New Particle Formation and Growth in Urban Atmospheres: From Observations to Molecular-Level Understanding

Aerosol particles, profoundly influenced by human activities, play pivotal roles in air quality and climate. The formation and growth of new atmospheric particles is a leading source of high-concentration aerosol particles in urban environments and also the largest source of uncertainties in global climate predictions. Recent advances in experimental and theoretical research have dramatically improved our understanding of urban new particle formation (NPF), showing that the abundant anthropogenic pollutants in complex urban atmospheres enable the fast formation of new particles that are highly selective toward the gaseous precursors and chemical processes. The uniqueness of urban atmospheres causes the underrepresentation of urban NPF in regional and global models, while the evolving urban environments complicate the prediction of future environmental and climate effects of NPF. In this review, we link the latest molecular-level chemical mechanisms and implications on climate predictions and air pollution control by assessing the methodology to investigate urban NPF, sorting out the latest mechanistic findings, and discussing their implementation in three-dimensional models.