Growth of Nanoparticles Driven by Distinct Chemical Composition Leads to Contrasting Hygroscopicity and CCN Potential Across Two Environments Over the Tibetan Plateau

New particle formation (NPF) is a major source of aerosols and cloud condensation nuclei (CCN) over the remote Tibetan Plateau (TP), yet the chemical drivers and climatic impacts of nanoparticle growth remain poorly understood. This study reveals a stark contrast in the hygroscopicity of 20–60 nm particles originating from NPF at two distinct TP sites: particles and their growth material at Yangbajing (YBJ, alpine meadow) showed moderate hygroscopicity (κ ≈ 0.2), suggesting water‐soluble compounds driving the growth, whereas those at Lulang (forested mountains) were nearly non‐hygroscopic (κ < 0.1), dominated by water‐insoluble organics. Consequently, despite frequent NPF at Lulang, its CCN contribution was limited due to its low hygroscopicity unless particles grew beyond ∼60 nm. In contrast, the higher hygroscopicity at YBJ enabled efficient CCN activation at smaller sizes, enhancing its overall CCN production. Our results emphasize that regional differences in NPF chemistry critically modulate aerosol‐cloud‐climate interactions over such climatic‐sensitive environments.