Spatio-temporal variations in NO₂ and PM_2.5 over the central plains economic region of china during 2005-2015 based on satellite observations

The Central Plains Economic Region (CPER) is located in central eastern China and has experienced tremendous economic growth in the last decade. Like many areas in China, the rapid economic development of the CPER has led to serious air pollution problems, including extremely high concentrations of nitrogen dioxide (NO₂) and particulate matter with an aerodynamic diameter less than 2.5 µm (PM_2.5). However, the current air pollution monitoring system lacks good spatial and temporal coverage. Therefore, we used high-resolution satellite remote sensing techniques to analyze the variation in NO₂ and PM_2.5 in the CPER from 2005 through 2015. The Ozone Monitoring Instrument (OMI) and the Moderate Resolution Imaging Spectroradiometer (MODIS) were used to retrieve the tropospheric NO₂ columns and ground-level PM_2.5 concentrations, respectively. High NO₂ and PM_2.5 concentrations were mainly located in the central and northern areas of the CPER. The highest 11-year average concentrations were found in the city of Jiaozuo for NO₂ (19.54 × 10¹⁵ molecules cm^–2) and in the city of Hebi for PM_2.5 (107.8 µg m^–3). The western and southern mountainous areas had lower NO₂ and PM_2.5 concentrations. The average seasonal NO₂ and PM_2.5 concentrations were both highest in winter and lowest in summer. The average monthly concentrations of NO₂ and PM_2.5 were as high as 24.60 × 10¹⁵ molecules cm^–2 and 152.2 µg m^–3, respectively, in January 2013 and as low as 43.86 × 10¹⁵ molecules cm^–2 and 40.2 µg m^–3, respectively, in July 2006. During the 11-year study period (2005–2015), the CPER concentrations of both NO₂ and PM_2.5 decreased from 2011 to 2015 by 31.5% and 36.8%, respectively. This study successfully applies satellite remote sensing data to quantitatively analyze the spatial-temporal distributions of tropospheric NO₂ and ground-level PM_2.5. This approach can support air pollution monitoring in the CPER, and the estimated concentrations can provide references for environmental policymaking.