中国超大城市综合实验:京、沪、穗气溶胶理化和吸湿特性

气溶胶对环境、气象和人体健康都有较大影响,这些影响与气溶胶理化特性(粒子尺度谱、化学组分、混合状态等)密切相关。为了深入研究气溶胶的环境和气候效应,发展了一套气溶胶在线综合观测系统。本文介绍了利用该系统在北京、上海、广州三个超大城市开展的综合观测实验结果。通过对比分析发现,广州气溶胶数浓度最高,其粒子尺度谱分布特征与北京特征相似,均以核模态为主,上海气溶胶数浓度则整体较低。对比三个超大城市的新粒子生成(New Particle Formation,NPF)特征发现,北京NPF的发生频率低于广州,主要由于北京地区大气中大粒径气溶胶更多,较高的碰并汇抑制了NPF的发生和发展。研究发现,观测期间北京和上海站点气溶胶的吸湿性强于广州,人为一次性排放气溶胶吸湿性较弱。气溶胶吸湿性日变化特征与人为活动、气溶胶老化程度密切相关。此外,三个超大城市中气溶胶光吸收系数的日变化特征存在明显差别,北京站点的气溶胶吸收系数呈现白天高、夜间低的特点,而广州站点气溶胶的吸收系数呈现相反的日变化趋势,这可能是由观测站周边的环境差异及大气边界层的变化特征差异造成的。

Physicochemical and hygroscopic properties of aerosols in Beijing,Shanghai and Guangzhou:a comprehensive experiment of Chinese megacities

Aerosols have great impacts on the environment,meteorology,and human health.These effects are closely related the physical and chemical properties of aerosols (particle size distribution,chemical composition,mixing state,etc.).In this paper,we develop an online,comprehensive aerosol observation system and report the results of comprehensive observation experiments of Beijing,Shanghai,and Guangzhou using this system to study aerosol environmental and climate effects.Through comparative analysis,it is found that Guangzhou has highest aerosol number concentration,but the pattern of its particle size distribution is similar to that of Beijing,both of which are dominated by smaller nuclear modes.However,the aerosol concentration in Shanghai is low in all modes.The comparison of new particle formation (NPF) in three megacities suggests that the occurrence frequency of NPF in Beijing is lower than that in Guangzhou,mainly due to more large-size aerosols in the atmosphere of Beijing,which inhibited the occurrence and development of NPF because of the higher coalescence sink.The results also show that aerosol hygroscopicity in Beijing and Shanghai is stronger than that in Guangzhou.Anthropogenic emissions could significantly weaken aerosol hygroscopicity in megacities,with the diurnal variation of aerosol hygroscopicity being closely related to anthropogenic activities and aerosol ageing processes.In addition,there are significant differences in the diurnal variation of the aerosol optical absorption coefficient in the three megacities,such that the absorption coefficient in Beijing is higher during the daytime than at night,while it is reversed in Guangzhou.This is likely caused by the differences in the environment surrounding the observation stations and the diverse characteristics of the atmospheric boundary layer.