Elucidating Mechanisms of Organic-Driven Nanoparticle Growth in China through Advanced Modeling

Nanoparticle growth is a critical process determining whether newly formed nanoparticles can survive to cloud condensation nuclei (CCN) and haze sizes, thereby influencing climate and air quality. The growth is primarily driven by the condensation of low-volatility organic vapors. Therefore, comprehensive and accurate understanding of organic-driven particle growth processes is crucial for accurately assessing their environmental, climatic, and health impacts, and for developing targeted mitigation strategies. Three-dimensional models are essential tools for elucidating regional-scale particle evolution mechanisms. However, existing 3D atmospheric models fail to characterize the formation and condensation of low-volatility organics driving particle growth, which hinders accurate simulation and mechanistic understanding of growth processes.

Here, we develop an advanced 3D numerical modeling framework for organic gas-phase oxidation and particle growth by implementing the integrated two-dimensional volatility basis set (I2D-VBS) and a kinetic gas-particle partitioning model in WRF-Chem. This model accurately simulates organic oxidation products across the full volatility range and their condensation-driven nanoparticle growth processes. The model effectively reproduces process-level particle growth observed at different sites and seasons across China, reducing growth rate errors from orders of magnitude to reasonable ranges and significantly enhancing simulations of particle number size distributions.

Based on the improved model, we conduct a comprehensive analysis of organic-driven particle growth in China and identify the primary organic sources driving particle growth. Results show that particle growth rates in China are predominantly contributed by oxidation products of intermediate/semi-volatile organic compounds (I/SVOCs), accounting for >65% in winter and >59% in summer across key regions including Beijing-Tianjin-Hebei, Yangtze River Delta, and Pearl River Delta. Anthropogenic VOCs (AVOCs) rank second in contribution, though the contribution from biogenic VOCs (BVOCs) may exceed that from AVOCs in some southeastern regions during summer. Among precursor categories, aromatics and aliphatics are the most important, followed by oxygenated aromatics. Finally, we further elucidate the impacts of organic condensation-driven growth on particle and CCN number concentrations. This study fills critical knowledge gaps regarding particle growth mechanisms and their environmental impacts in China.