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- Title
Model for acid-base chemistry in nanoparticle growth (MABNAG).
- Authors
Yli-Juuti, T.; Barsanti, K.; Hildebrandt Ruiz, L.; Kieloaho, A-J; Makkonen, U.; Petäjä, T.; Ruuskanen, T.; Kulmala, M.; Riipinen, I.
- Abstract
Climatic effects of newly-formed atmospheric secondary aerosol particles are to a large extent determined by their condensational growth rates. However, all the vapors condensing on atmospheric nanoparticles and growing them to climatically relevant sizes are not identified yet and the effects of particle phase processes on particle growth rates are poorly known. Besides sulfuric acid, organic compounds are known to contribute significantly to atmospheric nanoparticle growth. In this study a particle growth model MABNAG (Model for Acid-Base chemistry in NAnoparticle Growth) was developed to study the effect of salt formation on nanoparticle growth, which has been proposed as a potential mechanism lowering the equilibrium vapor pressures of organic compounds through dissociation in the particle phase and thus preventing their evaporation. MABNAG is a model for monodisperse aqueous particles and it couples dynamics of condensation to particle phase chemistry. Non-zero equilibrium vapor pressures, with both size and composition dependence, are considered for condensation. The model was applied for atmospherically relevant systems with sulfuric acid, one organic acid, ammonia, one amine and water in the gas phase allowed to condense on 3-20nm particles. The effect of dissociation of the organic acid was found to be small under ambient conditions typical for a boreal forest site, but considerable for base-rich environments (gas phase concentrations of about 1010 cm-3 for the sum of the bases). The contribution of the bases to particle mass decreased as particle size increased, except at very high gas phase concentrations of the bases. The relative importance of amine versus ammonia did not change significantly as a function of particle size. While our results give a reasonable first estimate on the maximum contribution of salt formation to nanoparticle growth, further studies on, e.g. the thermodynamic properties of the atmospheric organics, concentrations of low-volatility organic acids and amines, along with studies investigating the applicability of thermodynamics for the smallest nanoparticles are needed to truly understand the acid-base chemistry of atmospheric nanoparticles.
- Subjects
ATMOSPHERIC models; ACID-base chemistry; NANOPARTICLES; ATMOSPHERIC aerosols; CRYSTAL growth; DISSOCIATION (Chemistry); VAPOR pressure; THERMODYNAMICS
- Publication
Atmospheric Chemistry & Physics Discussions, 2013, Vol 13, Issue 3, p7175
- ISSN
1680-7367
- Publication type
Article
- DOI
10.5194/acpd-13-7175-2013