The Small Mobile Ozone Lidar (SMOL): instrument description and first results Atmospheric Measurement Techniques

Ozone profile measurements at high temporal and vertical resolution are needed to better understand physical and chemical processes driving tropospheric ozone variability and to validate the tropospheric ozone measurements from spaceborne missions such as TEMPO (Tropospheric Emissions: Monitoring Pollution). As part of the Tropospheric Ozone Lidar Network (TOLNet) efforts allocated to provide such measurements and leveraging on the experience of more than 20 years of ozone lidar measurements at Table Mountain Facility, the JPL lidar group developed the SMOL (Small Mobile Ozone Lidar), an affordable differential absorption lidar (DIAL) system covering all altitudes from 200 to 10 km above ground level (a.g.l.). The transmitter is based on a quadrupled Nd:YAG laser, which is further converted into a 289/299 nm wavelength pair using Raman shifting cells, and the receiver consists of three ozone DIAL pairs, including one that is 266/289 nm and two that are 289/299 nm. Two units were deployed in the Los Angeles basin area during the Synergistic TEMPO Air Quality Science (STAQS) and Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas (AEROMMA) campaigns in summer 2023. The comparison with airborne in situ and lidar measurements shows very good agreement, with systematic differences below 10 % throughout most of the measurement range. An additional comparison with nearby surface ozone measuring instruments indicates unbiased measurements by the SMOL lidars down to 200 m a.g.l. Further comparison with the Goddard Earth Observing System Composition Forecast (GEOS-CF) model suggests that such lidars are a critical tool to perform model validation and can potentially be used for assimilation to air quality forecasts.

为更深入理解驱动对流层臭氧变化的物理与化学过程，并验证诸如TEMPO (Tropospheric Emissions: Monitoring Pollution) 这类星载任务所获取的对流层臭氧测量数据，亟需具备高时间分辨率与垂直分辨率的臭氧廓线测量结果。作为旨在提供此类测量数据的对流层臭氧激光雷达网络 (Tropospheric Ozone Lidar Network, TOLNet) 计划的一部分，同时依托桌山设施 (Table Mountain Facility) 超过20年的臭氧激光雷达测量经验，美国喷气推进实验室 (Jet Propulsion Laboratory, JPL) 激光雷达团队研发了SMOL (Small Mobile Ozone Lidar，小型移动式臭氧激光雷达)——一套成本可控的差分吸收激光雷达 (differential absorption lidar, DIAL) 系统，可覆盖地面以上200米至10公里的全部高度范围。该系统的发射端基于四倍频Nd:YAG激光器 (Nd:YAG laser)，通过拉曼频移池 (Raman shifting cells) 进一步将激光转换为289 nm与299 nm的波长对；接收端则包含三组臭氧差分吸收激光雷达波长对，其中一组为266/289 nm，另外两组为289/299 nm。2023年夏季，两套该型激光雷达被部署于洛杉矶盆地区域，参与了协同TEMPO空气质量科学 (Synergistic TEMPO Air Quality Science, STAQS) 与特大城市至海洋区域大气排放及反应观测 (Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas, AEROMMA) 两项野外实验。与机载原位测量及激光雷达测量结果的对比显示，二者具有极佳的一致性，在绝大多数测量范围内的系统偏差均低于10%。此外，与附近地面臭氧测量仪器的对比结果表明，SMOL激光雷达在地面以上 (above ground level, a.g.l.) 200米高度处仍可实现无偏测量。进一步与戈达德地球观测系统组成预报 (Goddard Earth Observing System Composition Forecast, GEOS-CF) 模型的对比结果显示，此类激光雷达是开展模型验证的关键工具，且有望应用于空气质量预报的数值同化环节。