Buildings provide temporary protection from outdoor airborne pollution: outdoor air only gradually enters the building and mixes with the indoor air.

Although buildings provide some protection, they do not provide total protection. Even with all mechanical ventilation turned off and windows and doors shut, indoor-outdoor air exchange still take place through leaks and cracks. Contaminants are brought into the building by the infiltrating air. The rate of infiltration is affected by indoor-outdoor temperature differences and wind-induced pressure acting on the building envelope.

Residential air exchange rates have been studied extensively at LBNL for the past 20 years (Sherman, 1980). The rate predicted based on the strength of the driving forces, if information about the air-tightness of the house is available. The "tightness" of a house can be measured by a technique called "blower door pressurization" and is commonly quantified in terms of the effective leakage area, which can be thought of as the size of a single opening that would let in as much air as the sum of all of the building's cracks.

Click on the image to view a QuickTime movie demonstating the exposure prediction of a plume over time. (2.3 MB)

A large set of "blower door" measurements assembled by the Residential Energy Group at LBNL was analyzed. The statistical distribution of effective leakage area for a collection of homes can be predicted from parameters such as the ages and sizes of the homes. Housing age and other characteristics are available from the U.S. 2000 Census and American Housing Surveys, so the distribution of leakage areas can be predicted for any area of the country.

Air exchange is only one factor that influences indoor concentrations of outdoor pollutants. Building materials can also serve as filter where some of the agent could be removed. The fractional penetration of particles through building envelopes has been studied by Liu et al. (2000) at LBNL. Other phenomena affecting transport and fate of chemical and biological agents, such as sorption/desorption on surfaces, are also subjects of current research at LBNL.

Area Lead:

Ashok Gadgil, , (510) 486-4651
 

Phillip Price, , (510) 486-7875
 
Rengie Chan, , (510) 495-2459

Publications