Condensation Nuclei Research Articles

Assessment of the Cloud Seeding Efficiency over Tom Green County Texas, USA

The efficiency of cloud seeding in enhancing precipitation is a subject of active debate within the scientific community. This work examines the impacts of cloud seeding in changing cloud properties and dynamics over Tom Green County in West Texas, USA, from 2015 to 2020. Several cloud categories including small, large, and type B are considered. The effect of cloud-seeding missions in changing clouds’ lifetime, area, volume, and precipitation mass is investigated. The results show that the average increase in the lifetime of small, large, and type B is 53.6, 27, and 3.5%, respectively, while the average area increased by 47.1, 27.5, and 5.0% respectively, and their average volume increased by 63.6, 33, and 5.6% respectively. A significant increase in the precipitation mass of the small, large, and type B clouds is observed after the seeding missions. From 2015 to 2020, the precipitation rates in seeded clouds are higher than the unseeded clouds. Comparing precipitation rates during the 2015–2020 cloud-seeding campaigns to the period from 2010 to 2014 before the campaigns shows no trend of increasing precipitation except during 2015 and 2016.

Numerical simulation of aerosol concentration effects on cloud droplet size spectrum evolutions of warm stratiform clouds in Jiangxi, China

Abstract. Changes in aerosol amount and size distribution significantly impact cloud droplet size distribution, as aerosols act as cloud condensation nuclei (CCNs) and influence the relative dispersion (ε) of cloud droplet spectra. Relative dispersion plays a key role in parameterizing cloud processes in general circulation models (GCMs) and microphysical schemes, affecting precipitation estimates and climate predictions. However, the effects of varying aerosol modes on cloud microphysics remain debated, depending on thermodynamic conditions and cloud type. This study simulates a warm stratiform cloud in Jiangxi, China, using the Weather Research and Forecasting (WRF) Spectra–Bin Microphysics scheme (SBM-FAST) from 18:00 on 24 December 2014 to 06:00 on 25 December 2014 (UTC). Satellite and aircraft observations were used to validate the simulation, showing good agreement in cloud structure. Sensitivity experiments were conducted by increasing nucleation, accumulation, and coarse-mode aerosols 5-fold and by reducing the total aerosol concentration to 1/5 of the control. Results show that higher aerosol concentrations enhance cloud formation and broaden droplet spectra, while lower concentrations suppress cloud development. Accumulation-mode aerosols increase small-droplet concentrations, while nucleation- and coarse-mode aerosols favor larger droplets. The correlation between ε and volume-weighted radius (Rv) shifts from positive to negative as Rv increases. This transition is driven by cloud droplet collision–coalescence, condensation, and activation. Increased accumulation-mode aerosol concentrations shift the ε–Rv correlation from negative to positive in the Rv range of 4.5–8 µm, while reduced aerosol concentrations strengthen the negative correlation. Regardless of different coalescence intensities, ε converges with the increase in number concentration of cloud droplets (Nc).

Quantifying the Influence of Cloud Seeding on Ice Particle Growth and Snowfall Through Idealized Microphysical Modeling

Cloud seeding is a weather modification technique for enhancing precipitation in arid and semi-arid regions, including the Western U.S. However, designing an optimal cloud seeding operation based on comprehensive evaluation metrics, such as seeding agent dispersion and atmospheric conditions, has yet to be thoroughly explored for this region. This study investigated the impacts of cloud seeding, particularly utilizing silver iodide, on ice particle growth within clouds through numerical modeling. By leveraging the Snow Growth Model for Rimed Snowfall (SGMR), the microphysical processes involved in cloud seeding across five distinct events were simulated. The events were in the Lake Tahoe region, nestled within the Sierra Nevada Mountain ranges in the Western U.S. This model was executed based on six primary variables, including cloud top height, cloud base height, cloud top temperature, cloud base temperature, liquid water content, and ice water content. This study incorporated datasets from the Modern-Era Retrospective Analysis for Research and Applications Version 2 and the Clouds and the Earth Radiant Energy System. The findings revealed the importance of ice nucleation, aggregation, diffusion, and riming processes and highlighted the effectiveness of cloud seeding in enhancing ice particle number concentration, ice water content, and snowfall rates. However, event-specific analyses indicated diverse precipitation responses to cloud seeding based on initial atmospheric conditions. The SGMR modeling hints at the importance of improving ice microphysical processes and provides insights for future cloud seeding research using regional and global climate models.

Historical Research on Aerosol Number Concentrations, Classifications of Air Pollution Severity and Particle Retention: Lessons for Present-Day Researchers

Research into the adverse health effects of air pollution exposure has repeatedly considered smaller particles, to the point where particle number concentration might be a more relevant metric than mass concentration. Here, we highlight some historical research which developed metrics for air pollution severity based on particle number concentration. Because this work was published in a national journal and prior to the internet and open access, this historical research is not easy to find, and it was more through the history of the aerosol research community in Ireland that this work is now being presented. Multiple online searches for published research papers on “particle number concentrations” and “air pollution severity” were undertaken. Even when specific searches were undertaken using the author names and publication year, these featured papers were not found on any internet search. O’Dea and O’Connor proposed that air pollution severity could be classified based on particle number concentration of condensation nuclei, with ‘little’ air pollution <50 × 103 particles per cm3, ‘mean’ 50–70 × 103 particles per cm3, ‘strong’ 70–100 × 103 particles per cm3, and ‘very strong’ >100 × 103 particles per cm3. Applying their assumptions on density and mean particle size, equated to mass concentrations for a mean of 6 µgm−3, strong at 8.5 µgm−3, and very strong >10 µgm−3. These are consistent with the current WHO guideline values for PM2.5. Additionally, we highlight the 1955 work by Burke and Nolan on the retention of inhaled particles, where ~40% of the inhaled number concentration is retained in the respiratory system. This is also consistent with the more recently published work on particle retention. In summary, the proposed categories of pollution severity, based on number concentrations, could form a basis for the development of future guidelines. This paper highlights that sometimes research has already been published, but it is difficult to find. We challenge researchers to find publications from their own countries which pre-date the WWW to inform current and future research. Additionally, there is scope for a repository for such information on historical publications. We have presented historical research on aerosol number concentrations, classifications of air pollution severity, and particle retention, which present lessons for current researchers.

Isoprene nitrates drive new particle formation in Amazon’s upper troposphere

New particle formation (NPF) in the tropical upper troposphere is a globally important source of atmospheric aerosols1, 2, 3–4. It is known to occur over the Amazon basin, but the nucleation mechanism and chemical precursors have yet to be identified2. Here we present comprehensive in situ aircraft measurements showing that extremely low-volatile oxidation products of isoprene, particularly certain organonitrates, drive NPF in the Amazonian upper troposphere. The organonitrates originate from OH-initiated oxidation of isoprene from forest emissions in the presence of nitrogen oxides from lightning. Nucleation bursts start about 2 h after sunrise in the outflow of nocturnal deep convection, producing high aerosol concentrations of more than 50,000 particles cm−3. We report measurements of characteristic diurnal cycles of precursor gases and particles. Our observations show that the interplay between biogenic isoprene, deep tropical convection with associated lightning, oxidation photochemistry and the low ambient temperature uniquely promotes NPF. The particles grow over time, undergo long-range transport and descend through subsidence to the lower troposphere, in which they can serve as cloud condensation nuclei (CCN) that influence the Earth’s hydrological cycle, radiation budget and climate1,4, 5, 6, 7–8.

The Impact of Cumulus Clouds and CCN Regeneration on Aerosol Vertical Distribution and Size

Abstract This study employs a high-resolution (10m) System for Atmospheric Modeling (SAM) coupled with the Spectral Bin Microphysical (SBM) scheme to thoroughly investigate the processes governing the evolution of aerosol properties within and outside a shallow cumulus cloud. The model encompasses the complete life cycle of cloud droplets, starting from their formation through their evolution until their complete evaporation or sedimentation to the ground. Additionally, the model tracks the aerosols’ evolution both within droplets and in the air. Aerosols are transported within the droplets, grow by droplet coalescence, and are released into the atmosphere after droplet evaporation (regeneration process). The aerosol concentration increases by droplet evaporation and decreases along with falling drops. So, the effects of clouds on the surrounding aerosols depend on the microphysical and dynamic processes, which in turn depend on the amount of background aerosols; here, we compare clean and polluted conditions. It is shown that the regeneration process is highly important and that shallow trade cumulus clouds significantly impact the vertical profile of aerosol concentration in the lower troposphere, as well as their size distribution, and can serve as a source of large cloud condensation nuclei. Furthermore, it is shown that both precipitating and non-precipitating boundary layer clouds contribute to a substantial increase in aerosol concentration within the inversion layer due to intense evaporation.

Weak liquid water path response in ship tracks

Abstract. The assessment of aerosol–cloud interactions remains a major source of uncertainty in understanding climate change, partly due to the difficulty in making accurate observations of aerosol impacts on clouds. Ships can release large numbers of aerosols that serve as cloud condensation nuclei, which can create artificially brightened clouds known as ship tracks. These aerosol emissions offer a “natural”, or “opportunistic”, experiment to explore aerosol effects on clouds, while also disentangling meteorological influences. Utilizing ship positions and reanalysis wind fields, we predict ship track locations, colocating them with satellite data to depict the temporal evolution of cloud properties after an aerosol perturbation. Repeating our analysis for a null experiment does not necessarily recover zero signal as expected; instead, it reveals subtleties between different null-experiment methodologies. This study uncovers a systematic bias in prior ship track research, due to the assumption that background gradients will, on average, be linear. We correct for this bias, which is linked to the correlation between wind fields and cloud properties, to reveal the true ship track response. We find that, once this bias is corrected for, the liquid water path (LWP) response after an aerosol perturbation is weak on average. This has important implications for estimates of radiative forcings due to LWP adjustments, as previous responses in unstable cases were overestimated. A noticeable LWP response is only recovered in specific cases, such as marine stratocumulus clouds, where a positive LWP response is found in precipitating or clean clouds. This work highlights subtleties in the analysis of isolated opportunistic experiments, reconciling differences in the LWP response to aerosols reported in previous studies.

Characterization of atmospheric humic-like substances (HULIS) at a high elevation in North China: Abundance, molecular composition and optical properties

The optical absorption of large molecular compounds HULIS (humic-like substances) can significantly impact the aerosol light absorption and radiative forcing, influencing cloud condensation nuclei formation and thus the climate and atmospheric environment. This study collected aerosol (PM2.5) samples from the summit of Mount Tai in North China to investigate the concentration, molecular composition, and optical properties of HULIS. The average concentration of HULIS in the PM2.5 in this study was 1.26 ± 0.54 μg/m3, comprising for 56 % of the water-soluble organic carbon (WSOC), with levels lower than urban areas but higher than other mountainous regions. Mass spectrometry revealed that CHO and CHON components, with high aromaticity and phenolic groups, are major contributors to absorption and fluorescence. These results indicate that HULIS is mainly composed of lignin and proteins/amino sugars, derived from combustion and secondary formation, and possesses a high light absorption capacity (with MAE365 (mass absorption efficiency) and AAE (Ångström exponent) indices of 0.62 m2/g and 4.99, respectively). Parallel factor analysis identified three fluorescence components of HULIS, with proportions of 60.8 % for less oxygen humic-like substances, 21.0 % for high oxygen humic-like substances, and 18.2 % for protein-like substances. Our study highlights the significance of the light-absorbing capacity and secondary formation of HULIS at Mount Tai, laying the groundwork for investigation into the climate effects, formation mechanisms, and sources of HULIS generation.

Molecular Mechanisms of Aerosol Nucleation: from CLOUD Chamber Experiments to Field Observations

Atmospheric aerosol particles contribute to over four million premature deaths annually and play a critical role in modulating Earth’s climate. Most atmospheric particles and more than 50% of the cloud condensation nuclei are formed through a secondary process named new particle formation involving unique precursor vapors. This article summarizes current knowledge of how new atmospheric particles form, based on experiments at the CERN CLOUD chamber. While the role of sulfuric acid has long been known, other vapors like highly oxygenated organic molecules and iodine oxoacids are also important, along with stabilizers like ammonia, amines, and ions from cosmic rays. We explain how findings from CLOUD experiments help us understand particle formation in various atmospheric conditions and improve air quality and climate models.

Effect of grain boundary phase formed by Mn addition on initiation and propagation of fatigue cracks in homogenized Cu-6Ni-1.3Si alloy

High-strength cast Cu alloys often contain substantial quantities of alloying elements that promote the nucleation of heterogeneous particles, particularly at grain boundaries (GBs). In the Cu-6Ni-1.3Si alloy, intermetallic compounds such as Ni2Si form within the matrix and along the GBs following homogenization. Ni2Si particles within the matrix are homogeneously nucleated with diameters of a few tens of nanometers, which enhances matrix strength. However, heterogeneously nucleated Ni2Si particles at GBs, which can be several micrometers in size, negatively impact overall strength. To improve the strength of Cu-6Ni-1.3Si alloy, 2.1 wt% Mn was added. This Mn addition led to the formation of plate- or film-shaped intermetallic compounds, specifically Ni16Si7Mn6 (G-phase), at GBs after homogenization. Despite the Mn addition, Ni2Si precipitates with diameters of a few tens of nanometers still formed within the grains, but these were more densely distributed in the Mn-added alloy compared to the Mn-free alloy. Fatigue tests conducted on round bar specimens of both alloys showed that Mn addition enhanced fatigue strength. This enhancement is attributed to the suppression of both crack initiation and propagation along the GBs and within the matrix.

Role of Aerosol Ice‐Nucleus Effect in the Development of the “21⋅7” Henan Extreme Precipitation

AbstractThe aerosol ice‐nucleus (IN) effect, affecting heterogeneous ice nucleation and ultimately shaping cloud properties and precipitation efficiency, remains poorly understood and is overlooked in most operational numerical weather models. Therefore, this study aims to investigate the role of aerosol IN effect in the “21⋅7” Henan extreme precipitation event using two simulations based on an aerosol‐aware configuration of the WRF model. One prescribed spatially uniform ice nucleation particles (INP) concentration (labeled CTL), whereas the other incorporated MERRA2 aerosol concentration fields to represent a more realistic INP spatial distribution (labeled M2), which is marked by a west‐east gradient with higher INP concentration in the west. Results show that M2 simulated heavier precipitation near Zhengzhou closer to the observation regarding both spatial distribution and intensity than the CTL simulation. This improvement is attributed to an INP‐induced feedback akin to the aerosol lifetime effect. Specifically, the M2 simulation had higher INP concentration in the west, causing increased rates of heterogeneous ice nucleation as the convection progressed from west to east. This released additional latent heat, intensifying the convection and subsequently enhancing homogeneous ice nucleation, yielding more but smaller cloud ice particles in M2. These ice particles had reduced sedimentation speeds and lower aggregation rates, suppressing precipitation upstream of Zhengzhou. The intensified convection, carrying more water, propagated eastward, ultimately resulting in extremely heavy precipitation near Zhengzhou. This study underscores the aerosol IN effect on cloud microphysics, convection intensity, and regional rainfall distribution, elucidating the crucial role of aerosol‐meteorology coupling in accurately simulating moderate deep convective cloud precipitation.

Hygroscopic Flare-Based Cloud Seeding to Increase Rainfall Over Lake Toba

Hygroscopic Flare-Based Cloud Seeding to Increase Rainfall Over Lake Toba

Source apportionment of ultrafine particles in urban Europe

There is a body of evidence that ultrafine particles (UFP, those with diameters ≤ 100 nm) might have significant impacts on health. Accordingly, identifying sources of UFP is essential to develop abatement policies. This study focuses on urban Europe, and aims at identifying sources and quantifying their contributions to particle number size distribution (PNSD) using receptor modelling (Positive Matrix Factorization, PMF), and evaluating long-term trends of these source contributions using the non-parametric Theil-Sen’s method. Datasets evaluated include 14 urban background (UB), 5 traffic (TR), 4 suburban background (SUB), and 1 regional background (RB) sites, covering 18 European and 1 USA cities, over the period, when available, from 2009 to 2019. Ten factors were identified (4 road traffic factors, photonucleation, urban background, domestic heating, 2 regional factors and long-distance transport), with road traffic being the primary contributor at all UB and TR sites (56–95 %), and photonucleation being also significant in many cities. The trends analyses showed a notable decrease in traffic-related UFP ambient concentrations, with statistically significant decreasing trends for the total traffic-related factors of −5.40 and −2.15 % yr−1 for the TR and UB sites, respectively. This abatement is most probably due to the implementation of European emissions standards, particularly after the introduction of diesel particle filters (DPFs) in 2011. However, DPFs do not retain nucleated particles generated during the dilution of diesel exhaust semi-volatile organic compounds (SVOCs). Trends in photonucleation were more diverse, influenced by a reduction in the condensation sink potential facilitating new particle formation (NPF) or by a decrease in the emissions of UFP precursors. The decrease of primary PM emissions and precursors of UFP also contributed to the reduction of urban and regional background sources.

Electrochemical nucleation and growth kinetics: insights from single particle scanning electrochemical cell microscopy studies.

The kinetics of particle nucleation and growth are critical to a wide variety of electrochemical systems. While studies carried out at the single particle level are promising for improving our understanding of nucleation and growth processes, conventional analytical frameworks commonly employed in bulk studies may not be appropriate for single particle experiments. Here, we present scanning electrochemical cell microscopy (SECCM) studies of Ag nucleation and growth on carbon and indium tin oxide (ITO) electrodes. Statistical analyses of the data from these experiments reveal significant discrepancies with traditional, quasi-equilibrium kinetic models commonly employed in the analysis of particle nucleation in electrochemical systems. Time-dependent kinetic models are presented capable of appropriately analysing the data generated via SECCM to extract meaningful chemical quantities such as surface energies and kinetic rate constants. These results demonstrate a powerful new approach to the analysis of single particle nucleation and growth data which could be leveraged in differentiating behavior within spatially heterogeneous systems.

Increased Freezing Temperature of Clouds Over China Due To Anthropogenic Pollution

AbstractThe temperature for cloud glaciation importantly determines the initialization of precipitation and lifetime of clouds. The role of anthropogenic pollutants as ice nucleating particles (INPs) to determine the cloud glaciation remains uncertain. In this study, based on satellite radar and lidar observations, the clouds either in pure liquid or mixed‐phase with liquid top were statistically analyzed over China during 2006–2019, to obtain the transition freezing temperature (T*) of cloud top where mixed‐phase becomes more frequent than pure water, with further validation by the aircraft in situ measurements. Anthropogenic pollution was observed to raise T* up to −9°C, significantly increasing it by approximately 5°C per unit of aerosol optical depth. The results provide regional‐scale evidence that anthropogenic pollutants act as efficient INPs, increasing the freezing temperature of mixed‐phase clouds.

The impact of cloud microphysics and ice nucleation on Southern Ocean clouds assessed with single-column modeling and instrument simulators

Abstract. Supercooled liquid clouds are common at higher latitudes (especially over the Southern Ocean) and are critical for constraining climate projections. We take advantage of the Macquarie Island Cloud and Radiation Experiment (MICRE) to perform an analysis of observed and simulated cloud processes over the Southern Ocean in a region and season dominated by supercooled liquid clouds. Using a single-column version of the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS), we compare two different cloud microphysical schemes to ground-based observations of cloud, precipitation, and radiation over a 2.5-month period (1 January–17 March 2017). Both schemes are able to reproduce aspects of the cloud and radiation observations during MICRE to within the uncertainty of the data when the thermodynamic profile is prescribed with relaxation. There are differences in water mass and representation of reflectivity between the schemes. A sensitivity study of the cloud microphysics schemes, one a bulk one-moment scheme and the other a two-moment scheme with prediction of mass and number, indicates that several key processes create differences between the schemes. Surface radiative fluxes and total water path are highly sensitive to the formation and fall speed of precipitation. The prediction of hydrometeor number with the two-moment scheme yields a better comparison with observed reflectivity and radiative fluxes, despite predicting higher liquid water contents than observed. With the two-moment scheme, we are also able to test the sensitivity of the results to the input of liquid cloud condensation nuclei (CCN) and ice nuclei (IN). The cloud properties and resulting radiative effects are found to be sensitive to the CCN and IN concentrations. More CCN and IN increase liquid and ice water paths, respectively. Thus, both the dynamic environment and aerosols, integrated through the cloud microphysics, are important for properly representing Southern Ocean cloud radiative effects.

Examination of Cloud Seeding on Board of the International Space Station: Experimental and Modeling Approach

Examination of Cloud Seeding on Board of the International Space Station: Experimental and Modeling Approach

Frequent rainfall-induced new particle formation within the canopy in the Amazon rainforest

Atmospheric aerosol particles are essential for forming clouds and precipitation, thereby influencing Earth’s energy budget, water cycle and climate on regional and global scales. However, the origin of aerosol particles over the Amazon rainforest during the wet season is poorly understood. Earlier studies showed new particle formation in the outflow of deep convective clouds and suggested a downward flux of aerosol particles during precipitation events. Here we use comprehensive aerosol, trace gas and meteorological data from the Amazon Tall Tower Observatory to show that rainfall regularly induces bursts of nanoparticles in the nucleation size range. This can be attributed to rain-related scavenging of larger particles and a corresponding reduction of the condensation sink, along with an ozone injection into the forest canopy, which could increase the oxidation of biogenic volatile organic compounds, especially terpenes, and enhance new particle formation. During and after rainfall, the nucleation particle concentrations directly above the canopy are greater than those higher up. This gradient persists throughout the wet season for the nucleation size range, indicating continuous particle formation within the canopy, a net upward flux of newly formed particles and a paradigm shift in understanding aerosol–cloud–precipitation interactions in the Amazon. Particle bursts provide a plausible explanation for the formation of cloud condensation nuclei, leading to the local formation of green-ocean clouds and precipitation. Our findings suggest that an interplay of a rain-related reduction in the condensation sink, primary emissions of gases, mainly terpenes, and particles from the forest canopy, and convective cloud processing determines the population of cloud condensation nuclei in pristine rainforest air.

Stratus and Stratocumulus Cloud Microphysics and Drizzle Relationships With CCN Modality

AbstractHigh resolution extended‐range cloud condensation nuclei (CCN) spectral comparisons with cloud microphysics and drizzle of the Physics of Stratocumulus Tops (POST) field experiment confirmed results in the Marine Stratus/Stratocumulus Experiment (MASE). Both of these stratus cloud projects demonstrated that bimodal CCN spectra typically caused by cloud processing were associated with clouds that exhibited higher concentrations of smaller droplets with narrower distributions and less drizzle than clouds associated with unimodal CCN spectra. Resulting brighter clouds and increased cloudiness could enhance both indirect aerosol effects (IAE). These stratus findings are opposite of analogous measurements in two cumulus cloud projects, which showed bimodal CCN associated with fewer larger droplets more broadly distributed and with more drizzle than clouds associated with unimodal CCN. Resulting reduced cumulus brightness and cloudiness could reduce both IAE. Physics of Stratocumulus Tops (POST) flights in air masses with higher CCN concentrations, NCCN, showed more extremes of the stratus characteristics. However, POST flights with lower NCCN showed opposite droplet characteristics similar to the cumulus clouds, yet still showed less drizzle in clouds associated with bimodal CCN, but not as much less as the flights with higher NCCN. Since all MASE clouds were in polluted air masses, while the two cumulus projects were in clean air masses we deduce from these four projects that both the dynamic stratus/cumulus differences (vertical wind) and NCCN are responsible for the microphysics and drizzle differences among these projects. This is because the clean POST characteristics are a hybrid between MASE/POST high NCCN and the two cumulus projects.

Analyzing Morphology and Composition of Coarse Aerosol Particles in Bangkok, Thailand: Implications to Sources and Impacts of Aged Aerosols on Ecosystem Health and Climate Dynamics

During dry seasons, elevated aerosol levels across Thailand pose nationwide problems. Understanding and addressing this issue is challenging due to the dynamic nature of aerosol modification and generation during transport. This study investigates the morphology and elemental compositions of coarse aerosol particles in Bangkok, Thailand, during the dry seasons of 2020/21. Through scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectrometry (EDS), the study reveals a complex mixture of anthropogenic, mineral, biogenic, and marine aerosols. Anthropogenic sources, including biomass burning, vehicular emissions, and industrial activities, contribute to carbonaceous particles like soot aggregates and tar balls. Mineral dust particles, predominantly calcium-rich and aluminosilicate, originate from various sources including construction, industry, and natural processes. Aging processes alter the composition and properties of both carbonaceous and mineral particles, influencing nutrient deposition, carbon sequestration, cloud condensation nuclei formation, and light scattering. These processes have multifaceted impacts on ecosystem health and climate dynamics, highlighting the need for further research and mitigation strategies to address the environmental consequences of aged aerosol particles in urban environments like Bangkok.