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Updated: Apr 18, 2026

Exploring the Effects of Atmospheric Forcings on Evaporation: Experimental Integration of the Atmospheric Boundary Layer and Shallow Subsurface
Published on: June 8, 2015
Vapor intrusion attenuation factors relative to subslab and source, reconsidered in light of background data
Yijun Yao1, Yun Wu1, Eric M Suuberg2
1MOE Key Lab of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China; Research Center for Air Pollution and Health, Zhejiang University, Hangzhou 310058, China; Institute of Environmental Science, Zhejiang University, Hangzhou 310058, China.
Abstract:
The basis upon which recommended attenuation factors for vapor intrusion (VI) have been derived are reconsidered. By making a fitting curve to the plot showing the dependence of observed indoor air concentration (c(in)) on subslab concentration (c(ss)) for residences in EPA database, an analytical equation is obtained to identify the relationship among c(in), css and the averaged background level. The new relationship indicates that subslab measurements may serve as a useful guide only if c(ss) is above 500 μg/m(3). Otherwise, c(in) is independent of c(ss), with a distribution in good agreements with other studies of background levels. Therefore, employing this screening value (500 μg/m(3)), new contaminant concentration attenuation factors are proposed for VI, and the values for groundwater-to-indoor and subslab-to-indoor air concentration attenuation factors are 0.004 and 0.02, respectively. The former is applied to examining the reported temporal variations of c(in) obtained during a long-term monitoring study. The results show that using this new groundwater-to-indoor air concentration attenuation factor also provides a reasonably conservative estimate of c(in).
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