Measurement report: Analysis of aerosol optical depth variation at Zhongshan Station in Antarctica

Abstract. Our understanding of aerosol optical depth (AOD) in Antarctica remains limited due to the scarcity of ground observation stations and limited daylight days. Utilizing data from the CE318-T photometer spanning from January 2020 to April 2023 at Zhongshan Station, we analysed the seasonal, monthly, and diurnal variations in AOD and Ångström exponent (AE). AOD median values increased from spring (0.033) to winter (0.115), while AE peaked during summer (1.010) and autumn (1.034), declining in winter (0.381), indicating a transition in dominant aerosol particle size from fine to coarse mode between summer and winter. Monthly mean AOD variation closely paralleled the proportion of AE<1, suggesting fluctuations in coarse mode particle proportions drive AOD variation. Increases in AOD during spring and winter correlated with decreases in fine mode fraction, while increases during summer and winter related to fine mode particle growth and aging. We observed a peak in AOD (~0.06) at 14:00 local time at Zhongshan Station, possibly associated with a slight decrease in boundary layer height (BLH). Additionally, higher (lower) wind speeds corresponded to lower (higher) AOD values, indicating the diffusion (accumulation) effect. The temperature and AOD showed an insignificant positive correlation between (R = 0.22, p = 0.40), relative humidity exhibited a significant negative correlation with AOD (R = -0.59, p = 0.02). Backward trajectory analysis revealed that coarse particles from the ocean predominantly contributed to high AOD daily mean values in summer, while fine particles on low AOD days originated mainly from the air mass over the Antarctic Plateau.