A THERMODYNAMIC APPROACH USING GROUP-CONTRIBUTION METHODS TO MODEL THE PARTITIONING OF SEMIVOLATILE ORGANIC-COMPOUNDS ON ATMOSPHERIC PARTICULATE MATTER
M. Jang et al., A THERMODYNAMIC APPROACH USING GROUP-CONTRIBUTION METHODS TO MODEL THE PARTITIONING OF SEMIVOLATILE ORGANIC-COMPOUNDS ON ATMOSPHERIC PARTICULATE MATTER, Environmental science & technology, 31(10), 1997, pp. 2805-2811
Atmospheric particulate matter is a complex mixture consisting of orga
nic and inorganic chemicals. Their sources include various combustion
processes, aerosolized dusts and soils, and chemical reactions which p
roduce secondary aerosols. The partitioning of semivolatile toxic orga
nic compounds (SOCs) between particulate matter and the gas phase is s
trongly influenced by temperature. water concentration, chemical compo
sition of the particulate matter, and the organic fraction of the part
iculate matter. Many investigations have recently suggested that a con
siderable portion of the gas-particle (G/P) partitioning in the ambien
t atmosphere takes place between the liquid phase of organic aerosols
and the surrounding gas phase. It has been shown that the equilibrium
G/P partitioning constant, K-p, of an SOC partitioning to a given part
icle's liquid medium is inversely related to both the activity coeffic
ient (i) gamma(om) and its saturated subcooled liquid vapor pressure,
p(L)(o). Hence, in principal, the K-p of any SOC can be estimated from
its vapor pressure and activity coefficient in a given liquid mixture
. To calculate activity coefficients of SOCs in the liquid phase of di
fferent types of particles, semiempirical thermodynamic models based o
n additive chemical functional group methods were used, Outdoor chambe
rs were used to generate G/P partitioning data sets for a range of SOC
s in the presence of particles from wood and diesel combustion and sec
ondary aerosols from the reaction of alpha-pinene with ozone. The part
itioning SOCs ranged from nonpolar alkanes to polar organic acids. Plo
ts of log ((i) gamma(om)K(p)) vs log p(L)(o) showed a vast improvement
over typical log K-p vs log p(L)(o) plots. These results suggest that
equilibrium partitioning of many different types of SOCs can be estim
ated in almost any organic layer of an atmospheric aerosol.