posted on 1998-03-18, 00:00authored byMyoseon Jang, Richard M. Kamens
Humidity effects on the gas/particle partitioning of the
different types of semivolatile organic compounds (SOCs)
in the organic layer of wood soot, diesel soot, and
secondary aerosols were studied in outdoor environmental
chambers. Experimental partitioning coefficients,
Kp, of
different SOCs were measured using outdoor Teflon film
chambers and compared to theoretical Kp values
calculated
with the aid of activity coefficients and vapor pressures.
A
thermodynamic model based on group contribution methods
was used to estimate SOC activity coefficients in the
liquid organic layer of different atmospheric particles.
The
equilibrated water content in the organic phase of chemi
cally different particles was estimated from the activity
coefficient of water in the particle's organic liquid and
the
ambient relative humidity (RH). It was found that
predicted
SOC activity coefficients
(i
)
for diesel soot particles
were not a strong function of RH. There was, however,
a
dramatic change in
i
on wood soot particles for
hydrophobic compounds such as alkanes and polycyclic
aromatic hydrocarbons with changing RH. For polar
SOCs, such as n-alkanoic acids and substituted
phenols
on wood soot particles,
i
did not change with
increasing RH. Similar behavior to wood soot particles
was
observed for
i
on secondary aerosols from the reac
tion of α-pinene with O3. It was concluded that
humidity
effect on partitioning was most significant for
hydrophobic
compounds in polar aerosols.