An overview of atmospheric non-methane hydrocarbons over the Indian subcontinent: perspective for future research

This critical review delves into non-methane hydrocarbons (NMHCs), a class of volatile organic compounds (VOCs) that consist of carbon and hydrogen atoms, and are distinguished from methane due to their higher reactivity in the atmosphere. NMHCs play a critical role in tropospheric ozone formation and secondary aerosol production, with implications for air quality and human health. This review synthesizes existing findings on NMHC species, sources, and measurement techniques across diverse regions of India, highlighting elevated BTEX levels in urban-industrial regions, and the significant data scarcity in rural settings. Major gaps include fragmented datasets, inconsistent measurement protocols, and limited adoption of advanced techniques such as online GC-FID and PTR-MS. Health-based risk assessments indicate concerning levels of excess lifetime cancer risk from benzene exposure in megacities. The review underscores the need for harmonized monitoring practices, integrated source apportionment frameworks, and robust spatiotemporal datasets. It also outlines the limitations of conventional gas chromatography and highlights emerging NMHC species requiring further study. Quantitative evaluations, including ozone formation potentials and cancer risk assessments, reveal substantial public health and agricultural vulnerabilities. This assessment advocates for a nationwide NMHC monitoring network and the integration of atmospheric, geochemical, and epidemiological data to inform evidence-based mitigation strategies and policy interventions.