R. Kamens et al., SOME OBSERVATIONS ON TIMES TO EQUILIBRIUM FOR SEMIVOLATILE POLYCYCLICAROMATIC-HYDROCARBONS, Environmental science & technology, 29(1), 1995, pp. 43-50
The relative time scales at which semivolatile gas and particle PAH ap
proach equilibrium under both moderate and cool temperatures were inve
stigated. Combustion particles were added directly from a diesel car a
na a wood stove to a 190 m(3) outdoor Teflon film chamber. The rate of
migration of a gas-phase semivolatile PAH to combustion particles at
a warm outdoor temperature was explored by volatilizing solid deuterat
ed pyrene (d10-py) in a hot-injector(200 degrees C) into the rural bac
kground air in the chamber atmosphere. After 2 h, diesel exhaust was a
dded to the chamber. Results show an initial rapid migration of d10-py
from the gas to the particle phase in an attempt to re-establish equi
librium. The relative closeness to equilibrium was monitored by calcul
ating the-equilibrium c onstant K-p over time as measured by PAH(part)
/ (PAH(gas) x TSP). As gas-phase PAH concentrations changed in the cha
mber, due to wall losses, particle off-gassing occurred so that K-p wa
s reasonably constant over time. Under cool outdoor conditions (-1 to
-4 degrees C), PAH loss from the particle phase could not keep up with
gas-phase PAH wall losses, and the system departed from equilibrium.
Kinetic simulations suggested that ten of hours would be required to r
eestablish 90% of equilibrium concentrations for compounds like phenan
threne and pyrene once they had departed from equilibrium in the parti
cle phase by 34 and 18%, respectively.