Assessing Emission Characteristics of Cities Using Space-based Observations of CO2, CO, and NO2

Abstract:

With increased urbanization across the world, intensified anthropogenic activities and high levels of energy consumption in cities have led to the increase in emissions of CO₂ and air pollutants which greatly impact air quality. We explore the possibility of monitoring urban enhancements of CO₂ using observations from the Orbiting Carbon Observatory-2 (OCO-2) and of air pollutants CO and NO₂ from the Sentinel-5 Precursor TROPOspheric Monitoring Instrument (S-5P TROPOMI) in Northern Hemisphere cities during the winter season from December 2018 to March 2019. We use satellite observations to analyze urban enhancements of ΔXCO₂, ΔXCO, and XNO_2, and emission ratios, ΔXCO/ΔXCO₂ and XNO₂/ΔXCO₂, according to each city, and observe the relationship between CO₂ and air pollutants as well as the emission patterns of cities. Our analysis shows a positive relationship in the comparisons of ΔXCO/ΔXCO₂ and XNO₂/ΔXCO₂ to city population and GDP, which are indicators of anthropogenic activity, signifying that cities with larger populations and economies tend to show higher emission ratios, leading to poorer air quality. In addition, when cities are divided into ‘developed’ and ‘developing’ regions, a pattern is found where developed cities tend to have a higher ratio of emission ratios compared to developing cities. However, despite their low GDP, developing cities undergoing rapid economic development such as Mumbai, Kolkata, and Lahore have ΔXCO/ΔXCO₂ ratios (average of 1.15 × 10^-2 ± 2.86 × 10^-3 mol m^-2 ppm^-1) and XNO₂/ΔXCO₂ ratios (average of 3.81 × 10^-5 ± 1.27 × 10^-5 mol m^-2 ppm^-1) that are similar or even higher than that of developed cities. Our study shows that comparing satellite observations of CO₂ and air pollutants can provide an understanding about factors and sources that can affect air quality in cities such as low combustion efficiency, less stringent pollution measures, and geographical features. We also explore the possibilities of synergies of future satellite missions with longer periods of observation which will aid in policy-making for effective pollution reduction.

This work was supported by the Korea Environment Industry & Technology Institute (KEITI) through the Public Technology Program based on the Environmental Policy Program funded by the Korea Ministry of Environment (MOE)(2019000160007).