AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Mechanisms and Compounds in Atmospheric Acid-Base Particle Formation
NANNA MYLLYS, Tinja Olenius, Sabrina Chee, James Smith, University of California, Irvine
Abstract Number: 147 Working Group: Aerosol Chemistry
Abstract In atmospheric sulfuric acid-driven particle formation, ammonia and amines are the most commonly studied stabilizing compounds. As a stronger base, dimethylamine enhances particle formation rate several orders of magnitude more than ammonia. The base strength seems to be an important factor in particle formation, which leads to the following question: “Does our atmosphere contain stronger bases which would be more effective in particle formation than amines?”. Guanidine is a very strong organobase and its cationic form is an extraordinary stable. Guanidine and sulfuric acid form clusters, which have a high symmetry and a large number of intermolecular bonds. Thus, those clusters are very stable against evaporation and particle formation is fully collision driven. Guanidine enhances sulfuric acid-driven particle formation up to eight orders of magnitude more than dimethylamine. Guanidine was used as a model compound, and later found from Hyytiälä boreal forest. This indicates that atmosphere might contain a plethora of other strong bases which can significantly enhance particle formation.
Experimental studies have shown that when combining amines and ammonia together with sulfuric acid, particle formation rates are 10–100 times higher compared to two-component sulfuric acid–amine mixtures. This cannot be explained by base strength, and therefore, we have studied the cluster structures and energetics in order to answer the question: “What is the fundamental reason for the synergy between ammonia and amines?”. Even dimethylamine is a stronger base, ammonia is more likely to be protonated in mixed clusters. Ammonium is Td symmetric and capable of forming four intermolecular bonds. Thus, it can act as a bridge-former in sulfuric acid–dimethylamine clusters. At atmospheric conditions, ammonia-amine synergy might lead up to five orders of magnitude increase in particle formation rates compared to solely amine-enhanced particle formation.