Displacement of Ammonium from Aerosol Particles by Uptake of Triethylamine

The displacement of ammonium by triethylammonium (TEAH) in aerosol particles of about 15-35 mu m 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(4)HSO(4)), nitrate (NH(4)NO(3)), chloride (NH(4)Cl), and oxalate [(NH(4))(2)C(2)O(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))(2)SO(4) and NH(4)HSO(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))(2)SO(4) and (NH(4))(2)SO(4) experienced small mass increases of <5%, both of which were attributed to the hindered mass transfer of TEA in crystalline solids. However, TEA reacted with the amorphous solid NH(4)NO(3) particle at <3% RH as effectively as if it was in the aqueous NH(4)NO(3) droplet (50% RH) and formed TEAH nitrate. On the other hand, the amorphous NH(4)HSO(4) solid particle reacted with TEA at <3% RH to form crystalline (NH(4))(2)SO(4) and liquid TEAH bisulfate and sulfate. The formation of rather inert crystalline (NH(4))(2)SO(4) suppressed the ammonium exchange.