Drastic changes in carbon monoxide pollution in rural India (2000–2019) and its CMIP6 model future (2015–2100) projections

Carbon Monoxide (CO) is a reactive gas that plays a crucial role in the atmospheric carbon cycle. It has significant implications for human health, manifesting in both short and long-term effects such as fatigue, headaches, nausea and confusion, as well as impacts on ecosystems and climate. Here, we investigate the long-term changes in CO levels, utilising data from ground-based, satellite, reanalysis, emission inventory and climate model projections for the period 2000-2019, in rural India. This investigation reveals that rural regions of Indo-Gangetic Plain (IGP), North East India (NEI) and Central India (CI) exhibit elevated CO levels ranging from 150 to 400 ppbv. The highest levels are observed during the months followed by agricultural waste burning (AWB) in January-March in rural IGP (200 ppbv) and NEI (275 ppbv), but the rural Hilly Regions (HR) maintain the lowest CO concentrations in India throughout the year. We find a reversal in CO trend from 2006 onwards, with a significant decrease of -1.25 ppbv/yr throughout rural India in 2006-2019. This decline in CO, despite the rise in emissions from all sources, except road transport, reveals its role in regulating the CO pollution. The engagement and enforcement of proper regulations (e.g. implementation of stringent Bharat Stage standards) also might have contributed to this reduction. Future projections across all Shared Socioeconomic Pathways (SSP) scenarios, with the exception of SSP3-7.0, indicate a substantial decrease in CO pollution in rural India by the end of 21st century. The decrease in CO levels in rural India signifies improvement in air quality resulting from government initiatives, including the Bharat Stage regulations, Pradhan Mantri Ujjwala Yojana and the promotion of agricultural mechanisation for in-situ management of crop residue. This study, therefore, reiterates the significance of policies and their prompt execution in regulating CO pollution to enhance air quality and safeguard public health and environment.