Evidence for the role of organics in aerosol particle formation under atmospheric conditions

TLDR

Atmospheric new particle formation influences radiative forcing, yet its nucleation mechanisms remain poorly understood due to limited laboratory explanations. The study used a smog chamber to simulate photochemical H₂SO₄ and organic condensable species formation and examined new particle nucleation. Nucleation occurs at ambient H₂SO₄ levels, with rates proportional to the product of H₂SO₄ and an organic molecule, indicating a single H₂SO₄–organic pair in the rate‑limiting step, and incorporating this mechanism into a global aerosol model markedly improves agreement with observations.

Abstract

New particle formation in the atmosphere is an important parameter in governing the radiative forcing of atmospheric aerosols. However, detailed nucleation mechanisms remain ambiguous, as laboratory data have so far not been successful in explaining atmospheric nucleation. We investigated the formation of new particles in a smog chamber simulating the photochemical formation of H 2 SO 4 and organic condensable species. Nucleation occurs at H 2 SO 4 concentrations similar to those found in the ambient atmosphere during nucleation events. The measured particle formation rates are proportional to the product of the concentrations of H 2 SO 4 and an organic molecule. This suggests that only one H 2 SO 4 molecule and one organic molecule are involved in the rate-limiting step of the observed nucleation process. Parameterizing this process in a global aerosol model results in substantially better agreement with ambient observations compared to control runs.