Proof of concept for use of two-colour fibre laser technology for detection of multiple atmospheric species by laser-induced fluorescence spectroscopy

在本提案中，我们的目标是利用NovaWave Technologies（红杉城，CA）开发的新型光纤激光技术，将其集成到利兹FAGE（气体膨胀荧光测定）仪器中，使用激光诱导荧光（LIF）光谱法对HCHO自由基和NO2进行现场测量。原型激光技术已经存在，用于在353 nm处激发HCHO，并且在并入FAGE仪器之后，我们使用该激光器在1秒内预测50 ppt的灵敏度。光纤激光器技术的能力将通过采用可调谐辐射来扩展。530 nm的激光，通过LIF光谱检测NO2。光纤激光器的性能和可靠性在困难的环境中会更好，例如飞机机舱。我们打算与Frank Keutsch（威斯康星州大学）的团队密切合作，他们有在现场使用这些激光器进行LIF测量的经验。甲醛（HCHO）是最简单和最丰富的羰基物质之一，直接排放，并由生物和人为VOCs的OH引发氧化产生。HCHO的光解及其与OH的反应导致形成HO2，在NOx存在下导致对流层臭氧的形成，这是一种气候气体，高浓度时对人类和植物有害。甲醛的寿命相对较长，这意味着迁移过程会影响其收支，因此很难使用基于原位化学的光化学模型进行计算，直接测量至关重要。虽然有几种方法存在的测量甲醛，技术之间的协议往往是穷人，和数据集的甲醛是不广泛的，特别是在英国，严重限制了利用激进的数据在合作领域的运动。基于光纤的LIF仪器将能够在地面和飞机平台上进行具有良好时间分辨率的灵敏测量。

In this proposal we aim to exploit novel fibre laser technology developed by NovaWave Technologies (Redwood City, CA) for integration into the Leeds FAGE (fluorescence assay by gas expansion) instrument for the field measurement of HCHO radicals and NO2 using laser-induced fluorescence (LIF) spectroscopy. The prototype laser technology already exists for excitation of HCHO at 353nm, and following incorporation into the FAGE instrument we project a sensitivity of 50 ppt in 1 sec using this laser. The capabilities of the fibre laser technology will be extended by employing tunable radiation at ca. 530 nm from the laser to detect NO2 via by LIF spectroscopy. Performance and reliability of the fibre laser will be much better in difficult environments, for example aircraft cabins. We intend to collaborate closely with the group of Frank Keutsch (University of Wisconsin) who has experience of using these lasers for LIF measurements in the field. Formaldehyde (HCHO) is the simplest and one of the most abundant of carbonyl species, being emitted directly and generated from the OH initiated oxidation of biogenic and anthropogenic VOCs. The photolysis of HCHO and its reaction with OH leads to the formation of HO2, which in the presence of NOx leads to tropospheric ozone formation, which is a climate gas and harmful to humans and plants at high concentrations. The relatively long lifetime of HCHO means that transport processes influence its budget, making it very difficult to calculate using photochemical models based on situ chemistry, and direct measurements are essential. Although several methods exist for the measurement of HCHO, agreement between techniques has often been poor, and datasets for HCHO are not extensive, particularly in the UK, severely limiting the exploitation of radical data measured during collaborative field campaigns. The fibre based LIF instrument would enable sensitive measurements with good temporal resolution to be made on ground and aircraft platforms.