Molecular Characterization and Photoreactivity of Organic Aerosols Formed from Pyrolysis of Urban Materials during Fires at the Wildland-Urban Interface.

Fires at the wildland-urban interface (WUI) are increasing in magnitude and frequency, emitting organic aerosol (OA) with unknown composition and atmospheric impacts. In this study, we investigated the chemical composition of OA produced through the 600 °C pyrolysis of ten urban materials in nitrogen, which were subsequently aged under UV light for 2 h. The analysis utilized ultrahigh-performance liquid chromatography (UHPLC) separation, coupled with a photodiode array (PDA) detector and a high-resolution mass spectrometer (HRMS) for molecular characterization.

Isomeric Identification of the Nitroindole Chromophore in Indole + NO Organic Aerosol.

Oxidation of indole by nitrate radical (NO) was previously proposed to form nitroindole, largely responsible for the brown color of indole secondary organic aerosol (SOA). As there are seven known nitroindole isomers, we used chromatographic separation to show that a single nitroindole isomer is produced in the indole + NO reaction and definitively assigned it to 3-nitroindole by comparison with chromatograms of nitroindole standards. Mass spectra of aerosolized 3-nitroindole particles were recorded with an aerosol mass spectrometer and directly compared to mass spectra of SOA from smog chamber oxidation of indole by NO in order to help identify peaks unique to nitroindole (/ 162, 132, and 116).

Biogenic and Anthropogenic Secondary Organic Aerosols Become Fluorescent after Highly Acidic Aging.

Primary biological aerosol particles (PBAPs) and secondary organic aerosol (SOA) both contain organic compounds that share similar chemical and optical properties. Fluorescence is often used to characterize PBAPs; however, this may be hindered due to interferences from fluorophores in SOA. Despite extensive efforts to understand the aging of SOA under elevated particle acidity conditions, little is known about how these processes affect the fluorescence of SOA and thereby their interference with the measurements of PBAPs.

Secondary Organic Aerosol from OH-Initiated Oxidation of Mixtures of d-Limonene and β-Myrcene.

The chemical composition and physical properties of secondary organic aerosol (SOA) generated through OH-initiated oxidation of mixtures containing β-myrcene, an acyclic monoterpene, and d-limonene, a cyclic monoterpene, were investigated to assess the extent of the chemical interactions between their oxidation products. The SOA samples were prepared in an environmental smog chamber, and their composition was analyzed offline using ultraperformance liquid chromatography coupled with electrospray ionization high-resolution mass spectrometry (UPLC-ESI-HRMS). Our results suggested that SOA containing β-myrcene showed a higher proportion of oligomeric compounds with low volatility compared to that of SOA from d-limonene.

Chemical Analysis of Exhaled Vape Emissions: Unraveling the Complexities of Humectant Fragmentation in a Human Trial Study.

Electronic cigarette smoking (or vaping) is on the rise, presenting questions about the effects of secondhand exposure. The chemical composition of vape emissions was examined in the exhaled breath of eight human volunteers with the high chemical specificity of complementary online and offline techniques. Our study is the first to take multiple exhaled puff measurements from human participants and compare volatile organic compound (VOC) concentrations between two commonly used methods, proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) and gas chromatography (GC).

Formation of Chromophores from -Pinonaldehyde Aged in Highly Acidic Conditions.

Sulfuric acid in the atmosphere can participate in acid-catalyzed and acid-driven reactions, including those within secondary organic aerosols (SOA). Previous studies have observed enhanced absorption at visible wavelengths and significant changes in the chemical composition when SOA was exposed to sulfuric acid. However, the specific chromophores responsible for these changes could not be identified.

Reactive Oxygen Species Formation and Peroxide and Carbonyl Decomposition in Aqueous Photolysis of Secondary Organic Aerosols.

The mechanism and kinetics of reactive oxygen species (ROS) formation when atmospheric secondary organic aerosol (SOA) is exposed to solar radiation are poorly understood. In this study, we combined an in situ UV-vis irradiation system with electron paramagnetic resonance (EPR) spectroscopy to characterize the photolytic formation of ROS in aqueous extracts of SOA formed by the oxidation of isoprene, α-pinene, α-terpineol, and toluene. We observed substantial formation of free radicals, including OH, superoxide (HO), and organic radicals (R/RO) upon irradiation.

Ultrafast Excited-State Proton Transfer in 4-Nitrocatechol: Implications for the Photochemistry of Nitrophenols.

Nitrophenols are a class of environmental contaminants that exhibit strong absorption at atmospherically relevant wavelengths, prompting many studies of their photochemical degradation rates and mechanisms. Despite the importance of photochemical reactions of nitrophenols in the environment, the ultrafast processes in electronically excited nitrophenols are not well understood. Here, we present an experimental study of ultrafast electron dynamics in 4-nitrocatechol (4NC), a common product of biomass burning and fossil fuel combustion.

Overview of ICARUS-A Curated, Open Access, Online Repository for Atmospheric Simulation Chamber Data.

Atmospheric simulation chambers continue to be indispensable tools for research in the atmospheric sciences. Insights from chamber studies are integrated into atmospheric chemical transport models, which are used for science-informed policy decisions. However, a centralized data management and access infrastructure for their scientific products had not been available in the United States and many parts of the world.

Photoenhanced Radical Formation in Aqueous Mixtures of Levoglucosan and Benzoquinone: Implications to Photochemical Aging of Biomass-Burning Organic Aerosols.

The photochemical aging of biomass-burning organic aerosols (BBOAs) by exposure to sunlight changes the chemical composition over its atmospheric lifetime, affecting the toxicological and climate-relevant properties of BBOA particles. This study used electron paramagnetic resonance (EPR) spectroscopy with a spin-trapping agent, 5--butoxycarbonyl-5-methyl-1-pyrroline--oxide (BMPO), high-resolution mass spectrometry, and kinetic modeling to study the photosensitized formation of reactive oxygen species (ROS) and free radicals in mixtures of benzoquinone and levoglucosan, known BBOA tracer molecules. EPR analysis of irradiated benzoquinone solutions showed dominant formation of hydroxyl radicals (OH), which are known products of reaction of triplet-state benzoquinone with water, also yielding semiquinone radicals.

Insect Infestation Increases Viscosity of Biogenic Secondary Organic Aerosol.

Plant stress alters emissions of volatile organic compounds. However, little is known about how this could influence climate-relevant properties of secondary organic aerosol (SOA), particularly from complex mixtures such as real plant emissions. In this study, the chemical composition and viscosity were examined for SOA generated from real healthy and aphid-stressed Canary Island pine () trees, which are commonly used for landscaping in Southern California.

Spontaneous dark formation of OH radicals at the interface of aqueous atmospheric droplets.

Hydroxyl radical (OH) is a key oxidant that triggers atmospheric oxidation chemistry in both gas and aqueous phases. The current understanding of its aqueous sources is mainly based on known bulk (photo)chemical processes, uptake from gaseous OH, or related to interfacial O and NO radical-driven chemistry. Here, we present experimental evidence that OH radicals are spontaneously produced at the air-water interface of aqueous droplets in the dark and the absence of known precursors, possibly due to the strong electric field that forms at such interfaces.

Photolysis of Gas-Phase Atmospherically Relevant Monoterpene-Derived Organic Nitrates.

Organic nitrates (ONs) can impact spatial distribution of reactive nitrogen species and ozone formation in the atmosphere. While photolysis of ONs is known to result in the release of NO back to the atmosphere, the photolysis rate constants and mechanisms of monoterpene-derived ONs (MT-ONs) have not been well constrained. We investigated the gas-phase photolysis of three synthetic ONs derived from α-pinene, β-pinene, and d-limonene through chamber experiments.

Sunlight can convert atmospheric aerosols into a glassy solid state and modify their environmental impacts.

Secondary organic aerosol (SOA) plays a critical, yet uncertain, role in air quality and climate. Once formed, SOA is transported throughout the atmosphere and is exposed to solar UV light. Information on the viscosity of SOA, and how it may change with solar UV exposure, is needed to accurately predict air quality and climate.

Open questions on transition metals driving secondary thermal processes in atmospheric aerosols.

Transition metals are increasingly recognized as key drivers in the formation and aging of light-absorbing organic aerosols, known as brown carbon, which impact the energy flux in the atmosphere. Here the authors discuss somewhat overlooked condensed phase chemical processes and identify research needs to improve our fundamental understanding of atmospheric aerosols and ultimately reduce modelling uncertainties of the direct and indirect effects of aerosol particles on the climate.

Photochemical Degradation of 4-Nitrocatechol and 2,4-Dinitrophenol in a Sugar-Glass Secondary Organic Aerosol Surrogate.

The roles that chemical environment and viscosity play in the photochemical fate of molecules trapped in atmospheric particles are poorly understood. The goal of this work was to characterize the photolysis of 4-nitrocatechol (4NC) and 2,4-dinitrophenol (24DNP) in semisolid isomalt as a new type of surrogate for glassy organic aerosols and compare it to photolysis in liquid water, isopropanol, and octanol. UV/vis spectroscopy was used to monitor the absorbance decay to determine the rates of photochemical loss of 4NC and 24DNP.

Emissions Measurements from Household Solid Fuel Use in Haryana, India: Implications for Climate and Health Co-benefits.

A large concern with estimates of climate and health co-benefits of "clean" cookstoves from controlled emissions testing is whether results represent what actually happens in real homes during normal use. A growing body of evidence indicates that in-field emissions during daily cooking activities differ substantially from values obtained in laboratories, with correspondingly different estimates of co-benefits. We report PM emission factors from uncontrolled cooking ( = 7) and minimally controlled cooking tests ( = 51) using traditional chulha and angithi stoves in village kitchens in Haryana, India.

Atmospheric Photosensitization: A New Pathway for Sulfate Formation.

Northern China is regularly subjected to intense wintertime "haze events", with high levels of fine particles that threaten millions of inhabitants. While sulfate is a known major component of these fine haze particles, its formation mechanism remains unclear especially under highly polluted conditions, with state-of-the-art air quality models unable to reproduce or predict field observations. These haze conditions are generally characterized by simultaneous high emissions of SO and photosensitizing materials.

Reactive Oxygen Species Production from Secondary Organic Aerosols: The Importance of Singlet Oxygen.

Organic aerosols are subjected to atmospheric processes driven by sunlight, including the production of reactive oxygen species (ROS) capable of transforming their physicochemical properties. In this study, secondary organic aerosols (SOA) generated from aromatic precursors were found to sensitize singlet oxygen (O), an arguably underappreciated atmospheric ROS. Specifically, we quantified O, OH radical, and HO quantum yields within photoirradiated solutions of laboratory-generated SOA from toluene, biphenyl, naphthalene, and 1,8-dimethylnaphthalene.

Effect of Oxalate and Sulfate on Iron-Catalyzed Secondary Brown Carbon Formation.

Oxalate and sulfate are ubiquitous components of ambient aerosols with a high complexation affinity to iron. However, their effect on iron-driven secondary brown carbon formation in solution from soluble aromatic and aliphatic reagents was not studied. We report masses and hydrodynamic particle sizes of insoluble particles formed from the dark aqueous phase reaction of catechol, guaiacol, fumaric, and muconic acids with Fe(III) in the presence of oxalate or sulfate.