Reactive Volatile Organic Compounds Research Articles

Quantification and source apportionment of atmospheric oxidation capacity in urban atmosphere by considering reactive chlorine species and photochemical loss of VOCs.

Atmospheric oxidation capacity (AOC) reflects the potential of the atmosphere in converting primary pollutants into secondary aerosols and ozone (O3). In this study, the AOC at an urban supersite in Wuhan, a megacity in central China, was quantified by considering the reactions of volatile organic compounds (VOCs) and carbon monoxide (CO) with atmospheric oxidants (OH, NO3, O3, and Cl). Photochemical loss of total VOCs (13.7-23.7%) during transport was accounted for by monitoring the concentration ratio of o-xylene and ethylbenzene, a VOC pair with diverse reaction rate constants with OH. AOC would be underestimated by 9.0-25.2% in the 4 seasons if being estimated from the observed VOCs instead of photochemical-loss corrected VOCs. The atmospheric oxidants were measured or indirectly estimated using well-established parameterizations. In particular, hourly reactive chlorine species were measured using an iodide-based chemical ionization mass spectrometer (I-CIMS). Cl radical concentration was calculated by assuming a steady-state between the production from reactive chlorine species and the removal by O3 and VOCs. The result showed that AOC would be underestimated by 14.5% and 1.9% in winter and spring if Cl radicals were neglected. Based on the above quantification, the composition of AOC was further apportioned to atmospheric oxidants, VOC categories, as well as the sources of VOC and CO. In winter, CNG combustion exhaust, electronics industry, and secondary formation were critical for regulating the AOC. In spring, secondary formation was the most important AOC source, followed by electronics industry and biogenic sources.

Characteristics and Source Apportionment of Ambient Volatile Organic Compounds in Shijiazhuang High-tech Industrial Development Zone in Autumn

Utilizing the online monitoring data of volatile organic compounds （VOCs） and ozone （O3） in the Shijiazhuang high-tech industrial development zone during October 2020, the pollution characteristics of VOCs were analyzed. Subsequently, ·OH estimation, secondary organic aerosol formation potential （SOAP）, and ozone formation potential （OFP） were applied to assess the chemical reactivity of VOCs. Additionally, the source apportionment was identified using the positive matrix factorization （PMF） model. The results revealed that the hourly φ[total VOCs （TVOCs）] were （11-281）×10-9, and the components were ranked by volume fraction in the following order： oxygenated volatile organic compounds （OVOCs） （60.83%）, alkanes （19.98%）, halohydrocarbons （5.64%）, aromatics （5.91%）, alkenes （4.83%）, and alkynes （2.48%）. Although the VOC concentration levels posed negligible non-carcinogenic risks to human health, benzene and ethylbenzene presented carcinogenic risks. The m/p-xylene to ethylbenzene ratio （X/E） varied from 2.5 to 3.4, indicating short-range transport of fresh air masses. Based on the X/E value, the ·OH concentration was 1.75×106 molecule·cm-3, and the ·OH exposure from 07：00 to 14：00 was calculated as 3.77×1010 molecule·s·cm-3. Aromatics played a dominant role in SOA, with a contribution rate as high as 93.35%, while alkenes dominated O3 formation, with the OFP contribution rate reaching up to 46.79%. By applying the PMF model, five major VOC sources were identified, including industrial sources （37.20%）, process flow and solvent use （33.80%）, vehicle and oil/gas evaporation sources （15.47%）, combustion sources （8.03%）, and plant emissions （5.50%）. Industrial and process emissions emerged as the primary contributors to VOCs in the ambient air of the high-tech zone, necessitating targeted control measures within this region.

Engineering of lattice defects in supported Cu-Mn-Ce composite oxide catalysts through ultra-low Pd doping and plasma treatment for catalytic oxidation of hexane.

Despite the low cost of supported non-precious metal catalysts, their catalytic activity is significantly lower than that of precious metal catalysts in the catalytic oxidation reaction of volatile organic compounds (VOCs). In order to enhance the catalytic activity of supported non-precious metal catalysts, we introduced an ultra-low loading of palladium into the existing catalytic system and employed a plasma preparation process instead of the conventional impregnation method. The approach significantly improves the catalytic activity of the active sites on the catalyst. The results indicate that, compared to the supported Pd and CuMnCeOx catalysts prepared by conventional impregnation method, the Pd/CuMnCeOx/SiO2-P catalysts prepared via plasma exhibit a higher proportion of lattice defects (oxygen vacancies). Furthermore, the doping of the ultra-low Pd could facilitate the formation of additional lattice defects in the composite oxide. As a result, it can improve the content of surface active oxygen and enhance the adsorptive strength of hexane on the surface of the catalyst. The Pd/CuMnCeOx/SiO2-P catalysts exhibit high catalytic activity and stability in the catalytic oxidation of n-hexane. This work promotes the potential application in the preparation of catalyst with ultra-low precious metal loading.

Review of source analyses of ambient volatile organic compounds considering reactive losses: methods of reducing loss effects, impacts of losses, and sources

Abstract. Chemical losses of ambient reactive volatile organic compounds (VOCs) is a long-term issue yet to be resolved in VOC source apportionments. These losses substantially reduce the concentrations of highly reactive species in the apportioned factor profiles and result in the underestimation of source contributions. This review assesses the common methods and existing issues in ways to reduce losses and loss impacts in source analyses and suggests research directions for improved VOC source apportionments. Positive matrix factorization (PMF) is now the main VOC source analysis method compared to other mathematical models. The issue in using any apportionment tool is the processing of the data to be analyzed to reduce the impacts of reactive losses. Estimating the initial concentrations of ambient VOCs based on photochemical age has become the primary approach to reduce reactive loss effects in PMF, except for selecting low-reactivity species or nighttime data into the analysis. Currently, the initial concentration method only considers daytime reactions with hydroxyl (⚫OH) radicals. However, the ⚫OH rate constants vary with temperature, and that has not been considered. Losses from reactions with O3 and NO3 radicals, especially for alkene species, remain to be included. Thus, the accuracy of the photochemical age estimation is uncertain. Beyond developing accurate quantitative approaches for reactive losses, source analyses methods for the consumed VOCs and the accurate quantification of different source contributions to O3 and secondary organic aerosols are important additional directions for future research.

Characterization and source apportionment of ambient VOC concentrations: Assessing ozone formation potential in the Barnett shale oil and gas region

Atmospheric concentration and distribution of volatile organic compounds (VOC) are influenced by localized emissions and the fate and transport of secondary products formed through photochemical reactions. This study identifies the sources of VOC and its contribution to ozone formation in the Barnett Shale region, specifically in Denton, Texas, during the ozone seasons of 2015 through 2022. A total of 31 critical ozone precursor VOC compounds were observed at this site with an average total VOC concentration of 146 ppb-C, with n-alkanes from extensive oil and gas activities in the area contributing to 96.64% of the total VOC. Source apportionment using dispersion normalized positive matrix factorization (DN-PMF) identified eight VOC sources, with natural gas emissions (72%) being the dominant source followed by a combined source of natural gas combustion and aviation emissions (8.3%). Ozone formation potential (OFP) by VOC species was calculated using the propylene-equivalent concentration (propy-equiv) method. OFP calculated for all the apportioned sources highlighted that natural gas sources contributed significantly to the ozone formation in this region besides isoprene from biogenic sources and reactive alkenes from urban and industrial activities. This study underscores the critical role of slow-reacting n-alkanes along with other highly reactive VOC from urban and industrial sources influencing ambient air quality and it identifies strategies for mitigating ground-level ozone in urban areas affected by oil and gas extraction and production.

Human health impacts and indoor chemical reactions of VOCs from cleaning products and occupants

Occupants and indoor activities are sources of volatile organic compounds (VOCs). We propose a framework to simulate the pollutant pathway using the INCA-Indoor© model and VOC emission rates to derive dynamic concentrations, and the USEtox model to evaluate health impacts in DALYs (Disability-Adjusted Life Years). The applicability of the framework is tested on a case study, and the effect of indoor chemical reactions on health impacts is assessed. In this case study, health impacts were of 0.3 μDALY/day without and 0.4 μDALY/day (13 s/day) with indoor air chemistry (+28 %) out of which 12 % were linked to occupant breath and skin emissions. Cleaning activities led to the highest impacts without chemical reactions (terpinolene, responsible for 0.14 μDALY/day), but indoor air chemistry led to high impacts linked to formaldehyde formation (0.18 μDALY/day). These reactions led to the formation of more formaldehyde, hence leading to 20% more impacts, in summer than in winter. Occupants’ contribution to CO2 concentrations exceeded recommended limits under the given occupancy and ventilation scenario. Secondary organic aerosol (SOA) formation affected indoor particulate matter mass concentrations by up to a factor 1.2 and their number concentrations by up to a factor 25,000 in the presence of VOC emissions. Results of this study indicate that chemical reactions and SOA formation are important factors to consider in indoor air quality impact assessment. A larger number of activities and scenarios can be tested to improve the robustness of the conclusions, since, under different scenarios (for e.g. activities with lower emission rates) and with more complete toxicity data, these conclusions are likely to change.

Preparation of Mesoporous Analcime/Sodalite Composite from Natural Jordanian Kaolin

In this work, a meso-macroporous analcime/sodalite zeolite composite was produced by a hybrid synthesis process between a complex template method and hydrothermal treatment at 220 °C of naturally abundant kaolinitic-rich clay, using dodecyltrimethylammonium bromide as an organic soft template to enhance the mesoporous structure. The chemical and morphological properties of the developed zeolites composite were characterized using powder X-ray diffraction (PXRD), attenuated total Reflectance–Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), N2 adsorption/desorption; and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) methods were used to study the morphology, chemical composition and structure of the product. Two types of zeolite particles were obtained:(1) hollow microsphere with an attached analcime icositetrahedron of 30–40 µm in size and (2) sodalite microsphere with a ball-like morphology of 3–4 µm in size. Both N2 adsorption/desorption and surface area data confirmed the high potentiality of the produced zeolite composite to act as an excellent adsorbent to remove inorganic pollutants such as Cu, Cd, Cr, Ni, Zn, and Pb ions, organic pollutants such as dyes, phenolic compounds, and surfactants from water; and their high catalytic activity, especially in the oxidation reaction of volatile organic compounds. The catalytic activity and adsorption ability of the produced analcime/sodalite composite will be tested experimentally in future work.

Indoor Emission, Oxidation, and New Particle Formation of Personal Care Product Related Volatile Organic Compounds.

Personal care products (PCPs) contain diverse volatile organic compounds (VOCs) and routine use of PCPs indoors has important implications for indoor air quality and human chemical exposures. This chamber study deployed aerosol instrumentation and two online mass spectrometers to quantify VOC emissions from the indoor use of five fragranced PCPs and examined the formation of gas-phase oxidation products and particles upon ozone-initiated oxidation of reactive VOCs. The tested PCPs include a perfume, a roll-on deodorant, a body spray, a hair spray, and a hand lotion. Indoor use of these PCPs emitted over 200 VOCs and resulted in indoor VOC mixing ratios of several parts per million. The VOC emission factors for the PCPs varied from 2 to 964 mg g-1. We identified strong emissions of terpenes and their derivatives, which are likely used as fragrant additives in the PCPs. When using the PCPs in the presence of indoor ozone, these reactive VOCs underwent oxidation reactions to form a variety of gas-phase oxidized vapors and led to rapid new particle formation (NPF) events with particle growth rates up to ten times higher than outdoor atmospheric NPF events. The resulting ultrafine particle concentrations reach ∼34000 to ∼200000 cm-3 during the NPF events.

Using observed urban NOx sinks to constrain VOC reactivity and the ozone and radical budget in the Seoul Metropolitan Area

Abstract. Ozone (O3) is an important secondary pollutant that impacts air quality and human health. Eastern Asia has high regional O3 background due to the numerous sources and increasing and rapid industrial growth, which also impacts the Seoul Metropolitan Area (SMA). However, the SMA has also been experiencing increasing O3 driven by decreasing NOx emissions, highlighting the role of the local in situ O3 production on the SMA. Here, comprehensive gas-phase measurements collected on the NASA DC-8 during the National Institute of Environmental Research (NIER)/NASA Korea–United States Air Quality (KORUS-AQ) study are used to constrain the instantaneous O3 production rate over the SMA. The observed NOx oxidized products support the importance of non-measured peroxy nitrates (PNs) in the O3 chemistry in the SMA, as they accounted for ∼49 % of the total PNs. Using the total measured PNs (ΣPNs) and alkyl and multifunctional nitrates (ΣANs), unmeasured volatile organic compound (VOC) reactivity (R(VOC)) is constrained and found to range from 1.4–2.1 s−1. Combining the observationally constrained R(VOC) with the other measurements on the DC-8, the instantaneous net O3 production rate, which is as high as ∼10 ppbv h−1, along with the important sinks of O3 and radical chemistry, is constrained. This analysis shows that ΣPNs play an important role in both the sinks of O3 and radical chemistry. Since ΣPNs are assumed to be in a steady state, the results here highlight the role that ΣPNs play in urban environments in altering the net O3 production, but ΣPNs can potentially lead to increased net O3 production downwind due to their short lifetime (∼1 h). The results provide guidance for future measurements to identify the missing R(VOCs) and ΣPN production.

Theoretical study of the reaction of organic peroxyl radicals with alkenes and their accretion products involved in the atmospheric nucleation

Organic peroxy radicals, including alkyl peroxy radicals (RO2) and acyl peroxy radicals (RC(O)O2), are crucial intermediates in the atmospheric photochemical reactions of volatile organic compounds and directly or indirectly affect the distribution of other species (e.g., HO2 radicals, NOx, OH radicals, and alkenes). However, the atmospheric reactions of organic peroxyl radicals with alkenes (RO2 + alkene reactions) are not fully understood. The present study used theoretical calculations to investigate the reaction mechanisms of various organic peroxy radicals with different alkenes, with the aim of clarifying the influence of molecular structure on RO2 + alkene and RC(O)O2 + alkene reactions. Furthermore, we investigated the nucleation mechanisms of the subsequent oxidation products. The results show that the reaction rate constants for RC(O)O2 + alkene reactions are 1–6 orders of magnitude higher than those for RO2 + alkene reactions. The addition products formed by organic peroxy radicals with alkenes not only undergo monomolecular reactions to generate epoxides, but also participate in O2 addition to yield the accretion products ROOR’. H2SO4 molecules synergistically interact with low-volatility ROOR’ to grow clusters up to the 1–2 nm scale, and the ROOR’ molecules can form pure organic clusters larger than 1 nm, even in the absence of H2SO4 molecules. Our study provides a new perspective on the formation of accretion products in the atmosphere and their involvement in new particle formation.

Summertime Ozone Production at Carlsbad Caverns National Park, New Mexico: Influence of Oil and Natural Gas Development

AbstractSoutheastern New Mexico's Carlsbad Caverns National Park (CAVE) has increasingly experienced summertime ozone (O3) exceeding an 8‐hr average of 70 parts per billion by volume (ppbv). The park is located in the western part of the Permian oil and natural gas (O&G) basin, where production rates have increased fivefold in the last decade. We investigate O3–precursor relationships by constraining the F0AM box model to observations of nitrogen oxides (NOx = NO + NO2) and a suite of volatile organic compounds (VOCs) collected at CAVE during summer 2019. O&G‐related VOCs dominated the calculated VOC reactivity with hydroxyl radicals (OH) on days when O3 concentrations were primarily controlled by local photochemistry. Radical budget analysis showed that NOx levels were high enough to impose VOC sensitivity on O3 production in the morning hours, while subsequent NOx loss through photochemical consumption led to NOx‐sensitive conditions in the afternoon. Maximum daily O3 was responsive to both NOx and O&G‐related VOC reductions, with NOx reductions proving most effective. The model underestimated observed O3 during a 5‐day high O3 episode that was influenced by photochemically aged O&G emissions, as indicated by back‐trajectory analysis, low i‐/n‐pentane ratios, enhanced secondary VOCs, and low ratios of NOx to total reactive oxidized nitrogen (NOy). Model‐observation agreement was improved by constraining model NOx with observed NOy, which approximates NOx at the time of emission, indicating that a large fraction of O3 during this episode was formed nonlocally.

The impact of multi-decadal changes in VOC speciation on urban ozone chemistry: a case study in Birmingham, United Kingdom

Abstract. Anthropogenic non-methane volatile organic compounds (VOCs) in the United Kingdom have been substantially reduced since 1990, which is, in part, attributed to controls on evaporative and vehicle tailpipe emissions. Over time, other sources with a different speciation (for example, alcohols from solvent use and industry processes) have grown in both relative importance and, in some cases, in absolute terms. The impact of this change in speciation and the resulting photochemical reactivities of VOCs are evaluated using a photochemical box model constrained by observational data during a summertime ozone event (Birmingham, UK) and apportionment of sources based on the UK National Atmospheric Emission Inventory (NAEI) data over the period 1990–2019. Despite road transport sources representing only 3.3 % of UK VOC emissions in 2019, road transport continued being the sector with the largest influence on the local O3 production rate (P(O3)). Under case study conditions, the 96 % reduction in road transport VOC emissions that has been achieved between 1990 and 2019 has likely reduced daytime P(O3) by ∼ 1.67 ppbv h−1. Further abatement of fuel fugitive emissions was modeled to have had less impact on P(O3) reduction than abatement of VOCs from industrial processes and solvent use. The long-term trend of increased emissions of ethanol and methanol has somewhat weakened the benefits of reducing road transport emissions, increasing P(O3) by ∼ 0.19 ppbv h−1 in the case study. Abatement of VOC emissions from multiple sources has been a notable technical and policy success in the UK, but some future benefits (from an ozone perspective) of the phase-out of internal combustion engine passenger cars may be offset if domestic and commercial solvent use of VOCs continue to increase.

A better representation of VOC chemistry in WRF-Chem and its impact on ozone over Los Angeles.

The declining trend in vehicle emissions has underscored the growing significance of Volatile Organic Compound (VOC) emissions from Volatile Chemical Products (VCP). However, accurately representing VOC chemistry in simplified chemical mechanisms remains challenging due to its chemical complexity including speciation and reactivity. Previous studies have predominantly focused on VOCs from fossil fuel sources, leading to an underrepresentation of VOC chemistry from VCP sources. We developed an integrated chemical mechanism, RACM2B-VCP, that is compatible with WRF-Chem and is aimed to enhance the representation of VOC chemistry, particularly from VCP sources, within the present urban environment. Evaluation against the Air Quality System (AQS) network data demonstrates that our model configured with RACM2B-VCP reproduces both the magnitude and spatial variability of O3 as well as PM2.5 in Los Angeles. Furthermore, evaluation against comprehensive measurements of O3 and PM2.5 precursors from the Reevaluating the Chemistry of Air Pollutants in California (RECAP-CA) airborne campaign and the Southwest Urban NO x and VOC Experiment (SUNVEx) ground site and mobile laboratory campaign, confirm the model's accuracy in representing NOx and many VOCs and highlight remaining biases. Although there exists an underprediction in the total VOC reactivity of observed VOC species, our model with RACM2B-VCP exhibits good agreement for VOC markers emitted from different sectors, including biogenic, fossil fuel, and VCP sources. Through sensitivity analyses, we probe the contributions of VCP and fossil fuel emissions to total VOC reactivity and O3. Our results reveal that 52% of the VOC reactivity and 35% of the local enhancement of MDA8 O3 arise from anthropogenic VOC emissions in Los Angeles. Significantly, over 50% of this anthropogenic fraction of either VOC reactivity or O3 is attributed to VCP emissions. The RACM2B-VCP mechanism created, described, and evaluated in this work is ideally suited for accurately representing ozone for the right reasons in the present urban environment where mobile, biogenic, and VCP VOCs are all important contributors to ozone formation.

Temporal evolution of speciated volatile organic compound (VOC) emissions from solvent use sources in the Pearl River Delta Region, China (2006–2019)

Volatile organic compounds (VOCs) emitted from solvent use sources constitute an important part of ozone (O3) and secondary organic aerosols (SOA) in the Pearl River Delta (PRD) region, China. While stringent control measures targeting VOCs have been implemented in recent years, an assessment of historical trends is imperative to evaluate their effectiveness. In this study, trends of VOC emissions, compositions, and reactivity from solvent use sources in the PRD region from 2006 to 2019 were estimated using a developed methodology, which considered the improvement of manufacturing equipment and removal efficiency. Results showed that total VOC emissions from solvent use sources displayed an overall increase from 277 kt in 2006 to 400 kt in 2019 despites some fluctuations, with metal products contributing more than 20 % each year. Aromatics and oxygenated VOCs (OVOCs) accounted for over 70 % of total VOC emissions, increasing by 21 kt and 52 kt respectively. OFP and SOAFP increased by 40 % and 23 % respectively from 2006 to 2019. Specific aromatic species, including m/p-xylene, toluene, 1,2,3,5-tetramethylbenzene, o-xylene and ethylbenzene were identified as key species in both VOC emission amount and reactivity. This study aims to facilitate the understanding of VOC emission evolution from solvent use sources in the region and provide insights into the impact of enacted measures, aiding in the future development of more targeted and efficient strategies in the PRD region.

Multi-generation oxidation mechanism of M-xylene: Unexpected implications for secondary organic aerosol formation

Secondary organic aerosol (SOA) affects air quality, human health and climate. The multi-generation reactions of volatile organic compounds (VOCs) have become key process for explaining the SOA formation. M-xylene, as one of the most important VOCs in urban atmosphere, has got extensive study. However, the reaction mechanism of the first-generation products hydroperoxides (M-ROOH) and organonitrates (M-RONO2) remain unknown. In this work, the hydroxyl radicals (·OH) initiated reactions of M-ROOH and M-RONO2 were investigated by employing quantum chemical methods and kinetics modeling. The results show that new ring-retaining epoxides, a range of dialdehydes and less volatile hydroperoxides and organonitrates are formed, contributing to SOA formation. By adopting the unveiled new mechanism into the SOSAA box modeling, we found that the yield of SOA from m-xylene oxidation is up to 38%, which is comparable to the experimental value (36%). This work advances current understanding of multi-generation chemistry and elucidates the role of aromatic hydrocarbons oxidation in the formation of SOA.

A large role of missing volatile organic compound reactivity from anthropogenic emissions in ozone pollution regulation

Abstract. There are thousands of volatile organic compound (VOC) species in ambient air, while existing techniques can only detect a small part of them (approximately several hundred). The large number of unmeasured VOCs prevents us from understanding the photochemistry of ozone and aerosols in the atmosphere. The major sources and photochemical effects of these unmeasured VOCs in urban areas remain unclear. The missing VOC reactivity, which is defined as the total OH reactivity of the unmeasured VOCs, is a good indicator for constraining the photochemical effect of unmeasured VOCs. Here, we identified the dominant role of anthropogenic emission sources in the missing VOC reactivity (accounting for up to 70 %) by measuring missing VOC reactivity and tracer-based source analysis in a typical megacity in China. Omitting the missing VOC reactivity from anthropogenic emissions in model simulations will remarkably affect the diagnosis of sensitivity regimes for ozone formation, overestimating the degree of VOC-limited regimes by up to 46 %. Therefore, a thorough quantification of missing VOC reactivity from various anthropogenic emission sources is urgently needed for constraints of air quality models and the development of effective ozone control strategies.

Modulating the Electronic States of Pt Nanoparticles on Reducible Metal-Organic Frameworks for Boosting the Oxidation of Volatile Organic Compounds.

The adsorption and activation of pollutant molecules and oxygen play a critical role in the oxidation reaction of volatile organic compounds (VOCs). In this study, superior adsorption and activation ability was achieved by modulating the interaction between Pt nanoparticles (NPs) and UiO-66 (U6) through the spatial position effect. Pt@U6 exhibits excellent activity in toluene, acetone, propane, and aldehyde oxidation reactions. Spectroscopic studies, 16O2/18O2 kinetic isotopic experiments, and density functional theory (DFT) results jointly reveal that the encapsulated Pt NPs of Pt@U6 possess higher electron density and d-band center, which is conducive for the adsorption and dissociation of oxygen. The toluene oxidation reaction and DFT results indicate that Pt@U6 is more favorable to activate the C-H of toluene and the C═C of maleic anhydride, while Pt/U6 with lower electron density and d-band center exhibits a higher oxygen dissociation temperature and higher reactant activation energy barriers. This study provides a deep insight into the architecture-performance relation of Pt-based catalysts for the catalytic oxidation of VOCs.

Composition and Reactivity of Volatile Organic Compounds and the Implications for Ozone Formation in the North China Plain

Enhanced ozone (O3) pollution has emerged as a pressing environmental concern in China, particularly for densely populated megacities and major city clusters. However, volatile organic compounds (VOCs), the key precursors to O3 formation, have not been routinely measured. In this study, we characterize the spatial and temporal patterns of VOCs and examine the role of VOCs in O3 production in five cities (Dongying (DY), Rizhao (RZ), Yantai (YT), Weihai (WH), and Jinan (JN)) in the North China Plain (NCP) for two sampling periods (June and December) in 2021 through continuous field observations. Among various VOC categories, alkanes accounted for the largest proportion of VOCs in the cities. For VOCs, chemical reactivities, aromatic hydrocarbons, and alkenes were dominant contributors to O3 formation potential (OFP). Unlike inland regions, the contribution to OFP from OVOCs increased greatly at high O3 concentrations in coastal regions (especially YT). Model simulations during the O3 episode show that the net O3 production rates were 27.87, 10.24, and 10.37 ppbv/h in DY, RZ, and JN. The pathway of HO2 + NO contributed the most to O3 production in JN and RZ, while RO2 + NO was the largest contributor to O3 production in DY. The relative incremental reactivity (RIR) revealed that O3 formation in DY was the transitional regime, while it was markedly the VOC-limited regime in JN and RZ. The O3 production response is influenced by NOx concentration and has a clear daily variation pattern (the sensitivity is greater from 15:00 to 17:00). The most efficiencies in O3 reduction could be achieved by reducing NOx when the NOx concentration is low (less than 20 ppbv in this study). This study reveals the importance of ambient VOCs in O3 production over the NCP and demonstrates that a better grasp of VOC sources and profiles is critical for in-depth O3 regulation in the NCP.

Pollution Characteristics，Source Analysis，and Activity Analysis of Atmospheric VOCs During Winter and Summer Pollution in Zhengzhou

In order to study the pollution characteristics of volatile organic compounds （VOCs）， continuous monitoring of VOCs in two pollution processes was conducted in June and December 2021 in Zhengzhou. Combined with meteorological conditions， the pollution characteristics， source contributions， and reactivity of VOCs in winter and summer were compared and analyzed. The results showed that the volume fraction of atmospheric VOCs in two episodes were （27.92±12.68）×10-9 and （24.30±5.93）×10-9， respectively. The volume fraction of atmospheric VOCs in the haze pollution process in winter was larger than that in the ozone pollution process in summer. The analysis results of winter sources were as follows： industrial source （27.0%）， motor vehicle source （22.5%）， combustion source （20.1%）， solvent use source （16.3%）， and oil and gas volatilization source （14.1%）. The analysis results of summer sources were as follows： motor vehicle source （24.8%）， industrial source （24.1%）， solvent source （17.4%）， oil and gas volatilization source （14.2%）， combustion source （11.2%）， and plant source （8.4%）. The results of the smog production model showed that the proportion of days in the synergistic control zone of VOCs during the two pollution processes in summer （66.7%） was smaller than that in winter （100.0%）. The secondary reaction activity results showed that the average ·OH loss rate （L·OH） values in winter and summer were 4.12 s-1 and 4.75 s-1， respectively. The average ozone formation potential （OFP） values in summer were 108.36 μg·m-3. The olefins were dominant in the top ten species due to L·OH and OFP contributions in summer. The total SOAFP values in winter in Zhengzhou were 54.38 μg·m-3. Among the top ten species contributing to SOAFP in winter， nine were aromatic hydrocarbons.

Total oxidation of propane using titania-supported platinum nanoparticles prepared through sol-immobilization

A set of mono-metallic nanoparticles catalysts, including palladium, platinum, and gold supported on titania, were prepared via the sol-immobilization technique, and evaluated for the total oxidation of propane as a model reaction of volatile organic compounds (VOCs) oxidation, which is a wide-ranging group of organic pollutants that contribute to serious atmospheric problems. The results showed that 1 wt.% Pt/TiO2 was the most active catalyst toward CO2, as the catalyst was very active, and the complete conversion of propane was achieved with full selectivity toward CO2. The effect of the support type was investigated through the immobilization of platinum nanoparticles on CeO2 and γ-Al2O3. The results indicated that the catalytic activity follows the order 1% Pt/TiO2 > 1% Pt/CeO2 > 1% Pt/Al2O3. For the Pt/TiO2 catalyst, the influence of the calcination temperature and metal loading on the catalytic activity was investigated. There is a slight increase in the Pt particle size when raising the calcination temperature from 300 °C to 500 °C, which enhances the catalytic activity of 1% Pt/TiO2 at 500 °C. Furthermore, increasing the metal loading from 0.1 to 1 wt.% enhances the catalytic activity as a result of the increase in particle size. Different characterization techniques were utilized, including XRD, TEM, XPS, and MP-AES, to determine the structure-activity relationship, and together they indicate that the catalytic activity is influenced more by the particle size of Pt nanoparticles than by the oxidation state.