Impacts of changes of indoor air pressure and air exchange rate in vapor intrusion scenarios

Abstract

There has, in recent years, been increasing interest in understanding the transport processes of relevance in vapor intrusion of volatile organic compounds (VOCs) into buildings on contaminated sites. These studies have included fate and transport modeling. Most such models have simplified the prediction of indoor air contaminant vapor concentrations by employing a steady state assumption, which often results in difficulties in reconciling these results with field measurements. This paper focuses on two major factors that may be subject to significant transients in vapor intrusion situations, including the indoor air pressure and the air exchange rate in the subject building. A three-dimensional finite element model was employed with consideration of daily and seasonal variations in these factors. From the results, the variations of indoor air pressure and air exchange rate are seen to contribute to significant variations in indoor air contaminant vapor concentrations. Depending upon the assumptions regarding the variations in these parameters, the results are only sometimes consistent with the reports of several orders of magnitude in indoor air concentration variations from field studies. The results point to the need to examine more carefully the interplay of these factors in order to quantitatively understand the variations in potential indoor air exposures.

Three-dimensional vapor intrusion modeling approach that combines wind and stack effects on indoor, atmospheric, and subsurface domains

“…This pressure gradient around building influences the pressure difference between indoor and outdoor, which is an important feature that was not previously identified by VI models. 18, 20 …”

“…Song et al 19 assessed the influence of stack and wind effects on soil gas entry rate and outdoor air flowrate through the building, however the authors did not consider wind effect (or wind direction) on subsurface pressure, which influences on soil gas entry rate. 19 Shen and Suuberg 18 showed that the AER and indoor air pressure variation can result in substantial variation in indoor air contaminant concentration; however they did not indicate how wind and temperature influence AER or indoor air pressure. 18 Although these studies are important in highlighting the importance of aboveground processes on VI, these studies have not considered how AER and indoor air pressure are directly connected to wind and stack effects, and how together all of these parameters collectively alter VI exposure risks.…”

“…4, 12, 14, 15, 18, 19 Reichman et al 22 noted that existing VI models require users to input generic building pressures and AERs even though indoor air science research provides tools to determine AERs and building pressures based on building characteristics, occupant behavior and weather conditions.…”

How Does the Periodic Groundwater Table Fluctuation Impact on Chlorinated Vapor Intrusion?

“…Governing Equations. A 2D numerical model is built to investigate the influence of groundwater table fluctuations on vapor intrusion using a finite element code COMSOL Multiphysics, which has been widely adopted in previous studies to solve the problem of vapor transport from the contaminant source to the dwelling through the building foundation crack (e.g., [30][31][32][33]). The development and use of this code to solve typical vapor intrusion problems have been described in detail in Pennell et al [30].…”

A Review of Recent Vapor Intrusion Modeling Work

“…Diallo et al (2015) presented some semiempirical models to quantity the entry of VOCs into buildings as a function of a series of site-specific parameters such as soil diffusion coefficients, diffusion coefficients of the slab, source depth, and indoor ventilation rate. Shen and Suuberg (2016) used a 3D finite element model to examine the influence of indoor air pressure and air exchange rate on indoor air contaminant vapor concentrations showing how these parameters can influence the temporal indoor air contaminant vapor concentration changes. Yao et al (2020a) used a 3D numerical model to evaluate the impact of a building's indoor pressure fluctuations in the presence of an impervious pavement surrounding the building.…”