Air pollution imposes an unseen compound burden on outdoor thermal comfort across India

Abstract Air pollution and thermal stress are experienced together but assessed separately. Here we quantify modelled pollution-related shifts in outdoor thermal comfort across Indian states during 2016–2023, using 423 regulatory monitoring stations and reanalysis-based UTCI. At monthly state scale, pollutant anomalies show no statistically detectable association with UTCI anomalies after accounting for seasonality, consistent with nonlinear machine-learning results. A published index integrating both dimensions fails on transfer to India, producing unphysical comfort gains in clean regions. We therefore recalibrate it with Indian regulatory anchors. The recalibrated index estimates winter and post-monsoon comfort-index shifts concentrated across the Indo-Gangetic Plain, reaching 4°C-equivalent in Delhi. A population-weighted dual-exposure classification shows 2.98 billion person-months of model-defined compound exposure each year, two-thirds of India’s thermal-stress burden. This burden is invisible to thermal indices, and to the separate frameworks that currently govern heat and air quality.