Aerosol microdroplets exhibit a stable pH gradient

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dc.contributor.authorWei, Haoranen
dc.contributor.authorVejerano, Eric P.en
dc.contributor.authorLeng, Weinanen
dc.contributor.authorHuang, Qishenen
dc.contributor.authorWillner, Marjorie R.en
dc.contributor.authorMarr, Linsey C.en
dc.contributor.authorVikesland, Peter J.en
dc.contributor.departmentCivil and Environmental Engineeringen
dc.contributor.departmentInstitute for Critical Technology and Applied Science (ICTAS)en
dc.date.accessioned2019-09-16T19:02:43Zen
dc.date.available2019-09-16T19:02:43Zen
dc.date.issued2018-07-10en
dc.description.abstractSuspended aqueous aerosol droplets (< 50 mu m) are microreactors for many important atmospheric reactions. In droplets and other aquatic environments, pH is arguably the key parameter dictating chemical and biological processes. The nature of the droplet air/water interface has the potential to significantly alter droplet pH relative to bulk water. Historically, it has been challenging to measure the pH of individual droplets because of their inaccessibility to conventional pH probes. In this study, we scanned droplets containing 4-mercaptobenzoic acid-functionalized gold nanoparticle pH nanoprobes by 2D and 3D laser confocal Raman microscopy. Using surface-enhanced Raman scattering, we acquired the pH distribution inside approximately 20-mu m-diameter phosphate-buffered aerosol droplets and found that the pH in the core of a droplet is higher than that of bulk solution by up to 3.6 pH units. This finding suggests the accumulation of protons at the air/water interface and is consistent with recent thermodynamic model results. The existence of this pH shift was corroborated by the observation that a catalytic reaction that occurs only under basic conditions (i.e., dimerization of 4-aminothiophenol to produce dimercaptoazobenzene) occurs within the high pH core of a droplet, but not in bulk solution. Our nanoparticle probe enables pH quantification through the cross-section of an aerosol droplet, revealing a spatial gradient that has implications for acid-base-catalyzed atmospheric chemistry.en
dc.description.notesThis research was supported by National Institutes of Health Director's New Innovator Award 1-DP2-A1112243 (to L.C.M.) and National Science Foundation Grant CBET-1705653 (to P.J.V. and L.C.M.). Additional support for H.W. and M.R.W. was provided by the Virginia Tech Graduate School through the Sustainable Nanotechnology Interdisciplinary Graduate Education Program.en
dc.description.sponsorshipNational Institutes of Health [1-DP2-A1112243]; National Science Foundation [CBET-1705653]; Virginia Tech Graduate Schoolen
dc.format.mimetypeapplication/pdfen
dc.identifier.doihttps://doi.org/10.1073/pnas.1720488115en
dc.identifier.issn0027-8424en
dc.identifier.issue28en
dc.identifier.pmid29941550en
dc.identifier.urihttp://hdl.handle.net/10919/93720en
dc.identifier.volume115en
dc.language.isoenen
dc.rightsCreative Commons Attribution-NonCommercial-NoDerivatives 4.0 Internationalen
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/4.0/en
dc.subjectaerosolen
dc.subjectdropleten
dc.subjectpHen
dc.subjectinterfaceen
dc.subjectSERSen
dc.titleAerosol microdroplets exhibit a stable pH gradienten
dc.title.serialProceedings of the National Academy of Sciences of the United States of Americaen
dc.typeArticle - Refereeden
dc.type.dcmitypeTexten
dc.type.dcmitypeStillImageen

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