A Method for Forecasting Cloud Condensation Nuclei Using Predictions of Aerosol Physical and Chemical Properties from WRF/Chem

2011 ◽  
Vol 50 (7) ◽  
pp. 1601-1615 ◽  
Author(s):  
Daniel Ward ◽  
William Cotton
Keyword(s):  
Hydrological Cycle ◽  
Spatial Scales ◽  
Cloud Condensation Nuclei ◽  
Cloud Microphysics ◽  
Atmospheric Modeling ◽  
Number Concentration ◽  
Integrated System ◽  
Condensation Nuclei ◽  
Field Campaign ◽  
Physical And Chemical

AbstractModel investigations of aerosol–cloud interactions across spatial scales are necessary to advance basic understanding of aerosol impacts on climate and the hydrological cycle. Yet these interactions are complex, involving numerous physical and chemical processes. Models capable of combining aerosol dynamics and chemistry with detailed cloud microphysics are recent developments. In this study, predictions of aerosol characteristics from the Weather Research and Forecasting Model with Chemistry (WRF/Chem) are integrated into the Regional Atmospheric Modeling System microphysics package to form the basis of a coupled model that is capable of predicting the evolution of atmospheric aerosols from gas-phase emissions to droplet activation. The new integrated system is evaluated against measurements of cloud condensation nuclei (CCN) from a land-based field campaign and an aircraft-based field campaign in Colorado. The model results show the ability to capture vertical variations in CCN number concentration within an anthropogenic pollution plume. In a remote continental location the model-forecast CCN number concentration exhibits a positive bias that is attributable in part to an overprediction of the aerosol hygroscopicity that results from an underprediction in the organic aerosol mass fraction. In general, the new system for predicting CCN from forecast aerosol fields improves on the existing scheme in which aerosol quantities were user prescribed.

Effects of Number Concentration of Cloud Condensation Nuclei on Moist Convection Formation

2021 ◽  
Author(s):  
Yoshiaki Miyamoto
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Time Scale ◽  
Numerical Experiments ◽  
Cloud Condensation Nuclei ◽  
Cloud Microphysics ◽  
Number Concentration ◽  
Moist Convection ◽  
Condensation Nuclei

AbstractWe examined the sensitivity of the formation of moist convection to the number of aerosols that serve as cloud condensation nuclei (CCN) based on a set of numerical experiments using a nonhydrostatic model with a bin cloud microphysics model. Additionally, a linear stability analysis for an air parcel incorporating effects of the CCN number concentration (NCCN) has been conducted to further demonstrate the findings in numerical experiments. The results of the numerical experiments show that moist convection does not form when NCCN ≤ 10 cm−3. The sensitivity to NCCN can be divided into three regimes: when NCCN ≤ 10 cm−3, convection does not form or not fully develop; when 1 ≤ NCCN ≤ 102 cm−3, maximum vertical velocity increases with NCCN; and when NCCN ≥ 102 cm−3, the intensity of convection does not largely depend on NCCN. We demonstrate that the main reason convection does not form under environments with a small NCCN is that the time scale for condensation is longer than that to change environmental conditions. Given a supersaturated environment, fewer droplets form when NCCN is small and the size of droplets is potentially large. Consequently, the amount of latent heating is limited and the air parcel cannot obtain buoyancy within a reasonable time scale. Linear stability analysis using a parcel model considering the effect of NCCN without ice-phase processes shows unstable and stable regimes as a function of the number of droplets. The analytically obtained critical droplet number for the convection formation well corresponds to the minimum NCCN beyond which convection forms in the present numerical experiments.

scholarly journals Cloud condensation nuclei (CCN) from fresh and aged air pollution in the megacity region of Beijing

2011 ◽  
Vol 11 (21) ◽  
pp. 11023-11039 ◽  
Author(s):  
S. S. Gunthe ◽  
D. Rose ◽  
H. Su ◽  
R. M. Garland ◽  
P. Achtert ◽  
...  
Keyword(s):  
Size Dependence ◽  
Size Range ◽  
Hydrological Cycle ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Number Concentration ◽  
Optical Measurements ◽  
Average Particle ◽  
Condensation Nuclei ◽  
Mass Fractions

Abstract. Atmospheric aerosol particles serving as cloud condensation nuclei (CCN) are key elements of the hydrological cycle and climate. CCN properties were measured and characterized during the CAREBeijing-2006 campaign at a regional site south of the megacity of Beijing, China. Size-resolved CCN efficiency spectra recorded for a supersaturation range of S=0.07% to 0.86% yielded average activation diameters in the range of 190 nm to 45 nm. The corresponding effective hygroscopicity parameters (κ) exhibited a strong size dependence ranging from ~0.25 in the Aitken size range to ~0.45 in the accumulation size range. The campaign average value (κ =0.3 ± 0.1) was similar to the values observed and modeled for other populated continental regions. The hygroscopicity parameters derived from the CCN measurements were consistent with chemical composition data recorded by an aerosol mass spectrometer (AMS) and thermo-optical measurements of apparent elemental and organic carbon (EC and OC). The CCN hygroscopicity and its size dependence could be parameterized as a function of only AMS based organic and inorganic mass fractions (forg, finorg) using the simple mixing rule κp ≈ 0.1 · forg + 0.7 · finorg. When the measured air masses originated from the north and passed rapidly over the center of Beijing (fresh city pollution), the average particle hygroscopicity was reduced (κ = 0.2 ± 0.1), which is consistent with enhanced mass fractions of organic compounds (~50%) and EC (~30%) in the fine particulate matter (PM1). Moreover, substantial fractions of externally mixed weakly CCN-active particles were observed at low supersaturation (S=0.07%), which can be explained by the presence of freshly emitted soot particles with very low hygroscopicity (κ < 0.1). Particles in stagnant air from the industrialized region south of Beijing (aged regional pollution) were on average larger and more hygroscopic, which is consistent with enhanced mass fractions (~60%) of soluble inorganic ions (mostly sulfate, ammonium, and nitrate). Accordingly, the number concentration of CCN in aged air from the megacity region was higher than in fresh city outflow ((2.5–9.9) × 103 cm−3 vs. (0.4–8.3) × 103 cm−3 for S=0.07–0.86%) although the total aerosol particle number concentration was lower (1.2 × 104 cm−3 vs. 2.3 × 104 cm−3). A comparison with related studies suggests that the fresh outflow from Chinese urban centers generally may contain more, but smaller and less hygroscopic aerosol particles and thus fewer CCN than the aged outflow from megacity regions.

scholarly journals Regional scale effects of the aerosol cloud interaction simulated with an online coupled comprehensive chemistry model

2011 ◽  
Vol 11 (9) ◽  
pp. 4411-4423 ◽  
Author(s):  
M. Bangert ◽  
C. Kottmeier ◽  
B. Vogel ◽  
H. Vogel
Keyword(s):  
Cloud Condensation Nuclei ◽  
Regional Scale ◽  
Cloud Droplet ◽  
Cloud Microphysics ◽  
Model System ◽  
Number Concentration ◽  
Condensation Nuclei ◽  
Close Link ◽  
Cloud Droplet Number Concentration ◽  
The Mean

Abstract. We have extended the coupled mesoscale atmosphere and chemistry model COSMO-ART to account for the transformation of aerosol particles into cloud condensation nuclei and to quantify their interaction with warm cloud microphysics on the regional scale. The new model system aims to fill the gap between cloud resolving models and global scale models. It represents the very complex microscale aerosol and cloud physics as detailed as possible, whereas the continental domain size and efficient codes will allow for both studying weather and regional climate. The model system is applied in a first extended case study for Europe for a cloudy five day period in August 2005. The model results show that the mean cloud droplet number concentration of clouds is correlated with the structure of the terrain, and we present a terrain slope parameter TS to classify this dependency. We propose to use this relationship to parameterize the probability density function, PDF, of subgrid-scale cloud updraft velocity in the activation parameterizations of climate models. The simulations show that the presence of cloud condensation nuclei (CCN) and clouds are closely related spatially. We find high aerosol and CCN number concentrations in the vicinity of clouds at high altitudes. The nucleation of secondary particles is enhanced above the clouds. This is caused by an efficient formation of gaseous aerosol precursors above the cloud due to more available radiation, transport of gases in clean air above the cloud, and humid conditions. Therefore the treatment of complex photochemistry is crucial in atmospheric models to simulate the distribution of CCN. The mean cloud droplet number concentration and droplet diameter showed a close link to the change in the aerosol. To quantify the net impact of an aerosol change on the precipitation we calculated the precipitation susceptibility β for the whole model domain over a period of two days with an hourly resolution. The distribution function of β is slightly skewed to positive values and has a mean of 0.23. Clouds with a liquid water path LWP of approximately 0.85 kg m−2 are on average most susceptible to aerosol changes in our simulations with an absolute value of β of 1. The average β for LWP between 0.5 kg m−2 and 1 kg m−2 is approximately 0.4.

scholarly journals Cloud condensation nuclei (CCN) from fresh and aged air pollution in the megacity region of Beijing

2011 ◽  
Vol 11 (3) ◽  
pp. 9959-9997
Author(s):  
S. S. Gunthe ◽  
D. Rose ◽  
H. Su ◽  
R. M. Garland ◽  
P. Achtert ◽  
...  
Keyword(s):  
Size Dependence ◽  
Size Range ◽  
Hydrological Cycle ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Number Concentration ◽  
Optical Measurements ◽  
Average Particle ◽  
Condensation Nuclei ◽  
Mass Fractions

Abstract. Atmospheric aerosol particles serving as cloud condensation nuclei (CCN) are key elements of the hydrological cycle and climate. CCN properties were measured and characterized during the CAREBeijing-2006 campaign at a regional site south of the megacity of Beijing, China. Size-resolved CCN efficiency spectra recorded for a supersaturation range of S = 0.07% to 0.86% yielded average activation diameters in the range of 190 nm to 45 nm. The corresponding effective hygroscopicity parameters (κ) exhibited a strong size dependence ranging from ~0.25 in the Aitken size range to ~0.45 in the accumulation size range. The campaign average value (κ = 0.3 ± 0.1) was similar to the values observed and modeled for other populated continental regions. The hygroscopicity parameters derived from the CCN measurements were consistent with chemical composition data recorded by an aerosol mass spectrometer (AMS) and thermo-optical measurements of apparent elemental and organic carbon (ECa and OC). The CCN hygroscopicity and its size dependence could be parameterized as a function of AMS based organic and inorganic mass fractions using the simple mixing rule κ p ≈ 0.1 · forg + 0.7 · finorg. When the measured air masses originated from the north and passed rapidly over the center of Beijing (fresh city pollution), the average particle hygroscopicity was reduced (κ = 0.2 ± 0.1), which is consistent with enhanced mass fractions of organic compounds (~50%) and ECa (~30%) in the fine particulate matter (PM1). Moreover, substantial fractions of externally mixed weakly CCN-active particles were observed at low supersaturation (S = 0.07%), which can be explained by the presence of freshly emitted soot particles with very low hygroscopicity (κ<0.1). Particles in stagnant air from the industrialized region south of Beijing (aged regional pollution) were on average larger and more hygroscopic, which is consistent with enhanced mass fractions (~60%) of soluble inorganic ions (mostly sulfate, ammonium, and nitrate). Accordingly, the number concentration of CCN in aged air from the megacity region was higher than in fresh city outflow ((2.5–9.9) × 103 cm−3 vs. (0.4–8.3) × 103 cm−3) although the total aerosol particle number concentration was lower (1.2 × 104 cm−3 vs. 2.3 × 104 cm−3). A comparison with related studies suggests that the fresh outflow from Chinese urban centers generally may contain more, but smaller and less hygroscopic aerosol particles and thus fewer CCN than the aged outflow from megacity regions.

scholarly journals Measured and modelled cloud condensation nuclei number concentration at the high alpine site Jungfraujoch

2010 ◽  
Vol 10 (16) ◽  
pp. 7891-7906 ◽  
Author(s):  
Z. Jurányi ◽  
M. Gysel ◽  
E. Weingartner ◽  
P. F. DeCarlo ◽  
L. Kammermann ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Hydrological Cycle ◽  
Cloud Condensation Nuclei ◽  
Sensitivity Study ◽  
Research Station ◽  
Condensation Nuclei ◽  
Composition Data ◽  
Particle Mobility ◽  
Kohler Theory ◽  
Highly Correlated

Abstract. Atmospheric aerosol particles are able to act as cloud condensation nuclei (CCN) and are therefore important for the climate and the hydrological cycle, but their properties are not fully understood. Total CCN number concentrations at 10 different supersaturations in the range of SS=0.12–1.18% were measured in May 2008 at the remote high alpine research station, Jungfraujoch, Switzerland (3580 m a.s.l.). In this paper, we present a closure study between measured and predicted CCN number concentrations. CCN predictions were done using dry number size distribution (scanning particle mobility sizer, SMPS) and bulk chemical composition data (aerosol mass spectrometer, AMS, and multi-angle absorption photometer, MAAP) in a simplified Köhler theory. The predicted and the measured CCN number concentrations agree very well and are highly correlated. A sensitivity study showed that the temporal variability of the chemical composition at the Jungfraujoch can be neglected for a reliable CCN prediction, whereas it is important to know the mean chemical composition. The exact bias introduced by using a too low or too high hygroscopicity parameter for CCN prediction was further quantified and shown to be substantial for the lowest supersaturation. Despite the high average organic mass fraction (~45%) in the fine mode, there was no indication that the surface tension was substantially reduced at the point of CCN activation. A comparison between hygroscopicity tandem differential mobility analyzer (HTDMA), AMS/MAAP, and CCN derived κ values showed that HTDMA measurements can be used to determine particle hygroscopicity required for CCN predictions if no suitable chemical composition data are available.

scholarly journals Cloud activation properties of aerosol particles in a continental Central European urban environment

2021 ◽  
Vol 21 (14) ◽  
pp. 11289-11302
Author(s):  
Imre Salma ◽  
Wanda Thén ◽  
Máté Vörösmarty ◽  
András Zénó Gyöngyösi
Keyword(s):  
Chemical Composition ◽  
Particle Number ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Number Concentration ◽  
Urban Aerosol ◽  
Condensation Nuclei ◽  
Frequency Distributions ◽  
Remote Locations ◽  
Cloud Activation

Abstract. Collocated measurements using a condensation particle counter, differential mobility particle sizer and cloud condensation nuclei counter were realised in parallel in central Budapest from 15 April 2019 to 14 April 2020 to gain insight into the cloud activation properties of urban aerosol particles. The median total particle number concentration was 10.1 × 103 cm−3. The median concentrations of cloud condensation nuclei (CCN) at water vapour supersaturation (S) values of 0.1 %, 0.2 %, 0.3 %, 0.5 % and 1.0 % were 0.59, 1.09, 1.39, 1.80 and 2.5 × 103 cm−3, respectively. The CCN concentrations represented 7–27 % of all particles. The CCN concentrations were considerably larger but the activation fractions were systematically substantially smaller than observed in regional or remote locations. The effective critical dry particle diameters (dc,eff) were derived utilising the CCN concentrations and particle number size distributions. Their median values at the five supersaturation values considered were 207, 149, 126, 105 and 80 nm, respectively; all of these diameters were positioned within the accumulation mode of the typical particle number size distribution. Their frequency distributions revealed a single peak for which the geometric standard deviation increased monotonically with S. This broadening indicated high time variability in the activating properties of smaller particles. The frequency distributions also showed fine structure, with several compositional elements that seemed to reveal a consistent or monotonical tendency with S. The relationships between the critical S and dc,eff suggest that urban aerosol particles in Budapest with diameters larger than approximately 130 nm showed similar hydroscopicity to corresponding continental aerosol particles, whereas smaller particles in Budapest were less hygroscopic than corresponding continental aerosol particles. Only modest seasonal cycling in CCN concentrations and activation fractions was seen, and only for large S values. This cycling likely reflects changes in the number concentration, chemical composition and mixing state of the particles. The seasonal dependencies of dc,eff were featureless, indicating that the droplet activation properties of the urban particles remained more or less the same throughout the year. This is again different from what is seen in non-urban locations. Hygroscopicity parameters (κ values) were computed without determining the time-dependent chemical composition of the particles. The median values for κ were 0.15, 0.10, 0.07, 0.04 and 0.02, respectively, at the five supersaturation values considered. The averages suggested that the larger particles were considerably more hygroscopic than the smaller particles. We found that the κ values for the urban aerosol were substantially smaller than those previously reported for aerosols in regional or remote locations. All of these characteristics can be linked to the specific source composition of particles in cities. The relatively large variability in the hygroscopicity parameters for a given S emphasises that the individual values represent the CCN population in ambient air while the average hygroscopicity parameter mainly corresponds to particles with sizes close to the effective critical dry particle diameter.

Impacts of Nucleating Aerosol on Florida Storms. Part I: Mesoscale Simulations

2006 ◽  
Vol 63 (7) ◽  
pp. 1752-1775 ◽  
Author(s):  
Susan C. van den Heever ◽  
Gustavo G. Carrió ◽  
William R. Cotton ◽  
Paul J. DeMott ◽  
Anthony J. Prenni
Keyword(s):  
Hydrological Cycle ◽  
Cloud Condensation Nuclei ◽  
Supercooled Liquid ◽  
Atmospheric Modeling ◽  
Saharan Dust ◽  
Regional Study ◽  
Surface Precipitation ◽  
Convective Storms ◽  
Mixing Ratios ◽  
High Concentrations

Abstract Toward the end of the Cirrus Regional Study of Tropical Anvils and Cirrus Layer–Florida Area Cirrus Experiment (CRYSTAL–FACE) field campaign held during July 2002, high concentrations of Saharan dust, which can serve as cloud condensation nuclei (CCN), giant CCN (GCCN), and ice-forming nuclei (IFN) were observed over the peninsula of Florida. To investigate the impacts of enhanced aerosol concentrations on the characteristics of convective storms and their subsequent anvil development, sensitivity tests are conducted using the Regional Atmospheric Modeling System (RAMS) model, in which the initialization profiles of CCN, GCCN, and IFN concentrations are varied. These variations are found to have significant effects on the storm dynamics and microphysical processes, as well as on the surface precipitation. Updrafts are consistently stronger as the aerosol concentrations are increased. The anvils cover a smaller area but are better organized and have larger condensate mixing ratio maxima in the cases with greater aerosol concentrations. Cloud water mass tends to increase with increasing aerosol concentrations, with enhanced GCCN concentrations having the most significant influence. Increasing either the GCCN or IFN concentrations produces the most rainfall at the surface whereas enhanced CCN concentrations reduce surface rainfall. Higher IFN concentrations produce ice at warmer temperatures and deeper anvils, but simultaneously increasing the concentrations of CCN and GCCN leads to more supercooled liquid water available for freezing and greater ice mixing ratios. Graupel mixing ratios decrease and hail mixing ratios increase with increasing aerosol concentrations. Higher concentrations of GCCN and IFN result in greater accumulated surface precipitation initially. By the end of the simulation period, however, the accumulated precipitation is the greatest for the case in which the aerosol concentrations are lowest. Such changes in the dynamical and microphysical characteristics of convective storms as a result of the variations in aerosol concentrations have potential climate consequences, both through cloud radiative effects and the hydrological cycle. The impacts of varying CCN, GCCN, and IFN concentrations on the anvils will be discussed more fully in Part II.

scholarly journals Remote sensing the vertical profile of cloud droplet effective radius, thermodynamic phase, and temperature

2011 ◽  
Vol 11 (18) ◽  
pp. 9485-9501 ◽  
Author(s):  
J. V. Martins ◽  
A. Marshak ◽  
L. A. Remer ◽  
D. Rosenfeld ◽  
Y. J. Kaufman ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Energy Balance ◽  
Brightness Temperature ◽  
Vertical Profile ◽  
Water Cycle ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Cloud Microphysics ◽  
Condensation Nuclei ◽  
Thermodynamic Phase

Abstract. Cloud-aerosol interaction is a key issue in the climate system, affecting the water cycle, the weather, and the total energy balance including the spatial and temporal distribution of latent heat release. Information on the vertical distribution of cloud droplet microphysics and thermodynamic phase as a function of temperature or height, can be correlated with details of the aerosol field to provide insight on how these particles are affecting cloud properties and their consequences to cloud lifetime, precipitation, water cycle, and general energy balance. Unfortunately, today's experimental methods still lack the observational tools that can characterize the true evolution of the cloud microphysical, spatial and temporal structure in the cloud droplet scale, and then link these characteristics to environmental factors and properties of the cloud condensation nuclei. Here we propose and demonstrate a new experimental approach (the cloud scanner instrument) that provides the microphysical information missed in current experiments and remote sensing options. Cloud scanner measurements can be performed from aircraft, ground, or satellite by scanning the side of the clouds from the base to the top, providing us with the unique opportunity of obtaining snapshots of the cloud droplet microphysical and thermodynamic states as a function of height and brightness temperature in clouds at several development stages. The brightness temperature profile of the cloud side can be directly associated with the thermodynamic phase of the droplets to provide information on the glaciation temperature as a function of different ambient conditions, aerosol concentration, and type. An aircraft prototype of the cloud scanner was built and flew in a field campaign in Brazil. The CLAIM-3D (3-Dimensional Cloud Aerosol Interaction Mission) satellite concept proposed here combines several techniques to simultaneously measure the vertical profile of cloud microphysics, thermodynamic phase, brightness temperature, and aerosol amount and type in the neighborhood of the clouds. The wide wavelength range, and the use of multi-angle polarization measurements proposed for this mission allow us to estimate the availability and characteristics of aerosol particles acting as cloud condensation nuclei, and their effects on the cloud microphysical structure. These results can provide unprecedented details on the response of cloud droplet microphysics to natural and anthropogenic aerosols in the size scale where the interaction really happens.

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.

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