This paper aims to assess the impact of urbanization on air pollution in a selected group of 13 developing countries with low and middle incomes. These countries were chosen because they represent a structural shift from agriculture-based economies to industrial ones during the period from 1990 to 2023. To achieve this objective, the STIRPAT model was employed—an econometric model used to analyze the relationship between human activities (such as population, economic development, and urban growth) and environmental impacts (such as carbon emissions and environmental degradation). The analysis utilized both Fixed Effects and Random Effects models. The findings indicate a strong inverse relationship between the urban population as a percentage of the total population (LNURBAN) and the logarithm of per capita carbon dioxide emissions (LNCO2PC). Specifically, an increase in urbanization by 1,000 persons per km² leads to a 5.9% reduction in air pollution.