Long-term (13 years) measurements of SO2 fluxes over a forest and their control by surface chemistry

► Long-term fluxes (13 years) of sulphur dioxide (SO2) have been measured over a forest. ► Rain-wetted canopies were more efficient sinks compared to dew-wetted and dry canopies. ► Increased surface water acidity led to a lower deposition efficiency and a higher proportion of emission fluxes for all wetness categories. ► Long-term trends were coupled to changes in the NH3/SO2 ratio.