| A smooth and a rough surface of four high-calcium limestones (Salem, Cordova Cream, Cottonwood Top Ledge, and Monks Park) were characterized to determine the manner in which surface roughness, surface area, and porosity affect SO2 deposition onto limestone. The limestone's pore network was characterized using nitrogen gas adsorption, mercury intrusion porosimetry, fluorescent thin section analysis by confocal laser scanning microscopy, and epoxy pore cast evaluation by scanning electron microscopy. Surface roughness was measured by 3-D non-contact laser profilometry and BET surface area was determined by nitrogen gas adsorption.; The limestone specimens were exposed for 24 hours to a simulated outdoor SO2 environment (50 ppb SO2; 65% RH; 25°C; 4 m/s wind speed) in the NCPTT Environmental Exposure Chamber. The SO2 deposition was measured and the specimens were returned to background sulfate levels after each exposure and for a total of eight cycles. The first exposure cycle displayed the highest deposition velocities.; In this study, porosity emerged as the dominant factor influencing the dry deposition of SO2 onto limestone. While surface roughness and BET surface area both contributed to the deposition process their influence was secondary to porosity. The surface roughness features that played a significant role in deposition were deep valleys. The deepening of valleys correlated directly with increasing deposition velocity while the heightening of peaks demonstrated an inverse relationship to deposition. Additionally, statistical analysis revealed that the asymmetry of the surfaces, caused by the protruding peaks and valleys, was the primary surface roughness parameter influencing deposition.; Monks Park limestone exhibited the most extensive pore network, some of the largest surface roughness values, relatively high BET surface area, and, overall, the highest deposition velocities. Salem limestone contained the smallest pore network and the lowest BET surface area and surface roughness measurements and yielded the lowest deposition velocity measurements. Furthermore, Salem limestone demonstrated the highest correlation between surface roughness and deposition velocities, while Monks Park limestone appeared only minimally affected by surface roughness. |
