Understanding the Burst of Hydroxyl Radicals (OH) in Newly Formed Cloud Droplets

在全球气候模拟和预测工作中，气溶胶粒子和气溶胶与云的相互作用仍然是最不受限制的方面之一。为了帮助加深目前的理解，PI试图描述气溶胶颗粒的反应机制，这些颗粒最近显示会产生光诱导的最具氧化性的物质羟基自由基（OH）的初始爆发。重点将放在微量金属和有机过氧化物上，后者代表了在这方面需要研究的一类新的分子。环境气溶胶分析、实验室模拟和室内实验的结果将为OH产生的参数化提供信息，以便纳入更大规模的气候模式。该项目旨在增加对云滴中氢氧根在大气中产生机制的了解。这项工作的动机是PI观察到当气溶胶暴露于近紫外线辐射时，OH产生的初始和实质性爆发。确定云滴中的新OH源对影响全球气候和人类健康的许多化学和物理大气过程具有重要和潜在的变革性意义。三管齐下的实验方法包括测量(1)收集和化学分析的各种类型的环境气溶胶中的OH产量；（ii）受控实验室实验，使用一系列合成（氢）过氧化物、微量金属和不同的pH值、电导率和波长；（三）气室产生的气溶胶颗粒。一种新的半便携式仪器（直接到液体OH分析仪）正在寻求开发，它可以使气溶胶生长成液滴，在几十分钟到几小时的时间尺度上收集和分析OH的形成。实验方法的所有组成部分的结果的化学动力学建模将用于推导速率常数和参数化，以便在更大规模的模型中实现。两名研究生将通过该项目接受培训，一些来自弱势群体的本科生将从PI校园的现有项目中招收。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Aerosol particles and aerosol-cloud interactions remain one of the least constrained aspects in global climate modeling and prediction efforts. To help increase current understanding, the PI seeks to characterize reaction mechanisms in aerosol particles that have shown recently to produce light-induced initial bursts of the most oxidizing species, hydroxyl radical (OH). Focus will be on trace metals and organic peroxides, latter of which represent a new class of molecules to be studied in this context. Results from ambient aerosol analyses, laboratory simulations and chamber experiments will inform parametrization of OH production for incorporation into larger scale climate models. The project aims at increasing understanding of mechanisms of atmospheric production of OH in cloud droplets. The work is motivated by the PI’s observation of an initial and substantial burst in OH production when exposing aerosols to near-UV radiation. Identifying new OH sources in cloud droplets has important and potentially transformative implications on many chemical and physical atmospheric processes that affect global climate and human health. The three-pronged experimental approach consists of measuring OH production in (i) collected and chemically analyzed ambient aerosols of various types; (ii) controlled laboratory experiments using a series of synthesized (hydro)peroxides, trace metals, and varying pH, conductivity, and wavelength; and (iii) chamber generated aerosol particles. A new semi-portable instrument (direct-to liquid OH analyzer) is sought to be developed that allows aerosols to grow to droplets that are collected and analyzed for OH formation on the time scale of tens of minutes to hours. Chemical kinetic modeling of results from all components of the experimental approach will be used to derive rate constants and parametrization for implementation in larger scale models. Two graduate students will receive training through this project, and a number of undergraduate students from underrepresented populations will be recruited from existing programs on the PI’s campus.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.