The Potential Role of Criegee Intermediates in Nighttime Atmospheric Chemistry. A Modeling Study

We evaluate the role of Criegee intermediates (CI) from ozonolysis of alkenes on nighttime chemistry in areas impacted by ozone and high emissions of biogenic volatile organic compounds, for example, the Southeast United States, using the Master Chemical Mechanism. Criegee reactions with NO₂ may be an alternate source of NO₃. Reactions of CI with NO₃ have not been investigated but could influence NO_<i>x</i> recycling. Evaluation of these reactions depends on recently measured rate constants for CI reactions with water vapor, NO₂, and other trace gases. We vary the CI rate coefficients with NO₂ and H₂O and explore a range of initial conditions. We find that the CI production has the largest effects at low NO₂ (<1 ppbv), high isoprene (10 ppbv) and low RH (<50%). At higher RH that is characteristic of the southeast U.S. and other high biogenic emitting regions, the effects are negligible using current literature values for CI rate constants with H₂O. Under conditions for which CI reactions affect nighttime NO₃ chemistry in the model, NO₃ production from CI reaction with NO₂ increases by up to 70% and 47% at 10% and 50% relative humidity (RH), respectively, but are negligible (2%) at 80% RH. Organic nitrate formation is highly correlated with NO₃ production and increases up to 75%, 34%, and 1% at 10%, 50%, and 80% RH, respectively. Including CI chemistry increases formaldehyde production under all conditions. In addition to the rate constants for CI radicals with water vapor, model simulations are also sensitive to the rate constant for CI decomposition and to the yield of NO₃ from CI reaction with NO₂, which are uncertain

Single Exposure to near Roadway Particulate Matter Leads to Confined Inflammatory and Defense Responses: Possible Role of Metals

Inhalation of traffic-associated atmospheric particulate matter (PM2.5) is recognized as a significant health risk. In this study, we focused on a single (“subclinical response”) exposure to water-soluble extracts from PM collected at a roadside site in a major European city to elucidate potential components that drive pulmonary inflammatory, oxidative, and defense mechanisms and their systemic impacts. Intratracheal instillation (IT) of the aqueous extracts induced a 24 h inflammatory response characterized by increased broncho-alveolar lavage fluid (BALF) cells and cytokines (IL-6 and TNF-α), increased reactive oxygen species production, but insignificant lipids and proteins oxidation adducts in mouse lungs. This local response was largely self-resolved by 48 h, suggesting that it could represent a subclinical response to everyday-level exposure. Removal of soluble metals by chelation markedly diminished the pulmonary PM-mediated response. An artificial metal solution (MS) recapitulated the PM extract response. The self-resolving nature of the response is associated with activating defense mechanisms (increased levels of catalase and glutathione peroxidase expression), observed with both PM extract and MS. In conclusion, metals present in PM collected near roadways are largely responsible for the observed transient local pulmonary inflammation and oxidative stress. Simultaneous activation of the antioxidant defense response may protect against oxidative damage

Low Cytotoxicity of Inorganic Nanotubes and Fullerene-Like Nanostructures in Human Bronchial Epithelial Cells: Relation to Inflammatory Gene Induction and Antioxidant Response

The cytotoxicity of tungsten disulfide nano tubes (INT-WS₂) and inorganic fullerene-like molybdenum disulfide (IF-MoS₂) nanoparticles (NPs) used in industrial and medical applications was evaluated in comparison to standard environmental particulate matter. The IF-MoS₂ and INT-WS₂ reside in vesicles/inclusion bodies, suggestive of endocytic vesicles. In cells representing the respiratory, immune and metabolic systems, both IF-MoS₂ and INT-WS₂ NPs remained nontoxic compared to equivalent concentrations (up to 100 μg/mL in the medium) of silica dioxide (SiO₂), diesel engine-derived and carbon black NPs, which induced cell death. Associating with this biocompatibility of IF-MoS₂\INT-WS₂, we demonstrate in nontransformed human bronchial cells (NL-20) relative low induction of the pro-inflammatory cytokines IL-1β, IL-6, IL-8, and TNF-α. Moreover, IF-MoS₂ and INT-WS₂ activated antioxidant response as measured by the antioxidant response element (ARE) using a luciferase reporter, and induced Nrf2-mediated Phase II detoxification genes. Collectively, our findings suggest that the lower cytotoxicity of IF-MoS₂ and INT-WS₂ NPs does not reflect general biological inertness. Rather, compared to other NP’s, it likely results from decreased pro-inflammatory activation, but a comparable significant capacity to induce protective antioxidant/detoxification defense mechanisms

New Directions: Fundamentals of atmospheric chemistry: Keeping a three-legged stool balanced

New Directions: Fundamentals of atmospheric chemistry: Keeping a three-legged stool balance

Characterization of Light-Absorbing Oligomers from Reactions of Phenolic Compounds and Fe(III)

Phenolic compounds are common constituents of atmospheric aerosols. They form by pyrolysis of lignin and by biodegradation of plant material and are commonly found in biomass burning plumes, resuspended soil dust, and in anthropogenic secondary organic aerosols (SOA). In this study, we show that reactions of Fe­(III), a major constituent of mineral dust, with several phenolic compounds (guaiacol, catechol, syringol, o- and p-cresol) that are common in atmospheric aerosols, result in the formation of water insoluble light-absorbing compounds and reduced Fe­(II). The study was conducted under acidic conditions (pH = 1–2), relevant for areas impacted by biomass burning, anthropogenic emissions, and mineral dust. The reaction products have been characterized using a high-performance liquid chromatography coupled to photodiode array and high-resolution mass spectrometry detectors, UV–visible spectroscopy, X-ray photoelectron spectroscopy, and thermal gravimetric analysis. The major identified chromophores are oligomers of the reaction precursors that efficiently absorb light between 300 and 500 nm. The amounts of oligomers vary significantly between the systems studied. The highest amount was observed for guaiacol and catechol, and the least were detected in the syringol experiments, suggesting that the oligomerization proceeds through carbon–carbon coupling preferred at para- and ortho- positions, coupled to the reduction of Fe­(III) to Fe­(II). The results suggest that aqueous-phase radical reactions of phenolic compounds may be an efficient source of light-absorbing atmospheric organic compounds (brown carbon) that play important roles in Earth’s radiative forcing on global and regional scales and of quinones that can affect health

Molecular Chemistry of Atmospheric Brown Carbon Inferred from a Nationwide Biomass Burning Event

Lag Ba’Omer, a nationwide bonfire festival in Israel, was chosen as a case study to investigate the influence of a major biomass burning event on the light absorption properties of atmospheric brown carbon (BrC). The chemical composition and optical properties of BrC chromophores were investigated using a high performance liquid chromatography (HPLC) platform coupled to photo diode array (PDA) and high resolution mass spectrometry (HRMS) detectors. Substantial increase of BrC light absorption coefficient was observed during the night-long biomass burning event. Most chromophores observed during the event were attributed to nitroaromatic compounds (NAC), comprising 28 elemental formulas of at least 63 structural isomers. The NAC, in combination, accounted for 50–80% of the total visible light absorption (>400 nm) by solvent extractable BrC. The results highlight that NAC, in particular nitrophenols, are important light absorption contributors of biomass burning organic aerosol (BBOA), suggesting that night time chemistry of •NO₃ and N₂O₅ with particles may play a significant role in atmospheric transformations of BrC. Nitrophenols and related compounds were especially important chromophores of BBOA. The absorption spectra of the BrC chromophores are influenced by the extraction solvent and solution pH, implying that the aerosol acidity is an important factor controlling the light absorption properties of BrC

Exposure of Lung Epithelial Cells to Photochemically Aged Secondary Organic Aerosol Shows Increased Toxic Effects

Adverse health effects due to exposure to particulate matter (PM) are among the most important global environmental health risks. However, the effects of exposure to secondary organic aerosols (SOA), a major component of the global aerosol, are largely unknown. Here we exposed lung epithelial cells (A549) to fresh and aged SOA particles and investigated the effect of SOA atmospheric aging on cell viability and gene expression. Naphthalene- and α-pinene-derived SOA were formed in an oxidation flow reactor that simulates atmospheric SOA formation and aging dominated by OH radical oxidation under NO_<i>x</i>-free conditions. The SOA mass and chemical composition were characterized on-line using a scanning mobility particle sizer and aerosol mass spectrometer. Fresh and aged SOA were directed to an air–liquid interface cell exposure system. Aged naphthalene- and α-pinene-derived SOA were somewhat more toxic than fresh SOA. Aged naphthalene SOA contained peroxide levels that were higher than those of fresh SOA. The level of induction of Nrf2 signaling increased following exposure to aged naphthalene SOA. Given the global prevalence of SOA and its observed toxicity, this study calls for more studies aimed at understanding the underlying mechanics

Secondary Organic Aerosol Generated from Biomass Burning Emitted Phenolic Compounds: Oxidative Potential, Reactive Oxygen Species, and Cytotoxicity

Phenolic compounds are largely emitted from biomass burning (BB) and have a significant potential to form SOA (Phc-SOA). However, the toxicological properties of Phc-SOA remain unclear. In this study, phenol and guaiacol were chosen as two representative phenolic gases in BB plumes, and the toxicological properties of water-soluble components of their SOA generated under different photochemical ages and NOx levels were investigated. Phenolic compounds contribute greatly to the oxidative potential (OP) of biomass-burning SOA. OH-adducts of guaiacol (e.g., 2-methoxyhydroquinone) were identified as components of guaiacol SOA (GSOA) with high OP. The addition of nitro groups to 2,5-dimethyl-1,4-benzoquinone, a surrogate quinone compound in Phc-SOA, increased its OP. The toxicity of both phenol SOA (PSOA) and GSOA in vitro in human alveolar epithelial cells decreased with aging in terms of both cell death and cellular reactive oxygen species (ROS), possibly due to more ring-opening products with relatively low toxicity. The influence of NOx was consistent between cell death and cellular ROS for GSOA but not for PSOA, indicating that cellular ROS production does not necessarily represent all processes contributing to cell death caused by PSOA. Combining different acellular and cellular assays can provide a comprehensive understanding of aerosol toxicological properties

Evolution of the Complex Refractive Index of Secondary Organic Aerosols during Atmospheric Aging

The wavelength-dependence of the complex refractive indices (RI) in the visible spectral range of secondary organic aerosols (SOA) are rarely studied, and the evolution of the RI with atmospheric aging is largely unknown. In this study, we applied a novel white light-broadband cavity enhanced spectroscopy to measure the changes in the RI (400–650 nm) of β-pinene and <i>p</i>-xylene SOA produced and aged in an oxidation flow reactor, simulating daytime aging under NO_<i>x</i>-free conditions. It was found that these SOA are not absorbing in the visible range, and that the real part of the RI, <i>n</i>, shows a slight spectral dependence in the visible range. With increased OH exposure, <i>n</i> first increased and then decreased, possibly due to an increase in aerosol density and chemical mean polarizability for SOA produced at low OH exposures, and a decrease in chemical mean polarizability for SOA produced at high OH exposures, respectively. A simple radiative forcing calculation suggests that atmospheric aging can introduce more than 40% uncertainty due to the changes in the RI for aged SOA