Secondary organic aerosol formation from m-xylene, toluene, and benzene N. L. Ng1, J. H. Kroll1,*, A. W. H. Chan1, P. S. Chhabra1, R. C. Flagan1, and J. H. Seinfeld1 1Departments of Chemical Engineering and Environmental Science and Engineering, California Institute of Technology, Pasadena, CA 91125, USA *now at: Aerodyne Research, Inc. 45 Manning Road, Billerica, MA 01821, USA
Abstract. Secondary organic aerosol (SOA) formation from the photooxidation of
m-xylene, toluene, and benzene is investigated in the Caltech environmental
chambers. Experiments are performed under two limiting NOx conditions;
under high-NOx conditions the peroxy radicals (RO2) react only
with NO, while under low-NOx conditions they react only with HO2.
For all three aromatics studied (m-xylene, toluene, and benzene), the SOA
yields (defined as the ratio of the mass of organic aerosol formed to the
mass of parent hydrocarbon reacted) under low-NOx conditions
substantially exceed those under high-NOx conditions, suggesting the
importance of peroxy radical chemistry in SOA formation. Under low-NOx
conditions, the SOA yields for m-xylene, toluene, and benzene are constant
(36%, 30%, and 37%, respectively), indicating that the SOA formed
is effectively nonvolatile under the range of Mo(>10 μg m−3) studied. Under high-NOx conditions, aerosol growth
occurs essentially immediately, even when NO concentration is high. The SOA
yield curves exhibit behavior similar to that observed by Odum et al. (1996,
1997a, b), although the values are somewhat higher than in the earlier study.
The yields measured under high-NOx conditions are higher than previous
measurements, suggesting a "rate effect" in SOA formation, in which SOA
yields are higher when the oxidation rate is faster. Experiments carried out
in the presence of acidic seed aerosol reveal no change of SOA yields from
the aromatics as compared with those using neutral seed aerosol.
Citation: Ng, N. L., Kroll, J. H., Chan, A. W. H., Chhabra, P. S., Flagan, R. C., and Seinfeld, J. H.: Secondary organic aerosol formation from m-xylene, toluene, and benzene, Atmos. Chem. Phys., 7, 3909-3922, doi:10.5194/acp-7-3909-2007, 2007.