The NH₃ mass accommodation coefficient for uptake onto sulfuric acid solutions

The uptake of NH₃ onto particles with diameters of ∼100 nm composed of sulfuric acid and water was studied in a laminar flow reactor. The gas-phase loss of NH₃ was monitored with a chemical ionization mass spectrometer. Temperature ranged from 287 to 296.5 K. The mass accommodation coefficient, α, was found to be close to unity for NH₃ uptake onto the surface of 15-65 wt % H₂SO₄ solutions. The finding that α does not depend on composition over this range of acid content is at odds with recently published work on the same subject where the measured NH₃ mass accommodation coefficient was observed to decrease from unity on 70 wt% H₂SO₄ to 0.3(±0.05) on 20 wt% H₂SO₄. Possible reasons for this discrepancy and consequent implications for results from that experimental technique will be discussed. A value of unity for α indicates that the neutralization of sulfuric acid particles by atmospheric ammonia will be efficient.