Oxidation Products of Biogenic Emissions Contribute to Nucleation of Atmospheric Particles

TLDR

Atmospheric new‑particle formation, a key climate‑influencing process, remains poorly understood due to the atmosphere’s complexity and variability. CLOUD chamber experiments demonstrate that sulfuric acid combined with oxidized organic vapors at atmospheric concentrations can reproduce observed nucleation rates, and incorporating this cluster‑forming mechanism into a global aerosol model produces a seasonally varying particle concentration cycle that aligns with observations.

Abstract

Atmospheric new-particle formation affects climate and is one of the least understood atmospheric aerosol processes. The complexity and variability of the atmosphere has hindered elucidation of the fundamental mechanism of new-particle formation from gaseous precursors. We show, in experiments performed with the CLOUD (Cosmics Leaving Outdoor Droplets) chamber at CERN, that sulfuric acid and oxidized organic vapors at atmospheric concentrations reproduce particle nucleation rates observed in the lower atmosphere. The experiments reveal a nucleation mechanism involving the formation of clusters containing sulfuric acid and oxidized organic molecules from the very first step. Inclusion of this mechanism in a global aerosol model yields a photochemically and biologically driven seasonal cycle of particle concentrations in the continental boundary layer, in good agreement with observations.