Geology Reference
In-Depth Information
P
/Pa (at 298K)
OH
methane
CH
4
Cl
10
7
2,4- dichlorophenol
ethene
10
0
H
Cl
Cl
Cl
Cl
H
γ-HCH
(organochlorine insecticide)
10
6
H
propane
Cl
10
-1
Cl
H
Cl
H
H
isoprene
1,3- dimethylnaphthalene
(alkylated-PAH)
fluoranthene (PAH)
dichloromethane
CH
2
Cl
2
10
5
10
-2
n
-hexane
benzene
10
4
Cl
n
-heptadecane (
n
-C
17
)
CH
3
10
-3
Cl
acetone
O
Cl
trichlorinated naphthalene
(PCN)
pentachlorinated biphenyl
(PCB)
toluene
Cl
Cl
10
3
10
-4
α-pinene
(monoterpene)
Cl
10
2
10
-5
Cl
Cl
n
-decane
benzo[
a
]pyrene (PAH)
O
O
10
1
pinonaldehyde
(from α-pinene)
10
-6
Figure 1 Approximate vapour pressures (P) (10
7
10
6
Pa) for a diverse range of
organic compounds, many of which are mentioned in this chapter. Note the use
of common/trivial chemical names rather than IUPAC nomenclature
more polar condensates involved in aerosol formation and growth.
4
Monoterpenes (C
10
) released from different types of vegetation, contain
unsaturated double bonds and are therefore susceptible to reaction with O
3
.
The reaction of a-pinene, for example, gives rise to a number of carbonyl
and mono- and dicarboxylic acids, including pinonaldehyde and pinic acid
which have been detected in forest aerosols.
5
Semi-volatile organic compounds arise from a multitude of sources,
both anthropogenic and natural, but include the persistent organic pol-
lutants, many of which are halogenated aromatic compounds found at
trace levels in the environment, but are dispersed widely across the globe.
For aliphatic compounds such as petroleum hydrocarbons, the semi-
volatile constituents include longer chain alkanes (4C
15
), both normal
(n-alkanes), branched (iso-alkanes) and cyclic alkanes (cyclo-alkanes or
naphthenes) as well as a range of polycyclic compounds or terpanes
including tricyclic carpanes, tetracyclic hopanes and pentacyclic steranes.
Many of the hopanes and steranes are largely involatile, and in the
atmosphere are predominantly associated with particles.
6
They are im-
portant constituents of crude oils, arising principally from the decay of
bacterial/biotic matter and serve as useful biomarkers for different fuel
types, and are also widespread in sediments and soils from both biogenic
