The conventional two-wavelength differential absorption lidar (DIAL) has measured air pollutants such as nitrogen dioxide (NO₂). However, high concentrations of aerosol within the planetary boundary layer (PBL) can cause significant retrieval errors using only a two-wavelength DIAL technique to measure NO₂. We proposed a new technique to obtain more accurate measurements of NO₂ using a three-wavelength DIAL technique based on an optical parametric oscillator (OPO) laser. This study derives the three-wavelength DIAL retrieval equations necessary to retrieve vertical profiles of NO₂ in the troposphere. Additionally, two rules to obtain the optimum choice of the three wavelengths applied in the retrieval are designed to help increase the differences in the NO₂ absorption cross-sections and reduce aerosol interference. NO₂ retrieval relative uncertainties caused by aerosol extinction, molecular extinction, absorption of gases other than the gas of interest and backscattering are calculated using two-wavelength DIAL (438 and 439.5 nm) and three-wavelength DIAL (438, 439.5 and 441 nm) techniques. The retrieval uncertainties in aerosol extinction using the three-wavelength DIAL technique are reduced to less than 2 % of those when using the two-wavelength DIAL technique. Moreover, the retrieval uncertainty analysis indicates that the three-wavelength DIAL technique can reduce more fluctuation caused by aerosol backscattering than the two-wavelength DIAL technique. This study presents NO₂ concentration profiles which were obtained using the HU (Hampton University) three-wavelength OPO DIAL. As a first step to assess the accuracy of the HU lidar NO₂ profiles, we compared the NO₂ profiles to simulated data from the Weather Research and Forecasting Chemistry (WRF-Chem) model. This comparison suggests that the NO₂ profiles retrieved with the three-wavelength DIAL technique have similar vertical structure and magnitudes typically within ±0.1 ppb compared to modeled profiles.

中文翻译：

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使用三波长光学参量振荡器差分吸收激光雷达测量对流层 NO ₂

传统的双波长差分吸收激光雷达 (DIAL) 已测量二氧化氮 (NO ₂ )等空气污染物。然而，仅使用双波长 DIAL 技术测量 NO _{2 时}，行星边界层 (PBL) 内的高浓度气溶胶会导致显着的检索错误。我们提出了一种新技术，使用基于光学参量振荡器 (OPO) 激光器的三波长 DIAL技术来获得更准确的 NO ₂测量值。本研究推导出了反演 NO ₂垂直剖面所需的三波长 DIAL 反演方程在对流层。此外，还设计了两个规则，以获得在反演中应用的三个波长的最佳选择，以帮助增加 NO ₂吸收截面的差异并减少气溶胶干扰。NO ₂使用二波长 DIAL（438 和 439.5 nm）和三波长 DIAL（438、439.5 和 441 nm）技术计算由气溶胶消光、分子消光、除感兴趣气体以外的气体吸收和背向散射引起的反演相对不确定性。使用三波长 DIAL 技术在气溶胶消光中的反演不确定性降低到使用双波长 DIAL 技术时的 2% 以下。此外，反演不确定性分析表明，三波长 DIAL 技术比二波长 DIAL 技术能减少更多由气溶胶后向散射引起的波动。本研究提出 NO ₂使用 HU（汉普顿大学）三波长 OPO DIAL 获得的浓度分布。作为评估 HU 激光雷达 NO ₂剖面准确性的第一步，我们将 NO ₂剖面与来自天气研究和预测化学 (WRF-Chem) 模型的模拟数据进行了比较。这种比较表明，与模拟剖面相比，使用三波长 DIAL 技术检索的 NO ₂剖面具有相似的垂直结构和幅度，通常在± 0.1 ppb内。