Heterogeneous ice nucleation of viscous secondary organic aerosol produced from ozonolysis of <i>α</i>-pinene
There are strong indications that particles containing secondary organic aerosol (SOA) exhibit amorphous solid or semi-solid phase states in the atmosphere. This may facilitate heterogeneous ice nucleation and thus influence cloud properties. However, experimental ice nucleation studies of bioge...
Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2016-05-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/16/6495/2016/acp-16-6495-2016.pdf |
Summary: | There are strong indications that particles containing secondary organic
aerosol (SOA) exhibit amorphous solid or semi-solid phase states in the
atmosphere. This may facilitate heterogeneous ice nucleation and thus
influence cloud properties. However, experimental ice nucleation studies of
biogenic SOA are scarce. Here, we investigated the ice nucleation ability of
viscous SOA particles. <br><br>The SOA particles were produced from the ozone initiated oxidation of
<i>α</i>-pinene in an aerosol chamber at temperatures in the range from −38
to −10 °C at 5–15 % relative humidity with
respect to water to ensure their formation in a highly viscous phase state,
i.e. semi-solid or glassy. The ice nucleation ability of SOA particles with
different sizes was investigated with a new continuous flow diffusion
chamber. For the first time, we observed heterogeneous ice nucleation of
viscous <i>α</i>-pinene SOA for ice saturation ratios
between 1.3 and 1.4 significantly below the homogeneous freezing limit. The
maximum frozen fractions found at temperatures between −39.0 and
−37.2 °C ranged from 6 to 20 % and did not depend
on the particle surface area. Global modelling of monoterpene SOA particles
suggests that viscous biogenic SOA particles are indeed present in regions
where cirrus cloud formation takes place. Hence, they could make up an
important contribution to the global ice nucleating particle budget. |
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ISSN: | 1680-7316 1680-7324 |