Radiocarbon based fossil fuel CO ₂ observations in megacity Delhi: Temporal variations and effect of COVID-19 restrictions

This study employs radiocarbon measurements (Δ 14 C) to detect fossil fuel CO 2 (CO 2ff ) in the megacity Delhi from 2018 to 2022, offering unique insights into fossil fuel emissions. Our measurements reveal varying Δ 14 C values ranging from −56.2‰ to 7.5‰ and CO 2ff values ranging from 0.3 ppm to 25.2 ppm. We observed a distinct seasonality in Δ 14 C and CO 2ff , with higher CO 2ff (lower Δ 14 C) values during winter and post-monsoon seasons and lower CO 2ff (higher Δ 14 C) in summer and monsoon seasons. We have determined emission ratios (R CO and R NOx ), and compared them with other studies worldwide. Our study also examines the impact of the COVID-19 lockdown periods on CO 2ff and observed a notable decrease of 5.6 (4.8) ppm during the pandemic’s first (second) waves. These findings enhance our understanding of CO 2 emission inventories in megacity Delhi.