Reactive uptake of N<sub>2</sub>O<sub>5</sub> to internally mixed inorganic and organic particles: the role of organic carbon oxidation state and inferred organic phase separations
We measured N<sub>2</sub>O<sub>5</sub> reactive uptake onto mixed organic/inorganic submicron particles using organic compounds with a variety of oxidation states (using mainly atomic O : C ratios as a proxy) and molecular weights. The organic mass fraction, organic molecular...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2014-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/14/5693/2014/acp-14-5693-2014.pdf |
| _version_ | 1828224888215699456 |
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| author | C. J. Gaston J. A. Thornton N. L. Ng |
| author_facet | C. J. Gaston J. A. Thornton N. L. Ng |
| author_sort | C. J. Gaston |
| collection | DOAJ |
| description | We measured N<sub>2</sub>O<sub>5</sub> reactive uptake onto mixed organic/inorganic
submicron particles using organic compounds with a variety of oxidation
states (using mainly atomic O : C ratios as a proxy) and molecular weights.
The organic mass fraction, organic molecular composition, and relative
humidity (RH) were varied to assess their effects
separately on the N<sub>2</sub>O<sub>5</sub> uptake
coefficient, γ(N<sub>2</sub>O<sub>5</sub>). At a constant RH, mixtures of organic
components having an O : C < 0.5 with ammonium bisulfate
significantly suppressed the uptake of N<sub>2</sub>O<sub>5</sub>(g) compared to pure
ammonium bisulfate, even at small organic mass fractions (e.g., ≤
15%). The effect of the organic component became less pronounced at
higher RH. In general, highly oxygenated organic components
(O : C > 0.8) had a smaller or even negligible impact on
N<sub>2</sub>O<sub>5</sub>(g) uptake at all RHs probed; however, a few exceptions were
observed. Notably, γ(N<sub>2</sub>O<sub>5</sub>) for mixtures of ammonium
bisulfate with polyethylene glycol (PEG), PEG-300 (O : C = 0.56),
decreased nearly linearly as the PEG mass fraction increased at constant RH
until leveling off at the value measured for pure PEG. The response of
γ(N<sub>2</sub>O<sub>5</sub>) to increasing PEG mass fraction was similar to that
measured on ambient atmospheric particles as a function of organic mass
fraction. The effects of the organic mass fraction on γ(N<sub>2</sub>O<sub>5</sub>), for mixtures having an O : C < ~0.8,
were best described using a standard resistor model of reactive uptake
assuming the particles had an RH-dependent inorganic core–organic shell
morphology. This model suggests that the N<sub>2</sub>O<sub>5</sub> diffusivity and/or
solubility in the organic layer is up to a factor of 20 lower compared to
aqueous solution particles, and that the diffusivity, solubility, and
reactivity of N<sub>2</sub>O<sub>5</sub> within organic coatings and particles depend
upon both RH and the molecular composition of the organic medium. We use
these dependencies and ambient measurements of organic aerosol from the
global aerosol mass spectrometry (AMS) database to show that the typical
impact of organic aerosol components is to both uniformly decrease γ(N<sub>2</sub>O<sub>5</sub>), by up to an order of magnitude depending on the RH,
organic mass fraction, and O : C ratio, and to induce a stronger dependence
of γ(N<sub>2</sub>O<sub>5</sub>) upon RH compared to purely inorganic aqueous
solutions. |
| first_indexed | 2024-04-12T17:25:02Z |
| format | Article |
| id | doaj.art-0367f8fd99394096bfba20bc846dab8c |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-04-12T17:25:02Z |
| publishDate | 2014-06-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-0367f8fd99394096bfba20bc846dab8c2022-12-22T03:23:19ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242014-06-0114115693570710.5194/acp-14-5693-2014Reactive uptake of N<sub>2</sub>O<sub>5</sub> to internally mixed inorganic and organic particles: the role of organic carbon oxidation state and inferred organic phase separationsC. J. Gaston0J. A. Thornton1N. L. Ng2Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USADepartment of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USASchool of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USAWe measured N<sub>2</sub>O<sub>5</sub> reactive uptake onto mixed organic/inorganic submicron particles using organic compounds with a variety of oxidation states (using mainly atomic O : C ratios as a proxy) and molecular weights. The organic mass fraction, organic molecular composition, and relative humidity (RH) were varied to assess their effects separately on the N<sub>2</sub>O<sub>5</sub> uptake coefficient, γ(N<sub>2</sub>O<sub>5</sub>). At a constant RH, mixtures of organic components having an O : C < 0.5 with ammonium bisulfate significantly suppressed the uptake of N<sub>2</sub>O<sub>5</sub>(g) compared to pure ammonium bisulfate, even at small organic mass fractions (e.g., ≤ 15%). The effect of the organic component became less pronounced at higher RH. In general, highly oxygenated organic components (O : C > 0.8) had a smaller or even negligible impact on N<sub>2</sub>O<sub>5</sub>(g) uptake at all RHs probed; however, a few exceptions were observed. Notably, γ(N<sub>2</sub>O<sub>5</sub>) for mixtures of ammonium bisulfate with polyethylene glycol (PEG), PEG-300 (O : C = 0.56), decreased nearly linearly as the PEG mass fraction increased at constant RH until leveling off at the value measured for pure PEG. The response of γ(N<sub>2</sub>O<sub>5</sub>) to increasing PEG mass fraction was similar to that measured on ambient atmospheric particles as a function of organic mass fraction. The effects of the organic mass fraction on γ(N<sub>2</sub>O<sub>5</sub>), for mixtures having an O : C < ~0.8, were best described using a standard resistor model of reactive uptake assuming the particles had an RH-dependent inorganic core–organic shell morphology. This model suggests that the N<sub>2</sub>O<sub>5</sub> diffusivity and/or solubility in the organic layer is up to a factor of 20 lower compared to aqueous solution particles, and that the diffusivity, solubility, and reactivity of N<sub>2</sub>O<sub>5</sub> within organic coatings and particles depend upon both RH and the molecular composition of the organic medium. We use these dependencies and ambient measurements of organic aerosol from the global aerosol mass spectrometry (AMS) database to show that the typical impact of organic aerosol components is to both uniformly decrease γ(N<sub>2</sub>O<sub>5</sub>), by up to an order of magnitude depending on the RH, organic mass fraction, and O : C ratio, and to induce a stronger dependence of γ(N<sub>2</sub>O<sub>5</sub>) upon RH compared to purely inorganic aqueous solutions.http://www.atmos-chem-phys.net/14/5693/2014/acp-14-5693-2014.pdf |
| spellingShingle | C. J. Gaston J. A. Thornton N. L. Ng Reactive uptake of N<sub>2</sub>O<sub>5</sub> to internally mixed inorganic and organic particles: the role of organic carbon oxidation state and inferred organic phase separations Atmospheric Chemistry and Physics |
| title | Reactive uptake of N<sub>2</sub>O<sub>5</sub> to internally mixed inorganic and organic particles: the role of organic carbon oxidation state and inferred organic phase separations |
| title_full | Reactive uptake of N<sub>2</sub>O<sub>5</sub> to internally mixed inorganic and organic particles: the role of organic carbon oxidation state and inferred organic phase separations |
| title_fullStr | Reactive uptake of N<sub>2</sub>O<sub>5</sub> to internally mixed inorganic and organic particles: the role of organic carbon oxidation state and inferred organic phase separations |
| title_full_unstemmed | Reactive uptake of N<sub>2</sub>O<sub>5</sub> to internally mixed inorganic and organic particles: the role of organic carbon oxidation state and inferred organic phase separations |
| title_short | Reactive uptake of N<sub>2</sub>O<sub>5</sub> to internally mixed inorganic and organic particles: the role of organic carbon oxidation state and inferred organic phase separations |
| title_sort | reactive uptake of n sub 2 sub o sub 5 sub to internally mixed inorganic and organic particles the role of organic carbon oxidation state and inferred organic phase separations |
| url | http://www.atmos-chem-phys.net/14/5693/2014/acp-14-5693-2014.pdf |
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