scholarly journals Correlation between cloud condensation nuclei concentration and aerosol optical thickness in remote and polluted regions

2009 ◽  
Vol 9 (2) ◽  
pp. 543-556 ◽  
Author(s):  
M. O. Andreae
Keyword(s):  
Optical Thickness ◽  
Cloud Condensation Nuclei ◽  
Anthropogenic Pollution ◽  
Aerosol Optical Thickness ◽  
Condensation Nuclei ◽  
Desert Dust ◽  
Order Of Magnitude ◽  
The Mean ◽  
The Difference ◽  
Remote Sensing Techniques

Abstract. A large number of published and unpublished measurements of cloud condensation nuclei (CCN) concentrations and aerosol optical thickness (AOT) measurements have been analyzed. AOT measurements were obtained mostly from the AERONET network, and selected to be collocated as closely as possible to the CCN investigations. In remote marine regions, CCN0.4 (CCN at a supersaturation of 0.4%) are around 110 cm−3 and the mean AOT500 (AOT at 500 nm) is 0.057. Over remote continental areas, CCN are almost twice as abundant, while the mean AOT500 is ca. 0.075. (Sites dominated by desert dust plumes were excluded from this analysis.) Some, or maybe even most of this difference must be because even remote continental sites are in closer proximity to pollution sources than remote marine sites. This suggests that the difference between marine and continental levels must have been smaller before the advent of anthropogenic pollution. Over polluted marine and continental regions, the CCN concentrations are about one order of magnitude higher than over their remote counterparts, while AOT is about five times higher over polluted than over clean regions. The average CCN concentrations from all studies show a remarkable correlation to the corresponding AOT values, which can be expressed as a power law. This can be very useful for the parameterization of CCN concentrations in modeling studies, as it provides an easily measured proxy for this variable, which is difficult to measure directly. It also implies that, at least at large scales, the radiative and microphysical effects of aerosols on cloud physics are correlated and not free to vary fully independently. While the observed strong empirical correlation is remarkable, it must still be noted that there is about a factor-of-four range of CCN concentrations at a given AOT, and that there remains considerable room for improvement in remote sensing techniques for CCN abundance.

scholarly journals Correlation between cloud condensation nuclei concentration and aerosol optical thickness in remote and polluted regions

2008 ◽  
Vol 8 (3) ◽  
pp. 11293-11320 ◽  
Author(s):  
M. O. Andreae
Keyword(s):  
Remote Sensing ◽  
Optical Thickness ◽  
Cloud Condensation Nuclei ◽  
Anthropogenic Pollution ◽  
Aerosol Optical Thickness ◽  
Condensation Nuclei ◽  
Desert Dust ◽  
The Mean ◽  
The Difference ◽  
Remote Sensing Techniques

Abstract. A large number of published and unpublished measurements of cloud condensation nuclei (CCN) concentrations and aerosol optical thickness (AOT) measurements have been analyzed. AOT measurements were obtained mostly from the AERONET network, and selected to be collocated as closely as possible to the CCN investigations. In remote marine regions, CCN0.4 (CCN at a supersaturation of 0.4%) are around 110 cm−3 and the mean AOT500 (AOT at 500 nm) is 0.057. Over remote continental areas, CCN are almost twice as abundant, while the mean AOT500 is ca. 0.075. (Sites dominated by desert dust plumes were excluded from this analysis.) Some, or maybe even most of this difference must be because even remote continental sites are in closer proximity to pollution sources than remote marine sites. This suggests that the difference between marine and continental levels must have been smaller before the advent of anthropogenic pollution. Over polluted marine and continental regions, the CCN concentrations are about one magnitude higher than over their remote counterparts, while AOT is about five times higher over polluted than over clean regions. The average CCN concentrations from all studies show a remarkable correlation to the corresponding AOT values, which can be expressed as a power law. This can be very useful for the parameterization of CCN concentrations in modeling studies, as it provides an easily measured proxy for this variable, which is difficult to measure directly. It also implies that, at least at large scales, the radiative and microphysical effects of aerosols on cloud physics are correlated and not free to vary independently. While this strong empirical correlation is remarkable, it must still be noted that that there is about a factor-of-four range of CCN concentrations at a given AOT, and that there remains considerable room for improvement in remote sensing techniques for measuring CCN abundance.

scholarly journals Sensitivity of aerosol optical thickness and aerosol direct radiative effect to relative humidity

2009 ◽  
Vol 9 (7) ◽  
pp. 2375-2386 ◽  
Author(s):  
H. Bian ◽  
M. Chin ◽  
J. M. Rodriguez ◽  
H. Yu ◽  
J. E. Penner ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Temporal Resolution ◽  
Optical Thickness ◽  
Sensitivity Study ◽  
Horizontal Resolution ◽  
Aerosol Optical Thickness ◽  
Observation System ◽  
Anthropogenic Aerosol ◽  
The Difference ◽  
The Many

Abstract. We present a sensitivity study of the effects of spatial and temporal resolution of atmospheric relative humidity (RH) on calculated aerosol optical thickness (AOT) and the aerosol direct radiative effects (DRE) in a global model. We carry out different modeling experiments using the same aerosol fields simulated in the Global Modeling Initiative (GMI) model at a resolution of 2° latitude by 2.5° longitude, using time-averaged fields archived every three hours by the Goddard Earth Observation System Version 4 (GEOS-4), but we change the horizontal and temporal resolution of the relative humidity fields. We find that, on a global average, the AOT calculated using RH at a 1°×1.25° horizontal resolution is 11% higher than that using RH at a 2°×2.5° resolution, and the corresponding DRE at the top of the atmosphere is 8–9% and 15% more negative (i.e., more cooling) for total aerosols and anthropogenic aerosol alone, respectively, in the finer spatial resolution case. The difference is largest over surface escarpment regions (e.g. >200% over the Andes Mountains) where RH varies substantially with surface terrain. The largest zonal mean AOT difference occurs at 50–60° N (16–21%), where AOT is also relatively larger. A similar impact is also found when the time resolution of RH is increased. This increase of AOT and aerosol cooling with the increase of model resolution is due to the highly non-linear relationship between RH and the aerosol mass extinction efficiency (MEE) at high RH (>80%). Our study is a specific example of the uncertainty in model results highlighted by multi-model comparisons such as AeroCom, and points out one of the many inter-model differences that can contribute to the overall spread among models.

scholarly journals Comment on Kokkola et al. (2008) – Comparisons with analytical solutions from Khvorostyanov and Curry (2007) on the critical droplet radii and supersaturations of CCN with insoluble fractions

2009 ◽  
Vol 9 (2) ◽  
pp. 9537-9550
Author(s):  
V. I. Khvorostyanov ◽  
J. A. Curry
Keyword(s):  
Analytical Solutions ◽  
Cloud Condensation Nuclei ◽  
Dilute Solution ◽  
Condensation Nuclei ◽  
Critical Droplet ◽  
Critical Supersaturation ◽  
Diluted Solution ◽  
Major Discrepancy ◽  
The Difference ◽  
Similar Solutions

Abstract. Analytical solutions for the critical radii rcr and supersaturations scr of the cloud condensation nuclei with insoluble fractions were derived by Khvorostyanov and Curry (2007, hereafter KC07). Similar solutions were found later by Kokkola et al. (2008, hereafter Kok08); however, Kok08 used the approximation of an ideal dilute solution, while KC07 used more accurate assumptions that account for nonideality of solutions. Kok08 found a large discrepancy with KC07 in the critical supersaturations. Various possible reasons of this are analyzed. It is shown that the major discrepancy was caused by a simple mistake in Kok08 in the equation for the critical supersaturation: erroneous ''plus'' sign between the Kelvin and Raoult terms instead of correct ''minus'' sign. If this mistake is corrected, the equations from Kok08 mostly repeat the equations from KC07, except that Kok08 use the dilute solution approximation. If the mistake in Kok08 is corrected, then the differences in the critical radii and supersaturations do not exceed 16–18%, which characterizes the possible errors of an ideal diluted solution approximation. If the Kok08 scheme is corrected and applied to a nonideal solution, then the difference with KC07 does not exceed 0.4–1%.

scholarly journals New particle formation events observed at King Sejong Station, Antarctic Peninsula – Part 1: Physical characteristics and contribution to cloud condensation nuclei

2018 ◽  
Author(s):  
Jaeseok Kim ◽  
Young Jun Yoon ◽  
Yeontae Gim ◽  
Jin Hee Choi ◽  
Hyo Jin Kang ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Particle Formation ◽  
Physical Characteristics ◽  
Weddell Sea ◽  
New Particle Formation ◽  
Condensation Nuclei ◽  
Source Rate ◽  
The Mean

Abstract. The physical characteristics of aerosol particles during a particle burst observed at King Sejong Station in Antarctic Peninsula from March 2009 to December 2016 were analyzed. This study focuses on the seasonal variation in parameters related to particle formation such as the occurrence, formation rate (FR) and growth rate (GR), condensation sink (CS), and source rate of condensable vapor. The number concentrations during new particle formation (NPF) events varied from 1707 cm−3 to 83 120 cm−3, with an average of 20 649 ± 9290 cm−3, and the duration of the NPF events ranged from 0.6 h to 14.4 h, with a mean of 4.6 ± 1.5 h. The NPF event dominantly occurred during austral summer period (~ 72 %). The mean values of FR and GR of the aerosol particles were 2.79 ± 1.05 cm−3 s−1 and 0.68 ± 0.27 nm h−1, respectively showing enhanced rates in the summer season. The mean value of FR at King Sejong Station was higher than that at other sites in Antarctica, at 0.002–0.3 cm−3 s−1, while those of growth rates was relatively similar results observed by precious studies, at 0.4~4.3 nm h−1. The average values of CS and source rate of condensable vapor were (6.04 ± 2.74) × 10−3 s−1 and (5.19 ± 3.51) × 104 cm−3 s−1, respectively. The contribution of particle formation to cloud condensation nuclei (CCN) concentration was also investigated. The CCN concentration during the NPF period increased approximately 9 % compared with the background concentration. In addition, the effects of the origin and pathway of air masses on the characteristics of aerosol particles during a NPF event were determined. The FRs were similar regardless of the origin and pathway, whereas the GRs of particles originating from the Antarctic Peninsula and the Bellingshausen Sea, at 0.77 ± 0.25 nm h−1 and 0.76 ± 0.30 nm h−1, respectively, were higher than those of particles originating from the Weddell Sea (0.41 ± 0.15 nm h−1).

scholarly journals Size-resolved cloud condensation nuclei (CCN) activity and closure analysis at the HKUST Supersite in Hong Kong

2014 ◽  
Vol 14 (18) ◽  
pp. 10267-10282 ◽  
Author(s):  
J. W. Meng ◽  
M. C. Yeung ◽  
Y. J. Li ◽  
B. Y. L. Lee ◽  
C. K. Chan
Keyword(s):  
Particle Size ◽  
Hong Kong ◽  
Atmospheric Aerosols ◽  
Cloud Condensation Nuclei ◽  
Particle Diameter ◽  
Volume Ratio ◽  
Condensation Nuclei ◽  
Mixing State ◽  
Scanning Mobility Particle Sizer ◽  
The Mean

Abstract. The cloud condensation nuclei (CCN) properties of atmospheric aerosols were measured on 1–30 May 2011 at the HKUST (Hong Kong University of Science and Technology) Supersite, a coastal site in Hong Kong. Size-resolved CCN activation curves, the ratio of number concentration of CCN (NCCN) to aerosol concentration (NCN) as a function of particle size, were obtained at supersaturation (SS) = 0.15, 0.35, 0.50, and 0.70% using a DMT (Droplet Measurement Technologies) CCN counter (CCNc) and a TSI scanning mobility particle sizer (SMPS). The mean bulk size-integrated NCCN ranged from ~500 cm−3 at SS = 0.15% to ~2100 cm−3 at SS = 0.70%, and the mean bulk NCCN / NCN ratio ranged from 0.16 at SS = 0.15% to 0.65 at SS = 0.70%. The average critical mobility diameters (D50) at SS = 0.15, 0.35, 0.50, and 0.70% were 116, 67, 56, and 46 nm, respectively. The corresponding average hygroscopic parameters (κCCN) were 0.39, 0.36, 0.31, and 0.28. The decrease in κCCN can be attributed to the increase in organic to inorganic volume ratio as particle size decreases, as measured by an Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The κCCN correlates reasonably well with κAMS_SR based on size-resolved AMS measurements: κAMS_SR = κorg × forg + κinorg × finorg, where forg and finorg are the organic and inorganic volume fractions, respectively, κorg = 0.1 and κinorg = 0.6, with a R2 of 0.51. In closure analysis, NCCN was estimated by integrating the measured size-resolved NCN for particles larger than D50 derived from κ assuming internal mixing state. Estimates using κAMS_SR show that the measured and predicted NCCN were generally within 10% of each other at all four SS. The deviation increased to 26% when κAMS was calculated from bulk PM1 AMS measurements of particles because PM1 was dominated by particles of 200 to 500 nm in diameter, which had a larger inorganic fraction than those of D50 (particle diameter < 200 nm). A constant κ = 0.33 (the average value of κAMS_SR over the course of campaign) was found to give an NCCN prediction within 12% of the actual measured values. We also compared NCCN estimates based on the measured average D50 and the average size-resolved CCN activation ratio to examine the relative importance of hygroscopicity and mixing state. NCCN appears to be relatively more sensitive to the mixing state and hygroscopicity at a high SS = 0.70% and a low SS = 0.15%, respectively.

scholarly journals Improved information about the vertical location and extent of cloud layers from POLDER3 measurements in the oxygen A band

2013 ◽  
Vol 6 (2) ◽  
pp. 2533-2581 ◽  
Author(s):  
M. Desmons ◽  
N. Ferlay ◽  
F. Parol ◽  
L. Mcharek ◽  
C. Vanbauce
Keyword(s):  
Standard Deviation ◽  
Oxygen Pressure ◽  
Optical Thickness ◽  
Mean Difference ◽  
Vertical Extent ◽  
Satellite Platform ◽  
Cloud Optical Thickness ◽  
The Mean ◽  
The Difference ◽  
The One

Abstract. This paper describes new advances in the exploitation of oxygen A band measurements from POLDER3 sensor aboard PARASOL, satellite platform within the A-Train. These developments result from a better account of the dependence of POLDER oxygen parameters to cloud optical thickness τ and to the scene's geometrical conditions, but also and more importantly from the finer understanding of the sensitivity of these parameters to cloud vertical extent. This sensitivity is made possible thanks to the multidirectional character of POLDER measurements. In the case of monolayer clouds that represent most of cloudy conditions, new oxygen parameters are obtained and calibrated from POLDER3 data colocalized with the measurements of the two active sensors of the A-Train, CALIOP/CALIPSO and CPR/CloudSat. From a parameterization that is (μs, τ) dependent, with μs the cosine of the solar zenith angle, a cloud top oxygen pressure (CTOP) and a cloud middle oxygen pressure (CMOP) are obtained which are estimates of actual cloud top and middle pressures. The performance of CTOP and CMOP are presented for the most numerous ISCCP cases in 2008. The coefficient of the correlation between CMOP and the actual cloud middle pressure is 0.81 for cirrostratus, 0.79 for stratocumulus, 0.75 for deep convective clouds. The coefficient of the correlation between CTOP and the actual cloud top pressure is 0.75, 0.73, and 0.79 for the same cloud types respectively. The score obtained by CTOP, defined as the confidence in the retrieval for a particular range of infered value and for a given error, is higher than the one of MODIS CTP. For liquid and ice clouds, the score reaches 50 and 70% respectively for bin value of CTP superior in numbers and accepted errors of 30 and 50 hPa. From the difference between CTOP and CMOP, a first estimate of the cloud vertical extent H is possible. Then, the correlation between the angular standard deviation of POLDER oxygen pressure σPO2 and the cloud vertical extent is described in detail in the case of liquid clouds. The correlation is shown to be spatially and temporally robust, excepted for clouds above land during winter months. The study of the correlation's dependence to cloud optical thickness and to the scene's geometrical conditions leads to parameterizations which provide a second way for retrieving H for this type of clouds. For liquid water clouds above ocean in 2008, the mean difference between the actual cloud vertical extent and the one retrieved from σPO2 (from the pressure difference) is 5 m (−12 m). The standard deviation of the mean difference is close to 1000 m for the two methods. The score of 50% confidence for the retrieval of H corresponds to an error of 20 and 40% for ice and liquid clouds respectively over ocean. These promising results need to be validated outside of the CALIPSO/CloudSat track.

scholarly journals Indirect Impact of Atmospheric Aerosols in Idealized Simulations of Convective–Radiative Quasi Equilibrium. Part II: Double-Moment Microphysics

2011 ◽  
Vol 24 (7) ◽  
pp. 1897-1912 ◽  
Author(s):  
Wojciech W. Grabowski ◽  
Hugh Morrison
Keyword(s):  
Atmospheric Aerosols ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Bowen Ratio ◽  
Cloud Microphysics ◽  
Quasi Equilibrium ◽  
Double Moment ◽  
The Mean ◽  
The Difference ◽  
The Impact

Abstract This paper extends the previous cloud-resolving modeling study concerning the impact of cloud microphysics on convective–radiative quasi equilibrium (CRQE) over a surface with fixed characteristics and prescribed solar input, both mimicking the mean conditions on earth. The current study applies sophisticated double-moment warm-rain and ice microphysics schemes, which allow for a significantly more realistic representation of the impact of aerosols on precipitation processes and on the coupling between clouds and radiative transfer. Two contrasting cloud condensation nuclei (CCN) characteristics are assumed, representing pristine and polluted conditions, as well as contrasting representations of the effects of entrainment and mixing on the mean cloud droplet size. In addition, four sets of sensitivity simulations are also performed with changes that provide a reference for the main simulation set. As in the previous study, the CRQE mimics the estimates of globally and annually averaged water and energy fluxes across the earth’s atmosphere. There are some differences from the previous study, however, consistent with the slightly lower water vapor content in the troposphere and significantly reduced lower-tropospheric cloud fraction in current simulations. There is also a significant reduction of the difference between the pristine and polluted cases, from ∼20 to ∼4 W m−2 at the surface from ∼20 to ∼9 W m−2 at the top of the atmosphere (TOA). The difference between the homogeneous and extremely inhomogeneous mixing scenarios, ∼20 W m−2 in the previous study, is reduced to a mere 2 (1) W m−2 at the surface (TOA). An unexpected difference between the previous and current simulations is the lower Bowen ratio of the surface heat flux, the partitioning of the total flux into sensible and latent components. It is shown that most of the change comes from the difference in the representation of rain evaporation in the subcloud layer in the single- and double-moment microphysics schemes. The difference affects the mean air temperature and humidity near the surface, and thus the Bowen ratio. The differences between the various simulations are discussed, contrasting the process-level approach with the impact of cloud microphysics on the quasi-equilibrium state with a more appropriate system dynamics approach. The key distinction is that the latter includes the interactions among all the processes in the modeled system.

scholarly journals Comparison of three aerosol representations of NHM-Chem (v1.0) for the simulations of air quality and climate-relevant variables

2021 ◽  
Vol 14 (4) ◽  
pp. 2235-2264
Author(s):  
Mizuo Kajino ◽  
Makoto Deushi ◽  
Tsuyoshi Thomas Sekiyama ◽  
Naga Oshima ◽  
Keiya Yumimoto ◽  
...  
Keyword(s):  
Air Quality ◽  
Optical Thickness ◽  
Mineral Dust ◽  
Cloud Condensation Nuclei ◽  
Regional Scale ◽  
Sea Salt ◽  
Aerosol Optical Thickness ◽  
Absorption Enhancement ◽  
Equilibrium Method ◽  
Non Equilibrium

Abstract. This study provides comparisons of aerosol representation methods incorporated into a regional-scale nonhydrostatic meteorology–chemistry model (NHM-Chem). Three options for aerosol representations are currently available: the five-category non-equilibrium (Aitken, soot-free accumulation, soot-containing accumulation, dust, and sea salt), three-category non-equilibrium (Aitken, accumulation, and coarse), and bulk equilibrium (submicron, dust, and sea salt) methods. The three-category method is widely used in three-dimensional air quality models. The five-category method, the standard method of NHM-Chem, is an extensional development of the three-category method and provides improved predictions of variables relating to aerosol–cloud–radiation interaction processes by implementing separate treatments of light absorber and ice nuclei particles, namely, soot and dust, from the accumulation- and coarse-mode categories (implementation of aerosol feedback processes to NHM-Chem is still ongoing, though). The bulk equilibrium method was developed for operational air quality forecasting with simple aerosol dynamics representations. The total CPU times of the five-category and three-category methods were 91 % and 44 % greater than that of the bulk method, respectively. The bulk equilibrium method was shown to be eligible for operational forecast purposes, namely, the surface mass concentrations of air pollutants such as O3, mineral dust, and PM2.5. The simulated surface concentrations and depositions of bulk chemical species of the three-category method were not significantly different from those of the five-category method. However, the internal mixture assumption of soot/soot-free and dust/sea salt particles in the three-category method resulted in significant differences in the size distribution and hygroscopicity of the particles. The unrealistic dust/sea salt complete mixture of the three-category method induced significant errors in the prediction of the mineral dust-containing cloud condensation nuclei (CCN), which alters heterogeneous ice nucleation in cold rain processes. The overestimation of soot hygroscopicity by the three-category method induced errors in the BC-containing CCN, BC deposition, and light-absorbing aerosol optical thickness (AAOT). Nevertheless, the difference in AAOT was less pronounced with the three-category method because the overestimation of the absorption enhancement was compensated by the overestimation of hygroscopic growth and the consequent loss due to in-cloud scavenging. In terms of total properties, such as aerosol optical thickness (AOT) and CCN, the results of the three-category method were acceptable.

scholarly journals Cluster analysis of an impact of air back-trajectories on aerosol optical properties at Hornsund, Spitsbergen

2009 ◽  
Vol 9 (4) ◽  
pp. 15423-15451
Author(s):  
A. Rozwadowska ◽  
T. Zieliński ◽  
T. Petelski ◽  
P. Sobolewski
Keyword(s):  
Optical Thickness ◽  
Aerosol Optical Thickness ◽  
Hysplit Model ◽  
Local Conditions ◽  
Back Trajectories ◽  
Local Direction ◽  
The Mean ◽  
The Impact ◽  
Network Station ◽  
Average Cluster

Abstract. In this paper spectra of aerosol optical thickness from AERONET (AErosol RObotic NETwork) station at Hornsund in the southern part of Spitsbergen were employed to study the impact of air mass history on aerosol optical thickness (AOT(500)) and Angstrom coefficient. Backward trajectories computed by means of NOAA HYSPLIT model were used to trace air history. It was found that in spring changes in AOT values over the Hornsund station were influenced by the at least 8-day trajectories of air, which was advected both in free troposphere and in the boundary layer. However, the free tropospheric advection was dominating. In summer the AOT variability was created mainly by local conditions, local direction and speed of advection (1-day trajectories). During the ASTAR 2007 campaign aerosols near Hornsund showed low AOT values ranging from 0.06 to 0.09, which is lower than the mean AOT(500) for spring seasons from 2005 to 2007 (0.110±0.007; mean ± standard deviation of mean). The 9 April 2007 with AOT(500)=0.147 was an exception. Back-trajectories belonged to the clusters of low and average cluster mean AOT value. Beside the maximum AOT of the 9 April 2007, the observed AOT values were close to the means for the clusters to which they belonged or were lower than the means.

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