The NH3 Mass Accommodation Coefficient for Uptake onto Sulfuric Acid Solutions

The uptake of NH 3 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 NH 3 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 NH 3 uptake onto the surface of 15−65 wt % H 2 SO 4 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 NH 3 mass accommodation coefficient was observed to decrease from unity on 70 wt % H 2 SO 4 to 0.3(±0.05) on 20 wt % H 2 SO 4 . 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.