Abstract
Abstract. Silver birch (Betula pendula) is known to contain ice-nucleating macromolecules (INMs) to survive in harsh environments. However, little is known about the release and transport of INMs from birch trees into the atmosphere. In this study, we conducted in situ and in vivo investigations on INMs from nine birches growing in an alpine valley (Ötztal, Austria). A detailed analysis of drill cores showed that INM concentration increases towards outer layers, reaching its maximum near the surface. Aqueous extracts from the surfaces of leaves, bark, primary wood and secondary wood contained INMs (34∕36) with concentrations ranging from 9.9×105 to 1.8×109 INMs cm−2. In a field study, we analysed the effect of precipitation on the release of these INMs attached to the surface of the trees. These experiments showed that INMs are splashed and aerosolized into the environment during rainfall events, at concentrations and freezing temperatures similar to in vivo samples. Our work sheds new light on the release and transport of INMs from birch surfaces into the troposphere. Birches growing in boreal and alpine forests should be considered an important terrestrial source of INMs.
Highlights
If temperatures at ambient pressure fall below 0 ◦C, ice is the thermodynamically favourable state of water (Cantrell and Heymsfield, 2005; Hegg and Baker, 2009; Murray et al, 2010)
primary biological aerosol particles (PBAPs) include a wide variety of substances with varying sizes from millimetres down to nanometres, with cellular material carrying proteins being an important part of it (Jaenicke, 2005)
It is well known that many plants growing in boreal and alpine forests contain ice-nucleating particles (INPs) or ice-nucleating macromolecules (INMs) to survive in extreme conditions (Sakai and Larcher, 1987)
Summary
If temperatures at ambient pressure fall below 0 ◦C, ice is the thermodynamically favourable state of water (Cantrell and Heymsfield, 2005; Hegg and Baker, 2009; Murray et al, 2010). Particles that trigger higher freezing temperatures are referred to as ice-nucleating particles (INPs) (Vali et al, 2015). Among these are mineral dusts (Broadley et al, 2012; Zolles et al, 2015), soot (DeMott, 1990; Gorbunov et al, 2001) and biogenic particles (Pöschl et al, 2010), and when airborne they have the potential to affect cloud glaciation and weather and climate (Lohmann, 2002; Mishchenko et al, 1996; Forster et al, 2007; Baker, 1997). Our knowledge on the distribution and impact of PBAPs in the atmosphere is still rather limited
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