Effects of urbanization, scale, and geography on air pollution in India

Kurzfassung

Indian cities have recently emerged as some of the locations with the worst air pollution on Earth. However, the sources of these increases and potential mitigation paths are complex, involving an interplay between urbanization, economic growth, energy systems and environmental management. Here, we analyse an extensive set of satellite and ground-level air quality monitoring data sets to create a detailed examination of geographical and temporal patterns of NO2 pollution across all districts and most large cities in India. For the period 2005–19, we find that urbanization has an inverse relationship with NO2 increase, but at the same time, the most urbanized districts also have the highest NO2 burden. Districts at intermediate levels of urbanization (30 - 40%) show both high levels of NO2 and the largest increases in NO2 pollution. Our analysis also reveals that the region of the Indo-Gangetic Plain (IGP) is of particular concern both in terms of high absolute levels of NO2 and relative NO2 increase over the period from 2005 to 2019. Studying PM10 levels across 106 cities, we find that they exceed national air quality standards in over 80% of cases, with the problem also being particularly acute in IGP’s urban areas. Scaling analysis reveals that NO2 concentrations increase super-linearly with population in cities in the IGP, in contrast to the sublinear scaling observed for other cities. This implies that larger cities in the IGP are characterized by both higher NO2 concentrations and increased per capita exposure. Moreover, recent mitigation efforts in the largest cities could signal the flow of technologies and strategies down the urban hierarchy and impact the rising levels of air pollution across the nation and over time. For now, the impetus of development and poverty alleviation implies that environmental challenges are likely to worsen, unless immediate and sustained pollution mitigation can address the severe air quality problem in India, especially across the Indo-Gangetic Plain.