Benzene Concentrations Research Articles

Identify Primary Air Pollution Sources of BTEX by Using Positive Matrix Factorization (PMF): A Case Study of Ho Chi Minh City, Vietnam.

Ho Chi Minh City (HCMC) is one of the main socioeconomic and financial centers of Vietnam. The city also faces serious air pollution. However, the city polluted with benzene, toluene, ethylbenzene, and xylene (BTEX) has rarely been studied. We used positive matrix factorization (PMF) to analyze BTEX concentrations measured at two sampling locations to identify the main sources of BTEX in HCMC. The locations represented residential area (i.e., To Hien Thanh) and industrial area (i.e., Tan Binh Industrial Park). At the To Hien Thanh location, the average concentrations of benzene, ethylbenzene, toluene, and xylene were 6.9, 14.4, 4.9, and 12.7µg/m3, respectively. At the Tan Binh location, the average concentrations of benzene, ethylbenzene, toluene, and xylene were 9.8, 22.6, 2.4, and 9.2µg/m3, respectively. The results showed that PMF was a reliable model for source apportionment in HCMC. Traffic activities were the main sources of BTEX. Besides, industrial activities also contributed to BTEX emissions, especially the location near the industrial park. The majority of BTEXs at the To Hien Thanh sampling site come from traffic sources accounting for 56.2%. Activities from traffic and photochemical reactions (42.7%) and industrial sources (40.5%) were the main sources affecting BTEX emissions at the sampling site of Tan Binh Industrial Park. This study can be used as a reference for mitigation solutions to reduce the BTEX emission in HCMC.

Occurrence of and dermal exposure to benzene, toluene and styrene in sunscreen products marketed in the United States

Occurrence of volatile organic compounds (VOCs) such as benzene in personal care products is a topic of public health concern. Sunscreen products are extensively used to protect skin and hair from UV radiation from sun light. Nevertheless, little is known about exposure doses and risks of VOCs present in sunscreens. In this study, we determined the concentrations of and exposure to three VOCs, namely benzene, toluene and styrene, in 50 sunscreen products marketed in the United States. Benzene, toluene and styrene were found in 80 %, 92 % and 58 %, respectively, of the samples analyzed at mean concentrations of 45.8 ng/g (range: 0.007–862), 89.0 ng/g (range: 0.006–470) and 161 ng/g (range: 0.006–1650), respectively. The mean dermal exposure doses (DEDs) to benzene, toluene and styrene of children/teenagers were 68.3, 133 and 441 ng/kg-bw/d, respectively, whereas those of adults were 48.7, 94.6 and 171 ng/kg-bw/d, respectively. The lifetime cancer risk from benzene concentrations present in 22 sunscreen products (44 % of the samples) for children/teenagers and 19 sunscreen products (38 %) for adults, exceeded the acceptable benchmark risk level (1.0 × 10−6). This is the first study to comprehensively assess the concentrations of and risks to benzene, toluene and styrene present in sunscreen products.

Fractal behaviour of benzene concentration near refinery, traffic junctions and residential locations in India

Due to its carcinogenicity, benzene, a hazardous chemical created both naturally and via human activity, poses a major threat to human health. Even at low concentrations, short-term exposure can cause severe health issues. The study of temporal variations in the time series of benzene concentration can be useful to policymakers in air quality assessment and management. Fractal behaviour in benzene concentration at various locations with different land-use characteristics and prevalent sources is studied using detrended fluctuation analysis (DFA) and multifractal detrended fluctuation analysis (MF-DFA). The temporal characteristics of benzene concentration have not been studied earlier and it is of interest to assess the influence of land-use characteristics and dominant sources on the temporal intrinsic properties of the time series. 24 h benzene concentration time series during 2019–2021 at 10 locations is therefore selected for the study. Preliminary analysis using autocorrelation function, power spectral analysis and DFA suggested the existence of long-range correlations in benzene time series. Multifractal analysis pointed towards the dominance of small fluctuations that frequently occur in the benzene concentration time series at most of the locations. The analysis of the origin of multifractality revealed that removing the linear temporal correlations weakens the multifractality and broad probability density function also partly explains the multifractality in benzene time series. The knowledge of the fractality of the time series is useful in developing the prediction model which can account for the linear temporal correlations along with the multifractality to predict the APCs. The results can aid in improving air quality evaluations and the perceptive of the mechanisms regulating the evolution of air pollution time series.

55 Validation of Diffusive Sampling Methods for Accurate Low-Dose Benzene Exposure Assessment, Inhalation Monitoring

Abstract The present research project is aimed at providing an accurate low-dose benzene exposure assessment method, by validating diffusive monitoring techniques for benzene personal exposure measurements at workplaces where low benzene concentrations are expected. The experiments have been conducted following the EN 838:2010 standard in the range of 16 to 320 µg/m3 (0.005 to 0.1 ppm). The study is part of the Concawe project on “accurate low-dose benzene exposure assessment, dose-specific metabolism and potential early markers” aiming at developing a methodology to monitor benzene exposures at low levels in environments typical of the petroleum industry. Diffusive sampling offers a reliable alternative to pumped sampling methods, intrinsic safety in potentially explosive atmospheres, lightness and ease of use. The tested diffusive sampler is radiello™, two alternative configurations of the sampler can be used: RAD130, packed with activated charcoal, suitable for solvent desorption and analysis by HRGC-FID, and RAD145, packed with graphitised charcoal, suitable for thermal desorption and analysis by HRGC-MS. For both configurations the sampler performances have fulfilled all requisites of the EN 838:2010 standard, in particular: bias due to the selection of a non-ideal sorbent is lower than 10% (no significant back diffusion of benzene due to concentration change in the atmosphere); bias due to storage of samples for up to 2 months is lower than 10%; nominal uptake rate for benzene on RAD130 is 74.6 ml/min and on RAD145 is 32.3 ml/min; expanded uncertainty of the sampling and analytical method is 20.2% on RAD130 and 26.1% on RAD145.

Spray and explosion characteristics of methanol and methanol-benzene blends near azeotrope formation: Effects of temperature, concentration, and benzene content

The explosion hazard of flammable liquids leaking to form spray in storage and transportation at ambient temperature has not been systematically investigated. This work presents new results from experimental investigations of the atomization and explosion characteristics of methanol, and methanol-benzene blends forming near the azeotrope under different initial conditions (initial temperature (298.15–318.15 K), methanol concentration (198–514.8 g/m3) and benzene content (41–81%)) in a 20-L spherical vessel. The empirical formulas for Sauter Mean Diameter (SMD) of the droplets and the maximum explosion pressure with respect to the initial temperature and methanol concentration were obtained from the quantitative analysis. Compared to the explosion hazard of pure methanol and methanol-benzene blends spray, the results showed that the maximum rate of pressure rise and maximum explosion temperature of methanol-benzene blends were relatively low. Furthermore, the effect of carbon soot formation on the explosion hazard during explosion development was analyzed.

Combination of torrefaction and catalytic fast pyrolysis for aromatic hydrocarbon production from herbaceous medicine waste

The combination of torrefaction pretreatment and catalytic pyrolysis of herbaceous medicine waste (HMW) was performed. The effects of torrefaction, pyrolysis temperature, SiO2/Al2O3 atomic ratio (SAR) and catalyst-to-feedstock (C/F) ratio on the distribution of aromatic hydrocarbons (AHs) was investigated. The formation of coke and its effects on the catalytic performance of the catalyst were evaluated. The results demonstrated that zeolite can effectively convert the torrefied HMW into AHs. The liquid products were dominated by monocyclic aromatic hydrocarbons (MAHs), in which toluene and xylene were formed preferentially over other aromatics. The total content of benzene, toluene, ethylbenzene, p-xylene, and naphthalene (BTEXN) reached 49.23–76.31%. Temperature, SAR and C/F ratio exhibit a greater influence on AHs formation than the torrefaction agents. A higher pyrolysis temperature and C/F ratio can inhibit coke formation, while higher SAR is beneficial to coke formation. The catalyst with a lower SAR yield more AHs and less coke. Coke was initially formed on the surface of the catalyst at low temperature, but it was more likely to form in the pores of the catalyst at high temperatures. The results show that the combination of torrefaction and catalytic pyrolysis is a potential approach for converting HMW into valuable bio-oils.

Level of BTEX in the Areas of Domestic Waste Incinerators in Northern Vietnam: A Comprehensive Assessment of Contamination, Composition and Human Health Risk.

The trend of the treatment of solid domestic waste by the domestic waste incinerator system is an option to improve waste management and to reduce the negative impacts on the environment and human health. Benzene, toluene, ethylbenzene, and xylenes (o-, m- and p-) (BTEX) are toxic chemical environmental contaminants that are released from different sources such as the domestic waste incinerator system. To determine the concentration of BTEX in the ambient air from these incinerator areas, the research team conducted four sampling campaigns in April, June, September, and November 2021, with a total of 80 samples collected. Concentrations of benzene, toluene, (m,p)-xylenes, o- xylenes and ethylbenzene ranged from 4.53 to 36.75µg/m3, from 16.29µg/m3 to 125.36µg/m3, from 2.82µg/m3 to 31.45µg/m3, from 1.42µg/m3 to 25.61µg/m3, from 1.32µg/m3 to 10.79µg/m3, respectively. As a result of the risk assessment, it was determined that the incinerator's exhaust gas caused secondary environmental damage, impacting the health of not only workers but also people living in nearby communities. On that basis, the article recommends applying a number of management measures to minimize the negative impacts of the operation of the solid waste incinerator on the environment and the health of the workers operating the incinerator.

Study of a light hydrocarbon fraction spill migration that occurred in an area of the Mexican southeast using computational fluid dynamics

The present work aimed to study, predict and understand benzene migration that occurred during an industrial spill using numerical simulation by computational fluid dynamics. Advection, diffusion and adsorption were the main mechanisms considered that governed the spill incident. The incident occurred due to a fracture under a fuel oil storage tank. The tank was located on a hill 18m high, and the initial value of benzene concentration (soil saturation) was 60ppm. When the spill was discovered, samples in the affected zone were taken using an experimental design. Many samples showed a greater concentration of benzene than allowed by Mexican Official Standards (MOSs) (15ppm). The concentrations found 100m away from the spill were around 60 to 15ppm. Due to the spill being under the tank, it was difficult to discover. The numerical simulation provided an estimate that the spill started around 2years ago. The type of soil in the afflicted zone is rocky, and, consequently, it is difficult to estimate how long it will take to reach the concentration allowed by the MOSs, but the numerical simulation predicts that this concentration will be reached in 14years. Experimental values of the spill contaminant concentration were statistically similar to the CFD estimated data (p < 0.05).

Smoking is associated with elevated blood level of volatile organic compounds: a population-based analysis of NHANES 2017–2018

BackgroundThe study aims to explore the association between cigarette smoking with blood exposure to volatile organic compounds using population data from the National Health and Nutrition Examination Survey (NHANES) 2017–2018.MethodsBased on the data of NHANES 2017–2018, we identified 1117 participants aged 18 to 65 years, who had complete VOCs testing data and filled out the Smoking-Cigarette Use and Volatile Toxicant questionnaires. The participants consisted of 214 dual-smoking persons, 41 E-cigarette smokers, 293 combustible-cigarette smokers and 569 non-smokers. We used One-way ANOVA and Welch’s ANOVA to compare differences of VOCs concentration among 4 groups and multivariable regression model to confirm the factors associated with VOCs concentration.ResultsIn dual-smoking and combustible-cigarette smokers, blood concentration of 2,5-Dimethylfuran, Benzene, Benzonitrile, Furan, Isobutyronitrile were higher than non-smokers. When compared with people who never smoked, E-cigarette smokers had similar blood concentrations of VOCs. Blood concentrations of Benzene, Furan, and Isobutyronitrile were significant higher in combustible-cigarette smokers than in E-cigarette smokers. In the multivariable regression model, dual-smoking and combustible-cigarette smoking were associated with elevated blood concentrations of several VOCs except 1,4-Dichlorobenzene, while E-cigarette smoking was only associated with elevated 2,5-Dimethylfuran concentration.ConclusionsSmoking, mainly dual-smoking and combustible-cigarette smoking, is associated with elevated blood concentration of VOCs, while the effect is weak in E-cigarette smoking.

Characterization of lymphocyte subsets and intestinal short-chain fatty acids in benzene-induced immunosuppressive mice.

Exposure to benzene causes immunosuppression, but the mechanism has not been clarified. In this study, mice were subcutaneously injected with different concentrations (0, 6, 30 and 150 mg/kg) of benzene for four weeks. The lymphocytes of bone marrow (BM), spleen and peripheral blood (PB) and the level of short-chain fatty acids (SCFAs) in mouse intestine were measured. The results showed that benzene exposure led to a reduction in CD3+ and CD8+ lymphocytes in mouse BM, spleen and PB, and CD4+ lymphocytes were increased in mouse spleen but decreased in mouse BM and PB after 150 mg/kg benzene exposure. In addition, Pro-B lymphocytes were reduced in mouse BM in the 6 mg/kg group. Besides, the levels of IgA, IgG, IgM, IL-2, IL-4, IL-6, IL-17a, TNF-α and IFN-γ in mouse serum were reduced after benzene exposure. Furthermore, the levels of acetic, propionic, butyric and hexanoic acid were reduced in mouse intestine, and the AKT-mTOR signaling pathway was activated in mouse BM cells after benzene exposure. Our results demonstrate that benzene induced immunosuppression in mice, and the B lymphocytes in BM are more sensible to benzene-induced toxicity. The reduction in mouse intestinal SCFAs as well as the activation of AKT-mTOR signaling may be related to the occurrence of benzene immunosuppression. Our study provides new insight for further mechanistic research on benzene-induced immunotoxicity.

Achieving Simplified and Tunable Flexibility in Carborane-Based Emitters for Quantitative Vapochromic VOC Sensing.

Photoluminescence (PL) sensing of volatile organic compounds (VOCs) represents a convenient and economic detection method toward air pollutants. However, tetraphenylethylene (TPE)-based and recent carborane (Cb)-based sensors retained multiple sites that are responsive to VOC stimulation, making quantitative PL sensing rather challenging. Rendering the simplified and tunable flexibility in the PL sensors is key to achieve the quantitative target. In this work, we proposed a dimeric model of Cb-based emitters to deal with flexibility. Three emissive dibenzothiophene (DBT)-alkynylated carboranes (Cb-1/2/3) were designed and synthesized. Among them, Cb-3 contributed green and green-yellow emission in the crystals, as well as yellow and orange emission in the VOC-incorporated films, together unfolding its vapochromic properties. Crystallographic studies revealed that Cb-3 molecules were invariably dimerized in an interlocked fashion and the redshift in PL was caused by the successive through-space conjugation of DBT moieties. Theoretical calculations verified the thermodynamics stability of Cb-3 dimers and suggested that DBT could individually rotate different angles under the simulation of VOCs. Based on the above findings, we introduced DBT-alkynylated carboranes to detect the VOCs and established linear relationships between the photon energy at the PL maxima and the concentrations of benzene and tetrahydrofuran (THF) vapors. Aside from the successful implementation of quantitative vapochromic sensing, the fast response (6 s) and recovery (3∼5 s), as well as the good reusability, were also evidenced in the sensing of THF vapors.

Photo-Activated Direct Catalytic Oxidation of Gaseous Benzene with a Cu-Connected Serial Heterojunction Array of Co3 O4 /Cux O/Foam Cu Assembled via Layer upon Layer Oxidation.

The foam copper (FCu) has been first used as a promising supporting material to prepare a photo-activated catalyst of Co3 O4 /Cux O/FCu, in which the fine Co3 O4 particles are inlayed on the Cux O nanowires to form a Z-type heterojunction array connected by substrate Cu. The prepared samples have been used as a photo-activated catalyst to directly decompose gaseous benzene and the optimized Co3 O4 /Cux O/FCu demonstrates a 99.5% removal efficiency and 100% mineralizing rate within 15min in benzene concentration range from 350 to 4000ppm under simulate solar light irradiation. To track the reactive mechanism, a series of MOx /Cux O/FCu (M = Mn, Fe, Co, Ni, Cu, Zn) is prepared and a novel photo-activated direct catalytic oxidation route is proposed based on the comparative investigation of material properties. Moreover, the approach grew in situ via layer upon layer oxidation on FCu dedicates to the extra lasting reusability and the easy accessibility in the diverse situations. This work provides a novel strategy for the preparation of Cu connected series multidimensional heterojunction array and a promising application for the quick abatement of the high-leveled concentration gaseous benzene and its derivatives from the industrial discharged flow or the accident scene's leakage.

Sampling of Gas-Phase Intermediate Pyrolytic Species at Various Temperatures and Residence Times during Pyrolysis of Methane, Ethane, and Butane in a High-Temperature Flow Reactor

Air pollution in many major cities is endangering public health and is causing deterioration of the environment. Particulate emissions (PM) contribute to air pollution as they carry toxic polyaromatic hydrocarbons (PAHs) on their surface. Abatement of PM requires continuous strict emission regulation and, in parallel, the development of fuels with reduced formation of PM. Key processes in the formation of PM are the decomposition of hydrocarbon fuels and the synthesis of potential precursors that lead to the formation of benzene rings and thereafter growth to PAHs and eventually PM. Methane, ethane and butane are important components of natural gas and liquefied petroleum gas, and are also widely used in transportation, industrial processes and power generation. This paper reports on a quantitative investigation of the intermediate gaseous species present during pyrolysis of methane, ethane and butane in a laminar flow reactor. The investigation aimed to further the understanding of the decomposition process of these fuels and the subsequent formation of aromatic rings. The pyrolysis of methane, ethane and butane were carried out in a tube reactor under laminar flow conditions and within a temperature range of 869–1213 °C. The fuels were premixed in nitrogen carrier gas at a fixed carbon atom concentration of 10,000 ppm, and were pyrolysed under oxygen-free conditions. Intermediate gaseous species were collected from within the tube reactor at different residence times using a specially designed high-temperature ceramic sampling probe with arrangements to quench and freeze the reactions at entry to the probe. Identification and quantification of intermediate species were carried out using a gas chromatography-flame ionization detector (GC-FID). During methane pyrolysis, it was observed that as the concentration of acetylene increased, the concentration of benzene also increased, suggesting that the benzene ring is formed via the cyclo trimerisation of acetylene. With all three fuels, all intermediate species disappeared at higher temperatures and residence times, suggesting that those species converted into species higher than benzene, for example naphthalene. It was observed that increasing carbon chain length lowered the temperature at which fuel breakdown occurred and also affected the relative abundance of intermediate species.

The Impacts and Analysis of Individual and Social Risks of the Stochastic Emission of Benzene from Floating-Roof Tanks Using Response Surface Analysis and MPACT Model.

In the present study, the researchers used an integrated approach composed of response surface analysis (RSM) and MPACT model to predict fatality rates caused by benzene emitted from floating-roof tanks. RSM scenarios were configured in Expert Design (version 7.0) software using the central composite design (CCD) method and five variables of wind speed, relative humidity, atmospheric temperature, failure diameter, and emission height were considered. Continuous Pasquill-Gifford Gaussian model was used to estimate the results of the RSM scenarios. The response values were considered for exposure concentrations above 50ppm (slight damages), 150ppm (moderate damage), and 1000ppm (high damage). The analysis of individual and social risks for each scenario was done using the MPACT model in SAFETI program (version 8.22) by providing two variables of population characteristics and the frequency of tank wall failure. The results showed that atmospheric temperature, wind speed, failure diameter, and emission height have positive effects on the dispersion of the cloud of toxic benzene vapor with a concentration of 1000ppm. Intolerable individual risk distances were estimated to be lower for indoor environments than for outdoor. Maximum distances of intolerable individual risks for the worst-case scenarios were estimated up to 2500m from the emission point, which resulted from exposure to a concentration of 1000-ppm benzene. Results regarding the estimation of social risks showed that over 1600 fatalities should be expected under the worst-case scenarios. The three factors of high temperature, low wind speed, and low emission height play a major role in the occurrence of scenarios with the highest fatalities. High wind speed and high emission height were the most important factors in most scenarios with zero fatalities rate. Generally, the findings of this study show the necessity to provide an emergency response plan in the studied industry in both autumn and winter due to low wind speed. However, the coupling of the developed statistical models based on regional meteorological conditions with the MPACT model can help researchers to design an emergency response plan to deal with leakage incidents in petrochemical industries.

Transport and removal mechanism of benzene by Tradescantia zebrina Bosse and Epipremnum aureum (Linden ex André) G.S. Bunting in air-plant-solution system.

Phytoremediation is considered an effective method for indoor air pollution control. The removal rate and mechanism of benzene in air by two plants, Tradescantia zebrina Bosse and Epipremnum aureum (Linden ex André) G. S. Bunting, were investigated through fumigation experiments under the condition of plant hydroponics culturing. Results showed that the plant removal rates increased with increase in benzene concentration in air. When the benzene concentration in air was set at 432.25-1314.75 mg·m-3, the removal rates of T. zebrina and E. aureum ranged from 23.05 ± 3.07 to 57.42 ± 8.28 mg·kg-1·h-1 FW and from 18.82 ± 3.73 to 101.58 ± 21.20 mg·kg-1·h-1 FW, respectively. The removal capacity was positively related to the transpiration rate of plants, indicating that gas exchange rate could be a key factor for the evaluation of removal capacity. There existed fast reversible transport of benzene on air-shoot interface and root-solution interface. After shoot exposure to benzene for 1 h, downward transport was the dominant mechanism in the removal of benzene in air by T. zebrina, while in vivo fixation was the dominant mechanism at exposure time of 3 and 8 h. Within 1-8 h of shoot exposure time, in vivo fixation capacity was always the key factor affecting the removal rate of benzene in the air by E. aureum. Contribution ratio of in vivo fixation in the total benzene removal rate increased from 6.29 to 92.29% for T. zebrina and from 73.22 to 98.42% for E. aureum in the experimental conditions. Reactive oxygen species (ROS) burst induced by benzene exposure was responsible for the contribution ratio change of different mechanisms in the total removal rate, which also was verified by the change of activities of antioxidant enzymes (CAT, POD, and SOD). Transpiration rate and antioxidant enzyme activity could be considered parameters to evaluate the plant removal ability to benzene and to screen plants for establishment of plant-microbe combination technology.

Role of Catalyst Domain Size in the Hydrogenation of CO2 to Aromatics over ZnZrOx/ZSM-5 Catalysts

The direct conversion of carbon dioxide into aromatic compounds may provide an environmentally friendly resource for a family of chemical building blocks with high global demand─aromatic chemicals. An array of bifunctional catalysts composed of ZnZrOx for the conversion of CO2 to methanol and ZSM-5 for methanol aromatization is evaluated considering multiple operational and catalytic parameters, with a focus on the particle size of each catalyst functionality. Aromatic yields generally increase as the ZSM-5 domain size decreases for different configurations of catalyst domains─mixed powders, mixed pellets, and separate beds. However, for a physical mixture of the catalyst components prior to pelletization (mixed powder case), varying the ZSM-5 crystal size inversely impacts the particle size of ZnZrOx, leading to enlarged metal oxide domains and enhanced intermediate diffusion barriers for very small crystals of ZSM-5. Larger crystals of ZSM-5 can be employed to obtain a higher concentration of benzene, toluene, and xylene (BTX) among aromatics. Upon employing a physical mixture of the ZnZrOx/ZSM-5 catalyst with a Si/Al ratio of 300 and a ZSM-5 crystal size of 300 nm, a total aromatics selectivity of 44% at CO2 conversion of 6% was obtained at 320 °C, WHSV of 7200 mL gcatalyst–1 h–1, and H2/CO2 ratio of 3.

Pollution Characteristics and Risk Assessment of Volatile Organic Compounds in Songhua Lake, China

In order to assess the dangers to human health and the environment from Songhua Lake's volatile organic compounds (VOCs) pollution. A total of 18 VOCs were found in the water samples that were collected at 26 sampling locations in Songhua Lake utilizing the purge and trap technique and gas chromatography-mass spectrometry (GC-MS). Toluene and naphthalene had the highest detection rates among them, reaching 96.15%; trans-1,2-dichloroethylene, 1,2-dichloroethane, and isopropyl benzene had the lowest rates, only 3.85%. The maximum and average concentrations of 1,1-dichloroethane were 20.93 μg/L and 4.16 μg/L, respectively, the maximum concentration of isopropyl benzene was only 0.02 μg/L, and the average concentration was also the lowest. The spatial distribution of VOCs in Song Hua Lake was typically described as "high in the northwest and low in the southeast," with a concentration range of 0.00 to 23.21 μg/L. An examination of the current situation reveals that human activity-related ecological deterioration is the primary cause of the VOCs contamination in Songhua Lake. The results of the risk assessment revealed that there were only moderate ecological risks to aquatic organisms and that the non-carcinogenic and carcinogenic risk indices of Songhua Lake were within the safe range. Additionally, there were no non-carcinogenic or carcinogenic threats to the health of people as a whole.

Global impact of the COVID-19 lockdown on surface concentration and health risk of atmospheric benzene

Abstract. To curb the spread of the COVID-19 pandemic, many countries around the world imposed an unprecedented lockdown, producing reductions in pollutant emissions. Unfortunately, the lockdown-driven global ambient benzene changes still remain unknown. An ensemble machine-learning model coupled with chemical transport models (CTMs) was applied to estimate global high-resolution ambient benzene levels. Afterwards, the extreme gradient boosting (XGBoost) algorithm was employed to decouple the contributions of meteorology and emission reduction to ambient benzene. The change ratio (Pdew) of the deweathered benzene concentration from the pre-lockdown to lockdown period was in the order of India (−23.6 %) &gt; Europe (−21.9 %) &gt; the United States (−16.2 %) &gt; China (−15.6 %). The detrended change (P∗) of the deweathered benzene level (change ratio in 2020 − change ratio in 2019) followed the order of India (P*=-16.2 %) &gt; Europe (P∗=-13.9 %) &gt; China (P∗=-13.3 %) &gt; the United States (P∗=-6.00 %). Emission reductions derived from industrial activities and transportation were major drivers for the benzene decrease during the lockdown period. The highest decreasing ratio of ambient benzene in India might be associated with local serious benzene pollution during the business-as-usual period and restricted transportation after lockdown. Substantial decreases in atmospheric benzene levels had significant health benefits. The global average lifetime carcinogenic risk (LCR) and hazard index (HI) decreased from 4.89×10-7 and 5.90×10-3 to 4.51×10-7 and 5.40×10-3, respectively. China and India showed higher health benefits due to benzene pollution mitigation compared with other countries, highlighting the importance of benzene emission reduction.

Kinetic Aspects of Benzene Degradation over TiO2-N and Composite Fe/Bi2WO6/TiO2-N Photocatalysts under Irradiation with Visible Light

In this study, composite materials based on nanocrystalline anatase TiO2 doped with nitrogen and bismuth tungstate are synthesized using a hydrothermal method. All samples are tested in the oxidation of volatile organic compounds under visible light to find the correlations between their physicochemical characteristics and photocatalytic activity. The kinetic aspects are studied both in batch and continuous-flow reactors, using ethanol and benzene as test compounds. The Bi2WO6/TiO2-N heterostructure enhanced with Fe species efficiently utilizes visible light in the blue region and exhibits much higher activity in the degradation of ethanol vapor than pristine TiO2-N. However, an increased activity of Fe/Bi2WO6/TiO2-N can have an adverse effect in the degradation of benzene vapor. A temporary deactivation of the photocatalyst can occur at a high concentration of benzene due to the fast accumulation of non-volatile intermediates on its surface. The formed intermediates suppress the adsorption of the initial benzene and substantially increase the time required for its complete removal from the gas phase. An increase in temperature up to 140 °C makes it possible to increase the rate of the overall oxidation process, and the use of the Fe/Bi2WO6/TiO2-N composite improves the selectivity of oxidation compared to pristine TiO2-N.

Associations between the compositional patterns of blood volatile organic compounds and chronic respiratory diseases and ages at onset in NHANES 2003–2012

Backgroundand Purpose Volatile organic compounds (VOCs) pose a serious respiratory hazard. This study evaluated the relationship between the compositional patterns of blood VOCs and the risk and age at onset of chronic respiratory diseases (CRDs), including asthma, emphysema and chronic bronchitis, with the objective of preventing or delaying CRDs. MethodsParticipants from five cycles of the NHANES survey were included. Blood VOCs were clustered using k-means clustering. Differences in VOCs and age at onset between multiple groups were compared with the Kruskal‒Wallis test. Logistic regression and a generalized linear model were applied to examine the associations between different compositional patterns of blood VOCs and risk and age at onset of CRDs. Results12,386 participants were enrolled in this study. Three VOC compositional patterns were identified after clustering nine species of blood VOCs. The concentration of VOCs in pattern 2 was relatively low and stable. The concentrations of benzene, ethylbenzene, o-xylene, styrene, toluene and m-p-xylene in pattern 3 and the concentrations of 1,4-dichlorobenzene and MTBE in pattern 1 were significantly higher than those in pattern 2. After adjustment for covariates, the participants with VOC pattern 3 had an increased risk of asthma (OR = 1.23, 95% CI: 1.02, 1.49), emphysema (OR = 3.37, 95% CI: 2.24, 5.06) and chronic bronchitis (OR = 1.79, 95% CI: 1.30, 2.45). Meanwhile, VOC pattern 3 was negatively correlated with the age at onset of asthma (β = −5.61, 95% CI: 9.69, −1.52) and chronic bronchitis (β = −9.17, 95% CI: 13.96, −4.39). VOC pattern 1 was not associated with either risk or age at onset of the three CRDs after adjustment. ConclusionsChanging the compositional pattern of blood VOCs by reducing certain species of VOCs may be a new strategy to lengthen the ages at onset of CRDs and effectively prevent them.