Contribution of fine-particle sulfates to light scattering in St. Louis
The extent to which sulfates produce visibility reduction in the St. Louis area was examined. The contribution of fine aerosol sulfates to total light scattering was calculated from measured sulfur size distributions and Mie theory of light scattering. The aerosol was collected during both a summer and a winter season. Short sampling intervals (10 minutes to 3 hours) permitted observation of the fine structure of the sulfur size distribution and concentration, and involved only small changes in meteorology. Size separation was accomplished with an 8-stage low pressure impactor, which yielded size fractions in the range of 4 ..mu..m greater than or equal to d greater than or equal to 0.05 ..mu..m. Elemental sulfur was measured by flash volatilization and flame photometric detection. All fine sulfur was assumed to be in the form of (NH/sub 4/)/sub 2/SO/sub 4/. Water which might be associated with this deliquescent aerosol was estimated. The measured light scattering coefficient and (NH/sub 4/)/sub 2/SO/sub 4/ were extremely well correlated (r = 0.97) in the summer, but not as well correlated (r = 0.63) in the winter. Conversely, the light scattering coefficient and non-sulfate fine mass were well correlated (r = 0.85) in the winter, but poorly correlated (r = 0.24) in the summer. The light scattering efficiency of (NH/sub 4/)/sub 2/SO/sub 4/ plus associated water calculated from Mie theory and size distributions was 4.2 m/sup 2//g for the summer aerosol, but only 2.0 m/sup 2//g for the dry winter (NH/sub 4/)/sub 2/SO/sub 4/. Two basic types of sulfur size distributions were observed. The most common type observed during the summer had a major sulfur mass peak between 0.5 ..mu..m and 1.0 ..mu..m in diameter. The combination of large sulfate particles and high sulfate loadings led to the dominance of sulfates in visibility reduction during the summer.
- Research Organization:
- Washington Univ., St. Louis, MO (USA)
- OSTI ID:
- 5811952
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Atmospheric-- Chemicals Monitoring & Transport-- (-1989)
54 ENVIRONMENTAL SCIENCES
AEROSOLS
AIR POLLUTION
COLLOIDS
DISPERSIONS
FEDERAL REGION VII
FINE STRUCTURE
LIGHT SCATTERING
MISSOURI
NORTH AMERICA
OXYGEN COMPOUNDS
PARTICLE SIZE
POLLUTION
SCATTERING
SEASONAL VARIATIONS
SIZE
SOLS
SULFATES
SULFUR COMPOUNDS
USA
VARIATIONS
VISIBILITY