Urbanization, Economic Development, and Environmental Quality: Insights from Urban Growth and NO₂ Pollution in Megacities

Megacities, as epicenters of population growth and economic activity, contribute significantly to atmospheric emissions. Despite numerous studies either examining urban growth or air pollution trends in megacities, a systematic analysis that integrates both quantities within the context of economic development remains lacking. This study addresses this gap by leveraging Earth Observation (EO) data to investigate trends in settlement growth and tropospheric NO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> pollution across 38 megacities from 1996 to 2015. Using the World Bank’s income classifications, it is hypothesized whether the observed dynamics follows the Environmental Kuznets Curve (EKC), which posits a non-linear relationship between economic growth and environmental quality. The findings reveal an average annual NO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> increase of 5.06 ± 0.83% and settlement growth of 2.87%, with substantial variation across income groups. High-income cities show declining NO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> trends, attributed to advanced emission controls and stringent environmental policies, yet still exhibit high per capita pollution levels. Conversely, upper-middle-income cities experience rapid NO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> increases driven by industrial activity and urban sprawl. Settlement growth dynamics were observed to correlate with economic development phases, with upper-middle-income cities leading in urban expansion. The results support the theoretical framework of the EKC hypothesis, highlighting a non-linear interplay between urbanization, economic development and environmental quality. These insights into socio-economic transitions underscore the necessity of differentiated strategies, including investments in green technology, stricter emission standards, and enhanced international collaboration, to foster sustainable urbanization.