Insights into the high temporal variability of atmospheric carbon dioxide (CO₂) at a suburban station in the Indo-Gangetic Plain

Abstract. The unusual weather patterns and large anthropogenic emissions over the Indo-Gangetic Plain make it a hotspot of greenhouse gases like carbon dioxide (CO₂). Given the paramount significance of the IGP, a GHG observatory was set up at a suburban monitoring station, Sonipat, Haryana (28.95° N, 77.10° E), in the Delhi National Capital Region. Using continuous measurements of CO₂ using a ​​laser-based cavity ring-down spectroscopy (CRDS) technique, we investigated the temporal evolution of CO₂ concentrations from February 2023 to January 2025.  We observed an annual average CO₂ concentration of 440.8 ± 19.7 parts per million (ppm) with an unusually strong seasonal variability ranging from 422.6 ± 23.3 to 456.4 ± 30.8 ppm in monsoon and post-monsoon, respectively. A strong CO₂ diurnal amplitude of 29 ppm in May and 63 ppm in October was observed mainly due to seasonal changes in boundary layer mixing and biospheric activity. Further investigation of the drivers of this unique feature (strong seasonal and diurnal CO₂ variability) over IGP revealed a strong contrast to other global monitoring stations in the same latitude band. A strong correlation between CO₂ and CH₄ indicated a co-located emission source, while the strong positive correlation between CO₂ and carbon monoxide (CO) during post-monsoon indicates the footprint of crop residue burning on CO₂ concentrations. We demonstrate that the high temporal CO₂ variability in the IGP is driven by the interplay of local anthropogenic and biomass burning emissions, biospheric fluxes, and prevailing meteorology.