Clues that decaying leaves enrich Arctic air with ice nucleating particles

Decaying leaves from Arctic regions have previously been reported to produce large numbers of ice nucleating particles (IN). Their atmospheric relevance is unclear. Our initial observations at a coastal mountain observatory in northern Norway reveal a tripling in concentrations of IN active at −15 °C (IN -15 ) in oceanic air after about one day of passage over land (from 1.7 and 4.9 IN -15 m −3 , to 9.6 and 12.2 IN -15 m −3 ). Analysis of leaf litter collected near the observatory supports the earlier report of numerous IN associated with leaf litter on the ground (2 ⋅ 10 2 IN -15 μg −1 litter particles < 5 μm). Together, both findings suggest that decaying leaves are a strong emission source of IN to the Arctic boundary layer. • Ice nucleating particles (IN) were quantified at a coastal station in the Arctic. • Longer backtrajectories over land coincide with greater IN number concentrations. • Decaying leaf litter emitting biological particles is the most likely IN source.