoph Knote ◽  
Tobias Zinner ◽  
Florian Ewald ◽  
Tobias Kölling ◽  
...  
Keyword(s):  
Cloud Condensation Nuclei ◽  
Regional Scale ◽  
Cloud Droplet ◽  
Number Concentration ◽  
Effective Radius ◽  
Cloud Base ◽  
Condensation Nuclei ◽  
Aerosol Cloud ◽  
Microphysical Properties

Abstract. The realistic representation of cloud-aerosol interactions is of primary importance for accurate climate model projections. The investigation of these interactions in strongly contrasting clean and polluted atmospheric conditions in the Amazon area has been one of the motivations for several field observations, including the airborne Aerosol, Cloud, Precipitation, and Radiation Interactions and DynamIcs of CONvective cloud systems – Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON-CHUVA) campaign based in Manaus, Brazil in September 2014. In this work we combine in situ and remotely sensed aerosol, cloud, and atmospheric radiation data collected during ACRIDICON-CHUVA with regional, online-coupled chemistry-transport simulations to evaluate the model’s ability to represent the indirect effects of biomass burning aerosol on cloud microphysical properties (droplet number concentration and effective radius). We found agreement between modeled and observed median cloud droplet number concentrations (CDNC) for low values of CDNC, i.e., low levels of pollution. In general, a linear relationship between modeled and observed CDNC with a slope of two was found, which means a systematic underestimation of modeled CDNC as compared to measurements. Variability in cloud condensation nuclei (CCN) number concentrations and cloud droplet effective radii (reff) was also underestimated by the model. Modeled effective radius profiles began to saturate around 500 CCN per cm3 at cloud base, indicating an upper limit for the model sensitivity well below CCN concentrations reached during the burning season in the Amazon Basin. Regional background aerosol concentrations were sufficiently high such that the additional CCN emitted from local fires did not cause a notable change in modelled cloud microphysical properties. In addition, we evaluate a parameterization of CDNC at cloud base using more readily available cloud microphysical properties, aimed at in situ observations and satellite retrievals. Our study casts doubt on the validity of regional scale modeling studies of the cloud albedo effect in convective situations for polluted situations where the number concentration of CCN is greater than 500 cm−3.

scholarly journals Impact of aerosol composition on cloud condensation nuclei activity

2012 ◽  
Vol 12 (8) ◽  
pp. 3783-3790 ◽  
Author(s):  
Q. Zhang ◽  
J. Meng ◽  
J. Quan ◽  
Y. Gao ◽  
D. Zhao ◽  
...  
Keyword(s):  
Size Distribution ◽  
Field Experiments ◽  
Cloud Condensation Nuclei ◽  
Diffusion Chamber ◽  
Aerosol Size Distribution ◽  
Condensation Nuclei ◽  
Aerosol Composition ◽  
Rate Of Increase ◽  
The Impact ◽  
Ccn Activity

Abstract. The impact of aerosol composition on cloud condensation nuclei (CCN) activity were analyzed in this study based on field experiments carried out at downtown Tianjin, China in September 2010. In the experiments, the CCN measurements were performed at supersaturation (SS) of 0.1%, 0.2% and 0.4% using a thermal-gradient diffusion chamber (DMT CCNC), whereas the aerosol size distribution and composition were simultaneously measured with a TSI SMPS and an Aerodyne Aerosol Mass Spectrometer (AMS), respectively. The results show that the influence of aerosol composition on CCN activity is notable under low SS (0.1%), and their influence decreased with increasing SS. For example, under SS of 0.1%, the CCN activity increases from 4.5±2.6% to 12.8±6.1% when organics fraction decrease from 30–40% to 10–20%. The rate of increase reached up to 184%. While under SS of 0.4%, the CCN activity increases only from 35.7±19.0% to 46.5±12.3% correspondingly. The calculated NCCN based on the size-resolved activation ratio and aerosol number size distribution correlated well with observed NCCN at high SS (0.4%), but this consistence decreased with the falling of SS. The slopes of linear fitted lines between calculated and observed NCCN are 0.708, 0.947, and 0.995 at SS of 0.1%, 0.2% and 0.4% respectively. Moreover, the stand deviation (SD) of calculated NCCN increased with the decreasing of SS. A case study of CCN closure analyses indicated that the calculated error of NCCN could reach up to 34% at SS of 0.1% if aerosol composition were not included, and the calculated error decreased with the raising of SS. It is decreased to 9% at SS of 0.2%, and further decreased to 4% at SS of 0.4%.

scholarly journals Reallocation in modal aerosol models: impacts on predicting aerosol radiative effects

2014 ◽  
Vol 7 (1) ◽  
pp. 161-174 ◽  
Author(s):  
T. Korhola ◽  
H. Kokkola ◽  
H. Korhonen ◽  
A.-I. Partanen ◽  
A. Laaksonen ◽  
...  
Keyword(s):  
Size Distribution ◽  
Interaction Parameter ◽  
Reference Model ◽  
Cloud Droplet ◽  
Particle Growth ◽  
Number Concentration ◽  
Light Extinction ◽  
Aerosol Size Distribution ◽  
Light Extinction Coefficient ◽  
Aerosol Cloud

Abstract. Atmospheric models often represent the aerosol particle size distribution with a modal approach, in which particles are described with log-normal modes within predetermined size ranges. This approach reallocates particles numerically from one mode to another for example during particle growth, potentially leading to artificial changes in the aerosol size distribution. In this study we analysed how the modal reallocation affects climate-relevant variables: cloud droplet number concentration (CDNC), aerosol–cloud interaction parameter (ACI) and light extinction coefficient (qext). The ACI parameter gives the response of CDNC to a change in total aerosol number concentration. We compared these variables between a modal model (with and without reallocation routines) and a high resolution sectional model, which was considered a reference model. We analysed the relative differences in the chosen variables in four experiments designed to assess the influence of atmospheric aerosol processes. We find that limiting the allowed size ranges of the modes, and subsequent remapping of the distribution, leads almost always to an underestimation of cloud droplet number concentrations (by up to 100%) and an overestimation of light extinction (by up to 20%). On the other hand, the aerosol–cloud interaction parameter can be either over- or underestimated by the reallocating model, depending on the conditions. For example, in the case of atmospheric new particle formation events followed by rapid particle growth, the reallocation can cause on average a 10% overestimation of the ACI parameter. Thus it is shown that the reallocation affects the ability of a model to estimate aerosol climate effects accurately, and this should be taken into account when using and developing aerosol models.

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