The displacement of ammonium by triethylammonium (TEAH) in aerosol particles 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 heterogeneous uptake of about 40-ppm TEA by aqueous ammonium salts of sulfate ((NH4)2SO4), bisulfate (NH4HSO4), nitrate (NH4NO3), chloride (NH4Cl) and oxalate ((NH4)2C2O4) 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 (NH4)2SO4 and NH4HSO4 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 (NH4)2SO4 and (NH4)2C2O4 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 NH4NO3 particle at <3% RH as effectively as if it was in the aqueous NH4NO3 droplet (50% RH) and formed TEAH nitrate. On the other hand, the amorphous NH4HSO4 solid particle reacted with TEA at <3% RH to form crystalline (NH4)2SO4 and liquid TEAH bisulfate and sulfate. The formation of rather inert crystalline (NH4)2SO4 suppressed the ammonium exchange.

Displacement of ammonium from aerosol particles by uptake of triethylamine

243rd National Meeting (2012)

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