Open AccessA Fourier transform infrared study of the adsorption of SO 2 on n‐hexane soot from −130° to −40°C
Author(s) -
Koehler Birgit G.,
Nicholson Victoria T.,
Roe Henry G.,
Whitney Erin S.
Publication year - 1999
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1998jd100081
Subject(s) - soot , adsorption , saturation (graph theory) , monolayer , isothermal process , analytical chemistry (journal) , infrared , fourier transform infrared spectroscopy , chemistry , diffusion , materials science , chemical engineering , organic chemistry , thermodynamics , nanotechnology , combustion , physics , mathematics , engineering , combinatorics , optics
This paper focuses on the uptake of SO 2 on soot at temperatures below room temperature. Oxidation on soot may provide a mechanism for the oxidation of atmospheric SO 2 under conditions when the standard gas‐phase and aqueous‐phase mechanisms cannot explain the rapid rate of H 2 SO 4 production. An understanding of the uptake of SO 2 under dry conditions provides a useful step toward understanding the uptake and oxidation of SO 2 on soot under wet conditions. We find that rapid, reversible SO 2 adsorption on soot occurs within a few seconds, presumably by adsorption on the outer surfaces of the spherical soot particles. Subsequently, uptake continues slowly for over an hour, presumably by diffusion into micropores within the soot particles. We focused only on the rapid adsorption. An isothermal analysis of rapid SO 2 uptake revealed that a small fraction (<1%) of adsorption sites have a strong binding affinity (ΔH des = 42±4 kJ/mol), while the majority of adsorption sites bind SO 2 more weakly (26±4 kJ/mol). The lower‐limit saturation coverage of SO 2 on soot is 0.3 monolayer, but the more likely value is 0.7 monolayer. The uptake coefficient is 0.002 (plus or minus factor of 2) at low coverages.