Gas–particle partitioning of polyol tracers at a suburban site in Nanjing, east China: increased partitioning to the particle phase

• Main Authors: C. Qin, Y. Gou, Y. Wang, Y. Mao, H. Liao, Q. Wang, M. Xie
• Format: Article
• Language: English
• Published: Copernicus Publications 2021-08-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://acp.copernicus.org/articles/21/12141/2021/acp-21-12141-2021.pdf

<p>Gas–particle partitioning of water-soluble organic compounds plays a significant role in influencing the formation, transport, and lifetime of organic aerosols in the atmosphere, but is poorly characterized. In this work, gas- and particle-phase concentrations of isoprene oxidation products (C5-alkene triols and 2-methylterols), levoglucosan, and sugar polyols were measured simultaneously at a suburban site of the western Yangtze River Delta in east China. All target polyols were primarily distributed into the particle phase (85.9 %–99.8 %). Given the uncertainties in measurements and vapor pressure predictions, a dependence of particle-phase fractions on vapor pressures cannot be determined. To explore the impact of aerosol liquid water on gas–particle partitioning of polyol tracers, three partitioning schemes (<i>Cases 1–3</i>) were proposed based on equilibriums of gas vs. organic and aqueous phases in aerosols. If particulate organic matter (OM) is presumed as the only absorbing phase (Case 1), the measurement-based absorptive partitioning coefficients (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi>K</mi><mtext>p,OM</mtext><mi mathvariant="normal">m</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="29pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="839c752742c5b82ea1fa0b062b266767"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-12141-2021-ie00001.svg" width="29pt" height="17pt" src="acp-21-12141-2021-ie00001.png"/></svg:svg></span></span>) of isoprene oxidation products and levoglucosan were more than 10 times greater than predicted values (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi>K</mi><mtext>p,OM</mtext><mi mathvariant="normal">t</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="29pt" height="18pt" class="svg-formula" dspmath="mathimg" md5hash="4423b05b3f4afebe2e67c0544027cfbf"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-12141-2021-ie00002.svg" width="29pt" height="18pt" src="acp-21-12141-2021-ie00002.png"/></svg:svg></span></span>). The agreement between <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi>K</mi><mtext>p,OM</mtext><mi mathvariant="normal">m</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="29pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="18b359d62f63ad6ab630447de3b46710"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-12141-2021-ie00003.svg" width="29pt" height="17pt" src="acp-21-12141-2021-ie00003.png"/></svg:svg></span></span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi>K</mi><mtext>p,OM</mtext><mi mathvariant="normal">t</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="29pt" height="18pt" class="svg-formula" dspmath="mathimg" md5hash="1e209707addad0aff8d29329287c62a2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-12141-2021-ie00004.svg" width="29pt" height="18pt" src="acp-21-12141-2021-ie00004.png"/></svg:svg></span></span> was substantially improved when solubility in a separate aqueous phase was included, whenever water-soluble and water-insoluble OM partitioned into separate (Case 2) or single (Case 3) liquid phases, suggesting that the partitioning of polyol tracers into the aqueous phase in aerosols should not be ignored. The measurement-based effective Henry's law coefficients (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi>K</mi><mtext>H,e</mtext><mi mathvariant="normal">m</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="22pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="db4951c5ba2fcfce31c131e38cd83e24"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-12141-2021-ie00005.svg" width="22pt" height="16pt" src="acp-21-12141-2021-ie00005.png"/></svg:svg></span></span>) of polyol tracers were orders of magnitude higher than their predicted values in pure water (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi>K</mi><mtext>H,w</mtext><mi mathvariant="normal">t</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="67bd1541fa6120ee87219ecb68354005"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-12141-2021-ie00006.svg" width="23pt" height="17pt" src="acp-21-12141-2021-ie00006.png"/></svg:svg></span></span>). Due to the moderate correlations between <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>log⁡</mi><mo>(</mo><msubsup><mi>K</mi><mtext>H,e</mtext><mi mathvariant="normal">m</mi></msubsup><mo>/</mo><msubsup><mi>K</mi><mtext>H,w</mtext><mi mathvariant="normal">t</mi></msubsup><mo>)</mo></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="72pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="ff14261d7a38425034358933b47c8acc"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-12141-2021-ie00007.svg" width="72pt" height="17pt" src="acp-21-12141-2021-ie00007.png"/></svg:svg></span></span> and molality of sulfate ions, the gap between <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi>K</mi><mtext>H,e</mtext><mi mathvariant="normal">m</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="22pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="265ff29ee47d340ffe8338c1ad329248"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-12141-2021-ie00008.svg" width="22pt" height="16pt" src="acp-21-12141-2021-ie00008.png"/></svg:svg></span></span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi>K</mi><mtext>H,w</mtext><mi mathvariant="normal">t</mi></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="2e7f39e0482472d06eb2c50911196387"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-12141-2021-ie00009.svg" width="23pt" height="17pt" src="acp-21-12141-2021-ie00009.png"/></svg:svg></span></span> of polyol tracers could not be fully parameterized by the equation defining “salting-in” effects and might be ascribed to mechanisms of reactive uptake, aqueous phase reaction, “like-dissolves-like” principle, etc. These study results also partly reveal the discrepancy between observation and modeling of organic aerosols.</p>