Earth Observation-based analysis of NO2 pollution and settlement growth in megacities

Abstract

Megacities have become global centers of industrial production, trade and innovation, but also energy consumption, atmospheric emissions and air pollution. Despite several studies on NO2 changes in megacities, a systematic analysis in relation to settlement growth is still pending. In addition, previous studies do not refer to consistent spatial city concepts which distorts statistics in the comparison. In this study we examine the trends of NO2 air pollution in 30 megacities in relation to urban settlement growth by analyzing various Earth Observation data sets. Multi-annual records of tropospheric NO2 from GOME, SCIAMACHY, GOME-2A and GOME-2B are evaluated regarding yearly urban settlement growth as derived from the World Settlement Footprint for the period from 1996 to 2015. Compared to previous studies, this work strictly uses remote sensing data and the spatial concept of Functional Urban Areas. Therefore, uncertainties due to incomparable administrative units, heterogeneously reported local data and population counts are widely excluded to enable an appropriate comparison of megacities across the globe. We find a wide range of trends: relative NO2 pollution ranges from an increase of 16 %/year to a decrease of -3 %/year, settlement growth rates from 0,4 %/year to 8 %/year. Despite this variety, the results exhibit a pronounced relation to the income group following the world's economies classification of the World Bank. While the strongest NO2 pollution increases occur in megacities of lower middle-income countries, the strongest settlement growth rates are observed in upper middle-income countries. Megacities in high income countries are predominantly characterized by the smallest relative settlement growth rates and a decrease in NO2 air pollution.