Nitrogen oxides detected in urban regions are primarily emitted by transportation methods and are crucial precursors for air pollutants and climate forcers such as ozone and fine particulate matter. We investigate the trends of nitrogen dioxide (NO₂) obtained from a satellite instrument and surface monitors over the megacity, Seoul, South Korea, from 2005 to 2019. Both satellite Ozone Monitoring Instrument NO₂ and surface in situ concentrations decreased by up to 30% between 2015 and 2019 while significant trends were not observed between 2005 and 2015. Further analysis shows the continual reduction of NO₂ concentrations prior to and during the COVID-19 pandemic in 2020. This study highlights the efficacy of South Korean pollution control policies targeting vehicular emissions. However, this study also found inconsistencies between trends observed in the official bottom-up emission inventory and data collected from space and surface sites. Further research will be urgently needed to understand the causes for the discrepancies.

在城市地区检测到的氮氧化物主要通过运输方式排放，是空气污染物和气候强迫因素（如臭氧和细颗粒物）的重要前体。我们调查了2005 年至 2019 年从韩国首尔特大城市的卫星仪器和地表监测器获得的二氧化氮 (NO ₂ )的趋势。卫星臭氧监测仪器 NO ₂和地表原位浓度均下降了多达 30 % 2015 年至 2019 年，而 2005 年至 2015 年未观察到显着趋势。进一步分析显示 NO ₂持续减少2020 年 COVID-19 大流行之前和期间的浓度。这项研究强调了韩国针对车辆排放的污染控制政策的有效性。然而，这项研究还发现官方自下而上排放清单中观察到的趋势与从空间和地面站点收集的数据之间存在不一致。迫切需要进一步研究以了解差异的原因。