Biogenic particle formation over the southeastern Qinghai-Tibet Plateau is increasingly influenced by anthropogenic emissions

Aerosols formed on the Qinghai-Tibet Plateau, also known as the world's third pole, are more likely to enter the free troposphere due to its high altitude. This has far-reaching effects on radiative forcing and global climate. The southeastern Qinghai-Tibet Plateau, adjacent to the Himalayas, is commonly regarded as a pristine area that can offer insight into aerosol formation under pre-industrial conditions, free from the influence of human activities. Here we present observations taken at a representative site in southeast Tibet, a region covered by alpine forests and grasslands. The average aerosol particle nucleation rate (J_1.7) is 2.5 cm^-3s^-1, exceeding the kinetic limit of sulfuric acid (SA) nucleation in most cases due to the low SA concentrations (with a mean of 2.5×10⁵ cm^-3). The critical role of highly oxygenated organic molecules (HOMs) in in-situ aerosol production is then to be found. Ultra-low and extremely low volatile HOMs dominate particles' nucleation and initial growth, respectively. Furthermore, these organic vapors come from the atmospheric oxidation of biogenic precursors, mainly monoterpenes with some contributions from sesquiterpenes and diterpenes. Surprisingly, over half of the ultra- and extremely-low volatile HOMs are organic nitrates, mainly formed through RO₂ + NO terminations or NO₃-initiated oxidations. These findings suggest that anthropogenic emissions influence the chemistry that drives biogenic new particle formation in the southeastern Qinghai-Tibet Plateau. As human activity increases, this region is transitioning from a pre-industrial to a post-industrial environment. The potential impact of this process on aerosol production and climate should be given more consideration.