Growing Urbanization and the Impact on Fine Particulate Matter (PM 2.5 ) Dynamics

Changes in urban air quality and its relationship with growing urbanization provide an important insight into urban development strategies. Thus, we collected remotely sensed PM 2.5 concentrations, as well as urban population datasets, and analyzed the scaling relationship between changes in urban population and concentrations of PM 2.5 . The majority of large cities in North America and Europe had PM 2.5 concentrations which decreased significantly. Only 2.0% of large cities in the U.S. were found to have significant positive trends. PM 2.5 concentration trends of less than 0.5 μg/m 3 ·year were found in all large cities of Africa and Latin America. However, PM 2.5 concentration trends of more than 1.0 μg/m 3 ·year were found in 56.7% of the large cities in Asia, where only 2.3% of the cities in China were found with significant negative trends, and no cities in India were found with significant negative trends. Large cities in Asia were found with contributions of 4.12 ± 4.27 μg/m 3 ·year per million people, particularly large cities in China (5.40 ± 4.80 μg/m 3 ·year per million people) and India (4.07 ± 3.07 μg/m 3 ·year per million people). Significant negative or positive relationships were obtained between PM 2.5 trends and population change rates in large cities of North America (R 2 = 0.9195, p < 0.05) or Europe (R 2 = 0.9161, p < 0.05). Moreover, a significant inverse “U-type” relationship (R 2 = 0.8065, p < 0.05) was found between PM 2.5 trends and population change rates in large cities of Asia. In addition, the positive or negative relationships between the trends in population and PM 2.5 were obtained in typical low- and mid-income countries (e.g., China and India) or high-income countries (e.g., USA), respectively.