Evaluating CCN activity through size-resolved hygroscopicity: Synergistic observations and simulations in a tropical montane region

Document Type

Article

Publication Date

10-15-2026

Abstract

Aerosol hygroscopicity plays a crucial role in different atmospheric processes, influencing particle size distribution, local visibility, cloud formation, precipitation patterns etc. Hygroscopicity determines the ability of water uptake by the particles. It depends on the particles’ chemical composition. This study presents the importance of hygroscopicity (κ) in aerosols activation process through in-situ ambient measurements and direct numerical simulations (DNS). In-situ measurements were carried out over a one-month period (15 November to 15 December, 2019) by combining two instruments: Humidified Tandem Differential Mobility Analyzer (HTDMA) and Cloud Condensation Nuclei Counter (CCNC) at High Altitude Cloud Physics Laboratory (HACPL). The results from these observations indicate that for particles with diameters 50 nm & 75 nm, activation fraction (AF) increases sharply as κ increases in all supersaturation levels (except at 0.1%). For 110 nm & 150 nm sized particles, a similar trend was found only at lower supersaturation up to 0.3%. Thus, hygroscopicity influences the activation of Aitken mode particles. In the accumulation mode, where particle size primarily governs activation process, hygroscopicity still exerts a significant effect under lower supersaturation conditions. We identified a supersaturation vs size regime wherein hygroscopicity is a decisive factor in aerosol activation. Therefore, the inclusion of κ is essential in numerical models. Implementation of size-dependent κ distribution instead of fixed κ in DNS improves CCN prediction. Modelled activation fraction is within the standard deviation of observation for SS range of 0.3% to 0.7%.

Publication Title

Atmospheric Environment

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