Aerosol Chemistry and Physics - Aerosols: Measurement, Dosimetry, and Health Effects - page 162

Master
bedroom

Den

Garage

X Measurement

X

Kitchen
OX

Emission

O

Bedroom Bedroom

Treated room

Living room

Walls and ceiling, M wp Walls and ceiling, M wp

Adjoining
zone air, M aa

Primary treated
zone air, M ap

M ca M va

M cp M ct M vp M vt

Source

FIGURE 6.13 Indoor processes from the perspective of “multimedia” modeling, including fugacity analysis.
(From Bennett, D.H. and Furtaw, E.J., Environ. Sci. Technol ., 38, 2142, 2004. With permission.)

Indoor resuspension, R(d p ) (μg h −1 ).
Indoor aerosol generation, S i (d p ) (μg h −1 ); examples include cooking, smoking, etc.
Transformation processes T (μg h −1 ); these include particle formation via gas-particle conver-
sion; particle size change due to coagulation; particle size change from accumulation (hygroscopic
growth) or loss (desiccation) of water; particle formation or loss due to phase change.
Tracking processes; these are not a direct source of airborne particles, rather they contribute to the
source term for indoor resuspension. Material may be transported from outdoors to indoors or from
room to room—typically via the soles of shoes or attached to clothing or other objects. The uptake and
release processes that affect transport and mass transfer are poorly deined or quantiied at present.
Using these concepts and deinitions, the generalized mass-balance equation for aerosol concen-
trations in indoor air is given by

V dC (d )
dt

i p

= Q(in)P(d )C (d ) + Q oa ( )[ 1 ε − ( d )]C (d )+R(d ) S ( + d )

p o p p o p p i

p

∑

− Q ( ex ) C (d ) C (d ) − v (d )A − Q r ( )[ 1 ε − ( d )]C (d ) + T

(6.8)

i p i p j p j p i p

j

Note that in this description we have explicitly incorporated particle size (d p is the particle diameter)
as an important variable for most of the parameters in the equation. As will be discussed later, some of
these parameters are known to be highly dependent upon particle size. The irst four terms in Equation
6.8 describe the indoor particle sources—the irst term accounts for iniltrating outdoor air as an
aerosol source, the second term provides for air brought into the building via a mechanical (HVAC)
system, the third term represents resuspension of materials collected on the loor, and the fourth
term describes the generation of particles indoors (e.g., combustion, cooking). Resuspension can, in
principle, occur from materials collected on other surfaces, including other horizontal surfaces like a
table top, but the dominant source of resuspension is that due to occupant activity (such as walking,
vacuuming, etc.) on the loor surface. Note that all of the source terms are particle size dependent.
Three sink terms are shown here: the irst term is removal of particles by the airlow out of
the building (either due to exiltration or exhaust), the second term is deposition to surface j, and