Quantification of the pH of Aerosol Droplets via Nanoprobe Based Sensing

大气气溶胶液滴因其影响局部和全球空气质量的能力而被公认。迄今为止，在单个液滴水平上测量气溶胶酸度（或碱度）的努力在很大程度上是不成功的。这项工作支持了利用纳米技术和激光光谱学来量化液滴酸度（或碱度）的研究。预期的结果将提高对气溶胶液滴化学的理解，从而提高社会对气溶胶相互作用复杂性的认识。本科生和研究生都将接受先进光谱方法的培训，并将启动广泛的K-12外展工作。这项工作的主要研究目标是量化微米尺度气溶胶液滴的pH值，并评估它如何影响液滴的化学性质。pH值是所有天然水的决定性特征；然而，单个雾化液滴的pH值尚未通过直接测量得到很好的确定。在这项工作中，最近开发的新型纳米探针将用于探测单个微米级液滴内的pH值，以及研究反应气体对液滴pH值的影响。pi将利用基于金纳米粒子（AuNP）的探针所带来的空间灵敏度，这些探针被携带在15-40 ìm直径的液滴的密闭环境中。通过利用纳米级光学技术——表面增强拉曼光谱（SERS）， pi有望以300纳米的分辨率在二维和三维光谱中检测pH值的差异。将实现以下三个研究目标：目标1：确定微米尺度液滴内pH值的空间分布。目标2：确定pH值如何随相对湿度（RH）变化，因为气溶胶受到开花和潮解周期的影响。目标3：量化反应气体（CO2, SO2, NH3）对液滴ph的影响。以往的研究已经确定气态污染物在气溶胶液滴内发生转化。许多这样的反应是pH敏感的，如果初步的pH值结果是正确的，这些反应可以相对于体相预期加速或减速。这样的结果将对我们理解气溶胶在许多生态系统中的相互作用产生重大影响。参与该项目的不同个人将为科学工作做出贡献，但更重要的是，他们将通过弗吉尼亚理工大学可持续纳米技术（VTSuN）计划和美国国家科学基金会资助的纳米地球中心组织的外展活动与K-12和其他团体进行互动。

PI Name: VikeslandProposal Number: 1705653Atmospheric aerosol droplets are well recognized for their capacity to affect both local-scale as well as global air quality. To date, efforts to measure the acidity (or basicity) of aerosols at the individual droplet level have been largely unsuccessful. This effort supports research conducted to quantify droplet acidity (or basicity) using nanotechnology and laser-enabled spectroscopy. The expected results will provide an improved understanding of aerosol droplet chemistry and will thus enhance societal appreciation of the complexity of aerosol interactions. Both undergraduate and graduate students will receive training in advanced spectroscopic methods, and an extensive K-12 outreach effort will be initiated. The primary research goal of this effort is to quantify the pH of micron-scale aerosol droplets and evaluate how it affects droplet chemistry. pH is a defining characteristic of all natural waters; however, the pH of individual aerosolized droplets has not been well established through direct measurements. In this effort recently developed novel nanoprobes will be used to probe pH inside individual micron-scale droplets as well as to investigate the influence of reactive gases on droplet pH. The PIs will take advantage of the spatial sensitivity enabled by gold nanoparticle (AuNP) based probes that are entrained within the confined environment of a 15-40 ìm diameter droplet. By utilizing a nanoscale optical technique--surface enhanced Raman spectroscopy (SERS)--the PIs expect to spectroscopically detect differences in pH in both 2-D and 3-D with ~300 nm resolution. The following three research objectives will be met: Objective 1: Determine the spatial distribution of pH inside micron-scale droplets. Objective 2: Determine how pH changes with relative humidity (RH) as an aerosol is subjected to cycles of efflorescence and deliquescence. Objective 3: Quantify the effect of reactive gases (CO2, SO2, NH3) on droplet pH. Previous studies have established that gaseous pollutants undergo transformations inside aerosol droplets. Many such reactions are pH sensitive, and if the preliminary pH results are correct, these reactions could be either accelerated or decelerated relative to bulk phase expectations. Such an outcome would have a major impact on our understanding of aerosol interactions across many ecosystems. The diverse individuals engaged with this project will contribute to the scientific workforce, but more importantly they will interact with K-12 and other groups via outreach activities organized by the Virginia Tech Sustainable Nanotechnology (VTSuN) program and the NSF-funded NanoEarth Center.