The Pivotal Role of Heavy Terpenes and Anthropogenic Interactions in New Particle Formation on the Southeastern Qinghai-Tibet Plateau

Abstract

Aerosol particles originating from the Qinghai-Tibet Plateau (QTP) readily reach the free troposphere, potentially affecting global radiation and climate. Although new particle formation (NPF) is frequently observed at such high altitudes, its precursors and their underlying chemistry remain poorly understood. This study presents direct observational evidence of anthropogenic influences on biogenic NPF on the southeastern QTP, near the Himalayas. The mean particle nucleation rate (J_1.7) is 2.6 cm^–3 s^–1, exceeding the kinetic limit of sulfuric acid (SA) nucleation (mean SA: 2.4 × 10⁵ cm^–3). NPF is predominantly driven by highly oxygenated organic molecules (HOMs), possibly facilitated by low SA levels. We identified 1538 ultralow-volatility HOMs driving particle nucleation and 764 extremely low-volatility HOMs powering initial particle growth, with mean total concentrations of 1.5 × 10⁶ and 3.7 × 10⁶ cm^–3, respectively. These HOMs are formed by atmospheric oxidation of biogenic precursors, unexpectedly including sesquiterpenes and diterpenes alongside the commonly recognized monoterpenes. Counterintuitively, over half of HOMs are organic nitrates, mainly produced by interacting with anthropogenic NO_x via RO₂+NO terminations or NO₃-initiated oxidations. These findings advance our understanding of NPF mechanisms in this climate-sensitive region and underscore the importance of heavy terpene and NO_x-influenced chemistry in assessing anthropogenic-biogenic interactions with climate feedbacks.