Toward closure between predicted and observed particle viscosity over a wide range of temperatures and relative humidity
<p>Atmospheric aerosols can exist in amorphous semi-solid or glassy phase states whose viscosity varies with atmospheric temperature and relative humidity. The temperature and humidity dependence of viscosity has been hypothesized to be predictable from the combination of a water–organic binar...
Main Authors: | , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2021-01-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://acp.copernicus.org/articles/21/1127/2021/acp-21-1127-2021.pdf |
Summary: | <p>Atmospheric aerosols can exist in amorphous semi-solid or glassy phase
states whose viscosity varies with atmospheric temperature and relative
humidity. The temperature and humidity dependence of viscosity has
been hypothesized to be predictable from the combination of a water–organic
binary mixing rule of the glass transition temperature, a glass-transition-temperature-scaled viscosity fragility parameterization, and a water
uptake parameterization. This work presents a closure study between
predicted and observed viscosity for sucrose and citric acid. Viscosity
and glass transition temperature as a function of water content are
compiled from literature data and used to constrain the fragility
parameterization. New measurements characterizing viscosity of sub-100 <span class="inline-formula">nm</span> particles using the dimer relaxation method are presented. These
measurements extend the available data of temperature- and humidity-dependent viscosity to <span class="inline-formula">−28</span> <span class="inline-formula"><sup>∘</sup>C</span>. Predicted relationships agree well
with observations at room temperature and with measured isopleths
of constant viscosity at <span class="inline-formula">∼10<sup>7</sup></span> <span class="inline-formula">Pa s</span> at temperatures warmer
than <span class="inline-formula">−28</span> <span class="inline-formula"><sup>∘</sup>C</span>. Discrepancies at colder temperatures
are observed for sucrose particles. Simulations with the kinetic multi-layer
model of gas–particle interactions suggest that the observed deviations
at colder temperature for sucrose can be attributed to kinetic limitations
associated with water uptake at the timescales of the dimer relaxation
experiments. Using the available information, updated equilibrium
phase-state diagrams (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">80</mn><mspace linebreak="nobreak" width="0.125em"/><mrow class="unit"><msup><mi/><mo>∘</mo></msup><mi mathvariant="normal">C</mi></mrow><mo><</mo><mi>T</mi><mo><</mo><mn mathvariant="normal">40</mn><mspace linebreak="nobreak" width="0.125em"/><mrow class="unit"><msup><mi/><mo>∘</mo></msup><mi mathvariant="normal">C</mi></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="92pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="a8a5c5d34161296918d48810867ab97f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-1127-2021-ie00001.svg" width="92pt" height="11pt" src="acp-21-1127-2021-ie00001.png"/></svg:svg></span></span>, temperature, and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">0</mn><mspace width="0.125em" linebreak="nobreak"/><mrow class="unit"><mi mathvariant="normal">%</mi></mrow><mo><</mo><mtext>RH</mtext><mo><</mo><mn mathvariant="normal">100</mn><mspace linebreak="nobreak" width="0.125em"/><mrow class="unit"><mi mathvariant="normal">%</mi></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="89pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="e604a1ecdeb3f856b232be1639e45ed7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-1127-2021-ie00002.svg" width="89pt" height="10pt" src="acp-21-1127-2021-ie00002.png"/></svg:svg></span></span>, relative humidity) for sucrose
and citric acid are constructed and associated equilibration timescales
are identified.</p> |
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ISSN: | 1680-7316 1680-7324 |