2 research outputs found
Highly Oxidized Multifunctional Organic Compounds Observed in Tropospheric Particles: A Field and Laboratory Study
Very recent studies have reported
the existence of highly oxidized
multifunctional organic compounds (HOMs) with O/C ratios greater than
0.7. Because of their low vapor pressure, these compounds are often
referred as extremely low-volatile organic compounds (ELVOCs), and
thus, they are able to contribute significantly to organic mass in
tropospheric particles. While HOMs have been successfully detected
in the gas phase, their fate after uptake into particles remains unclear
to date. Hence, the present study was designed to detect HOMs and
related oxidation products in the particle phase and, thus, to shed
light on their fate after phase transfer. To this end, aerosol chamber
investigations of α-pinene ozonolysis were conducted under near
environmental precursor concentrations (2.4 ppb) in a continuous flow
reactor. The chemical characterization shows three classes of particle
constituents: (1) intact HOMs that contain a carbonyl group, (2) particle-phase
decomposition products, and (3) highly oxidized organosulfates (suggested
to be addressed as HOOS). Besides chamber studies, HOM formation was
also investigated during a measurement campaign conducted in summer
2013 at the TROPOS research station Melpitz. During this field campaign,
gas-phase HOM formation was found to be correlated with an increase
in the oxidation state of the organic aerosol
2‑Hydroxyterpenylic Acid: An Oxygenated Marker Compound for α‑Pinene Secondary Organic Aerosol in Ambient Fine Aerosol
An oxygenated MW 188 compound is
commonly observed in substantial
abundance in atmospheric aerosol samples and was proposed in previous
studies as an α-pinene-related marker compound that is associated
with aging processes. Owing to difficulties in producing this compound
in sufficient amounts in laboratory studies and the occurrence of
isobaric isomers, a complete assignment for individual MW 188 compounds
could not be achieved in these studies. Results from a comprehensive
mass spectrometric analysis are presented here to corroborate the
proposed structure of the most abundant MW 188 compound as a 2-hydroxyterpenylic
acid diastereoisomer with 2<i>R</i>,3<i>R</i> configuration.
The application of collision-induced dissociation with liquid chromatography/electrospray
ionization-ion trap mass spectrometry in both negative and positive
ion modes, as well as chemical derivatization to methyl ester derivatives
and analysis by the latter technique and gas chromatography/electron
ionization mass spectrometry, enabled a comprehensive characterization
of MW 188 isomers, including a detailed study of the fragmentation
behavior using both mass spectrometric techniques. Furthermore, a
MW 188 positional isomer, 4-hydroxyterpenylic acid, was tentatively
identified, which also is of atmospheric relevance as it could be
detected in ambient fine aerosol. Quantum chemical calculations were
performed to support the diastereoisomeric assignment of the 2-hydroxyterpenylic
acid isomers. Results from a time-resolved α-pinene photooxidation
experiment show that the 2-hydroxyterpenylic acid 2<i>R</i>,3<i>R</i> diastereoisomer has a time profile distinctly
different from that of 3-methyl-1,2,3-butanetricarboxylic acid, a
marker for oxygenated (aged) secondary organic aerosol. This study
presents a comprehensive chemical data set for a more complete structural
characterization of hydroxyterpenylic acids in ambient fine aerosol,
which sets the foundation to better understand the atmospheric fate
of α-pinene in future studies