Temporal Variation Characteristics Of Ultraviolet Radiation In Beijing And Its Response To Aerosols And Clouds

Ultraviolet radiation refers to the solar short-wave radiation spectral region in the 100-400nm radiation,ultraviolet radiation constrains most of the photochemical reactions in the atmosphere,and almost all homogeneous chemical processes in the atmosphere are directly or indirectly related to ultraviolet radiation;although its energy is only a small proportion of the solar radiation energy（about 5%）,but because of its strong biological and chemical effects,as well as the impact on human health,atmospheric environment,so the study of ultraviolet radiation is increasingly becoming the frontier of radiation observation research and hot topics.However,due to the late development of ultraviolet radiation observation,there are obvious shortcomings in the study of long-term variation characteristics of UV radiation and its causes.There is also a paucity of studies that quantitatively assess the effect of aerosols on UV radiation in conjunction with radiation transfer models.In order to make up for the deficiencies in the study of long-term variation characteristics of UV radiation,this paper analyzes the UV radiation variation characteristics of Beijing in the past 15 years by using the data of total radiation,UV radiation,PM_2.5mass concentration,conventional meteorological elements and aerosol optical characteristics observed by AERONET Beijing station from 2005 to 2020 observed by the Integrated Aerosol Cloud Radiation Observation Platform of the Tita Branch,Institute of Atmospheric Physics,Chinese Academy of Sciences.The influence of aerosol optical characteristics on the changes of ultraviolet radiation in Beijing was revealed;by analyzing the sensitivity of UV radiation to aerosol optical depth（AOD）and single scattering albedo（SSA）using the Troposphere ultraviolet and visible radiation model（TUV）,quantitative assessment of aerosol and cloud contributions to UV radiation attenuation,providing scientific data to support the study of aerosol cloud radiation changes in the region.The main findings of the study are as follows:1.The UV radiation shows obvious daily and seasonal variation characteristics.The daily variation shows a single-peaked variation curve,showing a pattern of small in the morning and small in the evening and large at noon.The maximum value of the day（16.26 W/m²）occurs at12:00 noon,and the minimum value of the day（5.64 W/m²）occurs at 8:00 am.The daily variation pattern of UV radiation in different seasons is consistent,showing the characteristics of summer is greater than spring is greater than autumn is greater than winter;but there are large differences in the daily average and extreme values.The daily average values of UV radiation in spring,summer,autumn and winter were 14.61 W/m²,15.52 W/m²,9.77 W/m²and 6.37 W/m²in order;the very small value（9.91 W/m²）of the daily variation of UV radiation in summer was basically equal to the very large value（10.11 W/m²）of UV radiation in winter;the maximum value of summer UV radiation（20.35 W/m²）tends to be twice as large as the maximum value of winter UV radiation.The seasonal pattern of UV radiation is as follows:strong in spring and summer,weak in autumn and winter,with the maximum and minimum values occurring in June（12.17 W/m²）and December（5.40 W/m²）,respectively.2.From 2005 to 2020,the UV radiation in Beijing showed fluctuating changes over the years,with a slight increase overall.The trend of UV radiation and clearness index in Beijing is basically the same,and they have a positive correlation with a correlation coefficient R of 0.85.UV radiation and aerosol optical depth（AOD）show an inverse phase trend with a correlation coefficient R of-0.7.UV radiation and PM_2.5in Beijing also show an inverse phase trend with a correlation coefficient R of-0.83.3.Quantitative assessment of the contribution of aerosols and clouds to the attenuation of UV radiation reaching the ground using TUV radiative transfer models in combination with in situ observations;sensitivity analysis reveals that UV radiation is more sensitive to changes in AOD,and when SSA was fixed at 0.9,UV radiation decreased from 21.16 W/m²to 12.64 W/m²,when AOD increased from 0.2 to 1.0,while when AOD was maintained at 0.64,UV radiation increased from 14.55 W/m²to 19.91 W/m²,when SSA increased from 0.7 to 0.95.The annual average values of attenuation rate of UV radiation by aerosols and clouds from 2005 to 2020 are 30.64%and40.22%,respectively;the monthly average values of attenuation rate of UV radiation by aerosols and clouds are 30.48%and 42.04%,respectively;the daily average values of attenuation rate of UV radiation by aerosols and clouds are 31.02%and 50.45%,respectively.