title: Depression of ammonia uptake to sulfuric acid aerosols by competing uptake of ambient organic gases.
abstract: The neutralization of acidic aerosols by ammonia has been studied through experiments which combine ambient air with laboratory generated sulfuric acid aerosol. Results indicated that acidic aerosol mixed with organic free air and ammonia was neutralized on a time scale<1 min, consistent with expectations. However, in the presence of ambient organic gases and ammonia, the rate of aerosol neutralization is significantly reduced. This reduction in ammonia uptake was concurrent with an increase in the amount of particle phase organics. A steady state in the NH4+/SO4(2-) in the presence of organic gases was established on time scales of 10 min to several hours, corresponding to NH3 uptake coefficients in the range of 4×10(-3)-2×10(-4). The degree to which neutralization was slowed was dependent upon the initial ammonia concentration and the organic mass added to the aerosols. These results suggest that inorganic equilibrium thermodynamic models may overestimate the rate of ammonia uptake and that ambient particles may remain acidic for longer than previously expected.
authors.affiliation: Atmospheric Science and Technology Directorate, Science and Technology Branch, Environment Canada, 4905 Dufferin Street, Toronto, Ontario M3H 5T4, Canada. john.liggio@ec.gc.ca
authors.forename: John
authors.initials: J
authors.lastname: Liggio
authors.forename: Shao-Meng
authors.initials: SM
authors.lastname: Li
authors.forename: Alexander
authors.initials: A
authors.lastname: Vlasenko
authors.forename: Craig
authors.initials: C
authors.lastname: Stroud
authors.forename: Paul
authors.initials: P
authors.lastname: Makar
mesh_terms: D000336:Aerosols / Q000032:analysis / Q000737:chemistry*; D000393:Air Pollutants / Q000032:analysis / Q000737:chemistry*; D000397:Air Pollution / Q000706:statistics & numerical data; D000641:Ammonia / Q000737:chemistry*; D001272:Atmosphere / Q000737:chemistry; D004784:Environmental Monitoring; D009930:Organic Chemicals / Q000737:chemistry*; D013464:Sulfuric Acids / Q000032:analysis / Q000737:chemistry*
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D009930:Organic Chemicals; D013464:Sulfuric Acids; D000641:Ammonia; C033158:sulfuric acid