Photomineralization mechanism changes the ability of dissolved organic matter to activate cloud droplets and to nucleate ice crystals
<p>An organic aerosol particle has a lifetime of approximately 1 week in the atmosphere during which it will be exposed to sunlight. However, the effect of photochemistry on the propensity of organic matter to participate in the initial cloud-forming steps is difficult to predict. In this stud...
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Copernicus Publications
2019-10-01
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language |
English |
format |
Article |
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author |
N. Borduas-Dedekind N. Borduas-Dedekind R. Ossola R. O. David L. S. Boynton V. Weichlinger Z. A. Kanji K. McNeill |
spellingShingle |
N. Borduas-Dedekind N. Borduas-Dedekind R. Ossola R. O. David L. S. Boynton V. Weichlinger Z. A. Kanji K. McNeill Photomineralization mechanism changes the ability of dissolved organic matter to activate cloud droplets and to nucleate ice crystals Atmospheric Chemistry and Physics |
author_facet |
N. Borduas-Dedekind N. Borduas-Dedekind R. Ossola R. O. David L. S. Boynton V. Weichlinger Z. A. Kanji K. McNeill |
author_sort |
N. Borduas-Dedekind |
title |
Photomineralization mechanism changes the ability of dissolved organic matter to activate cloud droplets and to nucleate ice crystals |
title_short |
Photomineralization mechanism changes the ability of dissolved organic matter to activate cloud droplets and to nucleate ice crystals |
title_full |
Photomineralization mechanism changes the ability of dissolved organic matter to activate cloud droplets and to nucleate ice crystals |
title_fullStr |
Photomineralization mechanism changes the ability of dissolved organic matter to activate cloud droplets and to nucleate ice crystals |
title_full_unstemmed |
Photomineralization mechanism changes the ability of dissolved organic matter to activate cloud droplets and to nucleate ice crystals |
title_sort |
photomineralization mechanism changes the ability of dissolved organic matter to activate cloud droplets and to nucleate ice crystals |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2019-10-01 |
description |
<p>An organic aerosol particle has a lifetime of approximately 1 week in the
atmosphere during which it will be exposed to sunlight. However, the effect of
photochemistry on the propensity of organic matter to participate in the
initial cloud-forming steps is difficult to predict. In this study, we
quantify on a molecular scale the effect of photochemical exposure of
naturally occurring dissolved organic matter (DOM) and of a fulvic acid
standard on its cloud condensation nuclei (CCN) and ice nucleation (IN)
activity. We find that photochemical processing, equivalent to 4.6 d in
the atmosphere, of DOM increases its ability to form cloud droplets by up to
a factor of 2.5 but decreases its ability to form ice crystals at a loss
rate of <span class="inline-formula">−0.04</span> <span class="inline-formula"><sup>∘</sup></span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow><msub><mi>T</mi><mn mathvariant="normal">50</mn></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="13pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="8b240bec1e343973563bdbfa5af70aba"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-12397-2019-ie00001.svg" width="13pt" height="10pt" src="acp-19-12397-2019-ie00001.png"/></svg:svg></span></span> h<span class="inline-formula"><sup>−1</sup></span> of sunlight at ground level.
In other words, the ice nucleation activity of photooxidized DOM can require
up to 4 <span class="inline-formula"><sup>∘</sup></span>C colder temperatures for 50 % of the droplets to activate
as ice crystals under immersion freezing conditions. This temperature change
could impact the ratio of ice to water droplets within a mixed-phase
cloud by delaying the onset of glaciation and by increasing the supercooled
liquid fraction of the cloud, thereby modifying the radiative properties and
the lifetime of the cloud. Concurrently, a photomineralization mechanism was
quantified by monitoring the loss of organic carbon and the simultaneous
production of organic acids, such as formic, acetic, oxalic and pyruvic
acids, CO and <span class="inline-formula">CO<sub>2</sub></span>. This mechanism explains and predicts the observed
increase in CCN and decrease in IN efficiencies. Indeed, we show that
photochemical processing can be a dominant atmospheric ageing process,
impacting CCN and IN efficiencies and concentrations. Photomineralization
can thus alter the aerosol–cloud radiative effects of organic matter by
modifying the supercooled-liquid-water-to-ice-crystal ratio in mixed-phase
clouds with implications for cloud lifetime, precipitation patterns and the
hydrological cycle.<br/><br/><strong>Highlights.</strong>
During atmospheric transport, dissolved organic matter (DOM) within aqueous
aerosols undergoes photochemistry. We find that photochemical processing of
DOM increases its ability to form cloud droplets but decreases its ability
to form ice crystals over a simulated 4.6 d in the atmosphere. A
photomineralization mechanism involving the loss of organic carbon and the
production of organic acids, CO and <span class="inline-formula">CO<sub>2</sub></span> explains the observed changes
and affects the liquid-water-to-ice ratio in clouds.</p> |
url |
https://www.atmos-chem-phys.net/19/12397/2019/acp-19-12397-2019.pdf |
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doaj-36286ca3f0884cb3bbad530233ea65a52020-11-25T01:33:45ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242019-10-0119123971241210.5194/acp-19-12397-2019Photomineralization mechanism changes the ability of dissolved organic matter to activate cloud droplets and to nucleate ice crystalsN. Borduas-Dedekind0N. Borduas-Dedekind1R. Ossola2R. O. David3L. S. Boynton4V. Weichlinger5Z. A. Kanji6K. McNeill7Institute for Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zurich, 8092, SwitzerlandInstitute for Atmospheric and Climate Sciences, ETH Zurich, Zurich, 8092, SwitzerlandInstitute for Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zurich, 8092, SwitzerlandInstitute for Atmospheric and Climate Sciences, ETH Zurich, Zurich, 8092, SwitzerlandInstitute for Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zurich, 8092, SwitzerlandInstitute for Atmospheric and Climate Sciences, ETH Zurich, Zurich, 8092, SwitzerlandInstitute for Atmospheric and Climate Sciences, ETH Zurich, Zurich, 8092, SwitzerlandInstitute for Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zurich, 8092, Switzerland<p>An organic aerosol particle has a lifetime of approximately 1 week in the atmosphere during which it will be exposed to sunlight. However, the effect of photochemistry on the propensity of organic matter to participate in the initial cloud-forming steps is difficult to predict. In this study, we quantify on a molecular scale the effect of photochemical exposure of naturally occurring dissolved organic matter (DOM) and of a fulvic acid standard on its cloud condensation nuclei (CCN) and ice nucleation (IN) activity. We find that photochemical processing, equivalent to 4.6 d in the atmosphere, of DOM increases its ability to form cloud droplets by up to a factor of 2.5 but decreases its ability to form ice crystals at a loss rate of <span class="inline-formula">−0.04</span> <span class="inline-formula"><sup>∘</sup></span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow><msub><mi>T</mi><mn mathvariant="normal">50</mn></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="13pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="8b240bec1e343973563bdbfa5af70aba"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-12397-2019-ie00001.svg" width="13pt" height="10pt" src="acp-19-12397-2019-ie00001.png"/></svg:svg></span></span> h<span class="inline-formula"><sup>−1</sup></span> of sunlight at ground level. In other words, the ice nucleation activity of photooxidized DOM can require up to 4 <span class="inline-formula"><sup>∘</sup></span>C colder temperatures for 50 % of the droplets to activate as ice crystals under immersion freezing conditions. This temperature change could impact the ratio of ice to water droplets within a mixed-phase cloud by delaying the onset of glaciation and by increasing the supercooled liquid fraction of the cloud, thereby modifying the radiative properties and the lifetime of the cloud. Concurrently, a photomineralization mechanism was quantified by monitoring the loss of organic carbon and the simultaneous production of organic acids, such as formic, acetic, oxalic and pyruvic acids, CO and <span class="inline-formula">CO<sub>2</sub></span>. This mechanism explains and predicts the observed increase in CCN and decrease in IN efficiencies. Indeed, we show that photochemical processing can be a dominant atmospheric ageing process, impacting CCN and IN efficiencies and concentrations. Photomineralization can thus alter the aerosol–cloud radiative effects of organic matter by modifying the supercooled-liquid-water-to-ice-crystal ratio in mixed-phase clouds with implications for cloud lifetime, precipitation patterns and the hydrological cycle.<br/><br/><strong>Highlights.</strong> During atmospheric transport, dissolved organic matter (DOM) within aqueous aerosols undergoes photochemistry. We find that photochemical processing of DOM increases its ability to form cloud droplets but decreases its ability to form ice crystals over a simulated 4.6 d in the atmosphere. A photomineralization mechanism involving the loss of organic carbon and the production of organic acids, CO and <span class="inline-formula">CO<sub>2</sub></span> explains the observed changes and affects the liquid-water-to-ice ratio in clouds.</p>https://www.atmos-chem-phys.net/19/12397/2019/acp-19-12397-2019.pdf |