Seasonal variation of CCN concentrations and aerosol activation properties in boreal forest
Seasonal variation of CCN concentrations and aerosol activation properties in boreal forest
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DOI：
10.5194/acp-11-13269-2011
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发表时间：
2010-11
影响因子：
6.3
通讯作者：
S. Sihto;J. Mikkilä;J. Vanhanen;M. Ehn;L. Liao;K. Lehtipalo;P. Aalto;J. Duplissy;T. Petäjä;V. Kerminen;M. Boy;M. Kulmala
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作者：
S. Sihto;J. Mikkilä;J. Vanhanen;M. Ehn;L. Liao;K. Lehtipalo;P. Aalto;J. Duplissy;T. Petäjä;V. Kerminen;M. Boy;M. Kulmala
抽象。作为EUCAARI活动的一部分，在芬兰Hyytiala的SMEAR II站使用云凝结核计数器和HTDMA（吸湿性串联微分迁移率分析仪）测量了云凝结核浓度的年周期和云滴激活的临界直径作为过饱和度的函数。CCN活化的临界直径根据（i）测量的CCN浓度和粒度分布数据，以及（ii）通过应用κ-科勒理论的吸湿生长因子进行估计，在两种情况下均假设内部混合气溶胶。用这两种方法得到的临界直径吻合得很好。研究了新粒子形成对云凝结核浓度和临界直径日变化的影响。观察到新颗粒的形成使CCN浓度增加70- 110%，这取决于过饱和水平。从吸湿性测量确定的κ-参数的平均值为κ = 0.18，并且它很好地预测了Hyytiala北方森林条件下的CCN活化。推导出的临界直径和κ参数证实了其他方法的早期发现，即Hyytiala中CCN尺寸的气溶胶颗粒大多是有机的，但也含有更多的吸湿性，可能是无机盐，如硫酸铵，使颗粒比纯二次有机气溶胶更具CCN活性。
Abstract. As a part of EUCAARI activities, the annual cycle of cloud condensation nuclei (CCN) concentrations and critical diameter for cloud droplet activation as a function of supersaturation were measured using a CCN counter and a HTDMA (hygroscopicity tandem differential mobility analyzer) at SMEAR II station, Hyytiala, Finland. The critical diameters for CCN activation were estimated from (i) the measured CCN concentration and particle size distribution data, and (ii) the hygroscopic growth factors by applying κ-Kohler theory, in both cases assuming an internally mixed aerosol. The critical diameters derived by these two methods were in good agreement with each other. The effect of new particle formation on the diurnal variation of CCN concentration and critical diameters was studied. New particle formation was observed to increase the CCN concentrations by 70–110%, depending on the supersaturation level. The average value for the κ-parameter determined from hygroscopicity measurements was κ = 0.18 and it predicted well the CCN activation in boreal forest conditions in Hyytiala. The derived critical diameters and κ-parameter confirm earlier findings with other methods, that aerosol particles at CCN sizes in Hyytiala are mostly organic, but contain also more hygrosopic, probably inorganic salts like ammonium sulphate, making the particles more CCN active than pure secondary organic aerosol.