近岸海洋大气中黑碳气溶胶的混合态及其对光吸收特性的影响研究

Recently, human health and marine environment are threatened by the increasing pollutions over the offshore marine atmosphere, especially the haze pollution. Black carbon (BC) is the dominant absorber of solar radiation in the atmospheric aerosols. Due to the light absorption property it can cause low visibility, regional haze, and affect the atmospheric radiative energy balance, making an important influence on the environment and climate on the regional and global scales. The light absorption properties of BC are very sensitive to the manner and degree in which BC mixed with other aerosols, a property referred to as mixing state. Large uncertainties still exist in estimates of the radiative forcing of BC because of the lack of detailed measurements of the mixing state and the associated optical properties. These uncertainties limit our ability to quantify the relative impacts of BC on climate and environment, thus limiting our ability to make effective policy decisions. To reduce the uncertainties and better understand its effects on the offshore marine atmosphere, it is essential to study the mixing state of BC and its effects on the optical properties. To study the mixing state of BC, obtain the aerosol types and their relative contribution ratios which externally or internally mixed with BC, on-line analyses such as single particle aerosol mass spectrometer and off-line analyses like transmission/scanning electron microscopy equipped with energy dispersive spectrometer, ion chromatography, high-resolution gas chromatography combined with mass spectrometry will be used to investigate aerosol particles collected from the typical emission sources and offshore marine atmosphere in this research. In this study, the light absorption of BC will be measured directly using the photo-acoustic technique, while its mass concentration will be determined by the thermal/optical reflectance method. The mass absorption coefficient will be calculated as the ratio of aerosol absorption coefficient to the mass concentration of BC. The relationship between the mass absorption coefficient and the number fractions of different mixing states of BC, such as the externally and internally mixing of BC with sulfate, sea salts, or organic matters, will be studied to quantify the effect of different mixing state on light absorption properties of BC, and the influence by the relative humidity and so on. Results of this research will provide critical support data which helps us to estimate the impact on the offshore marine air quality and marine ecological environment by BC, and provide scientific basis for the development of a reasonable abatement control method.

近年来，近岸海洋大气复合型污染日益明显直接威胁着人类健康和海洋生态环境，其中灰霾污染尤为显著。黑碳是气溶胶中最主要的光学吸收成分，能造成大气能见度下降、影响大气辐射能量平衡，是形成灰霾的重要污染物；而黑碳气溶胶的光吸收特性与其混合态密切相关。因此，为更好的研究黑碳气溶胶对近海大气环境的影响，本研究拟通过单颗粒气溶胶质谱仪等实时在线分析结合电镜微观形貌等离线分析手段，对典型源排放及近岸海洋大气中黑碳气溶胶的混合态特征进行综合研究，获得黑碳气溶胶的混合态特征及其变化规律；同时通过光声法、热光分析法等获得不同条件下黑碳的光吸收特性（质量吸收系数）；建立混合态与光吸收特性之间的定量关系，探讨混合态对黑碳气溶胶光吸收特性的影响以及近海高湿高盐等环境因素对其影响。本项目的开展将为评估黑碳气溶胶对近岸海域空气质量、海洋生态环境的影响提供关键的支持数据，并为制定合理的减排控制方法提供科学依据。

近年来，近岸海洋大气复合型污染日益明显直接威胁着人类健康和海洋生态环境，其中灰霾污染尤为显著。黑碳是气溶胶中最主要的光学吸收成分，能造成大气能见度下降、影响大气辐射能量平衡，是形成灰霾的重要污染物；而黑碳气溶胶的光吸收特性与其混合态密切相关。因此，为更好的研究黑碳气溶胶对近海大气环境的影响，本项目通过单颗粒气溶胶质谱仪等实时在线分析法、离线滤膜热光分析法、积分球光学测量法等多种分析手段相结合的方法，重点对厦门市近岸海洋大气中黑碳气溶胶的混合态及其光吸收特性等开展了综合研究，获得了厦门市不同季节中黑碳的质量吸收系数及混合态特征，探讨了混合态、湿度、海盐等对黑碳气溶胶质量吸收系数的影响。结果表明厦门近岸海洋大气中黑碳的质量吸收系数为6.80 m2∙ g-1-14.77 m2∙ g-1，且存在一定的季节性差异，其在春、夏、秋、冬四季中的平均值分别为9.19 m2∙ g-1、9.07 m2∙ g-1、10.13 m2∙ g-1和9.86 m2∙ g-1。黑碳的质量吸收系数仅在夏季中与环境湿度成正相关，其他季节受湿度影响不大。高比例的内混硫酸盐和海盐可能是造成秋季黑碳质量吸收系数较高的主要原因。此外，本项目还利用获得的多种观测分析数据对典型事件（节假日、雾霾、台风）影响下近岸海洋大气气溶胶的特征变化等进行了研究。本项目的开展将为进一步评估黑碳等气溶胶对近岸海域空气质量、海洋生态环境的影响提供关键的支持数据，并为制定合理的减排控制方法提供科学依据。