| 基于航测的云底气溶胶活化率与过饱和度估算 |
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| 引用本文： | 高茜,刘全,毕凯,王飞,盛久江,何晖,刘香娥.基于航测的云底气溶胶活化率与过饱和度估算[J].应用气象学报,2021,32(6):653-664. |
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| 作者姓名： | 高茜 刘全 毕凯 王飞 盛久江 何晖 刘香娥 |
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| 作者单位： | 1.北京市人工影响天气中心, 北京 100089 |
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| 摘 要： | 2016年11月13日在北京地区上空存在持续稳定的层状云天气背景下，利用飞机开展气溶胶粒径谱、化学组成、云滴谱等参量的垂直观测，研究该个例云底气溶胶的活化能力。结果表明:探测期间北京地区为轻度污染天气，地面气溶胶浓度(0.11~3 μm)达到4600 cm-3。云层高度为800~1200 m，云底气溶胶数浓度相对于近地面大幅度降低，有效粒径显著增大(0.3~0.6 μm)。同时，近地面气溶胶中疏水性的一次有机气溶胶贡献显著，而云底气溶胶中一次有机气溶胶的贡献大幅降低，无机组分和二次有机气溶胶的贡献明显增大，造成吸湿性参数κ由0.25(地面)增大至0.32(云底)。云中气溶胶和云滴的谱分布衔接较好，且两者的数浓度之和与云底气溶胶浓度一致，可分别代表未活化和已活化的粒子。基于云底气溶胶粒径谱和吸湿性参数计算得到不同过饱和比下云凝结核的活化率，通过与云中观测结果对比，反推得到云底过饱和度约为0.048%。
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| 关 键 词： | 水汽过饱和度 飞机观测 气溶胶理化性质 云滴谱 |
| 收稿时间： | 2021-07-28 |
Estimation of Aerosol Activation Ratio and Water Vapor Supersaturation at Cloud Base Using Aircraft Measurement |
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| Affiliation: | 1.Beijing Weather Modification Center, Beijing 1000892.State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 1000813.Key Laboratory of Atmospheric Chemistry of China Meteorological Administration, Beijing 1000814.Key Laboratory of Beijing for Cloud, Precipitation and Atmospheric Water Resources, Beijing 100089 |
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| Abstract: | The vertical evolution of aerosol physiochemical properties significantly influence the capacity of particle water uptake at different atmospheric levels, which are important for the estimation of direct and indirect radiative impacts of aerosol. However, as one of the most important environmental parameters during the formation of cloud or fog, water vapor supersaturation cannot be directly measured. An aircraft observation was carried out on 13 November 2016 with stable stratiform clouds covering Beijing area. The results of aircraft in-situ measured aerosol particle size distribution, chemical composition, cloud droplet spectrum, and vertical distribution of aerosol physicochemical properties and activation ability near the cloud base are analyzed. The results show that Beijing area is under polluted conditions during the flight detection with the surface aerosol concentration (0.11-3 μm) of 4600 cm-3. The height range of cloud layer is 800-1200 m. The number concentration of aerosols at the cloud base is greatly lower compared with the surface, and the effective diameter significantly increases from 0.3 μm to 0.6 μm. Aerosol composition varies drastically with altitudes. The hydrophobic primary organic aerosol (POA) has a significant contribution at surface, but sharply decreases at the cloud base. Meanwhile, the fraction of inorganic species and secondary organic aerosol (SOA) increase significantly from surface to cloud base, resulting in hygroscopic parameter (κ) increasing from 0.25 (ground) to 0.32 (cloud base). The number concentration size spectrum of cloud droplets and aerosols in the cloud can be well connected, which could be deemed as activated and un-activated particles respectively. Meanwhile, the sum of their number concentrations is approximately equal to the total aerosol concentration below the cloud, indicating aerosol particles below the cloud base has a dominant contribution to the cloud droplet formation near the cloud base by activation. Thereby, the actual activation ratio of aerosol particles serves as cloud condensation nuclei (CCN) in the measured cloud can be obtained. Combining with in-situ measured aerosol size distribution, chemical composition, and calculated hygroscopic parameter below the cloud base, the aerosol activation ratio under different supersaturation ratio can be derived. Estimated through the comparison of calculated activation rate and the measurement, the mean supersaturation near this stratiform cloud base is about 0.048%. It implies that the aerosol characteristics at surface may not represent that at upper levels, where the evolution in vertical direction should be considered in evaluating the contribution of surface emissions to cloud particle nucleation and their atmospheric lifetime. This supersaturation estimating method is mainly based on conventional measurement of aerosol and droplets, which has a potential value for further application on cloud analysis. |
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