Sensitive and Versatile Tropospheric Hydrogen Chloride (HCl) Instrument

氯化氢（HCl）气体是了解对流层卤素循环的关键，因为它是一种相对丰富的气相卤素，在化学反应性更强的氯化合物中充当源、中间体或最终产物。然而，它在对流层的采样量严重不足。为了更好地量化其来源、汇、运输，并最终更好地了解控制对流层卤素活化的过程，迫切需要对HCl进行准确的原位测量。该项目将开发一种超灵敏的HCl气体光学传感器。该传感器基于腔衰荡光谱（CRDS），这是一种高灵敏度的光学吸收方法。光谱学的最新进展使开发具有高灵敏度和时间响应的多功能（即小、轻、低功耗）、精确和特定的HCl传感器成为可能。HCl传感器将采用近红外二极管激光器用于连续波CRDS。虽然该传感器主要用于HCl检测，但它可以同时进行高灵敏度和高精度的甲烷检测。研制这样一种仪器将有助于研究盐酸在大气中的作用，并可能使其能够在船舶和飞机等移动平台上部署。提高对卤素活化的一般认识，特别是对盐酸的认识，对区域空气质量和气候的模拟具有广泛的意义。在受污染的沿海环境中，HCl是与海盐酸置换反应的主要产物，是氯原子的主要来源。涉及HCl的卤素活化循环也可能通过氧化甲烷和其他有机气体、将海洋硫排放转化为硫酸盐气溶胶以及潜在地调节对流层臭氧和其他氧化剂水平影响气候系统。就未来的仪器仪表而言，本文提出的传感器设计和架构将为开发与大气化学（如乙炔、氨）相关的其他物种的类似传感器提供蓝图。该项目还将为科罗拉多州立大学（CSU）机械工程专业的研究生和本科生提供独特的教育机会。将特别努力招收女学生和代表人数不足群体的学生参加该项目。学生们将设计和开发一种最先进的大气传感仪器，并将与科罗拉多州立大学、其他大学和附近联邦环境研究实验室的大气化学研究人员进行互动。研究结果将纳入科罗拉多州立大学的课程，并在学术会议上发表。

Hydrogen chloride (HCl) gas is key to the understanding of tropospheric halogen cycles, since it is a relatively abundant gas-phase halogen species that serves as a source, an intermediate, or an end product in the chemistry of more reactive chlorine compounds. It is, however, greatly undersampled in the troposphere. Accurate in situ measurements of HCl are critically needed to better quantify its sources, sinks, transport, and ultimately to better understand the processes that govern tropospheric halogen activation. This project will develop an ultra-sensitive optical sensor for HCl gas. The sensor is based on cavity ring-down spectroscopy (CRDS), a method for high-sensitivity optical absorption. Recent advances in optical spectroscopy make possible the development of a versatile (i.e., small, lightweight, low power consumption), accurate and specific HCl sensor with high sensitivity and time response. The HCl sensor will employ a near-infrared diode laser for continuous-wave CRDS. Although the sensor is primarily targeted at HCl detection, it will allow simultaneous methane detection with high sensitivity and precision. The development of such an instrument will facilitate studies of the atmospheric role of HCl and may enable deployment on mobile platforms, such as ships and aircraft.Improved understanding of halogen activation in general, and HCl in particular, has broad implications for modeling of both regional air quality and climate. Within polluted coastal environments, HCl is a primary product in acid displacement reactions with sea salt and is a key source for atomic chlorine. Halogen activation cycles involving HCl may also influence the climate system through the oxidation of methane and other organic gases, conversion of marine sulfur emissions to sulfate aerosol, and, potentially, regulation of tropospheric ozone and other oxidant levels. In terms of future instrumentation, the sensor design and architecture proposed here will provide a blueprint for development of similar sensors for other species relevant to atmospheric chemistry (e.g., acetylene, ammonia). The project will also provide unique educational opportunities for graduate and undergraduate students in mechanical engineering at Colorado State University (CSU). Particular efforts will be made to recruit women students and students from underrepresented groups to participate in the project. The students will design and develop a state-of-the-art instrument for atmospheric sensing and will interact with researchers in atmospheric chemistry at CSU, from other universities, and from nearby federal environmental research laboratories. Results of the research will be incorporated into courses at CSU, and disseminated at academic conferences.