Calibration and measurement uncertainties of a continuous-flow cloud condensation nuclei counter (DMT-CCNC): CCN activation of ammonium sulfate and sodium chloride aerosol particles in theory and experiment
Calibration and measurement uncertainties of a continuous-flow cloud condensation nuclei counter (DMT-CCNC): CCN activation of ammonium sulfate and sodium chloride aerosol particles in theory and experiment
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DOI：
10.5194/acp-8-1153-2008
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发表时间：
2007-06
影响因子：
6.3
通讯作者：
D. Rose;S. S. Gunthe-S.;E. Mikhailov;G. Frank;U. Dusek;M. Andreae;U. Pöschl
中科院分区：
文献类型：
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作者：
D. Rose;S. S. Gunthe-S.;E. Mikhailov;G. Frank;U. Dusek;M. Andreae;U. Pöschl
通过对直径为20-220 nm的硫酸铵和氯化钠气溶胶粒子的模型计算和定标实验，对用Droplet Measurement Technologies（DMT-CCNC）的连续流热梯度云凝结核计数器测量云凝结核（CCN）的实验和理论不确定度进行了评估。在实验室和现场测量活动中进行了实验，涵盖了广泛的仪器操作条件（650-1020 hPa压力，293-303 K入口温度，4-34 K m-1温度梯度，0.5-1.0 L min-1流速）。对于每组条件，有效水蒸气过饱和度（Seff，0.05-1.4%）由测量的CCN活化光谱（干颗粒活化直径）和科勒模型计算确定。在稳定的实验室条件下，获得了较高的测量精度，Seff的相对标准偏差低至± 1%。在现场测量过程中，相对偏差增加到± 5%左右，这主要是由于CCNC塔顶温度随环境温度的变化。将观察到的Seff对温度、压力和流速的依赖性与Lance等人（2006年）的CCNC流动模型进行比较。在高Seff时，流动模型与实验结果的相对偏差大多小于10%，而在Seff ≤0.1%时，相对偏差超过40%。因此，高精度CCN测量需要仔细的实验校准-特别是在低S eff下。对CCN研究中常用的各种科勒模型和热力学参数化方法进行了综合比较和不确定性分析，结果表明，不同方法之间的相对偏差对（NH 4）2SO 4和NaCl分别高达25%和12%。这些偏差主要是由于对两种盐水溶液中水活度的参数化方法不同造成的。为了确保结果的可比性，我们建议CCN研究应始终准确报告使用的科勒模型方程和参数。如果气溶胶无机物模型（AIM）可以作为（NH 4）2SO 4和NaCl高稀释溶液水活度数据的准确来源，则只有基于AIM或产生类似结果的科勒模型才能用于涉及这些盐的CCN研究，并以高精度为目标。用（NH 4）2SO 4和NaCl气溶胶进行的实验表明，粒子的产生条件和NaCl粒子的形状和微结构是它们在CCN活化实验中应用的关键（相对偏差达18%）。
Experimental and theoretical uncertainties in the measurement of cloud condensation nuclei (CCN) with a continuous-flow thermal-gradient CCN counter from Droplet Measurement Technologies (DMT-CCNC) have been assessed by model calculations and calibration experiments with ammonium sulfate and sodium chloride aerosol particles in the diameter range of 20–220 nm. Experiments have been performed in the laboratory and during field measurement campaigns, covering a wide range of instrument operating conditions (650–1020 hPa pressure, 293–303 K inlet temperature, 4–34 K m −1 temperature gradient, 0.5–1.0 L min −1 flow rate). For each set of conditions, the effective water vapor supersaturation ( S eff , 0.05–1.4%) was determined from the measured CCN activation spectra (dry particle activation diameters) and Kohler model calculations. High measurement precision was achieved under stable laboratory conditions, where the relative standard deviations of S eff were as low as ±1%. During field measurements, however, the relative deviations increased to about ±5%, which can be mostly attributed to variations of the CCNC column top temperature with ambient temperature. The observed dependence of S eff on temperature, pressure, and flow rate was compared to the CCNC flow model of Lance et al. (2006). At high S eff the relative deviations between flow model and experimental results were mostly less than 10%, but at S eff ≤0.1% they exceeded 40%. Thus, careful experimental calibration is required for high-accuracy CCN measurements – especially at low S eff . A comprehensive comparison and uncertainty analysis of the various Kohler models and thermodynamic parameterizations commonly used in CCN studies showed that the relative deviations between different approaches are as high as 25% for (NH 4 ) 2 SO 4 and 12% for NaCl. The deviations were mostly caused by the different parameterizations for the activity of water in aqueous solutions of the two salts. To ensure comparability of results, we suggest that CCN studies should always report exactly which Kohler model equations and parameters were used. Provided that the Aerosol Inorganics Model (AIM) can be regarded as an accurate source of water activity data for highly dilute solutions of (NH 4 ) 2 SO 4 and NaCl, only Kohler models that are based on the AIM or yield similar results should be used in CCN studies involving these salts and aiming at high accuracy. Experiments with (NH 4 ) 2 SO 4 and NaCl aerosols showed that the conditions of particle generation and the shape and microstructure of NaCl particles are critical for their application in CCN activation experiments (relative deviations up to 18%).