Ice Nucleating Particle Concentrations Increase When Leaves Fall in Autumn

Ice nucleating particles active at −8 °C or warmer (INP−8) are produced by plants and by microorganisms living from and on them. Laboratory studies have shown that large numbers of INP−8 are produced by decaying leaves. At three widely dispersed locations in Northwestern Eurasia, we saw, from an analysis of PM10 filter samples, that seasonal median concentrations of INP−8 in the boundary layer doubled from summer to autumn. Concentrations of INP−8 increased in autumn soon after the normalized differential vegetation index had started to decrease. Whether the large-scale phenological event of leaf senescence and shedding in autumn has an impact on ice formation in clouds is a justified question.