The urban heat island ($UHI$) refers to the land surface temperature (LST) difference between urban areas and their undeveloped or underdeveloped surroundings. It is a measure of the thermal influence of the urban built-up area expansion ($UBAE$), a topic that has been extensively studied. However, the impact of $UBAE$ on the LST differences between urban areas and rural areas ($UH{I}_{U-R}$) and between urban areas and emerging urban areas ($UH{I}_{U-S}$) in different seasons has seldom been investigated. Here, the $UH{I}_{U-S}$ and $UH{I}_{U-R}$ in 34 major metropolitan regions across China, and their spatiotemporal variations based on long-term space-borne observations during the period 2001–2020 were analyzed. The $UBAE$ quantified by the difference in landscape metrics of built-up areas between 2020 and 2000 and their impact on $UHI$ was further analyzed. The $UBAE$ is impacted by the level of economic development and topography. The $UBAE$ of cities located in more developed regions was more significant than that in less developed regions. Coastal cities experienced the most obvious $UBAE$, followed by plain and hilly cities. The $UBAE$ in mountainous regions was the weakest. On an annual basis, $UH{I}_{U-R}$ was larger than $UH{I}_{U-S}$, decreasing more slowly with $UBAE$ than $UH{I}_{U-S}$. In different seasons, the $UH{I}_{U-S}$ and $UH{I}_{U-R}$ were larger, more clearly varying temporally with $UBAE$ in summer than in winter, and their temporal variations were significantly correlated with $UBAE$ in summer but not in winter. The seasonal difference in $UH{I}_{U-R}$ was larger than that of $UH{I}_{U-S}$. Both the $UH{I}_{U-S}$ and $UH{I}_{U-R}$ in coastal cities were the lowest in summer, decreasing the fastest with $UBAE$, while those in mountain cities decreased the slowest. The change in the density of built-up lands was the primary driver affecting the temporal variations in $UH{I}_{U-S}$ and $UH{I}_{U-R}$ during $UBAE$, followed by changes in proportion and shape, while the impact of the speed of expansion was the smallest, all of which were more obvious in summer than in winter. The decreased density of built-up lands can reduce $UHI$. These findings provide a new perspective for a deeper understanding of the effect of urban expansion on LST in different seasons.

This study presents a comprehensive spatiotemporal analysis of air quality across various urban functional zones in China from 2017 to 2022, uncovering distinct impacts on air quality due to the unique characteristics of each zone. A general decrease in various pollutant concentrations is observed, a result of stringent pollution control policies. Specifically, the concentration of PM_2.5 decreased from 46.1–30.6 µg m⁻³. Residential, commercial, and industrial zones show significant declines, whereas the transportation zone experiences the least decrease. However, ozone levels rebound significantly in densely populated residential and commercial zones and exhibit distinct weekend effects. The research highlights U-shaped seasonal patterns for five key pollutants and inverse seasonal patterns for ozone, which gradually decrease. Furthermore, the daily and seasonal variations of pollutant concentrations in the industrial zone are the largest, while those in the public management and service zone are the smallest. For example, the seasonal fluctuation of PM_2.5 and PM₁₀ in the industrial zone was 50.5 and 66.1 µg m⁻³, respectively. Urban scale has the most significant impact on public management and service zone. Notably, spatial heterogeneity is evident, with regional pollutant distributions linked to local emissions, control measures, urban morphology, and climate variability. This study emphasizes the critical link between urbanization and air quality, advocating for continuous monitoring and the development of zone-specific air quality strategies to ensure sustainable urban environments.

This study presents a comprehensive spatiotemporal analysis of air quality across various urban functional zones in China from 2017 to 2022, uncovering distinct impacts on air quality due to the unique characteristics of each zone. A general decrease in various pollutant concentrations is observed, a result of stringent pollution control policies. Residential, commercial, and industrial zones show significant declines, whereas the transportation zone experiences the least decrease. However, ozone levels rebound significantly in densely populated residential and commercial zones, and exhibit distinct weekend effects. The research highlights U-shaped seasonal patterns for five key pollutants and inverse seasonal patterns for ozone, which gradually decrease. Furthermore, the daily and seasonal variations of pollutant concentrations in industrial zone are the largest, while those in the public management and service zone are the smallest. Notably, spatial heterogeneity is evident, with regional pollutant distributions linked to local emissions, control measures, urban morphology, and climate variability. These findings indicate that, in the future, the Chinese government should curb ozone pollution, strengthen air pollution control in transportation zone, and formulate more scientific and accurate air pollution control policies based on the local situation of each city. This study emphasizes the critical link between urbanization and air quality, advocating for continuous monitoring and the development of zone-specific air quality strategies to ensure sustainable urban environments.

This study presents a comprehensive spatiotemporal analysis of air quality across various urban functional zones in China from 2017 to 2022, uncovering distinct impacts on air quality due to the unique characteristics of each zone. A general decrease in various pollutant concentrations is observed, a result of stringent pollution control policies. Residential, commercial, and industrial zones show significant declines, whereas the transportation zone experiences the least decrease. However, ozone levels rebound significantly in densely populated residential and commercial zones, and exhibit distinct weekend effects. The research highlights U-shaped seasonal patterns for five key pollutants and inverse seasonal patterns for ozone, which gradually decrease. Furthermore, the daily and seasonal variations of pollutant concentrations in industrial zone are the largest, while those in the public management and service zone are the smallest. Notably, spatial heterogeneity is evident, with regional pollutant distributions linked to local emissions, control measures, urban morphology, and climate variability. These findings indicate that, in the future, the Chinese government should curb ozone pollution, strengthen air pollution control in transportation zone, and formulate more scientific and accurate air pollution control policies based on the local situation of each city. This study emphasizes the critical link between urbanization and air quality, advocating for continuous monitoring and the development of zone-specific air quality strategies to ensure sustainable urban environments.

This study presents a comprehensive spatiotemporal analysis of air quality across various urban functional zones in China from 2017 to 2022, uncovering distinct impacts on air quality due to the unique characteristics of each zone. A general decrease in various pollutant concentrations is observed, a result of stringent pollution control policies. Residential, commercial, and industrial zones show significant declines, whereas the transportation zone experiences the least decrease. However, ozone levels rebound significantly in densely populated residential and commercial zones, and exhibit distinct weekend effects. The research highlights U-shaped seasonal patterns for five key pollutants and inverse seasonal patterns for ozone, which gradually decrease. Furthermore, the daily and seasonal variations of pollutant concentrations in industrial zone are the largest, while those in the public management and service zone are the smallest. Notably, spatial heterogeneity is evident, with regional pollutant distributions linked to local emissions, control measures, urban morphology, and climate variability. These findings indicate that, in the future, the Chinese government should curb ozone pollution, strengthen air pollution control in transportation zone, and formulate more scientific and accurate air pollution control policies based on the local situation of each city. This study emphasizes the critical link between urbanization and air quality, advocating for continuous monitoring and the development of zone-specific air quality strategies to ensure sustainable urban environments.

This study presents a comprehensive spatiotemporal analysis of air quality across various urban functional zones in China from 2017 to 2022, uncovering distinct impacts on air quality due to the unique characteristics of each zone. A general decrease in various pollutant concentrations is observed, a result of stringent pollution control policies. Residential, commercial, and industrial zones show significant declines, whereas the transportation zone experiences the least decrease. However, ozone levels rebound significantly in densely populated residential and commercial zones, and exhibit distinct weekend effects. The research highlights U-shaped seasonal patterns for five key pollutants and inverse seasonal patterns for ozone, which gradually decrease. Furthermore, the daily and seasonal variations of pollutant concentrations in industrial zone are the largest, while those in the public management and service zone are the smallest. Notably, spatial heterogeneity is evident, with regional pollutant distributions linked to local emissions, control measures, urban morphology, and climate variability. These findings indicate that, in the future, the Chinese government should curb ozone pollution, strengthen air pollution control in transportation zone, and formulate more scientific and accurate air pollution control policies based on the local situation of each city. This study emphasizes the critical link between urbanization and air quality, advocating for continuous monitoring and the development of zone-specific air quality strategies to ensure sustainable urban environments.