气溶胶可作为云凝结核（CCN）影响云的微物理特性，进而改变全球能量辐射平衡而产生间接气候效应，是气候变化评估中最不确定的因子。解决这一问题的关键之一需弄清气溶胶转化为CCN的机制，了解气溶胶的吸湿和核化能力及制约这些能力的理化特性（人类密集区其状况更复杂）。本研究拟在北京开展气溶胶的多参数综合强化观测，（1）获得气溶胶粒径谱、化学组成、吸湿性、挥发性（混合态）及CCN谱的区域特征及变化规律；（2）研究气溶胶理化特性在形成CCN过程中的作用和贡献，重点研究粒子老化和混合态的影响；（3）基于寇拉理论模型，设计多方案（考虑分粒径段有机物的影响）估算CCN数浓度；通过闭合试验，揭示大气细粒子转化为CCN的机理；（4）结合前期华北区域已有观测资料，阐明代表高气溶胶背景浓度区域其理化特性与核化效率的定量关系，为建立适用于我国的CCN参数化方案奠定基础，旨在降低模式估算气溶胶间接气候效应的不确定性。

Aerosol particles can serve as cloud condensation nuclei (CCN) to vary the cloud physical and optical properties and further change global radiation balance. This is aerosol indirect effect, which has been one of the largest uncertainties in the quantification of the aerosol effects on climate. To reduce the uncertainty of aerosol indirect effects on the radiative balance of the atmosphere, it is important to gain a good knowledge of the ability of aerosol particles to form CCN at the typical supersaturations found in the atmosphere as well as the physiochemical properties of aerosol particles. Particularly, in urban/polluted areas, the situation is more complex. Intensive field campaigns will be performed in different seasons in urban Beijing. Also, in combination with the comprehensive observations of aerosol, CCN and atmospheric parameters from our previous intensive field campaigns in China North Plain, this study aims to (1) obtain aerosol size distribution, aerosol chemical composition, aerosol volatility, mixing state and its hygroscopic growth and CCN activity under different polluted conditions; (2) characterize the particle physical and chemical parameters impacting on CCN activation (focus on the influence of aerosol aging and mixing state on the CCN activity); (3) estimate CCN number concentrations and understand aerosol-CCN conversion mechanism based on Koehler theory and CCN closure test; (4) investigate the relationship between aerosol properties and activation efficiency under polluted and background conditions. Following these investigations, we will obtain comprehensive datasets, new and improved knowledge, most importantly, the fundamental understanding as to how various types of aerosols affect the CCN activity. All of the data and knowledge obtained from this project will play a significant role in providing scientific support for CCN parameterization in climate models.