G01_05

Atmospheric ¹⁴CO₂ observations in megacity Delhi: Inferences for fossil fuel CO₂ (CO₂ff ) emissions

Sharma R¹, Kumar Kunchala R¹, Ojha S², Kumar P², Gargari S², Chopra S²

¹Indian Institute of Technology Delhi, New Delhi, India, ²Inter University Accelerator Centre, New Delhi, India

Radiocarbon is an ideal tracer for fossil fuel CO₂ estimations in the atmosphere because of its absence in the fossil fuels. It is formed in the atmosphere by the interaction of cosmic rays with ¹⁴N atoms and distributed in the different reservoirs of earth systems in the form of ¹⁴CO₂. In present study, we have presented the analysis on the fossil fuel CO₂ emissions in megacity Delhi using ¹⁴CO₂ observations for the period from 2017 to 2022. Weekly and sub-weekly integrated atmospheric CO₂ samples are collected in the form of carbonates by absorbing CO₂ over sodium hydroxide at accelerator mass spectrometry (AMS) facility building in Inter University Accelerator Centre (IUAC), New Delhi. These carbonate samples are acid hydrolyzed using carbonate handling system (CHS) and graphitized using automated graphitization equipment (AGE). Radiocarbon in the form of ¹⁴C/¹²C ratio is measured using a 500 kV ion accelerator at IUAC – AMS facility with the precision between 2 to 3 ‰ and measured ¹⁴C/¹²C ratios are converted into Δ¹⁴C values and CO₂ff values are calculated using Δ¹⁴C values. Results of this study in terms of annual and seasonal variations of Δ¹⁴C and CO₂ff will be presented for the study period over Delhi. Correlations of Δ¹⁴C and CO₂ff with other pollutant concentrations (PM2.5, CO, NO₂, SO₂ etc.) from the nearest air quality monitoring stations and available bottom up CO₂ff inventories will also be discussed.