5 research outputs found
Aerosol Brown Carbon from Dark Reactions of Syringol in Aqueous Aerosol Mimics
We
performed a laboratory investigation of the chemical processing
of syringol, a representative model phenolic compound emitted from
wood burning, in concentrated aqueous salt solutions mimicking tropospheric
aerosol particles. For solutions containing chloride salts, we observed
the formation of light-absorbing organic products (“brown carbon”),
accompanied by a phase separation, within 10 h under dark conditions.
Products were characterized at the molecular level using ultraperformance
liquid chromatography interfaced to diode array detection and high-resolution
quadrupole time-of-flight mass spectrometry equipped with electrospray
ionization and matrix-assisted laser desorption/ionization interfaced
to high-resolution time-of-flight mass spectrometry. The ultraviolet–visible
spectra, together with high-resolution mass spectra results, suggest
that syringol can be oxidized by dissolved oxygen, and the presence
of Cl<sup>–</sup> promotes this reaction. Our results provide
new insights into the evolution of aerosol optical properties during
aging, specifically the formation of aerosol brown carbon in biomass-burning
plumes
Evidence for an Unrecognized Secondary Anthropogenic Source of Organosulfates and Sulfonates: Gas-Phase Oxidation of Polycyclic Aromatic Hydrocarbons in the Presence of Sulfate Aerosol
In the present study, formation of
aromatic organosulfates (OSs)
from the photo-oxidation of polycyclic aromatic hydrocarbons (PAHs)
was investigated. Naphthalene (NAP) and 2-methylnaphthalene (2-MeNAP),
two of the most abundant gas-phase PAHs and thought to represent “missing”
sources of urban SOA, were photochemically oxidized in an outdoor
smog chamber facility in the presence of nonacidified and acidified
sulfate seed aerosol. Effects of seed aerosol composition, acidity
and relative humidity on OS formation were examined. Chemical characterization
of SOA extracts by ultra performance liquid chromatography coupled
to electrospray ionization high-resolution quadrupole time-of-flight
mass spectrometry revealed the formation of OSs and sulfonates from
photo-oxidation in the presence of sulfate seed aerosol. Many of the
organosulfur compounds identified in the smog chamber extracts were
also measured in urban fine aerosol collected at Lahore, Pakistan,
and Pasadena, USA, demonstrating that PAH photo-oxidation in the presence
of sulfate aerosol is a hitherto unrecognized source of anthropogenic
secondary organosulfur compounds, and providing new PAH SOA tracers
Gene Expression Profiling in Human Lung Cells Exposed to Isoprene-Derived Secondary Organic Aerosol
Secondary
organic aerosol (SOA) derived from the photochemical
oxidation of isoprene contributes a substantial mass fraction to atmospheric
fine particulate matter (PM<sub>2.5</sub>). The formation of isoprene
SOA is influenced largely by anthropogenic emissions through multiphase
chemistry of its multigenerational oxidation products. Considering
the abundance of isoprene SOA in the troposphere, understanding mechanisms
of adverse health effects through inhalation exposure is critical
to mitigating its potential impact on public health. In this study,
we assessed the effects of isoprene SOA on gene expression in human
airway epithelial cells (BEAS-2B) through an air–liquid interface
exposure. Gene expression profiling of 84 oxidative stress and 249
inflammation-associated human genes was performed. Our results show
that the expression levels of 29 genes were significantly altered
upon isoprene SOA exposure under noncytotoxic conditions (<i>p</i> < 0.05), with the majority (22/29) of genes passing
a false discovery rate threshold of 0.3. The most significantly affected
genes belong to the nuclear factor (erythroid-derived 2)-like 2 (Nrf2)
transcription factor network. The Nrf2 function is confirmed through
a reporter cell line. Together with detailed characterization of SOA
constituents, this study reveals the impact of isoprene SOA exposure
on lung responses and highlights the importance of further understanding
its potential health outcomes
Secondary Organic Aerosol Formation via 2‑Methyl-3-buten-2-ol Photooxidation: Evidence of Acid-Catalyzed Reactive Uptake of Epoxides
Secondary
organic aerosol (SOA) formation from 2-methyl-3-buten-2-ol
(MBO) photooxidation has recently been observed in both field and
laboratory studies. Similar to the level of isoprene, the level of
MBO-derived SOA increases with elevated aerosol acidity in the absence
of nitric oxide; therefore, an epoxide intermediate, (3,3-dimethyloxiran-2-yl)methanol
(MBO epoxide), was synthesized and tentatively proposed to explain
this enhancement. In this study, the potential of the synthetic MBO
epoxide to form SOA via reactive uptake was systematically examined.
SOA was observed only in the presence of acidic aerosol. Major SOA
constituents, 2,3-dihydroxyisopentanol and MBO-derived organosulfate
isomers, were chemically characterized in both laboratory-generated
SOA and in ambient fine aerosol collected from the BEACHON-RoMBAS
field campaign during the summer of 2011, where MBO emissions are
substantial. Our results support the idea that epoxides are potential
products of MBO photooxidation leading to the formation of atmospheric
SOA and suggest that reactive uptake of epoxides may explain acid
enhancement of SOA observed from other biogenic hydrocarbons
Nitrogen-Containing, Light-Absorbing Oligomers Produced in Aerosol Particles Exposed to Methylglyoxal, Photolysis, and Cloud Cycling
Aqueous methylglyoxal chemistry has
often been implicated as an
important source of oligomers in atmospheric aerosol. Here we report
on chemical analysis of brown carbon aerosol particles collected from
cloud cycling/photolysis chamber experiments, where gaseous methylglyoxal
and methylamine interacted with glycine, ammonium, or methylammonium
sulfate seed particles. Eighteen N-containing oligomers were identified
in the particulate phase by liquid chromatography/diode array detection/electrospray
ionization high-resolution quadrupole time-of-flight mass spectrometry.
Chemical formulas were determined and, for 6 major oligomer products,
MS<sup>2</sup> fragmentation spectra were used to propose tentative
structures and mechanisms. Electronic absorption spectra were calculated
for six tentative product structures by an ab initio second order
algebraic-diagrammatic-construction/density functional theory approach.
For five structures, matching calculated and measured absorption spectra
suggest that they are dominant light-absorbing species at their chromatographic
retention times. Detected oligomers incorporated methylglyoxal and
amines, as expected, but also pyruvic acid, hydroxyacetone, and significant
quantities of acetaldehyde. The finding that ∼80% (by mass)
of detected oligomers contained acetaldehyde, a methylglyoxal photolysis
product, suggests that daytime methylglyoxal oligomer formation is
dominated by radical addition mechanisms involving CH<sub>3</sub>CO*.
These mechanisms are evidently responsible for enhanced browning observed
during photolytic cloud events