14. ABSTRACT (cont'd)
Both the qualitative and quantitative nature of the chemical signature above buried TNT is strongly a
function of temperature. At 23 and 4C, 2,4-DNT was present at the highest concentration in the head-
space vapor, 2,4,6-TNT being only a minor component. At 12C, the more volatile 1,3-DNB predomin-
ated. Vapors penetrate the soils in the order sand > silt > clay, with vapor concentrations in the same
order. Dry soils are very retentive of TNT vapors, while soil moisture facilitates movement of vapors to
the headspace.
Soilair partition coefficients, computed for these three soils at 23 and 4C for 2,4,6-TNT, ranged from
1.6 104 mL-air/g-soil for moist sand at 23C to 3.0 107 for moist clay at 4C. Partition coefficients for
2,4-DNT were about an order of magnitude lower. Vapor concentrations for several of the air-dried soils
were too low to measure and hence the partition coefficients for dry soils could not be estimated, but
were much higher than for the same soil with higher moisture. These results indicate that for detection of
buried mines, the largest mass of signature chemicals will be present in the surface soil rather than the
overlying air.
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