Anomalous increase in sea fog frequency along coastal China in the early 21st century and the aerosol influence

Sea fog hampers coastal activities, yet its decadal variability in coastal China remains insufficiently characterized. Using hourly marine observations from the International Comprehensive Ocean-Atmosphere Data Set (ICOADS), we identify an April–July sea fog frequency (SFF) trend reversal over fog-prone eastern coastal China: from a decrease of 1% per decade (1980–2000) to an increase of 3% per decade (2001–2011) (p < 0.01 for both trends). Hourly ERA5 reanalysis corroborates this reversal and links it to enhanced 2001–2011 near‑surface cooling, which strengthens near-surface inversions and stability. Daily CMIP6 model simulations indicate that aerosols are the primary driver of the 2001–2011 SFF increase, enhancing stability through radiative cooling and promoting water vapor condensation by supplying cloud condensation nuclei. Our findings highlight aerosols’ critical role in increasing SFF and underscore the need for sustained emission-reduction efforts in China to mitigate fog-related disruptions.