基于Google Earth Engine平台，结合PM2.5浓度、植被覆盖度、夜间地表温度数据构建了综合环境指数（Comprehensive Environmental Index，CEI），以全国和京津冀城市群、珠三角城市群、长三角城市群、成渝城市群和长江中游城市群为研究对象，识别不同城区（老城区、扩展区、城郊区）的城市环境变化特征与差异；同时，分析CEI空间分布特征、环境指标的均值与环境影响力空间分布特征，针对具体环境指标提出城市环境改善政策建议。
研究结果发现，在过去二十年内全国城市CEI整体呈“w”形变化趋势。2007年前CEI波动下降，2008年至2012年CEI波动平衡，2013年达到近二十年最低值，之后呈大幅上升趋势。五大城市群的环境质量整体低于全国平均水平，但自2013年来差异不断缩小。珠三角和长三角城市群环境质量好于京津冀、成渝和长江中游城市群。就不同城区而言，老城区环境质量最差（0.44），城郊区环境质量最好（0.50）。老城区、扩展区和城郊区间环境质量差异显著（p<0.05）。全国城市CEI的高-高值分布在黑龙江、吉林、福建等地；低-低值主要分布在河北、山东、湖北等地。

Based on the Google Earth Engine platform, we utilized PM2.5 concentration, vegetation coverage, and nighttime land surface temperature data to construct a Comprehensive Environmental Index (CEI). We focused on the national scale and urban agglomerations including the Beijing-Tianjin-Hebei, Pearl River Delta, Yangtze River Delta, Chengdu-Chongqing, and Middle Yangtze River urban agglomerations to identify urban environmental change characteristics and differences in various urban areas (old city areas, expansion areas, suburban areas). Additionally, we analyzed the spatial distribution characteristics of CEI, the mean values of environmental indicators, and the spatial distribution characteristics of environmental impact. We also proposed urban environmental improvement policy recommendations for specific environmental indicators.
The research revealed that over the past twenty years, Chinese cities' CEI exhibited a "W" shape change. Prior to 2007, the CEI fluctuated downward, balanced from 2008 to 2012, reached its lowest point in nearly twenty years in 2013, and then displayed a significant upward trend. Although the environmental quality of the five major urban agglomerations generally lagged behind the national average level, the differences have been narrowing since 2013. The Pearl River Delta and Yangtze River Delta urban agglomerations outperformed the Beijing-Tianjin-Hebei, Chengdu-Chongqing, and Middle Yangtze River urban agglomerations in environmental quality. In terms of different urban areas, old city areas exhibited the poorest environmental quality (0.44), while suburban areas demonstrated the highest quality (0.50). Significant differences in environmental quality existed between old city areas, expansion areas, and suburban areas (p <0.05). High-high CEI values were distributed in regions such as Heilongjiang, Jilin, and Fujian, while low-low values were predominantly found in regions such as Hebei, Shandong, and Hubei.