G01_P01

Changes in fossil CO₂ emissions in Mexico City during the Covid-19 lockdown deduced from atmospheric radiocarbon concentrations

Beramendi-Orosco L^1,3, González-Hernández G^2,3, Cienfuegos E^1,3, Otero F^1,3, Santos-Arévalo F⁴, Gómez-Martínez I⁴

¹Instituto de Geología, UNAM, Ciudad De México, Mexico, ²Instituto de Geofísica, UNAM, Ciudad de México, Mexico, ³Laboratorio Nacional de Geoquímica y Mineralogía, UNAM, Ciudad de México, Mexico, ⁴Centro Nacional de Aceleradores, Sevilla, Spain

The Mexico City Metropolitan Area is a complex megacity with a mixture of CO₂ emission sources, where atmospheric ¹⁴C variability is influenced mainly by changes in fossil fuels burning and wildfires in the mountains surrounding the valley, common during the hot-dry spring season. In this contribution we present atmospheric radiocarbon concentrations from CO₂ monthly-integrated samples taken between January 2019 – June 2021 at the southern area of the Mexico City Basin and explain the changes in terms of the Covid-19 lockdown and restrictions imposed form March 2020. To stop the spread of the Covid-19 epidemy, the Mexican government imposed a partial lockdown closing schools and universities on 20th of March 2020, extending the lockdown to all non-essential activities with a significant reduction in public transport services on 30th of March, and further restrictions with a complete lockdown imposed on 21st of April when the country started the phase of higher risk of Covid-19 transmission. This complete lockdown lasted up to 13th of May, and from 1st of July some non-essential activities were gradually opened with some restrictions in place up to 2021, and schools and universities remaining closed up to September 2021. Atmospheric radiocarbon concentrations clearly followed the different phases of the Covid-19 restrictions, with significantly higher values (p<0.001) during March – May 2020, indicating, as expected, an important reduction of fossil CO₂ emissions. Furthermore, the post-March 2020 values are higher with lower variability, ranging between 0.9906–1.0108, as compared to the pre-Covid-19 pandemic values, ranging between 0.9639–0.9951.