Winter-haze mediated dispersal of urban airborne bacteria across the Indo-Gangetic Plain of India

Winter haze across the Indo-Gangetic Plain (IGP) forms a dense, persistent atmospheric layer capable of transporting airborne bacteria over long distances, influencing human health, agricultural productivity, and climate dynamics. Present study investigates transports of bacterial communities through winter haze movement over IGP, analysing 20 airborne samples collected simultaneously in the winter of 2022-2023 from four urban cities along west-to-east traveling path from Delhi (28.49° N, 77.18° E) to Varanasi (25.26° N, 82.99° E) to Muzaffarpur (26.12° N, 85.39° E) and finally reaching to Ranchi (23.41° N, 85.44° E). Highest bacterial loading has been observed in Delhi, where the loading of bacterial ASV and genus reaches 71705 ± 4143 and 590 ± 70, respectively, representing a significantly higher loading (30%) of bacteria compared to the easternmost city of Ranchi. Venn diagram analysis confirmed widespread long-range transport, as demonstrated by a substantial overlap, where 500 bacterial genera were shared among all four geographically distinct sampling locations, accounting for approximately 50% of the total bacterial community that travelled along with winter haze movement. The health implications are underscored by the high prevalence of pathogenic ASVs, predominantly associated with respiratory and skin microbiomes, which ranged from 3,000 to over 5,000 ASVs per sample across the IGP, with Delhi and Muzaffarpur showing the highest concentration. Current result establishes that winter haze acts as an efficient vector for the high-load, long-distance transport of diverse bacterial communities, including potentially harmful human pathogens, across the most densely populated region in India.