Viscosity of aqueous ammonium nitrate–organic particles: equilibrium partitioning may be a reasonable assumption for most tropospheric conditions
<p>The viscosity of aerosol particles determines the critical mixing time of gas–particle partitioning of volatile compounds in the atmosphere. The partitioning of the semi-volatile ammonium nitrate (<span class="inline-formula">NH<sub>4</sub>NO<sub>3</sub&...
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Copernicus Publications
2024-12-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/24/13341/2024/acp-24-13341-2024.pdf |
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| author | L. K. Klein L. K. Klein A. K. Bertram A. Zuend F. Gregson U. K. Krieger |
| author_facet | L. K. Klein L. K. Klein A. K. Bertram A. Zuend F. Gregson U. K. Krieger |
| author_sort | L. K. Klein |
| collection | DOAJ |
| description | <p>The viscosity of aerosol particles determines the critical mixing time of gas–particle partitioning of volatile compounds in the atmosphere. The partitioning of the semi-volatile ammonium nitrate (<span class="inline-formula">NH<sub>4</sub>NO<sub>3</sub></span>) might alter the viscosity of highly viscous secondary organic aerosol particles during their lifetimes. In contrast to the viscosity of organic particles, data on the viscosity of internally mixed inorganic–organic aerosol particles are scarce. We determined the viscosity of an aqueous ternary inorganic–organic system consisting of <span class="inline-formula">NH<sub>4</sub>NO<sub>3</sub></span> and a proxy compound for a highly viscous organic, sucrose. Three techniques were applied to cover the atmospherically relevant humidity range: viscometry, fluorescence recovery after photobleaching, and the poke-flow technique. We show that the viscosity of <span class="inline-formula">NH<sub>4</sub>NO<sub>3</sub></span>–sucrose–<span class="inline-formula">H<sub>2</sub>O</span> with an organic to inorganic dry mass ratio of <span class="inline-formula">4:1</span> is 4 orders of magnitude lower than the viscosity of the aqueous sucrose under low-humidity conditions (30 % relative humidity (RH), 293 K). By comparing viscosity predictions of mixing rules with those of the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients Viscosity (AIOMFAC-VISC) model, we found that a mixing rule based on mole fractions performs similarly when data from corresponding binary aqueous subsystems are available. Applying this mixing rule, we estimated the characteristic internal mixing time of aerosol particles, indicating significantly faster mixing for inorganic–organic mixtures compared to electrolyte-free particles, especially at lower RH. Hence, the assumption in global atmospheric chemistry models of quasi-instantaneous equilibrium gas–particle partitioning is reasonable for internally mixed single-phase particles containing dissolved electrolytes (but not necessarily for phase-separated particles), for most conditions in the planetary boundary layer. Further data are needed to see whether this assumption holds for the entire troposphere at midlatitudes and at RH <span class="inline-formula">></span> 35 %.</p> |
| format | Article |
| id | doaj-art-dbfd2404da3c4d8f8edfaf9926f3de55 |
| institution | Kabale University |
| issn | 1680-7316 1680-7324 |
| language | English |
| publishDate | 2024-12-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj-art-dbfd2404da3c4d8f8edfaf9926f3de552024-12-03T14:05:12ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242024-12-0124133411335910.5194/acp-24-13341-2024Viscosity of aqueous ammonium nitrate–organic particles: equilibrium partitioning may be a reasonable assumption for most tropospheric conditionsL. K. Klein0L. K. Klein1A. K. Bertram2A. Zuend3F. Gregson4U. K. Krieger5Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, SwitzerlandDepartment of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA, USADepartment of Chemistry, University of British Columbia, Vancouver, BC, CanadaDepartment of Atmospheric and Oceanic Sciences, McGill University, Montreal, QC, CanadaDepartment of Chemistry, University of British Columbia, Vancouver, BC, CanadaInstitute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland<p>The viscosity of aerosol particles determines the critical mixing time of gas–particle partitioning of volatile compounds in the atmosphere. The partitioning of the semi-volatile ammonium nitrate (<span class="inline-formula">NH<sub>4</sub>NO<sub>3</sub></span>) might alter the viscosity of highly viscous secondary organic aerosol particles during their lifetimes. In contrast to the viscosity of organic particles, data on the viscosity of internally mixed inorganic–organic aerosol particles are scarce. We determined the viscosity of an aqueous ternary inorganic–organic system consisting of <span class="inline-formula">NH<sub>4</sub>NO<sub>3</sub></span> and a proxy compound for a highly viscous organic, sucrose. Three techniques were applied to cover the atmospherically relevant humidity range: viscometry, fluorescence recovery after photobleaching, and the poke-flow technique. We show that the viscosity of <span class="inline-formula">NH<sub>4</sub>NO<sub>3</sub></span>–sucrose–<span class="inline-formula">H<sub>2</sub>O</span> with an organic to inorganic dry mass ratio of <span class="inline-formula">4:1</span> is 4 orders of magnitude lower than the viscosity of the aqueous sucrose under low-humidity conditions (30 % relative humidity (RH), 293 K). By comparing viscosity predictions of mixing rules with those of the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients Viscosity (AIOMFAC-VISC) model, we found that a mixing rule based on mole fractions performs similarly when data from corresponding binary aqueous subsystems are available. Applying this mixing rule, we estimated the characteristic internal mixing time of aerosol particles, indicating significantly faster mixing for inorganic–organic mixtures compared to electrolyte-free particles, especially at lower RH. Hence, the assumption in global atmospheric chemistry models of quasi-instantaneous equilibrium gas–particle partitioning is reasonable for internally mixed single-phase particles containing dissolved electrolytes (but not necessarily for phase-separated particles), for most conditions in the planetary boundary layer. Further data are needed to see whether this assumption holds for the entire troposphere at midlatitudes and at RH <span class="inline-formula">></span> 35 %.</p>https://acp.copernicus.org/articles/24/13341/2024/acp-24-13341-2024.pdf |
| spellingShingle | L. K. Klein L. K. Klein A. K. Bertram A. Zuend F. Gregson U. K. Krieger Viscosity of aqueous ammonium nitrate–organic particles: equilibrium partitioning may be a reasonable assumption for most tropospheric conditions Atmospheric Chemistry and Physics |
| title | Viscosity of aqueous ammonium nitrate–organic particles: equilibrium partitioning may be a reasonable assumption for most tropospheric conditions |
| title_full | Viscosity of aqueous ammonium nitrate–organic particles: equilibrium partitioning may be a reasonable assumption for most tropospheric conditions |
| title_fullStr | Viscosity of aqueous ammonium nitrate–organic particles: equilibrium partitioning may be a reasonable assumption for most tropospheric conditions |
| title_full_unstemmed | Viscosity of aqueous ammonium nitrate–organic particles: equilibrium partitioning may be a reasonable assumption for most tropospheric conditions |
| title_short | Viscosity of aqueous ammonium nitrate–organic particles: equilibrium partitioning may be a reasonable assumption for most tropospheric conditions |
| title_sort | viscosity of aqueous ammonium nitrate organic particles equilibrium partitioning may be a reasonable assumption for most tropospheric conditions |
| url | https://acp.copernicus.org/articles/24/13341/2024/acp-24-13341-2024.pdf |
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