Simulation Research On Concentration And Impact Factors Of Atmospheric Mercury At A Coastal Site In The Summer Of Qingdao

Mercury,a heavy metal element with biotoxicity,is widely distributed in the environment,which is highly harmful to humans and ecosystems.Since the large-scale outbreak of Minamata disease in Japan in the mid-20th century,mercury has become a global pollutant of great concern.Atmosphere,as an important medium for the conversion and migration of mercury,plays an important position of the biogeochemical cycle of mercury.China is the largest world anthropogenic source of atmospheric mercury,and in the industrial zone along the eastern coast of China has a densely populated and economically developed.In order to understand the atmospheric mercury concentration characteristics and chemical conversion influencing factors in this zone,continuous observation of total gaseous mercury(TGM)was conducted at a coastal site in Qingdao,Shandong province during January-October 2019.We analyzed the seasonal pattern and diurnal pattern of TGM,discussed the effects of meteorological factors and conventional atmospheric pollutants.Finally,we developed a detailed atmospheric mercury chemical box model to simulate the concentration characteristics of reactive gaseous mercury(RGM),and quantify the contribution of impact factors.During the observation period,the average TGM concentration at the coastal site was 2.30±0.98 ng m-3 with the range of 0.87-19.17 ng m-3,which was 1.6 times the background value of the northern hemisphere and 20%-80%higher than the value of the background concentration in China.The daily variation showed that the concentration dropped after sunrise,then fluctuated at a stable low value until 15 p.m.,following reached the minimum value at about 18 p.m..Then,the TGM concentration level rose again and reached the maximum value in a day at 22 p.m.For the relatively stable and sunny summer day,the trend of daily variation still follows the trend of declining with sunrise,maintaining a stable low value in the afternoon,and becoming stable after the recovery in the evening.The difference is that the typical summer days’the recovery guidance is small in the evening,so that the morning sunrise is the highest TGM value for the whole day.In addition,through correlation analysis,it is found that TGM is weakly correlated with CO that way TGM over the site is less affected by anthropogenic emissions.It is speculated that TGM is to some extent influenced by meteorological factors such as temperature,boundary layer height and light intensity.In order to understand the variation of atmospheric mercury,this study used the Chemical reaction box model—BOXMOX(BOX Modeling eXtensions to KPP)—to modified the Chemical reaction Mechanism(MCM,the Main Chemical Mechanism),by adding halogen chemistry and atmospheric mercury chemistry,which built a detailed atmospheric mercury box model.Then the model was used to simulate RGM concentration characteristics and indirect quantitative influence of meteorological factors.With the improved model,observed TGM data was used to restrain the running of the model.In addition,the simulated RGM concentration in the coastal area of Qingdao was 0.76 ppqv in summer,and there was a significant daily variation driven by photochemical reactions.The highest daytime value was 1.23 ppqv at 2 p.m.In addition,the simulation suggested the dominant RGM species was HgO(92.1%of the total RGM).Besides,halogenic RGM comprised 5.2%of the total RGM,Hg(OH)2 contributed 2.7%.The O3,OH and reactive halogens were the important oxidants of GEM in Qingdao coastal site.The sensitivity simulations were used to quantify the effects of temperature,boundary layer height,gas-particle partitioning,and photochemistry on RGM concentration.The effect of temperature on RGM was different during daytime and nighttime.Boundary layer height had a negative influence on RGM.Solar radiation had a positive effect on RGM.In addition,the gas-particle distribution process has a particularly significant impact on the RGM,and the liquid water content in the aerosol,a key parameter of the process,had a significant negative impact on the concentration level of active gaseous mercury.