Uptake of gas-phase ammonia. 1. Uptake by aqueous surfaces as a function of pH
Ammonia in the atmosphere originates primarily from ground sources including decaying organic matter and chemical fertilizers. Significant amounts of NH{sub 3} (0.1--100 ppbv) are found in both clean and polluted atmospheres as well as in cloud and fog droplets. Since ammonia is the only soluble base found in the atmosphere in significant quantities, it plays a principal role in neutralizing acidic aerosols (H{sub 2}SO{sub 4}, HNO{sub 3}, and HCl) converting them to new nonvolatile or semivolatile components; (NH{sub 4}){sub 2}SO{sub 4}, NH{sub 4}HSO{sub 4}, NH{sub 4}NO{sub 3}, NH{sub 4}Cl. The process of neutralization influences the aqueous oxidation rates of S(IV) species. The uptake of gas-phase ammonia by aqueous surfaces was measured as a function of temperature, gas liquid interaction time, and pH in the range 0--13. Uptake measurements at low pH yielded values of the mass accommodation coefficient ({alpha}) as a function of temperature. The mass accommodation coefficient increases as the temperature decreases, from 0.08 at 290 K to 0.35 at 260 K. Time dependence of the uptake yielded values for the Henry's law constant. Uptake measurements at high pH indicate that an ammonia surface complex is formed at the interface. Codeposition studies in which an aqueous surface, initially at pH = 4, was simultaneously exposed to both gas-phase ammonia and SO{sub 2} were also performed. In such a codeposition experiment, the species entering the liquid neutralize each other and as a result the uptake of each species is enhanced. Modeling calculations indicate that the uptake of each species is in accord with bulk liquid-phase kinetics.
- Research Organization:
- Boston Coll., Chestnut Hill, MA (US)
- Sponsoring Organization:
- National Science Foundation; Environmental Protection Agency; US Department of Energy
- DOE Contract Number:
- FG02-91ER61208; FG02-94ER61854; FG02-98ER62581
- OSTI ID:
- 20003215
- Journal Information:
- Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory, Journal Name: Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory Journal Issue: 44 Vol. 103; ISSN JPCAFH
- Country of Publication:
- United States
- Language:
- English
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