Displacement of ammonium from aerosol particles by uptake of triethylamine

The displacement of ammonium by triethylammonium (TEAH) in aerosol particles of about 15-35 μm in diameter was investigated using an electrodynamic balance (EDB) coupled with in situ Raman spectroscopy. The phase state of particles played a crucial role in the extent of triethylamine (TEA) uptake. At 50 or 75% relative humidity (RH), the heterogenous uptake of about 40-ppm TEA by aqueous ammonium salts of sulfate [(NH ₄) ₂SO ₄], bisulfate (NH ₄HSO ₄), nitrate (NH ₄NO ₃), chloride (NH ₄Cl), and oxalate [(NH ₄) ₂C ₂O ₄] led to increases in particle mass of over 90%. A complete displacement of ammonium by TEAH was confirmed by direct EDB mass measurements and the Raman spectra obtained. TEAH sulfate was formed during the exposure of aqueous droplets of (NH ₄) ₂SO ₄ and NH ₄HSO ₄ to TEA vapor at 50% RH; but a fraction of it decomposed to TEAH bisulfate when the TEA supply was removed. Crystalline solid particles of (NH ₄) ₂SO ₄ and (NH ₄) ₂C ₂O ₄ experienced small mass increases of 4NO ₃ particle at 4NO ₃ droplet (50% RH) and formed TEAH nitrate. On the other hand, the amorphous NH ₄HSO ₄ solid particle reacted with TEA at 4) ₂SO ₄ and liquid TEAH bisulfate and sulfate. The formation of rather inert crystalline (NH ₄) ₂SO ₄ suppressed the ammonium exchange. © 2012 Copyright Taylor and Francis Group, LLC.