Contribution of pollen to atmospheric ice nuclei concentrations
Recent studies have suggested that the ice-nucleating ability of some types of pollen is derived from non-proteinaceous macromolecules. These macromolecules may become dispersed by the rupturing of the pollen grain during wetting and drying cycles in the atmosphere. If true, this mechanism might pro...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/14/5433/2014/acp-14-5433-2014.pdf |
| Summary: | Recent studies have suggested that the ice-nucleating ability of some types
of pollen is derived from non-proteinaceous macromolecules. These
macromolecules may become dispersed by the rupturing of the pollen grain
during wetting and drying cycles in the atmosphere. If true, this mechanism
might prove to be a significant source of ice nuclei (IN) concentrations
when pollen is present. Here we test this hypothesis by measuring ambient IN
concentrations from the beginning to the end of the 2013 pollen season in
Raleigh, North Carolina, USA. Air samples were collected using a swirling
aerosol collector twice per week and the solutions were analysed for ice
nuclei activity using a droplet freezing assay. Rainwater samples were
collected at times when pollen grain number concentrations were near their
maximum value and analysed with the drop-freezing assay to compare the
potentially enhanced IN concentrations measured near the ground with IN
concentrations found aloft. Ambient ice nuclei spectra, defined as the
number of ice nuclei per volume of air as a function of temperature, are
inferred from the aerosol collector solutions. No general trend was observed
between ambient pollen grain counts and observed IN concentrations,
suggesting that ice nuclei multiplication via pollen grain rupturing and
subsequent release of macromolecules was not prevalent for the pollen types
and meteorological conditions typically encountered in the southeastern US.
A serendipitously sampled collection after a downpour provided evidence for
a rain-induced IN burst with an observed IN concentration of approximately
30 per litre, a 30-fold increase over background concentrations at −20 °C.
The onset temperature of freezing for these particles was approximately
−12 °C, suggesting that the ice-nucleating particles were biological in
origin. |
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| ISSN: | 1680-7316 1680-7324 |