Cloud condensation nuclei (CCN) from fresh and aged air pollution in the megacity region of Beijing
Cloud condensation nuclei (CCN) from fresh and aged air pollution in the megacity region of Beijing
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DOI：
10.5194/acp-11-11023-2011
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发表时间：
2011-01-01
影响因子：
6.3
通讯作者：
Poeschl, U.
中科院分区：
文献类型：
--
作者：
Gunthe, S. S.;Rose, D.;Poeschl, U.
大气气溶胶粒子作为云凝结核（CCN）是水文循环和气候的关键要素。在CAREBeijing-2006活动期间，CCN的特性在中国北京南部的一个区域站点进行了测量和表征。在S = 0.07%至0.86%的过饱和范围内，记录的尺寸分辨CCN效率光谱的平均活化直径在190 nm至45 nm之间。相应的有效吸湿参数kappa表现出较强的粒径依赖性，范围从艾特肯粒径范围的0.25到累积粒径范围的0.45。运动平均值（kappa = 0.3+/-0.1）与其他人口稠密的大陆地区的观测值和模型相似。从CCN测量得到的吸湿性参数与气溶胶质谱仪（AMS）记录的化学成分数据以及表观元素和有机碳（EC和OC）的热光学测量结果一致。采用近似于0.1的简单混合规则kappa(p)，可以将CCN吸湿性及其大小依赖关系参数化为AMS有机和无机质量分数(f（org), f(inorg)）的函数。F (org) + 0.7。f (inorg)。当测量到的空气团来自北方并快速经过北京中心（新鲜城市污染）时，平均颗粒吸湿性降低（kappa = 0.2+/-0.1），这与细颗粒物（PM1）中有机化合物（约50%）和EC（约30%）的质量分数增加一致。此外，在低过饱和度（S = 0.07%）下，观察到大量外部混合的弱ccn活性颗粒，这可以解释为新排放的吸湿性非常低的煤烟颗粒（kappa < 0.1）的存在。京南工业化地区停滞空气中颗粒平均较大，吸湿性较强，这与可溶性无机离子（主要为硫酸盐、铵和硝酸盐）的质量分数增加（约60%）一致。因此，尽管总气溶胶粒子数浓度较低(1.2 × 10(4) cm（-3）比2.3 × 10(4) cm(-3))，但特大城市地区老化空气中CCN数浓度高于新鲜城市流出空气(（2.5-9.9）× 10(3) cm(-3) vs （0.4-8.3） × 10（3) cm(-3), S = 0.07- 0.86%）。与相关研究的比较表明，中国城市中心的新鲜流出物通常可能含有更多、但更小、更少的吸湿性气溶胶颗粒，因此CCN低于特大城市地区的老流出物。
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 (kappa) exhibited a strong size dependence ranging from similar to 0.25 in the Aitken size range to similar to 0.45 in the accumulation size range. The campaign average value (kappa = 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 (f(org), f(inorg)) using the simple mixing rule kappa(p) approximate to 0.1 . f(org) + 0.7 . f(inorg).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 (kappa = 0.2+/-0.1), which is consistent with enhanced mass fractions of organic compounds (similar to 50 %) and EC (similar to 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 (kappa < 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 (similar to 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) x 10(3) cm(-3) vs. (0.4-8.3) x 10(3) cm(-3) for S = 0.07-0.86 %) although the total aerosol particle number concentration was lower (1.2 x 10(4) cm(-3) vs. 2.3 x 10(4) 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.