The formation of SOA and chemical tracer compounds from the photooxidation of naphthalene and its methyl analogs in the presence and absence of nitrogen oxides 1National Exposure Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, USA
27 Sep 2012
2Alion Science and Technology, P.O. Box 12313, Research Triangle Park, North Carolina 27709, USA
Received: 14 Mar 2012 – Published in Atmos. Chem. Phys. Discuss.: 11 May 2012 Abstract. Laboratory smog chamber experiments have been carried out to investigate
secondary organic aerosol (SOA) formation from the photooxidation of
naphthalene and its methyl analogs, 1- and 2-methylnaphthalene (1-MN and
2-MN, respectively). Laboratory smog chamber irradiations were conducted in
a flow mode to ensure adequate collection of the aerosol at reasonably low
reactant concentrations and in the presence and absence of nitrogen oxides.
Phthalic acid and methyl analogs were identified following BSTFA
derivatization of the aerosol extract. These compounds were examined to
determine whether they could serve as reasonable molecular tracers to
estimate the contributions of these precursors to ambient PM2.5.
Measurements were also made to determine aerosol parameters from secondary
organic aerosol from naphthalene, 1-MN, and 2-MN.
Revised: 05 Sep 2012 – Accepted: 06 Sep 2012 – Published: 27 Sep 2012
A mass fraction approach was used to establish factors which could be
applied to phthalic acid concentrations in ambient aerosols, assuming a
negligible contribution from primary sources. Phthalic anhydride uptake (and
hydrolysis) was tested and found to represent a moderate filter artifact in
filter measurements with and without in-line denuders. This study provided
the opportunity to examine differences using authentic standards for
phthalic acid compared to surrogate standards. While the mass fraction based
on a surrogate compounds was somewhat lower, the differences are largely
unimportant. For naphthalene, mass fractions of 0.0199 (recommended for
ambient samples) and 0.0206 were determined in the presence and absence of
nitrogen oxides, respectively, based on phthalic acid standards.
The mass fractions determined from the laboratory data were applied to
ambient samples where phthalic acid was found and expressed "as
naphthalene" since phthalic acid was found to be produced in the particle
phase from other methylnaphthalenes. The mass fraction values were applied
to samples taken during the 2005 SOAR Study in Riverside, CA and 2010 CalNex
Study in Pasadena. In both studies an undetermined isomer of methylphthalic
acid was detected in addition to phthalic acid. Laboratory experiment
retention times and mass spectra suggest that the major precursor for this
compound is 2-MN. For the CalNex Study, SOC values for the 2-ring precursor
PAHs (as naphthalene) were found to range from below the detection limit to
20 ngC m−3 which with the laboratory mass fraction data suggests an
upper limit of approximately 1 μg m−3 for SOA due to 2-ring PAHs.
Temporal data over the course of the one-month CalNex study suggest that
primary sources of phthalic acid were probably negligible during this study
period. However, the values must still be considered upper limits given a
potential hydrolysis reaction or uptake of phthalic anhydride (subsequently
hydrolyzed) onto the collection media.
Citation: Kleindienst, T. E., Jaoui, M., Lewandowski, M., Offenberg, J. H., and Docherty, K. S.: The formation of SOA and chemical tracer compounds from the photooxidation of naphthalene and its methyl analogs in the presence and absence of nitrogen oxides, Atmos. Chem. Phys., 12, 8711-8726, doi:10.5194/acp-12-8711-2012, 2012.