Reducing uncertainties in OH radical measurements using an absolute optical technique

使用绝对光学技术降低 OH 自由基测量的不确定性

• 批准号: NE/X012239/1
• 负责人: Daniel Stone
• 金额: $ 11.25万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX012239%2F1
• 关键词: Reducing; uncertainties; OH; radical; measurements

Atmospheric oxidising capacity determines the rate at which trace species are removed from the atmosphere, thus controlling their impacts on air quality and climate. The dominant oxidising agent in the atmosphere is the hydroxyl radical (OH), the concentration of which determines the lifetimes of key species including methane (CH4), volatile organic compounds (VOCs), and NOx (NOx = NO + NO2), whilst also controlling the rate at which secondary pollutants such as ozone (O3) and secondary organic aerosol (SOA) are formed. Understanding the concentrations and behaviour of OH in the atmosphere is thus critical to understanding the lifetimes of many trace species which impact air quality and climate. The high reactivity of OH leads to significant challenges in its measurement, with techniques used to measure atmospheric OH such as laser-induced fluorescence (LIF) spectroscopy and chemical ionisation mass spectrometry (CIMS) providing the required sensitivity and specificity, but requiring calibration. Calibration can be achieved by a number of methods, but each method involves a number of steps, with the uncertainties associated with each step propagating through to uncertainties in OH radical observations. Even the most accurate calibration method is typically associated with uncertainties of up to ~30 %. In this work, we will develop the use of cavity enhanced absorption spectroscopy (CEAS) to measure OH radical concentrations in an atmospheric simulation chamber. CEAS is an absolute optical technique, requiring only knowledge of the absorption cross-sections for OH and the absorption path length to determine the concentration from the measured absorbance using the Beer-Lambert law. The use of CEAS will significantly reduce uncertainties associated with OH radical concentrations in the simulation chamber, and offers significant advantages for chamber studies of chemical mechanisms, and for validation of calibration methods for field instruments.

大气氧化能力决定了痕量物种从大气中去除的速度，从而控制它们对空气质量和气候的影响。大气中的主要氧化剂是羟基自由基（OH），其浓度决定了包括甲烷（CH 4）、挥发性有机化合物（VOC）和NOx（NOx = NO + NO2）在内的关键物质的寿命，同时也控制了臭氧（O3）和二次有机气溶胶（SOA）等二次污染物的形成速度。因此，了解大气中OH的浓度和行为对于了解影响空气质量和气候的许多痕量物种的寿命至关重要。OH的高反应性导致其测量面临重大挑战，用于测量大气OH的技术，如激光诱导荧光（LIF）光谱和化学电离质谱（CIMS），可提供所需的灵敏度和特异性，但需要校准。校准可以通过许多方法来实现，但每种方法都涉及许多步骤，与每个步骤相关的不确定性传播到OH自由基观测的不确定性。即使是最精确的校准方法，其不确定度也通常高达~ 30%。在这项工作中，我们将开发使用腔增强吸收光谱（CEAS）测量OH自由基浓度在大气模拟室。CEAS是一种绝对光学技术，仅需要了解OH的吸收截面和吸收路径长度，即可使用Beer-Lambert定律从测量的吸光度确定浓度。CEAS的使用将显着减少与OH自由基浓度在模拟室的不确定性，并提供了显着的优势，室的化学机制的研究，并验证现场仪器的校准方法。