Enhancing effect of dimethylamine in sulfuric acid nucleation in the presence of water – a computational study

V Loukonen,H Vehkamäki,T Kurtén,A A H Pádua,M Kulmala,I K Ortega,K Sellegri

doi:10.5194/acp-10-4961-2010

Abstract

Abstract. We have studied the hydration of sulfuric acid – ammonia and sulfuric acid – dimethylamine clusters using quantum chemistry. We calculated the formation energies and thermodynamics for clusters of one ammonia or one dimethylamine molecule together with 1–2 sulfuric acid and 0–5 water molecules. The results indicate that dimethylamine enhances the addition of sulfuric acid to the clusters much more efficiently than ammonia when the number of water molecules in the cluster is either zero, or greater than two. Further hydrate distribution calculations reveal that practically all dimethylamine-containing two-acid clusters will remain unhydrated in tropospherically relevant circumstances, thus strongly suggesting that dimethylamine assists atmospheric sulfuric acid nucleation much more effectively than ammonia.

Highlights

The fourth assessment report of the Intergovernmental Panel on Climate Change concludes that aerosols remain the dominant uncertainty in predicting radiative forcing and climate change (Intergovermental Panel for Climate Change, 2007; for a recent supplementary to the fourth IPCC report see e.g. The Copenhagen Diagnosis, 2009)
The results indicate that dimethylamine enhances the addition of sulfuric acid to the clusters much more efficiently than ammonia when the number of water molecules in the cluster is either zero, or greater than two
In order to compare the enhancing effects of dimethylamine and ammonia in sulfuric acid-water nucleation, we have calculated the Gibbs free energies of the addition of one H2SO4 molecule to clusters consisting of one sulfuric acid, ammonia or dimethylamine and 0–5 water molecules

Summary

Introduction

The fourth assessment report of the Intergovernmental Panel on Climate Change concludes that aerosols remain the dominant uncertainty in predicting radiative forcing and climate change (Intergovermental Panel for Climate Change, 2007; for a recent supplementary to the fourth IPCC report see e.g. The Copenhagen Diagnosis, 2009). Sulfuric acid concentrations have been observed to correlate with new-particle formation rates in a large variety of conditions (e.g., Weber et al, 1996, 1997; Kulmala et al, 2006; Sihto et al, 2006; Riipinen et al, 2007) and the ubiquitous water is most likely involved (Kulmala et al, 2004). It is known, based on both experimental and theoretical results, that most of the observed new-particle formation events can not be explained by electrically neutral binary sulfuric acid-water nucleation alone. Atmospheric nucleation mechanisms have been proposed to involve contributions from ions, ammonia or various organic compounds (Korhonen et al, 1999; Kavouras et al, 1999; Kulmala et al, 2000; Yu and Turco, 2000)

Objectives

Results

Conclusion