M. Jang et Rm. Kamens, A THERMODYNAMIC APPROACH FOR MODELING PARTITIONING OF SEMIVOLATILE ORGANIC-COMPOUNDS ON ATMOSPHERIC PARTICULATE MATTER - HUMIDITY EFFECTS, Environmental science & technology, 32(9), 1998, pp. 1237-1243
Humidity effects on the gas/particle partitioning of the different typ
es of semivolatile organic compounds (SDCs) in the organic layer of wo
od soot, diesel soot, and secondary aerosols were studied in outdoor e
nvironmental chambers. Experimental partitioning coefficients, K-p, of
different SOCs were measured using outdoor Teflon film chambers and c
ompared to theoretical K-p 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 i
n the liquid organic layer of different atmospheric particles. The equ
ilibrated water content in the organic phase of chemically different p
articles was estimated from the activity coefficient of water in the p
article's organic liquid and the ambient relative humidity (RH). It wa
s found that predicted SOC activity coefficients ((i) gamma(om)(infini
ty)) for diesel soot particles were not a strong function of RH. There
was, however, a dramatic change in (i) gamma(om)(infinity) on wood so
ot particles for hydrophobic compounds such as alkanes and polycyclic
aromatic hydrocarbons with changing RH. For polar SOCs, such as n-alka
noic acids and substituted phenols on wood soot particles, (i) gamma(o
m)(infinity) did not change with increasing RH. Similar behavior to wo
od soot particles was observed for i gamma(om)(infinity) on secondary
aerosols from the reaction of alpha-pinene with O-3. It was concluded
that humidity effect on partitioning was most significant for hydropho
bic compounds in polar aerosols.