PHOtolysis Reaction Mechanisms by Emerging and New Technologies - PhoRMENT

光化学控制着大量的自然和人造化学过程：光合作用，等离子体技术，太阳能，燃烧和大气化学。一个重要的例子是大气光氧化，它驱动大气自由基传播循环，分解初级污染物排放，但也控制二次污染物的形成，如臭氧和含氧挥发性有机化合物（VOC），这可能对气候，空气质量和人类健康产生重大影响。实验限制甚至抑制了对小气相分子与化学活性紫外线（UV）相互作用的最简单过程的研究。在这个项目中，你将利用新的和新兴的技术，如低成本的紫外线发光二极管，化学传感器（在约克开发）的敏感和选择性的自由基检测，在线质谱，和现代理论计算方法来研究大气中重要的光解反应。在大气中排放或产生的最大类别的化学品是“羰基化合物”-含有一个或多个羰基官能团的有机分子。羰基化合物被广泛用于工业应用，包括直接作为溶剂、杀虫剂和生物燃料，以及作为生产药物和芳香化学品的试剂。羰基化合物也普遍存在于室内和室外空气中。现场生产补充了直接排放，因为几乎所有有机化合物都通过大气氧化过程通过多代羰基中间体分解（图1），它们可以对空气质量和健康产生重大影响。例如，在犹他州东北部的尤尼塔盆地的石油和天然气“水力压裂”领域，羰基的光解作用已被证明会在冬季形成大量臭氧。在大气有机物中，它们通常会被大量的UV-A辐射分解（例如图2）。因此，这个项目特别及时，因为室内的光化学环境正在迅速变化。LED照明正在取代荧光灯和白炽灯技术，而紫外线和等离子体为基础的空气过滤系统越来越多地用于努力提高室内空气质量和抑制病毒的spread.Objectives：确定吸收截面和光解量子产率为各种重要的气相羰基物种;评估光解率和产品分支比，在一系列的室内和室外条件，因此空气质量的影响;确定羰基化合物的化学结构和附加功能如何影响光解速率。实验方法：（1）表征和开发新投入使用的快速流动反应器，结合使用化学传感器自由基阱和在线质谱法确定量子产率（2）紫外-可见光谱技术测量吸收截面（3）高斯量子化学工具包，用于理论热力学计算和化学结构确定（4）开发包含主化学机理的模型（MCM，mcm.york.ac.uk），用于实验设计和环境影响评估

Photochemistry controls a vast array of the natural and man-made chemical processes: photosynthesis, plasma technology, solar energy, combustion and atmospheric chemistry. An important example is atmospheric photo-oxidation, which drives the atmospheric radical propagation cycles that breakdown primary pollutant emissions, but also controls the formation of secondary pollutants such as ozone and oxygenated volatile organic compounds (VOC), which can have significant impacts on climate, air quality and human health.Despite the clear importance of the subject, experimental limitations have inhibited the study of even the simplest processes by which small gas-phase molecules interact with chemically active ultra violet (UV) light. In this project you will exploit new and emerging technologies such as low cost UV LEDs, chemosensors (developed in York) for sensitive and selective free-radical detection, online mass spectrometry, and modern theoretical computational methods to study atmospherically important photolysis reactions. Among the largest classes of chemicals emitted or produced in the atmosphere are "carbonyls" - organic molecules containing one or more carbonyl functionality. Carbonyls are used in in a vast array of industrial applications, including directly as solvents, pesticides and biofuels, and as reagents for production of pharmaceuticals and aromachemicals. Carbonyls are also ubiquitous in both indoor and outdoor air. Direct emissions are supplemented by in-situ production as virtually all organic compounds break-down through atmospheric oxidation processes via multiple generations of carbonyl intermediates (Figure 1), where they can significantly impact on air quality and health. As an example, carbonyl photolysis has been shown to drive large wintertime ozone formation in the oil and gas "fracking" fields of the Unitah Basin in northeastern Utah.The photochemistry of carbonyls is therefore both chemically interesting and important. Unusually amongst atmospheric organics, they are broken down by abundant UV-A radiation (e.g. Figure 2). Therefore this project is particularly timely, as the photochemical environment is rapidly changing indoors. LED lighting is replacing fluorescent and incandescent technology, whilst UV and plasma based air filtration systems are increasingly used in an effort to enhance indoor air quality and to suppress virus spread.Objectives:To determine absorption cross-sections and photolysis quantum yields for a variety of important gas-phase carbonyl species; to assess photolysis rates and product branching ratios, over a range of indoor and outdoor conditions, and hence air quality impacts; to identify how chemical structure and additional functionalities in carbonyls impact upon photolysis rates. Experimental Approach:(1) Characterisation and development of a newly commissioned fast-flow reactor, coupled to the use of chemosensor radical traps and on-line mass spectrometry for quantum yield determinations (2) UV-vis spectroscopy techniques for absorption cross-section measurements(3) GAUSSIAN quantum chemical toolkit for theoretical thermodynamic calculations and chemical structure determination(4) Development of models incorporating the master chemical mechanism (MCM, mcm.york.ac.uk) for experimental design and environmental impact assessment