Upper tropospheric SO₂ conversion into sulfuric acid aerosols and cloud condensation nuclei

Abstract

We have investigated the potential of upper tropospheric cloud condensation nuclei (CCN) formation from sulfur dioxide. This process involves three steps including SO 2 conversion to gaseous sulfuric acid (GSA), homogeneous bimolecular nucleation of GSA and water vapor leading to new aerosol particles, and new aerosol particle growth via mutual coagulation and GSA‐H 2 O condensation. Our investigation includes both measurements of SO 2 and GSA as well as model calculations of SO 2 conversion to new aerosol particles in the presence of preexisting aerosols which act as a competing sink for GSA. The model reproduces the measured abundance ratio GSA‐SO 2 reasonably well. Furthermore, the model predicts that efficient upper tropospheric CCN formation from SO 2 may, in fact, occur under certain plausible conditions. These conditions are explored utilizing the factor F CCN , defined as a ratio of the source and sink terms of gaseous sulfuric acid. In particular, a threshold F CCN value for efficient CCN formation is calculated with the model.