Project description:In this study, we evaluated photosensitized chemistry at the air-sea interface as a source of secondary organic aerosols (SOA). Our results show that, in addition to biogenic emissions, abiotic processes could also be important in the marine boundary layer. Photosensitized production of marine secondary organic aerosol was studied in a custom-built multiphase atmospheric simulation chamber. The experimental chamber contained water, humic acid (1-10 mg L(-1)) as a proxy for dissolved organic matter, and nonanoic acid (0.1-10 mM), a fatty acid proxy which formed an organic film at the air-water interface. Dark secondary reaction with ozone after illumination resulted in SOA particle concentrations in excess of 1000 cm(-3), illustrating the production of unsaturated compounds by chemical reactions at the air-water interface. SOA numbers via photosensitization alone and in the absence of ozone did not exceed background levels. From these results, we derived a dependence of SOA numbers on nonanoic acid surface coverage and dissolved organic matter concentration. We present a discussion on the potential role of the air-sea interface in the production of atmospheric organic aerosol from photosensitized origins.
Project description:Isoprene is a key reactive organic gas involved in organic aerosol formation. While biogenic isoprene from terrestrial plants has been extensively studied and is recognized as a major contributor to secondary organic aerosol (SOA), high levels of observed SOA, especially in winter, cannot be fully explained by biogenic isoprene alone. In this study, we developed a comprehensive bottom-up emission inventory for isoprene, incorporating both biogenic and combustion sources and modeling their contributions to SOA in China from 2000 to 2016. Combustion-related isoprene emissions from open biomass burning and residential fuel combustion were estimated at 52.0 (39.1-65.7) Gg in 2000, declining to 14.8 (10.6-19.0) Gg by 2016. Open biomass burning contributes ∼40% of combustion-related isoprene emissions. Though, annually, combustion-related isoprene emissions were much smaller than the biogenic emissions, they did account for 32%-80% of total isoprene emissions in many north and west provinces in the colder months in 2016, and were even higher during the early 2000s owing to more biofuel-burning emissions. Model simulation results indicated that combustion-related isoprene could contribute 25%-40% of winter SOA in northern regions. Wintertime isoprene-derived SOA levels declined since 2000, corresponding with decreased combustion-related isoprene emissions; however, the extent of this decline varied regionally due to the influence of other precursors like nitrogen oxides (NOx). In the northeast region with high NOx levels, while combustion-related isoprene emissions decreased by >80% from 2000 to 2016, isoprene-derived SOA declined by only ∼20%. These findings highlight the previously underappreciated contributions of combustion-related isoprene to observed high wintertime isoprene-derived SOA levels.
Project description:Isoprene is a significant source of atmospheric organic aerosol; however, the oxidation pathways that lead to secondary organic aerosol (SOA) have remained elusive. Here, we identify the role of two key reactive intermediates, epoxydiols of isoprene (IEPOX = beta-IEPOX + delta-IEPOX) and methacryloylperoxynitrate (MPAN), which are formed during isoprene oxidation under low- and high-NO(x) conditions, respectively. Isoprene low-NO(x) SOA is enhanced in the presence of acidified sulfate seed aerosol (mass yield 28.6%) over that in the presence of neutral aerosol (mass yield 1.3%). Increased uptake of IEPOX by acid-catalyzed particle-phase reactions is shown to explain this enhancement. Under high-NO(x) conditions, isoprene SOA formation occurs through oxidation of its second-generation product, MPAN. The similarity of the composition of SOA formed from the photooxidation of MPAN to that formed from isoprene and methacrolein demonstrates the role of MPAN in the formation of isoprene high-NO(x) SOA. Reactions of IEPOX and MPAN in the presence of anthropogenic pollutants (i.e., acidic aerosol produced from the oxidation of SO(2) and NO(2), respectively) could be a substantial source of "missing urban SOA" not included in current atmospheric models.
Project description:Prdx2 is a peroxiredoxin (Prx) family protein that protects cells from attack via reactive oxygen species (ROS), and it has an important role in improving the resistance and scavenging capacity of ROS in fungi. Arthrobotrys oligospora is a widespread nematode-trapping fungus that can produce three-dimensional nets to capture and kill nematodes. In this study, AoPrdx2, a homologous protein of Prx5, was investigated in A. oligospora via gene disruption, phenotypic analysis, and metabolomics. The deletion of Aoprdx2 resulted in an increase in the number of mycelial septa and a reduction in the number of nuclei and spore yield. Meanwhile, the absence of Aoprdx2 increased sensitivity to oxidative stresses, whereas the ∆Aoprdx2 mutant strain resulted in higher ROS levels than that of the wild-type (WT) strain. In particular, the inactivation of Aoprdx2 severely influenced trap formation and pathogenicity; the number of traps produced by the ∆Aoprdx2 mutant strain was remarkably reduced and the number of mycelial rings of traps in the ∆Aoprdx2 mutant strain was less than that of the WT strain. In addition, the abundance of metabolites in the ∆Aoprdx2 mutant strain was significantly downregulated compared with the WT strain. These results indicate that AoPrdx2 plays an indispensable role in the scavenging of ROS, trap morphogenesis, and secondary metabolism.
Project description:Volume concentrations of secondary organic aerosol (SOA) are measured in 139 steady-state, single precursor hydrocarbon oxidation experiments after passing through a temperature controlled inlet. The response to change in temperature is well predicted through a feedforward Artificial Neural Network. The most parsimonious model, as indicated by Akaike's Information Criterion, Corrected (AIC,C), utilizes 11 input variables, a single hidden layer of 4 tanh activation function nodes, and a single linear output function. This model predicts thermal behavior of single precursor aerosols to less than ±5%, which is within the measurement uncertainty, while limiting the problem of overfitting. Prediction of thermal behavior of SOA can be achieved by a concise number of descriptors of the precursor hydrocarbon including the number of internal and external double bonds, number of methyl- and ethyl- functional groups, molecular weight, and number of ring structures, in addition to the volume of SOA formed, and an indicator of which of four oxidant precursors was used to initiate reactions (NOx photo-oxidation, photolysis of H2O2, ozonolysis, or thermal decomposition of N2O5). Additional input variables, such as chamber volumetric residence time, relative humidity, initial concentration of oxides of nitrogen, reacted hydrocarbon concentration, and further descriptors of the precursor hydrocarbon, including carbon number, number of oxygen atoms, and number of aromatic ring structures, lead to over fit models, and are unnecessary for an efficient, accurate predictive model of thermal behavior of SOA. This work indicates that predictive statistical modeling methods may be complementary to descriptive techniques for use in parametrization of air quality models.
Project description:To eliminate the spread of a novel coronavirus breaking out in the end of 2019 (COVID-19), the Chinese government has implemented a nationwide lockdown policy after the Chinese lunar New Year of 2020, resulting in a sharp reduction in air pollutant emissions. To investigate the impact of the lockdown on aerosol chemistry, the number fraction, size distribution and formation process of oxalic acid (C2) containing particles and its precursors were studied using a single particle aerosol mass spectrometer (SPAMS) at the urban site of Liaocheng in the North China Plain (NCP). Our results showed that five air pollutants (i.e., PM2.5, PM10, SO2, NO2, and CO) decreased by 30.0-59.8% during the lockdown compared to those before the lockdown, while O3 increased by 63.9% during the lockdown mainly due to the inefficient titration effect of O3 via NO reduction. The increased O3 concentration can boost the atmospheric oxidizing capacity and further enhance the formation of secondary organic aerosols, thereby significantly enhancing the C2 particles and its precursors as observed during the lockdown. Before the lockdown, C2 particles were significantly originated from biomass burning emissions and their subsequent aqueous-phase oxidation. The hourly variation patterns and correlation analysis before the lockdown suggested that relative humidity (RH) and aerosol liquid water content (ALWC) played a key role in the formation of C2 particles and the increased aerosol acidity can promote the conversion of precursors such as glyoxal (Gly) and methyglyoxal (mGly) into C2 particles in the aqueous phase. RH and ALWC decreased sharply but O3 concentration and solar radiation increased remarkably during the lockdown, the O3-dominated photochemical pathways played an important role in the formation of C2 particles in which aerosol acidity was ineffective. Our study indicated that air pollution treatment sponges on a joint-control and balanced strategy for controlling numerous pollutants.
Project description:The formation of secondary organic aerosol (SOA) indoors is one of the many consequences of the rich and complex chemistry that occurs therein. Given particulate matter has well documented health effects, we need to understand the mechanism for SOA formation indoors and its resulting composition. This study evaluates some uncertainties that exist in quantifying gas-to-particle partitioning of SOA-forming compounds using an indoor detailed chemical model. In particular, we investigate the impacts of using different methods to estimate compound vapour pressures as well as simulating the formation of highly oxygenated organic molecules (HOM) via auto-oxidation on SOA formation indoors. Estimation of vapour pressures for 136 α-pinene oxidation species by six investigated methods led to standard deviations of 28-216%. Inclusion of HOM formation improved model performance across three of the six assessed vapour pressure estimation methods when comparing against experimental data, particularly when the NO2 concentration was relatively high. We also explored the predicted SOA composition using two product classification methods, the first assuming the molecule is dominated by one functionality according to its name, and the second accounting for the fractional weighting of each functional group within a molecule. The SOA composition was dominated by the HOM species when the NO2-to-α-terpineol ratio was high for both product classification methods, as these conditions promoted formation of the nitrate radical and hence formation of HOM monomers. As the NO2-to-α-terpineol ratio decreased, peroxides and acids dominated the simple classification, whereas for the fractional classification, carbonyl and alcohol groups became more important.
Project description:Biomass-burning organic aerosol(s) (BBOA) are rich in brown carbon, which significantly absorbs solar irradiation and potentially accelerates global warming. Despite its importance, the multiphase photochemistry of BBOA after light absorption remains poorly understood due to challenges in determining the oxidant concentrations and the reaction kinetics within aerosol particles. In this study, we explored the photochemical reactivity of BBOA particles in multiphase S(IV) oxidation to sulfate. We found that sulfate formation in BBOA particles under light is predominantly driven by photosensitization involving the triplet excited states (3BBOA*) instead of iron, nitrate, and S(IV) photochemistry. Rates in BBOA particles are three orders of magnitude higher than those observed in the bulk solution, primarily due to the fast interfacial reactions. Our results highlight that the chemistry of 3BBOA* in particles can greatly contribute to the formation of sulfate, as an example of the secondary pollutants. Photosensitization of BBOA will likely become increasingly crucial due to the intensified global wildfires.
Project description:Defective reactive oxygen species (ROS) production by genetically determined variants of the NADPH oxidase 2 (NOX2) complex component, NCF4, leads to enhanced production of autoantibodies to collagen type II (COL2) and severe collagen-induced arthritis (CIA) in mice. To further understand this process, we used mice harboring a mutation in the lipid endosomal membrane binding site (R58A) of NCF4 subunit. This mutation did not affect the extracellular ROS responses but showed instead decreased intracellular responses following B cell stimulation. Immunization with COL2 led to severe arthritis with increased antibody levels in Ncf458A mutated animals without significant effects on antigen presentation, autoreactive T cell activation and germinal center formation. Instead, plasma cell formation was enhanced and had altered CXCR3/CXCR4 expression. This B cell intrinsic effect was further confirmed with chimeric B cell transfer experiments and in vitro LPS or CD40L with anti-IgM stimulation. We conclude that NCF4 regulates the terminal differentiation of B cells to plasma cells through intracellular ROS.
Project description:Ferroptosis is a form of oxidative cell death that is characterized by enhanced lipid peroxidation and mitochondrial impairment. The enzymes acyl-CoA synthetase long-chain family member 4 (ACSL4) and lysophosphatidylcholine acyltransferase (LPCAT) play an essential role in the biosynthesis of polyunsaturated fatty acid (PUFA)-containing phospholipids, thereby providing the substrates for lipid peroxidation and promoting ferroptosis. To examine the impact of mitochondria in ACSL4/LPCAT2-driven ferroptosis, HEK293T cells overexpressing ACSL4 and LPCAT2 (OE) or empty vector controls (LV) were exposed to 1S, 3R-RSL3 (RSL3) for induction of ferroptosis. The ACSL4/LPCAT2 overexpression resulted in higher sensitivity against RSL3-induced cell death compared to LV-transfected controls. Moreover, mitochondrial parameters such as mitochondrial reactive oxygen species (ROS) formation, mitochondrial membrane potential, and mitochondrial respiration deteriorated in the OE cells, supporting the conclusion that mitochondria play a significant role in ACSL4/LPCAT2-driven ferroptosis. This was further confirmed through the protection of OE cells against RSL3-mediated cell death by the mitochondrial ROS scavenger mitoquinone (MitoQ), which exerted protection via antioxidative properties rather than through previously reported metabolic effects. Our findings implicate that mitochondrial ROS production and the accompanying organelle disintegration are essential for mediating oxidative cell death initiated through lipid peroxidation in ferroptosis.