High frequency of urban new particle formation on the Tibetan Plateau: quantifying formation rates, growth rates, and CCN production

Abstract

New particle formation (NPF) strongly influences aerosol number size distributions and cloud condensation nuclei (CCN), yet its characteristics and climatic relevance in high-altitude urban environments over the Tibetan Plateau (TP) remain poorly constrained. We conducted in situ observations at Tibet University (TU) in Lhasa during the spring and autumn observation periods. NPF event frequencies were 86.2 % during the autumn observation period and 62.1 % during the spring observation period. Observation days were classified as NPF, Undefined, or Non-Event days based on PNSD evolution, supported by size-segregated particle number concentrations and particle growth rates. Observation-period comparisons indicate clear differences in the factors associated with NPF: NPF during the autumn observation period may have been favored by greater sulfur-precursor availability, whereas no single dominant controlling factor could be identified during the spring observation period. Estimated CCN concentrations were higher on NPF days (mean ± standard deviation: (2.3±1.5)×103 cm −3 ; median: 1.9×10 3 cm −3 ). Corresponding mean ± standard deviation and median values were (0.9±0.4)×103 and 0.81×10 3 cm −3 on Undefined days and (1.3±0.7)×103 and 1.1×10 3 cm −3 on Non-Event days, respectively. The impact of NPF on CCN depends not only on nucleation, but also on the continued growth and survival of newly formed particles. This study provides new insights into urban NPF characteristics and its potential contribution to CCN on the TP, improving our understanding of aerosol–climate interactions in high-altitude urban environments.