AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Nanoparticle Growth and Salt Formation - a Modeling Study
TAINA YLI-JUUTI, Kelley C. Barsanti, Lea Hildebrandt Ruiz, Antti-Jussi Kieloaho, Ulla Makkonen, Tuukka Petäjä, Taina Ruuskanen, Markku Kulmala, Ilona Riipinen, University of Helsinki
Abstract Number: 273 Working Group: Aerosol Chemistry
Abstract New particle formation through gas-to-particle phase transformation produces significant fraction of atmospheric aerosol particles. The climatic effect of these nanoparticles depends on whether they grow fast enough to survive to sizes of several tens of nanometers before being scavenged by coagulation to larger particles. Large fraction of the nanoparticle growth is known to be due to condensation of organic vapors, but not all the mechanisms related to the growth are yet identified. The compounds condensing on the nanoparticles need to be low-volatile, or transfer into low-volatile compounds in the particle phase. Recent observations of semi-volatile organic acids and amines in atmospheric nanoparticles suggest that particle phase processes may be important for the growth, as these compounds would not be expected to exist in the particle phase in large amounts based on simple gas-particle partitioning.
In this study we used particle growth model MABNAG to study the role of salt formation on the growth of 3-20 nm nanoparticles. MABNAG couples the condensation/evaporation of vapors to/from particles with the thermodynamics of particle phase acid dissociation and base protonation. Based on gas phase concentrations and initial particle composition the model predicts evolution of particle size and composition. System including sulfuric acid, organic acid, ammonia, amine and water as condensing vapors was studied. The effect of salt formation for the organic acid was predicted to be small at typical boreal forest conditions, but significant at base-rich environments. In all cases, all the particle phase amine and ammonia was predicted to be protonated, indicating the importance of the salt formation for the condensation of the bases. The relative roles of the two bases stayed rather constant through the growth between 3-20 nm and depended strongly on their relative gas phase concentrations.