Atmospheric Non-Methane Hydrocarbons over Indian Region: From Initial Measurements to Latest Results

Increased non-methane hydrocarbons (NMHCs) emissions brought on by urbanisation, industrialisation, and a warming planet have significantly modulated regional atmospheric photochemistry, ground-level ozone formation, oxidant levels, and secondary organic aerosol production. India, being a country with fast-paced changes with excessive and variable emissions like in the Indo-Gangetic Plains, a comprehensive understanding of the temporal and spatial evolution of NMHCs over this region is crucial to decipher contributing sources and quantify their impacts. In this context, we have evaluated peer-reviewed observational studies employing established analytical techniques on the detection of NMHCs over the Indian subcontinent, classified into major geographical realms (West, North, IGP, East, South, and Central). The study accesses measurement techniques, concentration levels, spatio-temporal variability, NMHC ratios and inter-relationships among species over multiple Indian locations representing diverse topographical, meteorological, and urbanization regimes. The reviewed research consistently shows that major urban regions like Delhi, Mumbai, Hyderabad, and Kanpur experience significantly higher NMHC levels in comparison to background and rural locations like Mount Abu, Nainital and Ajmer. Background regions also exhibit an increase under burgeoning emissions. Increasing contributions to the atmospheric NMHCs from the solvent usage sector has been observed in urbanized locations. The study emphasises how improvements in NMHC measurement methods—from conventional canister samplers to contemporary real-time devices like PTR-ToF-MS have improved evaluations of air quality. This review, based on over 15 study locations over India, underscores the need for expanded and sustained NMHC monitoring networks, adoption of cleaner fuels, and stricter emission control strategies to effectively mitigate NMHC-driven air quality degradation in India.