Vertical distribution of near-surface aerosol extinction over North China and its impacts on tower photothermal power generation

In the process of tower photothermal power generation, solar radiation undergoes the attenuation of the whole atmosphere, reaches the heliostat and then is reflected to the heat collector. The transfer of solar radiation from the heliostat to the heat collector occurs at an altitude of 0 to 300m from the ground, which is defined to be the near-surface layer in this study and is concentrated with high aerosol loadings. Thus, the extinction effects of near-surface aerosols are crucial in the site selection of photothermal power generation and in the evaluation of photothermal power generation efficiency.

In this work, we first analyzed the vertical distribution of near-surface aerosol extinction over North China (NC) and its correlation with meteorological factors. CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) is a satellite-borne lidar instrument aboard CALIPSO satellite, which provide globally aerosol vertical profiles with unprecedented coverage and spatial resolution. To circumvent data scarcity of longer-term in situ surface measurement of aerosol vertical profiles over the NC region, here CALIOP Level 2 version 4.1 aerosol profile product at 532 nm from January 2019 to December 2019 were adopted. The screened daytime CALIOP L2 data over the NC region were assigned and aggregated into horizontal grids with a resolution of 0.5°×0.5°. The vertical distribution of aerosol extinction coefficient reveals that in winter, Spring and autumn, the aerosol extinction values from near surface to about 1.5km are significantly higher than that above 1.5km. Especially in winter, high aerosol extinction values are found below 1km, indicating weak vertical mixing in winter. The relatively constant aerosol extinction values from near surface to above 2km indicates a higher well-mixed planetary boundary layer (pbl) height in summer. Aerosol extinction between 0-300m accounts for 32%, 17%, 9% and 20% of the aerosol extinction of the whole atmosphere in winter, spring, summer and autumn separately. PM_2.5 concentration and surface relative humidity are positively correlated with near-surface aerosol extinction (r=0.4 and 0.31 respectively). Meanwhile, surface visibility is negatively related to the near-surface aerosol extinction (r=-0.45).

Then the aerosol extinction coefficient in the near-surface layer was adopted in the SMARTS model and we simulated the radiation transfer between 0 to 300m under different weather conditions. Simulation results of SMARTS model considered near-surface aerosol extinction are closer to radiation observations of a 325m meteorological tower in Beijing than the results of the original SMARTS model under all typical weather conditions.

Knowledge of the attenuation of aerosol to solar radiation from the heliostat to the heat collector in the process of tower photothermal power generation is of critical economic importance for the site selection of power station and the evaluation of power generation efficiency.