The NH3 mass accommodation coefficient for uptake onto sulfuric acid solutions

The uptake of NH3 onto particles with diameters of similar to100 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, alpha, was found to be close to unity for NH3 uptake onto the surface of 15-65 wt % H2SO4 solutions. The finding that alpha 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 alpha indicates that the neutralization of sulfuric acid particles by atmospheric ammonia will be efficient.