Spatial⁻Temporal Variations in NO₂ and PM_2.5 over the Chengdu⁻Chongqing Economic Zone in China during 2005⁻2015 Based...

The Chengdu⁻Chongqing Economic Zone (CCEZ), which is located in southwestern China, is the fourth largest economic zone in China. The rapid economic development of this area has resulted in many environmental problems, including extremely high concentrations of nitrogen dioxide (NO₂) and fine particulate matter (PM_2.5). However, current ground observations lack spatial and temporal coverage. In this study, satellite remote sensing techniques were used to analyze the variation in NO₂ and PM_2.5 from 2005 to 2015 in the CCEZ. The Ozone Monitoring Instrument (OMI) and the Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD) product were used to retrieve tropospheric NO₂ vertical columns and estimate ground-level PM_2.5 concentrations, respectively. Geographically, high NO₂ concentrations were mainly located in the northwest of Chengdu and southeast of Chongqing. However, high PM_2.5 concentrations were mainly located in the center areas of the basin. The seasonal average NO₂ and PM_2.5 concentrations were both highest in winter and lowest in summer. The seasonal average NO₂ and PM_2.5 were as high as 749.33 × 10¹³ molecules·cm^-2 and 132.39 µg·m^-3 in winter 2010, respectively. Over 11 years, the annual average NO₂ and PM_2.5 values in the CCEZ increased initially and then decreased, with 2011 as the inflection point. In 2007, the concentration of NO₂ reached its lowest value since 2005, which was 230.15 × 10¹³ molecules·cm^-2, and in 2015, the concentration of PM_2.5 reached its lowest value since 2005, which was 26.43 µg·m^-3. Our study demonstrates the potential use of satellite remote sensing to compensate for the lack of ground-observed data when quantitatively analyzing the spatial⁻temporal variations in regional air quality.