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. 2020 Jul 21;745:141023. doi: 10.1016/j.scitotenv.2020.141023

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Fig. 4 — Tropospheric NO₂ vertical column density (TropNO₂VCD) changes and variations over East China during lunar new year (LNY) holiday seasons by OMI and TROPOMI (with corrections applied). Panel (a) shows the predicted TropNO₂VCD changes during 2019–2020 LNY holidays, and panels (b) and (c) plot tropospheric NO₂ reductions over East China during 2019–2020 LNY, respectively, based on OMI and TROPOMI observations. Panel (d) shows temporal variations of TropNO₂VCDs during 2005–2020 LNY holiday seasons, with a zoom-in view for 2019–2020, in major metropolitan areas marked by different colors accordingly. The solid lines with solid dots and triangles represent TropNO₂VCDs in LNY holiday seasons observed by OMI and TROPOMI with correction applied, respectively. The dashed line with different colors represents tropospheric NO₂ regressions by the quadratic regression model in different metropolitan areas, accordingly.