Civil Engineering Reference
In-Depth Information
2.7 Volatile Organic Compounds
Different definitions of the term volatile organic compound (VOC) are provided by
national and international organisations based on volatility, photochemical reac-
tivity or toxicity (Directive 2008/50/CE; California Environmental Protection
Agency
2009
). Simply, the term VOC comprises a wide variety of carbon-
containing chemicals with low-boiling points. The boiling points of the VOCs
considered in this chapter ranges from -19 C for formaldehyde, to 218 C for
naphthalene. This last compound can also be considered as a semi-volatile organic
compound (SVOC), partitioned between the gas phase and solid phase and, being
formed by two fused benzene rings, it is also the simplest PAH (see
Sect. 2.6
).
Major indoor sources of VOCs are building materials and furnishings, leading
to higher concentrations in newly constructed buildings or on those where refur-
bishment or redecoration has recently taken place (Jones
1999
; Liu et al.
2012
;
Shin and Jo
2012
). Other indoor sources and activities emitting VOCs are
smoking, pesticides, consumer products, burning devices and cooking (Barro et al.
2009
; Jia et al.
2008
). Human beings may also significantly emit organic pollu-
tants, such as isoprene, acetone, ethanol, methanol and other alcohols (Fenske and
Paulson
1999
, Vereb et al.
2011
).
Apart from potential indoor sources, accumulation and formation processes
driven by indoor organic chemistry may affect VOCs' concentrations (Morrison
2009
). A variety of VOCs may be emitted when cleaning agents and fresheners are
used, but they may also be produced secondary pollutants when indoor reactions
occur (Nazaroff and Weschler
2004
). VOCs' concentration may also be affected by
sink effect, being adsorbed by building materials and furnishings and reemitted
later. Materials such as carpets, vinyl floor tiles, painted drywalls and ceiling tiles
tend to adsorb VOCs (An et al.
1999
).
Due to the presence of numerous indoor sources and accumulation and forma-
tion processes, concentrations of VOCs indoors are very frequently higher than
outdoors (Edwards et al.
2001
; Ohura et al.
2006
). Organic pollutants are present
indoors as complex mixtures of many compounds at low concentrations, making
difficult the estimation of the risk associated with the exposure of VOCs. In the past,
the term total volatile organic compounds (TVOC) were used as an indicator of the
exposure to mixtures of VOCs (Bernstein et al.
2008
). Nevertheless, considering
the differences in health effects regarding toxicity and carcinogenity (see Table
2
),
individual VOC should be considered separately (Mølhave and Nielsen
1992
).
2.7.1 Benzene
The molecule of benzene, C
6
H
6
, contains six atoms of carbon forming a ring with
alternate double and single bonds, namely three conjugated bonds, making the
molecule more stable than expected. Benzene is the simplest aromatic hydrocar-
bon and it may be present in the air, water and soil. Inhalation is the main pathway
