Experimental Study on the Turbulence Characteristics and Flux Acquisition of PM2.5

Abstract The authors use the high-frequency sampling function of the fine particle mass concentration measurement instrument E-sampler and the eddy covariance method to calculate PM2.5 concentration fluctuation and turbulent flux of the multiple pollution events of the Dezhou city atmospheric environment experimental station in Shandong Province from December 27, 2018 to January 7, 2019, and the turbulence characteristics of PM2.5 concentration are discussed. The results show that the mean value of the turbulent flux of PM2.5 concentration during the observation period is 0.026 μg/(m2·s). The transmission direction of the turbulent flux of PM2.5 concentration in different pollution processes is different, indicating that the sink or source property is not static. With the increase of turbulence statistical characteristic quantities (such as turbulent kinetic energy, standard deviation of horizontal wind speed, standard deviation of vertical wind speed, horizontal wind speed, momentum flux and sensible heat flux), the vertical flux of PM2.5 decreases exponentially, namely, it decreases sharply, and 1. Laboratory for Climate and Oceanic-atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871; 2. Collaborative Innovation Center for West Ecological Safety, Lanzhou University, Lanzhou 730000; 3. State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871; † Corresponding author, E-mail: hsdq@pku.edu.cn

then changes little with the increase of each variable. With the increase of the concentration of PM2.5, the absolute value of the turbulent flux of PM2.5 shows an increasing trend. The turbulent vertical flux of PM2.5 concentration is related to the PM2.5 concentration and the intensity of turbulence. The normalized standard deviation of PM2.5 concentration and the stability parameter ζ = z/l follow the −1/3 power relationship under unstable conditions, that is σc/c*=6.7(−ζ)−1/3. Under stable conditions, the experimental results are relatively discrete. In addition, the variance spectrum curve of PM2.5 concentration satisfies the −2/3 power exponential rate in the high frequency range, and the covariance spectrum curve of the PM2.5 concentration and the vertical wind speed satisfies the −4/3 power exponential rate in the high frequency band. The result shows that 1 Hz high-frequency sampling function of E-sampler can obtain continuous and effective turbulent flux of PM2.5 concentration. Key words turbulent flux of PM2.5 concentration; turbulence statistics; turbulence energy spectrum; pollution process