Long-term atmospheric cadmium deposition and its time-lagged response to policy measures in southern China

Atmospheric deposition is the main pathway for cadmium (Cd) input into soils and crops, elucidating its long-term patterns is crucial for mitigating Cd pollution and protecting agricultural safety. However, the lack of long-term monitoring data in China has severely hindered a clear assessment of its temporal trends and the effectiveness of emission reduction policies. This study analyzed the first decade-long dataset from the core of the Pearl River Delta megacity (Guangzhou: GZ, 2009-2019) and an adjacent ecologically sensitive nature reserve (Dinghushan: DHS, 2009-2023) in southern China. We systematically evaluated long-term trends in Cd deposition fluxes, the effects of emission control policies, the impact of climatic factors, and the lagged response of deposition to emissions. The results revealed significant reductions in Cd deposition fluxes at GZ and DHS, reflecting the effectiveness of China's regulatory policies (DHS: -4.8 %/year, P <0.001; GZ: -10.2 %/year, P < 0.001). Moreover, emission reduction measures mitigated the amplification of deposition fluctuations caused by meteorological variability. However, short-term variability in Cd deposition fluxes driven by precipitation still accounted for 28.9 %-51.4 % of the residual variance. El Niño-Southern Oscillation further contributed to interannual fluctuations through the regulation of wet deposition processes. Additionally, Cd emissions from coal-fired power plants and biomass/municipal combustion sectors continuously increased, with a maximum lag time of 3 years. These findings indicate the necessity of strictly controlling these sources and strengthening regional collaborative governance to sustain long-term reductions in Cd deposition fluxes.