Unraveling the process of aerosols secondary formation and dissipation based on cosmogenic beryllium-7 and beryllium-10
Mr Xu-Ke Liu1,2, Dr Yun-Chong Fu1,3,4, Prof. Wei-Jian Zhou1,3,4, Dr Li Zhang1,4, Mr Guo-Qing Zhao1,4, Dr Qi-Yuan Wang1
1Institute Of Earth Environment, Chinese Academy Of Sciences, Xi’an, China, 2University of Chinese Academy of Sciences, Beijing, China, 3Xi’an Jiaotong University, Xi’an, China, 4Xi’an AMS Center, Xi’an, China
The production and dissipation process of aerosols is extremely complicated, which has a great impact on the environment and human health. For example, the new production process of secondary aerosols (SA) can further deteriorate air quality. However, at present, the accuracy of SA estimation has not been fully recognized, and the measurement process of multiple substances (such as NH4+, NO3- and SO42- for secondary inorganic aerosols, and organic carbon and elemental carbon for secondary organic aerosols) is complicated. Explore other single element tracing methods that may make up for these shortcomings. In addition, it is a more ideal way to focus not only on the SA new production process but also on the aerosol dissipation and removal process. Cosmogenic 7Be and 10Be in the atmosphere are rapidly adsorbed on aerosols after being formed, and their production rate and geochemical properties are relatively stable. We have noticed that the 7Be and 10Be attached to the aerosol will no longer return to the atmospheric storage after being deposited on the surface (except for the effects of resuspended dust, which will be discussed later), and they are not used as precursors for SA formation. Therefore, 7Be and 10Be may provide different aerosol chemical pathways from traditional tracers. In addition, since the production and deposition of 7Be and 10Be are closely related to aerosols, their deposition process can also represent the physical removal process of aerosols (such as the removal process of rainfall and vertical atmospheric movement, etc.). Here, we measured the daily resolution atmospheric 7Be and 10Be in autumn and winter of Xi’an (heavy pollution period in a typical polluted area) by AMS, And it is found that the actual 10Be/7Be ratio obtained after deducting the influence of the resuspended dust in the 10Be can realize the accurate judgment of the atmospheric vertical stability. It is confirmed by SA tracers (such as NH4+, NO3-, and SO42-) and precursors (such as SO2, NO2) that a large amount of SA is formed during these stable periods judged by the 10Be/7Be ratio. The 7Be and 10Be concentration in these stable periods is significantly negatively correlated with the aerosol concentration (R2﹥0.9, P<0.001). Therefore, the SA relative content in aerosols can be estimated by the dilution degree of 7Be and 10Be, reflecting the second generation process of aerosol chemistry. In addition, we also used 7Be and 10Be washout to further quantitatively estimate removal of aerosol by rain and its residence time and based on the change of 10Be/7Be ratio. We found that the rapid dissipation of aerosols in some periods of Xi’an may be caused by the atmospheric vertical movement. In summary, atmospheric 7Be and 10Be will provide a new view angle to study the process of secondary chemical generation and physical elimination of aerosols.
Liu Xuke, a PhD student at the Institute of Earth Environment, Chinese Academy of Sciences. The main research is the tracing of atmospheric motion of cosmic genesis and the application of accelerator mass spectrometry technology. E-mail: email@example.com.