Tropospheric NO₂ vertical column densities retrieved from ground-based MAX-DOAS measurements at Shangdianzi regional atmospheric background station in China

Ground-basedMulti-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements were performed at Shangdianzi (SDZ) regional atmospheric background station in northern China from March 2009 to February 2011. The tropospheric NO₂ vertical column densities (VCDs) were retrieved to investigate the background condition of the Beijing-Tianjin-Hebei developed economic circle in China. The seasonal variation of mean NO₂ tropospheric VCDs (VCD_Trop) at SDZ is apparent, with the maximum (1.3 × 10¹⁶ molec/cm²) in February and the minimum (3.5 × 10¹⁵ molec/cm²) in August, much lower than those observed at the Beijing city center. The average daytime diurnal variations of NO₂ VCD_Trop are rather consistent for all four seasons, presenting the minimum at noon and the higher values in the morning and evening. The largest and lowest amplitudes of NO₂ VCD_Trop diurnal variation appear in winter and in summer, respectively. The diurnal pattern at SDZ station is similar to those at other less polluted stations, but distinct from the ones at the urban or polluted stations. Tropospheric NO₂ VCDs at SDZ are strongly dependent on the wind, with the higher values being associated with the pollution plumes from Beijing city. Tropospheric NO₂ VCDs derived from ground-based MAX-DOAS at SDZ show to be well correlated with corresponding OMI (Ozone Monitoring Instrument) satellite products with a correlation coefficient R = 0.88. However, the OMI observations are on average higher than MAX-DOAS NO₂ VCDs by a factor of 28%, probably due to the OMI grid cell partly covering the south of SDZ which is influenced more by the pollution plumes from the urban areas.