Spatial and Temporal Trends in Global Emissions of Nitrogen Oxides from 1960 to 2014

The quantification of nitrogen oxide (NOx) emissions is critical for air quality modeling. Based on updated fuel consumption and emission factor databases, a global emission inventory was compiled with high spatial (0.1 degrees X 0.1 degrees), temporal (monthly), and source (87 sources) resolutions for the period 1960 to 2014. The monthly emission data have been uploaded online (http://inventory.pku.edu.cn), along with a number of other air pollutant and greenhouse gas data for free download. Differences in source profiles, not global total quantities, between our results and those reported previously were found. There were significant differences in total and per capita emissions and emission intensities among countries, especially between the developing and developed countries. Globally, the total annual NOx emissions finally stopped increasing in 2013 after continuously increasing over several decades, largely due to strict control measures taken in China in recent years. Nevertheless, the peak year of NOx emissions was later than for many other major air pollutants. Per capita emissions, either among countries or over years, follow typical inverted U-shaped environmental Kuznets curves, indicating that the emissions increased during the early stage of development and were restrained when socioeconomic development reached certain points. Although the trends are similar among countries, the turning points of developing countries appeared sooner than those of developed countries in terms of development status, confirming late-move advantages.