Oxygenated Organic Molecules over the Boundary Layer Aloft in Beijing.

Reutilization of Cr-Y zeolite obtained by biosorption in the catalytic oxidation of volatile organic compounds

<p>Glyoxal (CHOCHO) is the simplest and one of the most abundant atmospheric α-dicarbonyls. In the atmosphere, it is mainly produced by the oxidation of other non-methane volatile organic compounds originating from natural and anthropogenic sources. Against photooxidation, it has a rather short lifetime of about 1 to 3 hours. Due to its high solubility, it quickly partitions into cloud droplets and deliquescent aerosols where it is known to form oligomers leading to secondary organic aerosols (SOA). In order to assess its significance for air pollution, it is thus necessary that global atmospheric chemistry models satisfactorily predict its abundance.</p><p>On board of the Sentinel-5 Precursor satellite, the TROPOspheric Monitoring Instrument (TROPOMI) provides tropospheric glyoxal columns. These tropospheric columns are generated with an improved version of the BIRA-IASB scientific retrieval algorithm relying on the Differential Optical Absorption Spectroscopy (DOAS) approach. By combining these retrievals with glyoxal measurements obtained during multiple air-borne campaigns using the High Altitude and Long Range Research Aircraft (HALO), we evaluate the capabilities of the ECHAM/MESSy Atmospheric Chemistry (EMAC) model to reproduce the global distribution and abundance of glyoxal. In its standard configuration, EMAC uses the detailed Mainz Organic Mechanism (MOM) to represent gas-phase chemistry. Additionally, we use the Model of Emissions of Gases and Aerosols from Nature (MEGAN) and the Emissions Database for Global Atmospheric Research (EDGAR, v4.3.2) to represent natural and anthropogenic emissions, respectively. When analysing an EMAC simulation using this standard configuration, we find that EMAC tends to overestimate tropospheric glyoxal columns over continental regions close to strong natural (e.g., Amazon Basin) and anthropogenic emission sources (e.g., China). At the same time, EMAC tends to underestimate glyoxal columns over tropical oceanic regions.</p><p>In this study, we perform a series of sensitivity simulations and demonstrate that the model bias over continental regions is mainly resolved by including detailed aqueous-phase chemistry from the Jülich Aqueous-phase Mechanism of Organic Chemistry (JAMOC) and by reducing biogenic emissions towards the latest estimates. In addition, by implementing additional glyoxal precursors from oceanic sources, we demonstrate that the model bias over the tropical ocean is reduced. Following the more realistic model representation of glyoxal levels, we present a revised tropospheric glyoxal budget.</p>

The work presents Pd-containing catalysts for practical application with enhanced low-temperature activity in the complete oxidation of volatile organic compounds (VOCs) using innovative combinations of reduced graphene oxide (RGO) and alumina. The catalysts were characterized by XRD, SEM, TEM, XPS, low-temperature N2-adsorption, and CO chemisorption. The tests on complete catalytic oxidation of different VOC (propane, butane, hexane, dimethyl ether, toluene, propylene) and CO were carried out. The reaction kinetics and the mechanism of the reaction of complete oxidation of toluene are being investigated in detail. The results show that the new catalyst design makes it able to completely oxidize the studied VOCs and CO at low temperatures (100–350 °C) with long-term stability. Using a variety of instrumental methods, it was established that for high activity and long-term stability, the optimal ratio Pd/PdO should be close to 1:1. The most probable mechanism of complete toluene oxidation is the mechanism of Langmuir–Hinshelwood. The high activity and the weak effect of water on the catalyst performance leads to further perspectives for the application of the currently developed approach for the preparation of large-scale monolithic catalytic systems for air pollution control.

General study of catalytic oxidation of various VOCs over La0.8Sr0.2MnO3+x perovskite catalyst—influence of mixture

<p><strong>       </strong>Highly oxygenated organic molecules (HOM) are found to play an important role in the formation and growth of secondary organic aerosol (SOA). SOA is an important type of aerosol with significant impact on air quality and climate. Compared to the oxidation of volatile organic compounds by O<sub>3</sub> and OH, HOM formation in the oxidation by NO<sub>3</sub> radical, an important oxidant at night-time and dawn, has received less attention. In this study, HOM formation in the reaction of isoprene with NO<sub>3</sub> was investigated in the SAPHIR chamber (Simulation of Atmospheric PHotochemistry In a large Reaction chamber). A large number of HOM including monomers (C<sub>5</sub>), dimers (C<sub>10</sub>), and trimers (C<sub>15</sub>), both closed-shell compounds and open-shell peroxy radicals, were detected. HOM were classified into various series according to their formula, which included monomers containing one or more N atoms, dimers containing 1-4 N atoms, and trimers containing 3-5 N atoms. Tentative formation pathways of HOM were proposed reflecting known NO<sub>3</sub> and RO<sub>2</sub> chemistry in the literature under consideration of the autoxidation via peroxy pathways and peroxy-alkoxy pathways. Further mechanistic constraints were given by the time profiles of HOM after sequential isoprene addition which enabled to differentiate first- and second-generation products. Total HOM molar yield was estimated, which suggests that HOM may contribute a significant fraction to SOA yield in the reaction of isoprene with NO<sub>3</sub>.</p>

The role of lattice oxygen on the activity of manganese oxides towards the oxidation of volatile organic compounds

<strong class="journal-contentHeaderColor">Abstract.</strong> Secondary organic aerosol (SOA) is formed through the oxidation of volatile organic compounds (VOC), which can be of both natural and anthropogenic origin. While the hydroxyl radical (OH) and ozone (O₃) are the main atmospheric oxidants during the day, the nitrate radical (NO₃) becomes more important during the night time. Yet, atmospheric nitrate chemistry has received less attention compared to OH and O₃. The Nitrate Aerosol and Volatility Experiment (NArVE) aimed to study the NO₃-induced SOA formation and evolution from three biogenic VOCs (BVOC), namely isoprene, &alpha;-pinene and &beta;-caryophyllene. The volatility of aerosol particles was studied using isothermal evaporation chambers, temperature-dependent evaporation in a volatility tandem differential mobility analyzer (VTDMA), and thermal desorption in a filter inlet for gases and aerosols coupled to a chemical ionization mass spectrometer (FIGAERO-CIMS). Data from these three setups present a cohesive picture of the volatility of the SOA formed in the dark from the three biogenic precursors. Under our experimental conditions, the SOA formed from NO₃ + &alpha;-pinene was generally more volatile than SOA from &alpha;-pinene ozonolysis, while the NO₃ oxidation of isoprene produced similar, although slightly less volatile SOA than &alpha;-pinene under our experimental conditions. &beta;-caryophyllene reactions with NO₃ resulted in the least volatile species. Three different parametrizations for estimating the saturation vapor pressure of the oxidation products were tested for reproducing the observed evaporation in a kinetic modelling framework. Our results show that the SOA from nitrate oxidation of &alpha;-pinene or isoprene is dominated by low volatility organic compounds (LVOC) and semivolatile organic compounds (SVOC), while the corresponding SOA from &beta;-caryophyllene consists primarily of extremely low volatility organic compounds (ELVOC) and LVOC. The parameterizations yielded variable results in terms of reproducing the observed evaporation, and generally the comparisons pointed to a need for re-evaluating the treatment of the nitrate group in such parameterizations. Strategies for improving the predictive power of the volatility parameterizations, particularly in relation to the contribution from the nitrate group, are discussed.

Secondary Organic Aerosol (SOA) production and chemical composition play a crucial role in the urban air pollution. Here, we used observations from two summer campaigns in Beijing in 2017 and 2023 to show that nighttime production of NOz (NOy - NOx) is particularly enhanced in specific conditions and that can play a significant role for SOA the next day. The observations showed nocturnal peaks of NOz&amp;#160;of about 40 ppb, correlated with very high NO and NO2. We employed the Framework for 0-D Atmospheric Modeling (F0AM) model, based on the Master Chemical Mechanism (MCM), running simulations to investigate the organic nitrates (ONs) speciation, and founding that during the night the alkyl nitrates is the most abundant ONs, produced by oxidation of volatile organic compounds (VOCs) by the nitrate radical (NO3). Finally, we used the Framework for 0-D Atmospheric Modeling- Washington Aerosol Module (F0AM-WAM) model, which couple the gas phase chemistry with the SIMPOL representation for the particle phase, to correlate the nocturnal ONs peaks, that we suggested to be mainly in gas phase, to the diurnal particle growth events registered in Beijing.

The oxidation of volatile organic compounds (VOCs) affects particulate matter and oxidant levels in the troposphere, making it vital to simulate for climate models and to predict air quality. Full-complexity oxidation mechanisms for VOCs such as isoprene, however, are too large to be simulated in a 3-dimensional atmospheric chemical transport model. Reduced VOC oxidation mechanisms have been developed, but all must make a small number of reactions represent a much larger set, leading to imprecision in stoichiometric coefficients. Some of the sacrifice of accuracy incurred in the reduction process can be recuperated by optimizing the stoichiometric coefficients after reduction. In this work, we present Coefficient Optimization for Automated MOdel REduction (CO-AMORE), a new set of tools for the optimization of reduced mechanism stoichiometric coefficients using graph theory-assisted gradient descent. These methods include the application of gradient descent and two new algorithms for preprocessing coefficients: Anti-Community Clustering (ACC) and Bipartite Graph Sorting (BGS). Our application of gradient descent with data preprocessed using our ACC algorithm improved the accuracy of a reduced isoprene mechanism by up to 40% in a box model simulation. Gradient descent with data preprocessed using BGS was able to achieve similar levels of optimization as ACC across multiple mechanisms. In addition, ACC was over four times faster than standard gradient descent, showing the promise of this novel methodology. Optimized reduced mechanisms allow atmospheric models to be more accurate, enabling a better understanding of particulate matter sources and offering the potential to benefit public health.

Space‐confined catalysis can help create unique nanoscale chemical environments partitioned from the surrounding bulk space and has become a feasible strategy for designing high‐efficiency catalysts for various reactions. Confinement effects can affect both the reacting molecules and confined metal/metal‐oxide nanoparticles. This review mainly documents the progress in the design and applications of confined catalysts used in environmental catalysis (selective catalytic reduction (SCR) of NOx with ammonia, catalytic oxidation of CO and volatile organic compounds (VOCs), photocatalytic oxidation of VOCs, and photocatalytic CO2 reduction). Throughout the review, the impact of confinement effects on the activity, selectivity, and stability of catalysts is emphasised. Materials such as carbon nanotubes (CNTs), titanate nanotubes (TNTs), zeolites, mesoporous TiO2, and metal−organic frameworks (MOFs) are common confined hosts. In the NH3‐SCR reaction, confined catalysts, which are non‐noble metals confined in titanate/carbon nanotubes catalysts, have been widely studied. The protection offered by the confined space can shield metal/metal‐oxide nanoparticles from toxic components (e. g., SO2, alkali metals, and heavy metals), while improving the activity of the catalysts. In the field of catalytic oxidation of CO and VOCs, noble metals are always confined in the host without aggregating, sintering, or poisoning and show enhanced activity. In the photocatalytic oxidation of VOCs and photocatalytic reduction of CO2, the application of confined catalysts can prolong the contact time of reactants and improve visible‐light absorption and electron transfer, leading to better catalytic performance.

With the rapid development of urbanization and industrialization, environmental pollution has become more severe. Volatile organic compounds (VOCs) could be originated from the following sources: domestic, mobile and industrial sources. As important air pollutants, VOCs could cause serious harm to the environment and human health. Therefore, removing VOCs has become a priority research direction of ecological issues. Among the many elimination methods, catalytic oxidation approaches are among the most effective and economical methods which can transform VOCs into CO2 and H2O. MnOx catalysts are among the most active catalysts, which can be further modified by different cations such as Cu2+, Co2+, Cr3+, Ni2+ and Ce4+ to form mixed oxides to improve the catalytic oxidation of VOCs activity. Moreover, MnOx can be loaded on the carrier, improving the redox and oxygen storage capacity and improving its stability and activity. This review explores the structure, preparation and oxidation state of Mn-based catalysts.

ABSTRACTA photocatalytic paint based on carbon‐doped titanium dioxide as a pigment replacement was tested for the oxidation of volatile organic compounds (VOCs) under visible‐light illumination in indoor environments. The photocatalytic paint was characterized by X‐ray photoelectron spectroscopy, scanning and transmission electron microscopy, and diffuse reflectance and transmittance spectral measurements. The effects of environmental conditions, including inlet concentration, relative humidity (RH), incident radiation flux, and residence time, on the degradation of toluene, an aromatic VOC, were investigated. At certain operating conditions, toluene degradation efficiency increased, from 38% to 61%, with the rise in the incident radiation flux from 6.86 to 42.34 W/m2, while it declined with increasing RH from 10% to 70%. A one‐directional heterogeneous model predicted these trends, highlighting the opposing effects of incident radiation flux and humidity on toluene oxidation kinetics. In binary mixtures of toluene and acetaldehyde, representing aromatic and aliphatic VOCs, respectively, the presence of acetaldehyde had a negligible effect on toluene conversion, whereas acetaldehyde degradation was significantly reduced—by 36% and 65%—when co‐fed with 3.5 and 6.5 ppmv of toluene, respectively, indicating a strong competitive effect between pollutants. This study highlights the benefit of using photocatalytic paint for indoor air decontamination and provides new insights into its performance under more realistic environmental conditions, particularly in the presence of mixed VOCs.

Glyoxal (CHOCHO) is an intermediate product of the oxidation of volatile organic compounds (VOCs) and has anthropogenic, biogenic and pyrogenic sources. It is an indicator of formation of secondary organic aerosols in the atmosphere and plays a role in the photochemical reactions of ozone in the troposphere. Additionally, at high concentrations glyoxal is harmful for humans. The lifetime of glyoxal in the atmosphere is short (a few hours) and it is removed from the atmosphere by photolysis, oxidation by OH, and deposition. Due to the different sources and short lifetime of glyoxal, its abundance in the atmosphere can vary between several parts per trillion (ppt) e.g., in remote parts of the oceans, to parts per billion (ppb) in the presence of strong sources, like biomass burning, industrial processes, fossil fuel combustion or over tropical rainforest regions.Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) instruments are capable of measuring glyoxal, but the retrieval is difficult due to its relatively weak absorption compared to other trace gases. Therefore, further improvements of current MAX-DOAS glyoxal retrievals are needed.Glyoxal was one of the target species during CINDI-3, the third semi-blind intercomparison campaign of UV-Vis DOAS instruments in Cabauw, The Netherlands. Based on the large scatter of the measurements among the participating instruments, it was identified as one of the more challenging trace gases to retrieve. A task group has been formed to develop a common and improved approach to retrieve glyoxal, using the data collected by several instruments and institutes during the campaign, and applying different retrieval software. In this study, we present the initial glyoxal retrievals from the campaign, and outline the development of improved retrieval settings, which we want to propose as a new standard for future glyoxal measurements.

Three‐dimensional modeling studies have been performed to investigate the short‐timescale photochemical generation of carbon monoxide (CO) on a regional basis in two very distinct areas of the United States: New England (mixed biogenic and anthropogenic influence) and the South Coast Air Basin (SoCAB, dominated by anthropogenic influence) of California. For the New England study, the Caltech Atmospheric Chemistry Mechanism (CACM) was incorporated into the Community Multiscale Air Quality model and applied to 3–4 August 2004. For the SoCAB, CACM was applied to 8–9 September 1993 using the California Institute of Technology three‐dimensional regional atmospheric model. Results indicate that in each location, on a relative scale, the photochemical generation of CO is responsible for less than 10% (3–9% for the eastern United States and approximately 1% in the SoCAB) of the total simulated mixing ratio for the respective dates based on domain‐wide, calendar‐based 24‐hour averages. In the eastern United States, simulations indicate that isoprene is the major volatile organic compound (VOC) source for CO and that VOC oxidation can lead to up to approximately 20 parts per billion by volume (ppb) of CO in New England. In the SoCAB, anthropogenic short‐chain alkenes lead to the greatest amount of photochemical CO generation; VOC oxidation in its entirety can lead to up to approximately 45 ppb of photochemically generated CO in the SoCAB. Therefore studies on the regional scale that use CO as a marker of primary combustion emissions may overestimate the importance of primary emissions, depending on location and time.

Catalytic oxidation of toluene and m-xylene by activated carbon fiber impregnated with transition metals