基于OMI的汾渭平原对流层NO2长期变化趋势

利用2007~2020年臭氧检测仪（OMI） OMNO2d对流层NO₂垂直柱浓度（TVCD）数据、欧盟基本气候变量质量保证计划（QA4ECV）基于卫星观测约束下的NO_x日排放估算数据（DECSO）、大气红外探测仪（AIRS）臭氧（O₃）垂直廓线AIRS2SUP数据，研究了汾渭平原NO₂TVCD长期变化趋势及其对NO_x排放变化的响应，以及二者变化对于对流层中下层O₃的影响.结果表明，汾渭平原NO₂TVCD于2012年达峰，峰值为（9.8±4.6） x10¹⁵molec/cm²，2013年后基本呈现逐年下降趋势；NO₂TVCD冬季最高，夏季最低，冬季均值约为夏季3.6倍；NO₂TVCD并非随NO_x人为源减排单调下降，夏季NO₂TVCD低百分位上升；NO₂TVCD变率为（-1.5±0.6）%/a，低于NO_x排放降幅的1/3，可能与人为NO_x大量减排的背景下，对流层NO_x自然源的贡献大且相对贡献不断上升有关；对流层中下层O₃变率仅为（-0.2±0.2）%/a，近地层O₃变率为（0.8±0.1）%/a，汾渭平原对流层O₃生成基本处于VOCs控制区或者VOCs-NO_x过渡区，减排NO_x无法降低对流层O₃；汾渭平原NO_x减排可有效降低城市高排放区NO₂，乡村地区受NO_x自然源影响较大，人为减排收效不明显.

Long-term trends of tropospheric NO2 over the Fenwei Plain of China based on OMI data

This study explored the long-term trends of NO₂ tropospheric vertical column density (NO₂ TVCD) and its responses to NO_x emissions, as well as their impacts on the lower tropospheric O₃ over the Fenwei Plain of China. The long-term observations from 2007 to 2020 used here consist of:NO₂ TVCD data of Ozone Monitoring Instrument (OMI) OMNO2d, NO_x emissions of European Quality Assurance for Essential Climate Variables project (QA4ECV) products by Daily Emission estimation Constrained by Satellite Observations (DECSO) algorithm, and ozone (O₃) vertical profile data of Atmospheric Infrared Sounder instrument (AIRS) AIRS2SUP. The results showed that:(1) NO₂ TVCD peaked at (9.8±4.6)×10¹⁵molec/cm² in 2012, then tended to decline generally after 2013; (2) NO₂ TVCD was higher by 260% in winter than in summer; (3) The variations in NO₂ TVCD were not exactly consistent with the anthropogenic mitigation of NO_x emissions but increased in Summer at its lower percentiles with a rate of (-1.5±0.6)%/a (less than a third of the reduction in NO_x emissions), which was probably due to the large contribution of natural sources of tropospheric NO_x and its increasing relative contribution under the background of massive anthropogenic NO_x emissions mitigation; (4) The O₃ variability was (-0.2±0.2)%/a in the middle-lower troposphere and (0.8±0.1)%/a in the near surface, indicating that the tropospheric O₃ generation in the Fenwei Plain was basically within the VOCs-limited or VOCs-NO_x transitional regimes, and the anthropogenic NO_x emissions reduction could not reduce the tropospheric O₃; (5) The anthropogenic NO_x emission reduction could effectively reduce NO₂ in urban high emission areas, but in the rural areas where natural NO_x sources dominated. Generally, the efficiency of the anthropogenic NO_x emissions reduction was not significant over the Fenwei Plain.