山西夏季臭氧光化学生成敏感区分布和变化

利用 2013~2022年的 5~8月臭氧检测仪（OMI）的甲醛柱浓度（HCHO）和对流层二氧化氮柱浓度（NO₂）卫星遥感数据，结合地面臭氧（O₃）观测数据，计算了山西 FNR（HCHO/NO₂）的阈值，研究了山西夏季近地面 O₃光化学生成敏感区的分布和变化 .结果表明：①2013~2022年夏季，山西 VOCs敏感区（FNR < 2.3）明显缩小，VOCs-NO_x过渡区（FNR介于 2.3~4.1）先增后减，NO_x敏感区（FNR > 4.1）显著扩张；②2013~2019年夏季，HCHO柱浓度上升与对流层 NO₂柱浓度下降，共同导致 FNR上升，2016年起山西总体处于 NO_x敏感区，但 NO_x减排的进程中城市区域由 VOCs敏感区逐渐向 VOCs-NO_x过渡区转变，导致 O₃污染加重且普遍存在；2020~2022年，HCHO与 NO₂协同下降，O₃浓度有所降低 .③2022年夏季，临汾和运城出现了 O“3周末效应”的反转，其余 9个城市仍存在 O“3周末效应”，O“3周末效应”并不完全取决于前体物排放的变化，还与 O₃光化学生成敏感性密切相关 .山西 O₃污染治理需NO_x和 VOCs协同减排，此外太原、阳泉、运城、晋城应继续深入推进 NO_x减排 .

Spatiotemporal Distributions and Variations in Summertime Ozone Photochemical Production Regimes over Shanxi

Satellite-based formaldehyde（HCHO）columns and tropospheric nitrogen dioxide columns were observed using the Ozone Monitoring Instrument（OMI），and groundbased observations of ozone（O₃）for May-August from 2013 to 2022 were connected to calculate the threshold values of the HCHO to NO₂ ratio（FNR）in Shanxi Province. Then，the spatiotemporal distributions and variations in summertime ozone photochemical production regimes were analyzed. The results showed that：① The volatile organic compound（VOC） -sensitive regime area（FNR < 2.3）was obviously reduced，while the VOCs-NO_x transitional regime（FNR between 2.3-4.1）area increased in the early years and then decreased， and NO x -sensitive regime area expanded significantly in summer from 2013 to 2022 over Shanxi Province. ② The increased summertime FNR during 2013 to 2019 was associated with the co-effect of increased HCHO columns and decreased tropospheric NO₂ columns. The Shanxi Province was generally under an NO_x regime since 2016，which reflected the remarkable effect of NO x emission reductions；however，there was a shift from a VOC-sensitive regime to a VOCs-NO_x transitional regime，in which O₃ pollution aggravation was widespread under the background of decreased NO_x emissions. The decrease in O₃ concentration during 2020 to 2022 followed the synergistical declines in HCHO columns and tropospheric NO₂ columns. ③ The O₃ weekend effects were reversed in Linfen and Yuncheng but were persistent in the other nine cities. Satellite-based weekend HCHO and NO₂ levels were higher than those on weekdays in some cities of Shanxi Province，indicating that the O₃ weekend effect was not only dependent on the changes of precursors emissions but was also closely related to O₃ photochemical production sensitivity. The results indicated the necessity of simultaneous controls in NO_x emissions and VOCs emissions for ozone abatement plans over Shanxi Province. In addition，Taiyuan，Yangquan，Yuncheng，and Jincheng should continue to promote reduction in NO_x emissions.