Environmental Engineering Reference
In-Depth Information
to emission sources and different atmosphere state (including temperature, wind
velocity, sunlight, relative humidity, oxidants, etc.). Particulate phase concentrations
increased from lowest values at deep night (21:00−03:00) to the highest values in
the afternoon (12:00−18:00). As the typical oxygenated organics, the total organic
acids in particulate phase accounted for about 30% of OOA mass, and the
concentration line exhibited a time trend similar to OOA i n Fig. 1. The correlation
between particulate organic acids and OOA was strong ( r = 0.93, n = 48, p <
0.001). In addition, Low-molecular-weight (LMW) dicarboxylic acids (C 2 -C 4 ) in
particles showed strong correlation with ambient oxidants ( r = 0.72 for C 2 ; r =
0.74 for C 3 , r = 0.74 for C 3 , r = 0.67 for C 4 , n = 48, p < 0.001), related to
atmospheric oxidation processes.
Further, gas-particle partitioning of individual organic acid was shown in Fig.
2. The average abundances in gaseous phase to the total of organic acids ([G]/[P +
G]) were 36%. LMW dicarboxylic acids (C 2 -C 4 ) and ketocarboxylic acids (WC 2
and Pyr) had higher abundances in particulate phase (>61%), however unsaturated
dicarboxylic acids (M and F) had higher abundances in gaseous phase (>87%). It
is expected that compounds with decreasing vapor pressures will have increasing
abundances in particulate phase. Interestingly, C 4 -C 6 acids were observed with
relative higher abundances in gaseous phase compared to C 3 , though vapor
pressures of C 4 -C 6 are much lower (1.0E-05 mm Hg for C 3 , 6.9E-07 mm Hg for
C 4 , 4.1E-06 mm Hg for C 5 , 1.50E-07 mm Hg for C 6 ). C 3 has relatively higher
acidity and solubility in water, and will be more efficiently scavenged from the
gas phase into the particulate phase compared to C 4 -C 6 . It can be said that gas-
particle partitioning depends not only on the vapor pressure, but also on other
physical and chemical processes influencing the gaseous phase to particulate
phase partition (Limbeck et al., 2005). For example adsorption onto available
particle surfaces or absorption into a liquid phase of an individual compound will
allow some gas to particle conversion to occur even when the gas phase pressure
is below its saturation vapor pressure (Pankow 1994).
To discuss gas-to-particle sorption according to physical interactions, gas-particle
sorption equilibrium constant K p was used (Pankow, 1994). The distribution of mass
between gaseous and particulate phases at equilibrium can be described by K p:
K p = [ P ]/([ TSP ]*[ G ])
(1)
where [ TSP ] is the concentration of total suspended particles, [ G ] is the gaseous
phase concentration for the target compound, and [P] is the particulate phase
concentration. When we take the logarithm of the K p equation and put the log K p
for y -axis and log [ TSP ] for x -axis, the curve is linear with a slope of −1:
log K p = −log[ TSP ] + log([ P ]/[ G ])
(2)
During the sampling period, daily TSP concentrations were not available; instead
we use the concentrations of SO 4 2− , NO 3 , NH 4 + , organics, and water content in
PM 1 instead of TSP as the sorption medium in the gas-particle sorption equilibrium.
In summer, log [ K p] showed relatively strong correction with log [ water content ]
in the model (slope = −0.68, r = 0.73, n = 48, p < 0.001) in Fig. 3, followed by log
Search WWH ::




Custom Search