Changes in CO₂ Emission Sources in Mexico City Metropolitan Area Deduced from Radiocarbon Concentrations in Tree Rings

Abstract

We present radiocarbon (14C) in tree rings from Mexico City and a reconstruction of fossil CO2 concentrations for the last five decades, as part of a research program to understand the 14C dynamics in this complex urban area. Background values were established by 14C concentrations in tree rings from a nearby clean area. Agreement between background and NH-zone 2 values indicate Taxodium mucronatum is a good biomonitor for annual atmospheric 14C variations. Values for the urban tree rings were significantly lower than background values, indicating a 14C depletion from fossil CO2 emissions. There is an increasing trend of fossil CO2 between 1960 and 1990, in agreement with the population growth and the increasing demand for fossil fuels in Mexico City. Between 1990 and 2000, there is an apparent decrease in fossil CO2 concentration, increasing again after 2000. The decrease in 2000, despite being of the same magnitude as the overall uncertainty, may reflect environmental policies that improved the energy efficiency and reduced CO2 emissions in the area. The increase in fossil CO2 concentration between 2000 and 2010 may be attributable to the significant growth of motor vehicle usage in Mexico City, which made transportation the main energy-demanding and -emitting sector.

14C-AMS measurements in modern tree rings to trace local fossil fuel-derived CO2 in the greater Xi'an area, China

“…The equations we obtained here (eq. 10 and 12) are different than reported by other authors in the tree-ring radiocarbon literature (Rakowski et al 2008a, Beramendi-Orosco et al 2017.…”

“…We believe the equation reported by others (Rakowski et al 2008a, Beramendi-Orosco et al 2017, based on the mass balance equations of Levin et al (1989Levin et al ( , 2003, is probably wrong. We recommend using our equations (10 and 12) depending on the required variables.…”

From Trees to Ecosystems: Spatiotemporal Scaling of Climatic Impacts on Montane Landscapes Using Dendrochronological, Isotopic, and Remotely Sensed Data

“…Tree δ 13 C ratios in our study were slightly lower than those reported for P. hartwegii in nearby forests (Gómez‐Guerrero et al, 2013; Silva et al, 2015). However, these values consistently reflect a dilution effect ( 13 C‐Suess effect) of CO 2 due to the release of 13 C‐depleted CO 2 from combusted fossil C fuels into the atmosphere (Figure 4a) (Beramendi‐Orosco et al, 2018). After correcting for the Suess effect, our results indicate that even with short‐time periods of tree ring measurements, such as 17 years, it is possible to capture high‐frequency events related to year‐to‐year variations in tree physiological performance, which scale up to landscapes.…”

CHANGES IN FOSSIL CO2 EMISSIONS IN MEXICO CITY DURING THE COVID-19 LOCKDOWN DEDUCED FROM ATMOSPHERIC RADIOCARBON CONCENTRATIONS

“…The Mexico City Metropolitan Area (MCMA) is a complex megacity with a mixture of CO 2 emission sources, where atmospheric radiocarbon ( 14 C) variability is influenced mainly by changes in fossil fuel combustion and biomass burning from residential combustion, agricultural burning and wildfires in the mountains surrounding the valley, common during the dry season (winter and spring) (Beramendi-Orosco et al 2015, 2018. Previous studies have reported Δ 14 C levels in MCMA up to 75‰ and 27‰ higher than regional background values during the hot and dry season (Vay et al 2009 andBeramendi-Orosco et al 2015, respectively), attributed to the release of 14 C-enriched CO 2 resulting from the burning of soil organic matter during agricultural and wild fires in the basin, suggesting this is a significant CO 2 emission source as it cancels out the 14 C dilution resulting from the vast amount of fossil fuels burned this metropolitan area with high population density.…”

“…Previous studies have reported Δ 14 C levels in MCMA up to 75‰ and 27‰ higher than regional background values during the hot and dry season (Vay et al 2009 andBeramendi-Orosco et al 2015, respectively), attributed to the release of 14 C-enriched CO 2 resulting from the burning of soil organic matter during agricultural and wild fires in the basin, suggesting this is a significant CO 2 emission source as it cancels out the 14 C dilution resulting from the vast amount of fossil fuels burned this metropolitan area with high population density. These observations could result in an underestimation of the atmospheric fossil CO 2 concentration in the MCMA, hampering the direct use of 14 C as a tracer of fossil CO 2 emissions in such a complex urban area (Beramendi-Orosco et al 2018). main fuels.…”