Comment on acp-2022-440

Abstract

New particle formation (NPF) is an important source of cloud condensation nuclei (CCN), which affects Earth’s radiative balance and global climate. The mechanism and CCN contribution of NPF at the high-altitude mountains, especially in the Tibetan Plateau (TP), was unclear due to lack of measurements. In this study, intensive measurements were conducted at Nam Co station (4379 m a.s.l) in the central TP during both pre-monsoon and summer monsoon seasons. The frequencies of NPF events exhibited extreme distinction with 15 % in pre-monsoon season and 80 % in monsoon season. The level of organic vapours governed the occurrence of NPF events, while condensation sink and gaseous sulfuric acid had no effect. The frequent NPF events in summer monsoon season resulted from the higher concentration of organic vapours, which was brought from northeast India by the strong southerly monsoon. It had increased the aerosol number concentrations and CCN at supersaturation of 1.2 % by more than 2 and 0.5 times compared with those in pre-monsoon season, respectively. Considering that the smaller particles formed by NPF may further grow and reach CCN size during the following days due to the low-level coagulation sink, the amount of potential CCN in monsoon season could be much larger than our local measurement results. Our results emphasized the importance of organics to NPF in high-altitude atmosphere, and the seasonal effect of NPF at the high-altitude sites should be carefully considered in model simulations to reduce the uncertainty of global CCN budget.