Liquid–liquid phase separation and viscosity within secondary organic aerosol generated from diesel fuel vapors

<p>Information on liquid–liquid phase separation (LLPS) and viscosity (or diffusion) within secondary organic aerosol (SOA) is needed to improve predictions of particle size, mass, reactivity, and cloud nucleating properties in the atmosphere. Here we report on LLPS and viscosities within SOA...

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Main Authors:	M. Song, A. M. Maclean, Y. Huang, N. R. Smith, S. L. Blair, J. Laskin, A. Laskin, W.-S. W. DeRieux, Y. Li, M. Shiraiwa, S. A. Nizkorodov, A. K. Bertram
Format:	Article
Language:	English
Published:	Copernicus Publications 2019-10-01
Series:	Atmospheric Chemistry and Physics
Online Access:	https://www.atmos-chem-phys.net/19/12515/2019/acp-19-12515-2019.pdf

id	doaj-b52d5d50ee5748539c15c16655af41ec
record_format	Article
collection	DOAJ
language	English
format	Article
sources	DOAJ
author	M. Song M. Song A. M. Maclean Y. Huang N. R. Smith S. L. Blair J. Laskin A. Laskin W.-S. W. DeRieux Y. Li M. Shiraiwa S. A. Nizkorodov A. K. Bertram
spellingShingle	M. Song M. Song A. M. Maclean Y. Huang N. R. Smith S. L. Blair J. Laskin A. Laskin W.-S. W. DeRieux Y. Li M. Shiraiwa S. A. Nizkorodov A. K. Bertram Liquid–liquid phase separation and viscosity within secondary organic aerosol generated from diesel fuel vapors Atmospheric Chemistry and Physics
author_facet	M. Song M. Song A. M. Maclean Y. Huang N. R. Smith S. L. Blair J. Laskin A. Laskin W.-S. W. DeRieux Y. Li M. Shiraiwa S. A. Nizkorodov A. K. Bertram
author_sort	M. Song
title	Liquid–liquid phase separation and viscosity within secondary organic aerosol generated from diesel fuel vapors
title_short	Liquid–liquid phase separation and viscosity within secondary organic aerosol generated from diesel fuel vapors
title_full	Liquid–liquid phase separation and viscosity within secondary organic aerosol generated from diesel fuel vapors
title_fullStr	Liquid–liquid phase separation and viscosity within secondary organic aerosol generated from diesel fuel vapors
title_full_unstemmed	Liquid–liquid phase separation and viscosity within secondary organic aerosol generated from diesel fuel vapors
title_sort	liquid–liquid phase separation and viscosity within secondary organic aerosol generated from diesel fuel vapors
publisher	Copernicus Publications
series	Atmospheric Chemistry and Physics
issn	1680-7316 1680-7324
publishDate	2019-10-01
description	<p>Information on liquid–liquid phase separation (LLPS) and viscosity (or diffusion) within secondary organic aerosol (SOA) is needed to improve predictions of particle size, mass, reactivity, and cloud nucleating properties in the atmosphere. Here we report on LLPS and viscosities within SOA generated by the photooxidation of diesel fuel vapors. Diesel fuel contains a wide range of volatile organic compounds, and SOA generated by the photooxidation of diesel fuel vapors may be a good proxy for SOA from anthropogenic emissions. In our experiments, LLPS occurred over the relative humidity (RH) range of <span class="inline-formula">∼70</span> % to <span class="inline-formula">∼100</span> %, resulting in an organic-rich outer phase and a water-rich inner phase. These results may have implications for predicting the cloud nucleating properties of anthropogenic SOA since the presence of an organic-rich outer phase at high-RH values can lower the supersaturation with respect to water required for cloud droplet formation. At <span class="inline-formula">≤10</span> % RH, the viscosity was <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>≥</mo><mn mathvariant="normal">1</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">8</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="46pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="d3becb04dea2544bfec575e486a5f107"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-12515-2019-ie00001.svg" width="46pt" height="14pt" src="acp-19-12515-2019-ie00001.png"/></svg:svg></span></span> Pa s, which corresponds to roughly the viscosity of tar pitch. At 38 %–50 % RH, the viscosity was in the range of <span class="inline-formula">1×10<sup>8</sup></span> to <span class="inline-formula">3×10<sup>5</sup></span> Pa s. These measured viscosities are consistent with predictions based on oxygen to carbon elemental ratio (<span class="inline-formula">O:C</span>) and molar mass as well as predictions based on the number of carbon, hydrogen, and oxygen atoms. Based on the measured viscosities and the Stokes–Einstein relation, at <span class="inline-formula">≤10</span> % RH diffusion coefficients of organics within diesel fuel SOA is <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>≤</mo><mn mathvariant="normal">5.4</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">17</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="65pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="81f85a19804ee0bbb25c62f30c9dfc4e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-12515-2019-ie00002.svg" width="65pt" height="14pt" src="acp-19-12515-2019-ie00002.png"/></svg:svg></span></span> cm<span class="inline-formula"><sup>2</sup></span> s<span class="inline-formula"><sup>−1</sup></span> and the mixing time of organics within 200 nm diesel fuel SOA particles (<span class="inline-formula"><i>τ</i><sub>mixing</sub></span>) is 50 h. These small diffusion coefficients and large mixing times may be important in laboratory experiments, where SOA is often generated and studied using low-RH conditions and on timescales of minutes to hours. At 38 %–50 % RH, the calculated organic diffusion coefficients are in the range of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">5.4</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">17</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="55pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="b8aaddae8a73d2d23727b0f38112daf7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-12515-2019-ie00003.svg" width="55pt" height="14pt" src="acp-19-12515-2019-ie00003.png"/></svg:svg></span></span> to <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">1.8</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">13</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="55pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="bfcea12d119b18040d27e13eb2907160"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-12515-2019-ie00004.svg" width="55pt" height="14pt" src="acp-19-12515-2019-ie00004.png"/></svg:svg></span></span> cm<span class="inline-formula"><sup>2</sup></span> s<span class="inline-formula"><sup>−1</sup></span> and calculated <span class="inline-formula"><i>τ</i><sub>mixing</sub></span> values are in the range of <span class="inline-formula">∼0.01</span> h to <span class="inline-formula">∼50</span> h. These values provide important constraints for the physicochemical properties of anthropogenic SOA.</p>
url	https://www.atmos-chem-phys.net/19/12515/2019/acp-19-12515-2019.pdf
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spelling	doaj-b52d5d50ee5748539c15c16655af41ec2020-11-25T01:35:53ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242019-10-0119125151252910.5194/acp-19-12515-2019Liquid–liquid phase separation and viscosity within secondary organic aerosol generated from diesel fuel vaporsM. Song0M. Song1A. M. Maclean2Y. Huang3N. R. Smith4S. L. Blair5J. Laskin6A. Laskin7W.-S. W. DeRieux8Y. Li9M. Shiraiwa10S. A. Nizkorodov11A. K. Bertram12Department of Earth and Environmental Sciences, Chonbuk National University, Jeollabuk-do, 54896, Republic of KoreaDepartment of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z1, CanadaDepartment of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z1, CanadaDepartment of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z1, CanadaDepartment of Chemistry, University of California Irvine, Irvine, CA 92697, USADepartment of Chemistry, University of California Irvine, Irvine, CA 92697, USADepartment of Chemistry, Purdue University, West Lafayette, IN 47907, USADepartment of Chemistry, Purdue University, West Lafayette, IN 47907, USADepartment of Chemistry, University of California Irvine, Irvine, CA 92697, USADepartment of Chemistry, University of California Irvine, Irvine, CA 92697, USADepartment of Chemistry, University of California Irvine, Irvine, CA 92697, USADepartment of Chemistry, University of California Irvine, Irvine, CA 92697, USADepartment of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada<p>Information on liquid–liquid phase separation (LLPS) and viscosity (or diffusion) within secondary organic aerosol (SOA) is needed to improve predictions of particle size, mass, reactivity, and cloud nucleating properties in the atmosphere. Here we report on LLPS and viscosities within SOA generated by the photooxidation of diesel fuel vapors. Diesel fuel contains a wide range of volatile organic compounds, and SOA generated by the photooxidation of diesel fuel vapors may be a good proxy for SOA from anthropogenic emissions. In our experiments, LLPS occurred over the relative humidity (RH) range of <span class="inline-formula">∼70</span> % to <span class="inline-formula">∼100</span> %, resulting in an organic-rich outer phase and a water-rich inner phase. These results may have implications for predicting the cloud nucleating properties of anthropogenic SOA since the presence of an organic-rich outer phase at high-RH values can lower the supersaturation with respect to water required for cloud droplet formation. At <span class="inline-formula">≤10</span> % RH, the viscosity was <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>≥</mo><mn mathvariant="normal">1</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">8</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="46pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="d3becb04dea2544bfec575e486a5f107"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-12515-2019-ie00001.svg" width="46pt" height="14pt" src="acp-19-12515-2019-ie00001.png"/></svg:svg></span></span> Pa s, which corresponds to roughly the viscosity of tar pitch. At 38 %–50 % RH, the viscosity was in the range of <span class="inline-formula">1×10<sup>8</sup></span> to <span class="inline-formula">3×10<sup>5</sup></span> Pa s. These measured viscosities are consistent with predictions based on oxygen to carbon elemental ratio (<span class="inline-formula">O:C</span>) and molar mass as well as predictions based on the number of carbon, hydrogen, and oxygen atoms. Based on the measured viscosities and the Stokes–Einstein relation, at <span class="inline-formula">≤10</span> % RH diffusion coefficients of organics within diesel fuel SOA is <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>≤</mo><mn mathvariant="normal">5.4</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">17</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="65pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="81f85a19804ee0bbb25c62f30c9dfc4e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-12515-2019-ie00002.svg" width="65pt" height="14pt" src="acp-19-12515-2019-ie00002.png"/></svg:svg></span></span> cm<span class="inline-formula"><sup>2</sup></span> s<span class="inline-formula"><sup>−1</sup></span> and the mixing time of organics within 200 nm diesel fuel SOA particles (<span class="inline-formula"><i>τ</i><sub>mixing</sub></span>) is 50 h. These small diffusion coefficients and large mixing times may be important in laboratory experiments, where SOA is often generated and studied using low-RH conditions and on timescales of minutes to hours. At 38 %–50 % RH, the calculated organic diffusion coefficients are in the range of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">5.4</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">17</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="55pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="b8aaddae8a73d2d23727b0f38112daf7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-12515-2019-ie00003.svg" width="55pt" height="14pt" src="acp-19-12515-2019-ie00003.png"/></svg:svg></span></span> to <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">1.8</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">13</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="55pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="bfcea12d119b18040d27e13eb2907160"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-12515-2019-ie00004.svg" width="55pt" height="14pt" src="acp-19-12515-2019-ie00004.png"/></svg:svg></span></span> cm<span class="inline-formula"><sup>2</sup></span> s<span class="inline-formula"><sup>−1</sup></span> and calculated <span class="inline-formula"><i>τ</i><sub>mixing</sub></span> values are in the range of <span class="inline-formula">∼0.01</span> h to <span class="inline-formula">∼50</span> h. These values provide important constraints for the physicochemical properties of anthropogenic SOA.</p>https://www.atmos-chem-phys.net/19/12515/2019/acp-19-12515-2019.pdf

Liquid–liquid phase separation and viscosity within secondary organic aerosol generated from diesel fuel vapors

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