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Topics in 2020



Statistical analysis of urban CO2 emission signals

Cities are responsible for the largest anthropogenic CO2 emissions and are key to effective emission reduction strategies. Urban CO2 emissions estimated from vertical atmospheric measurements can contribute to an independent quantification of the reporting of national emissions and will thus have political implications. We analyzed vertical atmospheric CO2 mole fraction data obtained onboard commercial aircraft in proximity to 36 airports worldwide, as part of the Comprehensive Observation Network for Trace gases by Airliners (CONTRAIL) program. At many airports, we observed significant flight-to-flight variations of CO2 enhancements downwind of neighboring cities, providing advective fingerprints of city CO2 emissions. Observed CO2 variability increased with decreasing altitude, the magnitude of which varied from city to city. We found that the magnitude of CO2 variability near the ground (~1 km altitude) at an airport was correlated with the intensity of CO2 emissions from a nearby city. Our study has demonstrated the usefulness of commercial aircraft data for city-scale anthropogenic CO2 emission studies.

Variability of atmospheric CO2 enhancement over Tokyo Narita Airport (NRT). (a,b) Maximum excess CO2 values observed in wind direction (angle) and speed (distance from the center) bins at 4.0–4.5 km and 1.0–1.5 km altitude, respectively. (c) Histograms of excess CO2 at 4.0–4.5 km (solid purple) and 1.0–1.5 km (solid red line) altitudes. (d) The CO2 measurement positions at altitudes of <2 km (black circles).


Maps of magnitude of CO2 variability over airports worldwide. Large and red circles indicate large variability. Cities are denoted by nearby airport codes. It was found that the CO2 variability was large over airports where a nearby city has large CO2 emissions.

Reference