Aerosol Chemistry and Physics - Aerosols: Measurement, Dosimetry, and Health Effects - page 159

Ventilation

Exfiltration

Phase change
Indoor air/surface
chemistry

Infiltration

C i

C o

Desorption

HVAC

Indoor
source

Sorption

FIGURE 6.10 Indoor processes involving the interaction of volatile and semi-volatile species with indoor
surfaces (building materials, furnishings, and particles).

assessed using the octanol/air partitioning coeficient. In a more recent article, the same authors
reviewed data from 19 studies reporting measurements of dustborne and airborne SVOCs in more
than 1000 buildings, which included 66 different SVOCs whose octanol/air partition coeficients
span more than 5 orders of magnitude (Weschler and Nazaroff, 2010). The authors veriied that the
octanol/air partition coeficient is a strong predictor of the abundance of a particular compound
in settled dust relative to its gas-phase concentration, and predicted dustborne mass fractions that
correlated well with measured mass fractions. Also, for SVOCs with high octanol/air partitioning
coeficients, they observed that settled dust likely did not have suficient time to equilibrate with the
gas-phase levels. This approach was also veriied in the case of the partitioning of phthalate esters
(plastic additives) measured in settled dust, by using those values to estimate their concentration in
airborne particles (Weschler et al., 2008).

6.4.4 i ndoor a erosol F orMation
In addition to combustion (Section 6.2.1), at least two other pathways for indoor aerosol generation
have been identiied: nucleation from reemitted SVOC and secondary aerosol formation from reac-
tion of unsaturated hydrocarbons with ozone or hydroxyl radicals.

6.4.4.1 Semi-Volatile Organic Compounds Reemission
Johansson et al. (1993) observed the formation of small (10-20 nm) particles in a closed room
(100 m 3 ) that had been sealed after the ventilation phase of experiments with high concentrations of
secondhand tobacco smoke (SHS). They also showed how the particle size distribution evolved as
the particles coagulated. Apte et al. (2004) conirmed the phenomenon of nanoparticle ingrowth in
an environmental chamber whose walls had been conditioned with environmental tobacco smoke.
Like Johansson et al., they could only observe particle formation when the chamber had been
sealed after ventilation with particle-free air. As soon as uniltered ambient air was admitted to
the chamber, the size distribution changed as the small nucleation-mode particles were scavenged
by collision with ambient accumulation mode particles. These observations can now be explained
as instances of SVOC reemission from the walls of the conditioned smoking rooms, followed by
particle nucleation, condensation, and coagulation.

6.4.4.2 Reactive Organics and Ozone
Indoor chemistry is a relatively young discipline that developed over the past two decades, prin-
cipally describing the role of ozone and other reactive atmospheric species in gas-phase and
heterogeneous reactions that lead to the formation of secondary pollutants and aerosol particles