Methane sources from waste and natural gas sectors detected in Pune, India, by concentration and isotopic analysis Abirlal Metya a,b , Amey Datye a , Supriyo Chakraborty a,b, ⁎ , Yogesh K. Tiwari a , Prabir K. Patra c , Charuta Murkute a a Indian Institute of Tropical Meteorology, Ministry of Earth Sciences, Pune, India b Department of Atmospheric and Space Sciences, Savitribai Phule Pune University, Pune, India c Research Institute for Global Change, JAMSTEC, Yokohama 236-0001, Japan HIGHLIGHTS • Methane concentration and isotopic values were measured the first time in India. • Methane concentration but not the isoto- pic values shows seasonality in Pune. • Isotopic analysis shows waste sector is the significant source of methane in Pune. • No lockdown effect was found on meth- ane records. GRAPHICAL ABSTRACT ABSTRACT ARTICLE INFO Editor: Pingqing Fu Methane (CH 4 ) is a potent greenhouse gas and also plays a significant role in tropospheric chemistry. High-frequency (sub-hourly) measurements of CH 4 and carbon isotopic ratio (δ 13 CH 4 ) have been conducted at Pune (18.53°N, 73.80°E), an urban environment in India, during 2018–2020. High CH 4 concentrations were observed, with a mean of 2100 ± 196 ppb (1844–2749 ppb), relative to marine background concentrations. The δ 13 CH 4 varied between −45.11 and −50.03 ‰ for the entire study period with an average of −47.41 ± 0.94 ‰. The diurnal variability of CH 4 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). CH 4 concentration at Pune showed a strong seasonality (470 ppb), much higher than that at Mauna Loa, Hawaii. On the other hand, δ 13 CH 4 records did not show distinct seasonality at Pune. The δ 13 CH 4 values revealed that the sig- nificant sources of CH 4 in Pune were from the waste sector (enhanced during the monsoon season; signature of de- pleted δ 13 CH 4 ), followed by the natural gas sector with a signature of enriched δ 13 CH 4 . Our analysis of Covid-19 lockdown (April to May 2020) effect on the CH 4 variability showed no signal in the CH 4 variability; however, the iso- topic analysis indicated a transient shift in the CH 4 source to the waste sector (early summer of 2020). Keywords: Methane Carbon-13 isotope Monsoon Lockdown effect 1. Introduction Methane, ranked 2nd among the man-made greenhouse gases (GHGs), after carbon dioxide (CO 2 ), based on its contribution to the Earth's radiative forcing change since pre-industrial times, circa 1750 (Stocker et al., 2013). Science of the Total Environment 842 (2022) 156721 ⁎ Corresponding author at: Department of Atmospheric and Space Sciences, Savitribai Phule Pune University, Pune, India. E-mail address: supriyo@tropmet.res.in (S. Chakraborty). http://dx.doi.org/10.1016/j.scitotenv.2022.156721 Received 7 October 2021; Received in revised form 9 May 2022; Accepted 11 June 2022 Available online 16 June 2022 0048-9697/© 2022 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv