scholarly journals Size-resolved and bulk activation properties of aerosols in the North China Plain

2011 ◽  
Vol 11 (8) ◽  
pp. 3835-3846 ◽  
Author(s):  
Z. Z. Deng ◽  
C. S. Zhao ◽  
N. Ma ◽  
P. F. Liu ◽  
L. Ran ◽  
...  
Keyword(s):  
Size Distribution ◽  
North China Plain ◽  
North China ◽  
Cloud Condensation Nuclei ◽  
Number Concentration ◽  
Anthropogenic Aerosol ◽  
Number Size Distribution ◽  
The North ◽  
The North China Plain ◽  
Activation Ratio

Abstract. Size-resolved and bulk activation properties of aerosols were measured at a regional/suburban site in the North China Plain (NCP), which is occasionally heavily polluted by anthropogenic aerosol particles and gases. A Cloud Condensation Nuclei (CCN) closure study is conducted with bulk CCN number concentration (NCCN) and calculated CCN number concentration based on the aerosol number size distribution and size-resolved activation properties. The observed CCN number concentration (NCCN-obs) are higher than those observed in other locations than China, with average NCCN-obs of roughly 2000, 3000, 6000, 10 000 and 13 000 cm−3 at supersaturations of 0.056, 0.083, 0.17, 0.35 and 0.70%, respectively. An inferred critical dry diameter (Dm) is calculated based on the NCCN-obs and aerosol number size distribution assuming homogeneous chemical composition. The inferred cut-off diameters are in the ranges of 190–280, 160–260, 95–180, 65–120 and 50–100 nm at supersaturations of 0.056, 0.083, 0.17, 0.35 and 0.7%, with their mean values 230.1, 198.4, 128.4, 86.4 and 69.2 nm, respectively. Size-resolved activation measurements show that most of the 300 nm particles are activated at the investigated supersaturations, while almost no particles of 30 nm are activated even at the highest supersaturation of 0.72%. The activation ratio increases with increasing supersaturation and particle size. The slopes of the activation curves for ambient aerosols are not as steep as those observed in calibrations with ammonium sulfate suggesting that the observed aerosols is an external mixture of more hygroscopic and hydrophobic particles. The calculated CCN number concentrations (NCCN-calc) based on the size-resolved activation ratio and aerosol number size distribution correlate well with the NCCN-obs, and show an average overestimation of 19%. Sensitivity studies of the CCN closure show that the NCCN at each supersaturation is well predicted with the campaign average of size-resolved activation curves. These results indicate that the aerosol number size distribution is critical in the prediction of possible CCN. The CCN number concentration can be reliably estimated using time-averaged, size-resolved activation efficiencies without accounting for the temporal variations.

scholarly journals Size-resolved and bulk activation properties of aerosols in the North China plain: the importance of aerosol size distribution in the prediction of CCN number concentration

2011 ◽  
Vol 11 (1) ◽  
pp. 1333-1366 ◽  
Author(s):  
Z. Z. Deng ◽  
C. S. Zhao ◽  
N. Ma ◽  
P. F. Liu ◽  
L. Ran ◽  
...  
Keyword(s):  
Size Distribution ◽  
North China Plain ◽  
North China ◽  
Number Concentration ◽  
Aerosol Size Distribution ◽  
Number Size Distribution ◽  
The North ◽  
The North China Plain ◽  
Wide Range ◽  
Activation Ratio

Abstract. Size-resolved and bulk activation properties of aerosols were measured at a regional/suburban site in the North China Plain (NCP), which is occasionally heavily polluted by anthropogenic aerosol particles and gases. A CCN (Cloud Condensation Nuclei) closure study is conducted with bulk CCN number concentration (NCCN) and calculated NCCN based on the aerosol number size distribution and size-resolved activation properties. The observed NCCN are higher than those observed in other locations than China, with average NCCN of roughly 2000, 3000, 6000, 10 000 and 13 000 cm−3 at supersaturations of 0.056, 0.083, 0.17, 0.35 and 0.70%, respectively. An inferred critical dry diameter (Dm) is calculated based on the measured NCCN and aerosol number size distribution assuming homogeneous chemical composition. This inferred cut off diameter varies in a wide range, indicating that it is impossible to predict NCCN with a fixed critical diameter. Size-resolved activation measurements show that most of the 300 nm particles are activated at the investigated supersaturations, while almost no particles of 30 nm are activated even at the highest supersaturation of 0.72%. The activation ratio increases with increasing supersaturation and particle size. The slopes of the activation curves for ambient aerosols are not as steep as those observed in calibrations with ammonium sulfate suggesting that the observed aerosols is an external mixture of more hygroscopic and hydrophobic particles. This conclusion is confirmed by hygroscopicity measurements performed during two intensive field studies in 2009. The calculated NCCN based on the size-resolved activation ratio and aerosol number size distribution correlate well with the measured NCCN, and show an average overestimation of 19%. Sensitivity studies of the CCN closure show that the NCCN for each supersaturation is well predicted with the campaign average of size-resolved activation curves. These results indicate that the aerosol number size distribution is critical in the prediction of possible CCN. The NCCN can be estimated with average activation curve, along with a well described aerosol number size distribution.

scholarly journals A New Method for Calculating Number Concentrations of Cloud Condensation Nulcei Based on Measurements of A Three-wavelength Humidified Nephelometer System

2017 ◽  
Author(s):  
Jiangchuan Tao ◽  
Chunsheng Zhao ◽  
Ye Kuang ◽  
Gang Zhao ◽  
Chuanyang Shen ◽  
...  
Keyword(s):  
Light Scattering ◽  
North China Plain ◽  
North China ◽  
Cloud Condensation Nuclei ◽  
Number Concentration ◽  
New Method ◽  
Ambient Atmosphere ◽  
The North ◽  
The North China Plain ◽  
Direct Measurements

Abstract. The number concentration of cloud condensation nuclei (CCN) plays a fundamental role in cloud physics. Instrumentations of direct measurements of CCN number concentration (NCCN) based on chamber technology are complex and costly, thus a simple way for measuring NCCN is needed. In this study, a new method for NCCN calculation based on measurements of a three-wavelength humidified nephelometer system is proposed. A three-wavelength humidified nephelometer system can measure aerosol light scattering coefficient (σsp) at three wavelengths and the light scattering enhancement factor (fRH). The Angstrom exponent (Å) inferred from σsp at three wavelengths provides information on mean predominate aerosol size and hygroscopicity parameter (κ) can be calculated from the combination of fRH and Å. Given this, a look-up table that involves σsp, κ and Å is established to predict NCCN. This method is validated with direct measurements of NCCN using a CCN counter on the North China Plain. Results show that relative deviations between calculated NCCN and measured NCCN are within 30 % and confirm the robustness of this method. This method enables simpler NCCN measurements because the humidified nephelometer system is easily operated and stable. Compared with the method of CCN counter, another advantage of this newly proposed method is that it can obtain NCCN at lower supersaturations in the ambient atmosphere.

scholarly journals A closure study of cloud condensation nuclei in the North China Plain using droplet kinetic condensational growth model

2011 ◽  
Vol 11 (10) ◽  
pp. 28969-29002
Author(s):  
F. Yang ◽  
H. Xue ◽  
Z. Deng ◽  
C. Zhao ◽  
Q. Zhang
Keyword(s):  
Kinetic Model ◽  
Growth Model ◽  
Equilibrium Model ◽  
North China Plain ◽  
North China ◽  
Cloud Condensation Nuclei ◽  
The North ◽  
The North China Plain ◽  
Time Period ◽  
Condensational Growth

Abstract. Aerosol size distribution and cloud condensation nuclei (CCN) number concentration were measured in the North China Plain from 31 December 2009 to 20 January 2010. CCN closure study was performed using these data and droplet kinetic condensational growth model. The calculated CCN concentration with the assumption of pure ammonium sulfate aerosol is 40–140% higher than that observed for the supersaturations in this study. Sensitivity test on aerosol solubility and mixing state indicates that 60–70% mass fraction of ammonium sulfate externally mixed with insoluble material can lead to the calculated CCN concentrations fitting the observations best in the North China Plain during the time period of the field observations, suggesting that a relatively simple scheme may be used for CCN prediction in climate models for this region. Finally, we compare the calculated CCN concentrations from the kinetic condensational growth model and the equilibrium model. The kinetic condensational growth model can simulate droplet growth in a time period under a certain supersaturation, while the equilibrium model only predicts whether a certain aerosol can be activated as CCN under that supersaturation. The CCN concentration calculated with the kinetic model is higher than that with the equilibrium model at supersaturations of 0.056% and 0.083%, because some particles that are not activated from the equilibrium point of view can grow large enough to be considered as CCN in the kinetic model. While at a supersaturation of 0.17%, CCN concentration calculated with the kinetic model is lower than that with the equilibrium model, due to the limitation of droplet kinetic growth. The calculated CCN concentrations using the kinetic model and the equilibrium model are the same at supersaturations of 0.35% and 0.70%.

scholarly journals Characteristics of regional new particle formation in urban and regional background environments in the North China Plain

2013 ◽  
Vol 13 (24) ◽  
pp. 12495-12506 ◽  
Author(s):  
Z. B. Wang ◽  
M. Hu ◽  
J. Y. Sun ◽  
Z. J. Wu ◽  
D. L. Yue ◽  
...  
Keyword(s):  
Urban Environment ◽  
North China Plain ◽  
North China ◽  
Particle Formation ◽  
Number Concentration ◽  
Particle Nucleation ◽  
New Particle Formation ◽  
Aerosol Formation ◽  
The North ◽  
The North China Plain

Abstract. Long-term measurements of particle number size distributions were carried out both at an urban background site (Peking University, PKU) and a regional Global Atmospheric Watch station (Shangdianzi, SDZ) from March to November in 2008. In total, 52 new particle formation (NPF) events were observed simultaneously at both sites, indicating that this is a regional phenomenon in the North China Plain. On average, the mean condensation sink value before the nucleation events started was 0.025 s−1 in the urban environment, which was 1.6 times higher than that at regional site. However, higher particle formation and growth rates were observed at PKU (10.8 cm−3 s−1 and 5.2 nm h−1) compared with those at SDZ (4.9 cm−3 s−1 and 4.0 nm h−1). These results implied that precursors were much more abundant in the polluted urban environment. Different from the observations in cleaner environments, the background conditions of the observed particle homogeneous nucleation events in the North China Plain could be characterized as the co-existing of a stronger source of precursor gases and a higher condensational sink of pre-existing aerosol particles. Secondary aerosol formation following nucleation events results in an increase of particle mass concentration, particle light scattering coefficient, and cloud condensation nuclei (CCN) number concentration, with consequences on visibility, radiative effects, and air quality. Typical regional NPF events with significant particle nucleation rates and subsequent particle growth over a sufficiently long time period at both sites were chosen to investigate the influence of NPF on the number concentration of "potential" CCN. As a result, the NPF and the subsequent condensable growth increased the CCN number concentration in the North China Plain by factors in the range from 5.6 to 8.7. Moreover, the potential contribution of anthropogenic emissions to the CCN number concentration was more than 50%, to which more attention should be drawn in regional and global climate modeling, especially in the polluted urban areas.

scholarly journals Variation of CCN activity during new particle formation events in the North China Plain

2016 ◽  
Author(s):  
N. Ma ◽  
C. S. Zhao ◽  
J. C. Tao ◽  
Z. J. Wu ◽  
S. Kecorius ◽  
...  
Keyword(s):  
North China Plain ◽  
North China ◽  
Critical Diameter ◽  
Particle Formation ◽  
New Particle Formation ◽  
The North ◽  
The North China Plain ◽  
Ratio Curve ◽  
Activation Ratio ◽  
Ccn Activity

Abstract. The aim of this investigation was to obtain a better understanding of the variability of the cloud condensation nuclei (CCN) activity during new particle formation (NPF) events in an anthropogenically polluted atmosphere of the North China Plain (NCP). We investigated the size-resolved activation ratio as well as particle number size distribution, hygroscopicity and chemical composition during an intensive field experiment at a regional atmospheric observatory at Xianghe. Interestingly, two types of NPF events were found, in which the growth of the newly formed particles is dominated by either sulfate or organic matters. The particle CCN activity therefore significantly differs in those NPF events, indicating that it might be difficult to find a simple parameterization of particle CCN activity during NPF events over the NCP. For an accurate estimation of the potential CCN number concentration (NCCN) during NPF events, the variation of CCN activity has to be taken into account. Considering that a fixed activation ratio curve or critical diameter are usually used to calculate NCCN, the influence of the variation of particle CCN activity on the calculation of NCCN during NPF events was evaluated based on these two parameterizations. It was found that NCCN might be underestimated by up to 30 % if a fix activation ratio curve (representative of the region and season) is used in the calculation; and might be underestimated by up to 50 % if a fix critical diameter (representative of the region and season) is used. Therefore, we suggest not using a fixed critical diameter in the prediction of NCCN in NPF seasons. If real-time CCN activity data is not available, using a proper fixed activation ratio curve can be a compromising choice.

scholarly journals Variation of CCN activity during new particle formation events in the North China Plain

2016 ◽  
Vol 16 (13) ◽  
pp. 8593-8607 ◽  
Author(s):  
Nan Ma ◽  
Chunsheng Zhao ◽  
Jiangchuan Tao ◽  
Zhijun Wu ◽  
Simonas Kecorius ◽  
...  
Keyword(s):  
North China Plain ◽  
North China ◽  
Critical Diameter ◽  
Particle Formation ◽  
New Particle Formation ◽  
The North ◽  
The North China Plain ◽  
Ratio Curve ◽  
Activation Ratio ◽  
Ccn Activity

Abstract. The aim of this investigation was to obtain a better understanding of the variability of the cloud condensation nuclei (CCN) activity during new particle formation (NPF) events in an anthropogenically polluted atmosphere of the North China Plain (NCP). We investigated the size-resolved activation ratio as well as particle number size distribution, hygroscopicity, and volatility during a 4-week intensive field experiment in summertime at a regional atmospheric observatory in Xianghe. Interestingly, based on a case study, two types of NPF events were found, in which the newly formed particles exhibited either a higher or a lower hygroscopicity. Therefore, the CCN activity of newly formed particles in different NPF events was largely different, indicating that a simple parameterization of particle CCN activity during NPF events over the NCP might lead to poor estimates of CCN number concentration (NCCN). For a more accurate estimation of the potential NCCN during NPF events, the variation of CCN activity has to be taken into account. Considering that a fixed activation ratio curve or critical diameter are usually used to calculate NCCN, the influence of the variation of particle CCN activity on the calculation of NCCN during NPF events was evaluated based on the two parameterizations. It was found that NCCN might be underestimated by up to 30 % if a single activation ratio curve (representative of the region and season) were to be used in the calculation; and might be underestimated by up to 50 % if a fixed critical diameter (representative of the region and season) were used. Therefore, we suggest not using a fixed critical diameter in the prediction of NCCN in NPF. If real-time CCN activity data are not available, using a proper fixed activation ratio curve can be an alternative but compromised choice.

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