Methane sources from waste and natural gas sectors detected in Pune, India, by concentration and isotopic analysis

Methane (CH4) is a potent greenhouse gas and also plays a significant role in tropospheric chemistry. High-frequency (sub-hourly) measurements of CH4 and carbon isotopic ratio (δ13CH4) have been conducted at Pune (18.53°N, 73.80°E), an urban environment in India, during 2018–2020. High CH4 concentrations were observed, with a mean of 2100 ± 196 ppb (1844–2749 ppb), relative to marine background concentrations. The δ13CH4 varied between −45.11 and −50.03 ‰ for the entire study period with an average of −47.41 ± 0.94 ‰. The diurnal variability of CH4 typically showed maximum values in the morning (08:00–09:00 local time) and minimum in the afternoon (15:00 local time). The deepest diurnal amplitude of ~500 ppb was observed during winter (December–February), which was reduced to less than half, ~200 ppb, during the summer (March–May). CH4 concentration at Pune showed a strong seasonality (470 ppb), much higher than that at Mauna Loa, Hawaii.