Atmospheric deposition of 7Be in the southeast of China: A case study in Xiamen

Abstract

Atmospheric deposition of7Be was measured at a time-series station in the southeast of China (Xiamen) from 2011 to 2013. The deposition fluxes of7Be ranged from 0.05 Bq m–2 d–1 to 7.42 Bq m–2 d–1, averaging 1.87 ± 0.10 Bq m–2 d–1. High fluxes occurred in months with northeast monsoon, and low values were observed in the southwest monsoon prevailing months. The significant correlations between7Be deposition and precipitation, existing in both northeast and southwest monsoon seasons, suggested the dominant removal of atmospheric7Be via precipitation. However, the correlations showed a large slope for the northeast monsoon season, indicating higher7Be contents in the atmosphere during the northeast monsoon prevailing months, supported by the precipitation-normalized7Be and the temporal variability of7Be/210Pb ratios. Such a scenario revealed more intensive exchange of air mass between the stratosphere and troposphere during the northeast monsoon prevailing months. Together with the high pollutant concentrations in ambient air observed in these seasons, the results indicated that the pollutants in Xiamen might enter into the upper troposphere via vertical air mass exchange.