To clarify three-dimensional (3-D) spatiotemporal variations and horizontal–vertical transport processes in nitrogen dioxide (NO₂) over urban areas, combined NO₂ profile observations by multiple Multi AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) and direct wind observations by 3-D coherent Doppler lidar were made over an urban area in Japan. MAX-DOAS measurements were conducted at Yakuin and Fukuoka University in Fukuoka urban area with high temporal resolution of four minutes.

Enhanced NO₂ concentrations were often observed over the city center. We conducted a case study on 29 November 2018 under clear sky conditions and NO₂ profiles were well retrieved. Using MAX-DOAS at two locations, high NO₂ concentrations were observed near the surface of the city center in the morning. Higher NO₂ concentrations appearing gradually at higher altitudes over the city center and disappearing in the afternoon are explained using direct evidence of a 3-D wind field: an airmass with a high NO₂ concentration was transported upward over the city center. Then, the airmass was advected landward by a sea breeze. Multiple MAX-DOAS combined with 3-D Doppler lidar constitutes a powerful tool for elucidating horizontal–vertical transport processes. It can contribute to the improvement of data retrieval by satellites for urban areas.

为了弄清城市地区二氧化氮（NO ₂）中的三维（3-D）时空变化和水平-垂直传输过程，结合了多种多轴差动光吸收光谱法（MAX-DOAS）和直接风对NO ₂剖面的观测结果3-D相干多普勒激光雷达的观测是在日本市区进行的。MAX-DOAS测量是在福冈市区的雅库恩大学和福冈大学进行的，时间分辨率为4分钟。

在市中心经常观察到NO ₂浓度升高。我们于2018年11月29日在晴朗的天空条件下进行了案例研究，并很好地检索了NO ₂剖面。在两个位置使用MAX-DOAS，早晨市中心附近表面观察到高NO ₂浓度。使用3-D风场的直接证据解释了较高的NO ₂浓度在市中心的较高海拔逐渐出现并在下午消失的现象：高NO ₂的气团注意力集中在市中心上空。然后，海风使气团向内平移。多个MAX-DOAS与3-D多普勒激光雷达相结合，构成了用于阐明水平垂直传输过程的强大工具。它可以有助于改善城市地区卫星的数据检索。