General
Audience Oral Presentations Abstracts
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1.
New Mass Spectrometric Tools and Their Application to Organic
Aerosol Characterization
Murray
V. Johnston, Michael P. Tolocka, Berk Oktem, Matthew Dreyfus
Chemistry and Biochemistry Department, University
of Delaware, Newark, DE 19716
The
organic fraction of airborne particulate matter is a complex mixture
of compounds with a combined concentration on the order of 1 to
10 micrograms per cubic meter. Thousands of compounds may be present
in a sample, with individual concentrations between about 0.1
and 10 nanograms per cubic meter. The complexity and low concentration
levels associated with ambient samples present a significant analytical
challenge. We have been exploring the use of new methods for off-line
and on-line analysis of organic matter in particles to study aerosol
reactions.
Off-line analysis is performed with electrospray ionization and
matrix-assisted laser desorption ionization in combination with
exact mass measurements and tandem mass spectrometry. These methods
have allowed us to characterize hundreds of high molecular weight
compounds formed by secondary polymerization of the primary products
of a-pinene ozonolysis. Aerosols were produced by the reaction
of a-pinene and ozone in the presence of acid seed aerosol and
characterized by exact mass measurements and tandem mass spectrometry.
Oligomeric products between 200 and 900 u were detected with both
electrospray ionization and matrix-assisted laser desorption ionization.
The exact masses and dissociation products of these ions were
consistent with various combinations of the known primary products
of this reaction (“monomers”) with or without the
expected acid-catalyzed decomposition products of the monomers.
Chemical reactions leading to oligomer formation provide a reasonable
answer to a difficult problem associated with secondary organic
aerosol production in the atmosphere. It is unlikely that monomers
alone play an important role in the formation and growth of nuclei
in the atmosphere as their Kelvin vapor pressures are too high
for them to significantly partition into the particle phase. Polymerization
provides a mechanism by which partitioning to the particle phase
becomes favored. These methods are also being used by our group
to characterize biological material in ambient filter samples.
Preliminary results will be presented at the meeting.
On-line measurements are made with a field-deployable photoionization
aerosol mass spectrometer (PIAMS) that provides relatively “soft”
ionization of both aliphatic and aromatic compounds. Soft ionization
is needed to reduce the spectral congestion that is normally observed
from complex samples when separation prior to mass analysis is
not performed. With PIAMS, we are able to distinguish various
sources of ambient organic aerosol (diesel and gasoline emissions,
meat cooking, wood burning, cigarette smoke) by the distribution
of compounds detected. The mass spectra are consistent with previous
off-line measurements by gas chromatography mass spectrometry.
The current detection limit per “compound” (includes
all isomers and isobars at a single m/z) is in the range 7-70
ng/m3 for a 1 minute time average. We have used PIAMS for real-time
characterization of organic aerosols in flames and smog chambers
on this timescale. Instrumental improvements are underway to increase
sensitivity and thereby facilitate ambient measurements.
References
B.
Oktem, M.P. Tolocka, M.V. Johnston, “On-Line Analysis of
Organic Components in Fine and Ultrafine Particles by Photoionization
Aerosol Mass Spectrometry”, Analytical Chemistry (2004)
Jan. 15 issue.
M.P.
Tolocka, M.Jang, J.M. Ginter, F.J. Cox, R.M. Kamens, M.V. Johnston,
“Formation of Oligomeric Species in Secondary Organic Aerosols”,
Environmental Science and Technology (2004) in press.
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2. Primary Biopolymer Associations with Fine Particulate
Matter: Comparisons of Protein, Carbohydrate and Endotoxin content
of Temperate Urban PM2.5 with Selected Sources
Lisa
Clarke1, Lars Angenent2, Allen Robinson3,
and Mark Hernandez1
1Department of Civil, Environmental, and Architectural
Engineering, University of Colorado at Boulder, Boulder, Colorado
2Department of Chemical Engineering & Environmental Engineering
Science Program, Washington University in St. Louis, St. Louis,
Missouri
3Department of Mechanical Engineering, Carnegie Mellon University,
Pittsburgh, Pennsylvania
From
July 2001 to August 2002, high-volume samplers collected fine
airborne particulate matter (PM2.5) from a site in the Pittsburgh
metropolitan on 37 mm polycarbonate filters. The particulate matter
impacted on these filters was composited over 24 hour periods,
and analyzed for carbohydrate, protein and endotoxin content.
After eluting the samples into sterile, pyrogen-free water, the
following methods were used to quantify common biopolymers: (i)
a colorimetric, dextrose-standardized acid digestion for carbohydrate
measurement; (ii) a fluorometric, albumen-standardized intercalating
assay for protein measurements; and (iii) a commercially standardized
enzyme assay for endotoxin measurements. Carbohydrates were measurable
and correlated with airborne particulate matter (detection limit
c.a. 0.1 mg/m3) during approximately 90% of the monitoring period,
and seasonal trends emerged where the averaged levels monitored
during the summer and fall months were markedly higher than those
monitored in the winter and spring. During this period, PM-associated
carbohydrate levels varied between 0.2 and 2.2 mg/m3, and comprised
between 2% and 60% of the total organic carbon on an averaged
mass basis. Proteins were also measurable and correlated with
airborne particulate matter (detection limit c.a. 0.05 mg/m3)
during about 74% of days observed, and seasonal trends emerged
where the averaged levels monitored during the fall and winter
months were markedly higher than those monitored during the spring
and summer months. Throughout this time, PM-associated protein
levels varied between 0.006 and 1.3 mg/m3 and comprised between
0.5 and 7.5% of the total organic carbon on an averaged mass basis.
Endotoxin analyses were executed for the four mid-season months
– July 2001, October 2001, January 2002, and April 2002.
Endotoxin levels were always lower than 5 EU/m3 during these months,
and were consistent with outdoor levels reported elsewhere. These
results suggest that microscopic primary biological materials
may have a significant contribution to airborne organic carbon
levels, and be seasonally associated with airborne particulate
matter in this region.
For
comparison to the ambient recoverires, samples of diesel exhausts,
wood smokes, and vegetative detritus were collected in this same
metropolitan area between May and September 2003 and were analyzed
for their biopolymer content. These source samples were collected
on filters with a design loading of 200 mg of fine particulate
matter; actual loading was based on mass concentration estimates
from a Scanning Mobility Particle Sizer (SMPS). The diesel exhausts
did not yield any proteins or carbohydrates above method detection
limits. Wood smoke generated a range of carbohydrates, and moderate
levels of proteins, depending on the smoke source (e.g. flaming
or smoldering). Vegetative detritus produced extremely high levels
of carbohydrates, beyond the upper detection limit of the method
(150 mg/m3), and moderate levels of proteins. These results suggest
that common sources of primary biological materials may promote
biopolymer associations with airborne particulate matter, and
may be a noteworthy component of particle-associated organic carbon.
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