Aerosol interplay with meteorology in a biodiversity-rich high-altitude site in India: impacts of southwest monsoon on aerosol chemical characteristics

Atmospheric aerosols significantly impact climate, and the hydrological cycle, in high-altitude regions like the Western Ghats in India, where monsoon dynamics play a critical role. Here we present the first Q-ACSM-based characterization of non-refractory submicron aerosol (NR-PM 1 ) and organic aerosol (OA) source apportionment from Munnar, Kerala, during the Southwest monsoon season (06 June—25 July 2021). The organics comprised the largest fraction of NR-PM 1 (42.1 ± 23.7%), closely followed by sulfate (41.0 ± 19.6%). Aerosol composition was strongly controlled by meteorological regime: sulfate dominated during active monsoon periods and exhibited a persistent high-speed W–SW transport signature consistent with strong marine influence, while organics became the dominant fraction (52%) during the mixed period. OA source apportionment, conducted using Positive Matrix Factorization (PMF), identified four key factors: hydrocarbon-like OA (HOA, 11.4 ± 10.4%), biomass-burning OA (BBOA, 14.0 ± 13.8%), Biomass-Burning-derived Oxygenated OA (BB-OOA, 40.2 ± 23.0%), and Oxygenated OA (OOA, 34.3 ± 24.3%), suggesting dominance of secondary aerosols in the region. These findings highlight the contrasting roles of long-range marine transport and local secondary processing in shaping fine aerosol composition at high-altitude monsoon sites, with implications for aerosol hygroscopicity and cloud condensation nuclei activity over the Western Ghats.