Characteristics Of VOCs Research Articles

Equilibrium adsorption of diethyl ketone on activated carbon in a supercritical CO2 environment: Measurements and thermodynamic modeling

This study focuses on the equilibrium adsorption of diethyl ketone, a VOC widely used in the printing industry, on activated carbon in a supercritical CO2 environment at pressures in the range of 10 MPa to 20 MPa and temperatures between 313 K and 353 K, which provides a wider range of equilibrium adsorption data for diethyl ketone under different pressure and temperature conditions and allows a comparative analysis with other ketone VOCs. It is found that the equilibrium adsorption of diethyl ketone on activated carbon exceeds that of methyl ethyl ketone, probably due to differences in their respective affinities for activated carbon and their different volatilities in a supercritical fluid context. The Dubinin-Astakhov model was used to interpret the data and showed an average relative deviation of approximately 3.8 % between modeled and observed values. Additional analysis of the model parameters influenced by CO2 density and VOC characteristics was performed to gain a better insight into the adsorption dynamics and to contribute to the design and improvement of the activated carbon regeneration process.

Process-specified emission factors and characteristics of VOCs from the auto-repair painting industry

Daily use of passenger vehicles leads to considerable emission of volatile organic compounds (VOCs), which are key precursors to the ground-level ozone pollution. While evaporative and tailpipe emission of VOCs from the passenger vehicles can be eliminated largely, or even completely, by electrification, VOCs emission from the use of coatings in auto-repair is unavoidable and has long been ignored. Here, we present for the first time, to the best of our knowledge, a comprehensive investigation on the emission factors and process-specified characteristics of VOCs from auto-repair painting, based on field measurements over 15 representative auto-repair workshops in the Pearl-River-Delta area, China. Replacement of solvent-borne coatings with water-borne counterparts, which was only achieved partially in the Basecoat step but not in the Putty, Primer and Clearcoat steps, could reduce the per automobile VOCs emission from 756.5 to 489.6 g and the per automobile ozone formation potential (OFP) from 2776.5 to 1666.4 g. Implementation of exhaust after-treatment led to a further reduction of the per automobile VOCs emission to 340.9 g, which is still ca. 42% higher than that from the state-of-art painting processes for the manufacture of passenger vehicles. According to the analysis of VOCs compositions, the Putty process was dominated by the emission of styrene, while Primer, Basecoat (solvent-borne) and Clearcoat steps were all characterized by the emission of n-butyl acetate and xylenes. By contrast, water-borne Basecoat step showed a prominent emission of n-amyl alcohol. Notably, for the full painting process to repair an automobile, n-butyl acetate emerged as the most abundant species in the VOCs emission, whereas xylenes contributed most significantly to the OFP. Scenario analysis suggested that reducing VOCs contents in the coatings, as well as improving the after-treatment efficiency, were highly potential solutions for effective reduction of VOCs emission from auto-repair. Our study contributes to an update of industrial inventories of VOCs emission, and may provide valuable insights for reducing VOCs emission and OFPs from the auto-repair industry.

Analysis of Volatile Compounds in Processed Cream Cheese Models for the Prediction of "Fresh Cream" Aroma Perception.

Controlling flavor perception by analyzing volatile and taste compounds is a key challenge for food industries, as flavor is the result of a complex mix of components. Machine-learning methodologies are already used to predict odor perception, but they are used to a lesser extent to predict aroma perception. The objectives of this work were, for the processed cream cheese models studied, to (1) analyze the impact of the composition and process on the sensory perception and VOC release and (2) predict "fresh cream" aroma perception from the VOC characteristics. Sixteen processed cream cheese models were produced according to a three-factor experimental design: the texturing agent type (κ-carrageenan, agar-agar) and level and the heating time. A R-A-T-A test on 59 consumers was carried out to describe the sensory perception of the cheese models. VOC release from the cheese model boli during swallowing was investigated with an in vitro masticator (Oniris device patent), followed by HS-SPME-GC-(ToF)MS analysis. Regression trees and random forests were used to predict "fresh cream" aroma perception, i.e., one of the main drivers of liking of processed cheeses, from the VOC release during swallowing. Agar-agar cheese models were perceived as having a "milk" odor and favored the release of a greater number of VOCs; κ-carrageenan samples were perceived as having a "granular" and "brittle" texture and a "salty" and "sour" taste and displayed a VOC retention capacity. Heating induced firmer cheese models and promoted Maillard VOCs responsible for "cooked" and "chemical" aroma perceptions. Octa-3,5-dien-2-one and octane-2,3-dione were the two main VOCs that contributed positively to the "fresh cream" aroma perception. Thus, regression trees and random forests are powerful statistical tools to provide a first insight into predicting the aroma of cheese models based on VOC characteristics.

Preparation of a Novel Straw-Sludge Activated Biochar and Its Adsorption Mechanisms for Removal of VOCs.

To simultaneously achieve the objectives of waste resource utilization and clean production, a novel approach involving the utilization of corn straw-sludge hybrid biochar was proposed for the adsorption of VOCs emitted from biomass power plants. This study analyzed the effect of straw-sludge biochar on the adsorption characteristics of VOCs (toluene, isopentane, and ethylene) under different preparation conditions (raw material ratio, activation temperature, and activation time). The findings revealed that the adsorption efficiency of the mixed biochar was significantly superior to that of individual corn straw biochar and sludge biochar. The adsorption of methylbenzene, isopentane, and ethylene was 78.32, 40.81, and 41.18% higher, respectively, compared to the control groups consisting of pure sludge biochar and pure corn straw biochar. Moreover, the adsorption performance of the activated biochar followed the sequence of ethylene < isopentane < methylbenzene in terms of both saturation time and adsorption capacity. The adsorption capacity of VOCs on straw biochar-sludge biochar demonstrated a consistent correlation with the boiling point and molecular weight of the adsorbate, with higher adsorption capacities observed for adsorbates with larger boiling points and molecular weights, specifically methylbenzene > isopentane > ethylene.

Characteristics Analysis of Volatile Organic Compounds Pollution in Residential Buildings in Northeast China Based on Field Measurement

A total of 8 mechanically ventilated residential buildings and 8 naturally ventilated residential buildings were selected to analyze the pollution characteristics of indoor VOCs under different ventilation modes in the severe cold area of northeast China. On typical meteorological days in each season, VOCs were detected on site, and ventilation modes were investigated by long-term online monitoring. The test results showed that the TVOC (total volatile organic compounds) concentrations varied greatly in different seasons or different functional rooms, and the TVOC concentration was the highest in winter, with a value of 0.994 mg/m3. The kitchen was the place with the most serious VOC pollution, and the TVOC concentration could reach 1.403 mg/m3. Benzene series and methylsiloxane had the highest detection rates, but the detected concentrations were low, and the average concentrations were 0.025 mg/m3 and 0.013 mg/m3 respectively. Among the VOC types with a detection rate greater than 50%, the average proportions of aldehydes, alkanes, and benzene series were 18.7%, 15.39%, and 14.38%, respectively. And their mass ratios were also high, which were 14.90%, 30.85%, and 15.70%, respectively. The annual daily average ventilation duration of mechanically ventilated residential buildings was 7.84 h longer than that of naturally ventilated residential buildings. The median TVOC concentrations of mechanically ventilated residential buildings and naturally ventilated residential buildings were 0.621 mg/m3 and 0.707 mg/m3, respectively. The fresh air system was applicable in the severe cold area of northeast China.

Evaporative emission characteristics of VOCs from in-use light-duty gasoline vehicles

VOCs are an important precursor pollutant of ozone (O3) and secondary organic aerosols (SOA). Vehicle evaporative emission is an essential source of VOCs in urban area, among which lack of localized tests of running loss process in China. This study tested all the evaporative emission processes of in-use light-duty gasoline vehicles (LDGVs), including refueling, running loss, hot soak, and 48-h diurnal breathing loss (DBL) based on the variable temperature Sealed Housing for Evaporative Determination (VT-SHED) of REU (China 4, China 5) vehicles and REC (China 6, with Onboard Refueling Vapor Recovery system) vehicles. The emission factors (EFs), species profiles, Ozone formation potential (OFP), and SOA formation potential (SOAP) of all evaporative emission processes of REU and REC vehicles were obtained. We found that the running loss emissions was less affected by the Onboard Refueling Vapor Recovery (ORVR) system, the average running loss EFs of REU and REC vehicles was 9.386 mg/km; refueling and DBL EFs of REC vehicles was 1.491 mg/L and 0.179 g/day, respectively, 99.8% and 56.0% lower than those of REU vehicles, the hot soak EFs was 0.087 g/h in average. The refueling emissions process was dominated by alkanes (REU: 77.8%; REC: 75.4%), and C4 and C5 species dominated (REU: 75.6%; REC: 67.6%). Among the running loss, hot soak and DBL emissions, alkanes, oxygenated VOCs (OVOCs) and aromatics were the dominant VOCs groups, OVOCs account for a higher proportion in REC vehicles than in REU vehicles. REC vehicles had higher proportion of C1–C3 than REU vehicles, it may be that ORVR has a better adsorption effect on species with large carbon numbers. Running loss VOCs species had a strong correlation with hot soak VOCs species. The OFP of running loss in REU and REC vehicles were 0.9–1.3 and 0.3–0.7 times higher than those of refueling and 48-h DBL, while the SOAP were 10.7–12.9 and both 1.1 times higher, respectively. These findings can provide valuable basis for emission estimation and characteristic analysis for evaporative process of LDGVs and support the development of appropriate pollution-control policy.

Characteristics of VOCs and Assessment of Emission Reduction Effect During the Epidemic Lockdown Period in Shenzhen Urban Area

To prevent disease spreading during the COVID-19 epidemic, Shenzhen adopted lockdown measures in March of 2022. This provided an opportunity to study the response of changes in anthropogenic volatile organic compounds (AVOCs) in Shenzhen to emission reduction and to evaluate the effectiveness of current emission reduction measures. This study analyzed the variety of AVOCs before, during, and after the epidemic lockdown based on the online observation data of pollutants at Lianhua Station in Shenzhen from March 7, 2022 to March 27, 2022. Additionally, the sensitivity of ozone formation and the assessment of the reduction effect of precursors was conducted by an observation based model(OBM). The results showed that:affected by regional influences and the interference of meteorological conditions, the average value of AVOCs in Shenzhen urban areas did not drop significantly during the lockdown period compared to that before the lockdown. However, the peak of AVOCs at the morning peak time under the influence of "sea and land wind" during the epidemic lockdown period dropped by 46% on average compared with that during the non-lockdown period, and the aromatic hydrocarbon component dropped the most by 59%. Additionally, under the influence of continuous easterly wind, or during the accumulation and increase of AVOCs affected by regional transmission, aromatic components also decreased by an average of 25% and 21%, respectively. During the lockdown period of the epidemic in Shenzhen, the O3 formation in urban areas was still AVOCs-limited. Increasing the emission reduction ratio of AVOCs was the most effective measure to reduce O3 in the short term. In order to ensure the effectiveness of emission reduction, it was recommended that the coordinated emission reduction ratio of AVOCs and NOx should be greater than 1:2. It was only possible to enter the downward channel of O3 if the deep emission reduction was more than 60%. This study revealed that the emission reduction of AVOCs during the morning traffic peak during the epidemic lockdown period was conducive to inhibiting the formation of O3, whereas the control of NOx would promote it. Strengthening the control of local aromatic hydrocarbon components during the regional impact process could also significantly reduce O3 production. At this stage, Shenzhen should strengthen the management and control of industrial solvents, especially to reduce the aromatic hydrocarbon components in the solvent source that have a greater impact on the generation of O3. Further, Shenzhen should continue to promote the reform of the energy structure of motor vehicles to reduce the emission of VOCs in fuel combustion.

A study on the Characteristics of HAPs in Residential areas affected by Industrial Complex using SIFT-MS

Objectives:The purpose of this study is to provide basic data so that the emission sources of industrial complexes can be effectively managed through a characteristic study of hazardous air pollutants in residential areas adjacent to the national industrial complex in Ulsan.Methods:In Yaeum-dong, a residential area near the industrial complex, SIFT-MS, which enables real-time continuous measurement, was used to identify the characteristics of VOCs and odorous substances.Results and Discussion:When looking at the concentrations by chemical substance group, aliphatic hydrocarbons accounted for a significant portion, showing different characteristics from other large cities. This indicates that the Yaeum-dong area is directly affected by the emission source of the nearby petrochemical complex. As an individual substance, ammonia showed the highest concentration among HAPs. Seasonal HAPs concentrations generally tended to be high in summer and low in winter. When examining concentrations by time of day, it showed characteristics of industrial areas affected by VOCs scattered and volatilized in national industrial complexes. In addition, it was confirmed that the characteristics of urban areas appearing in general metropolitan traffic congestion zones appeared at the same time. Compared with the results of other previous studies, in general, there was no significant difference in concentrations from the results of measurements in residential areas near petrochemical complexes. And it showed a much lower concentrations than the measured value in industrial complex. As a result of CPF analysis for estimating the source of pollutants, most HAPs showed high concentrations in the south wind direction, indicating that the measurement point was affected by the industrial complex.Conclusion:As a result of the study on the characteristics of HAPs in residential areas near the industrial complex, it can be estimated that both characteristics appear in industrial and urban areas.

Influence of marine main engine operation on characteristics of VOCs in the ambient air of the ship main cabins

目的: 了解某舰主机运行工况对舱室整体环境空气污染物浓度的影响,为舱室空气改善和作业人员健康保障提供基础支撑。方法: 利用标准Tenax TA吸附管采样-热脱附/气相色谱-质谱法测定主机转速分别在(55±5)、(75±5)、(110±5)、(145±5)、(170±5)r/min下某蒸汽动力舰船舱室环境空气中挥发性有机化合物(VOCs)的特征。结果: 不同工况下主机舱环境空气VOCs的组成和浓度基本一致,主要由正十一烷、正癸烷等脂肪烃,二甲苯、乙苯、BHT、苯等芳香烃,以及四氯乙烯、二氯甲烷等卤代烃组成。结论: 主机运行工况变化对主机舱环境空气VOCs特征的影响不显著,因此主机工况变化不影响面向主机舱环境空气VOCs控制的通风、净化系统设计和运行策略制定。.

Partitioning characteristics of indoor VOCs on impermeable surfaces covered by film-phase DnBP and DEHP

PAEs usually adsorb on indoor surfaces to form organic films, which could be more hazardous after enriching VOCs. Two typical PAEs, DnBP and DEHP, in the film phase, were chosen to explore the enrichment capacity of gaseous toluene, hexanol, and benzyl alcohol in this study. Exposed to gaseous VOCs less than 250 ppb, film-phase DnBP and DEHP could capture benzyl alcohol significantly and hexanol slightly from the air, respectively, while toluene was hardly absorbed in the films. Henry's law constants and partition coefficients (K) of VOCs in DnBP or DEHP films were derived, supposing films as dilute solution systems. The K value of VOC in DnBP or DEHP films was 1∼2 orders larger than the octanol-air partition coefficient (Koa), indicating that the surface film composition greatly influences VOC adsorption. Benzyl alcohol was the largest VOC component in surface films, agreeing well with the molecular dynamics simulation results. The hydroxyl and phenyl groups of benzyl alcohol molecules may be key factors in VOC enrichment. They form hydrogen bonds with the ester group and π-π stacking interaction with the phenyl group of DnBP or DEHP molecules, respectively. After enriching VOCs, film-phase PAEs could evoke combined exposure risks to human beings.

Important revelations of different degrees of COVID-19 lockdown on improving regional air quality: a case study of Shijiazhuang, China.

To control the spread of COVID-19, Shijiazhuang implemented two lockdowns of different magnitudes in 2020 (lockdown I) and 2021 (lockdown II). We analyzed the changes in air quality index (AQI), PM2.5, O3, and VOCs during the two lockdowns and the same period in 2019 and quantified the effects of anthropogenic sources during the lockdowns. The results show that AQI decreased by 13.2% and 32.4%, and PM2.5 concentrations decreased by 12.9% and 42.4% during lockdown I and lockdown II, respectively, due to the decrease in urban traffic mobility and industrial activity levels. However, the sudden and unreasonable emission reductions led to an increase in O3 concentrations by 160.6% and 108.4%, respectively, during the lockdown period. To explore the causes of the O3 surge, the major precursors NOx and VOCs were studied separately, and the main VOCs species affecting ozone formation during the lockdown period and the source variation of VOCs were identified, and it is important to note that the relationship between diurnal variation characteristics of VOCs and cooking became apparent during the lockdown period. These findings suggest that regional air quality can be improved by limiting production, but attention should be paid to the surge of O3 caused by unreasonable emission reductions, clarifying the control priorities for urban O3 management.

Characteristics of VOCs emitted from Arabica coffee bin powder

Characteristics of VOCs emitted from Arabica coffee bin powder

Pollution Characteristics and Source Apportionment of Atmospheric Volatile Organic Compounds in Summer in Yuncheng City

Based on the online monitoring data of VOCs, O3, and NO2 in Yuncheng City from June to August 2020, the pollution characteristics of VOCs in Yuncheng City in summer were analyzed. At the same time, the main emission sources were determined using a PMF model, and the chemical reactivity of VOCs was evaluated using the maximum incremental reactivity (MIR) method and fractional aerosol coefficients (FAC). The results showed that the urban area of Yuncheng was seriously polluted by VOCs and NO2 in the early morning and evening during summer, the peak value of VOCs daily variation occurred at 08:00 and 20:00, respectively, and was mainly affected by the morning and evening peaks in traffic. The ρ(VOCs) from June to August was 50.52 μg·m-3, and the species with the highest proportion were alkanes (39.39%) and oxygenated volatile organic compounds (OVOCs, 34.63%). Five VOCs emission sources were determined by the PMF model, of which the largest contribution was from motor vehicle exhaust emission sources (33.10%), followed by industrial emission sources (29.46%), natural gas and coal combustion sources (17.31%), solvent use sources (11.94%), and plant emission sources (8.19%). Controlling motor vehicle exhaust emission sources is the key to alleviate VOCs pollution in summer in Yuncheng City. The average ozone formation potential (OFP) of VOCs was 162.88 μg·m-3, in which OVOCs had the highest contribution rate (45.37%); acetaldehyde, propionaldehyde, ethylene, isoprene, and toluene were the key active components; and industrial emission sources were the emission sources with the highest contribution rate. The average value of secondary organic aerosol formation potential (SOAp) of VOCs was 0.40 μg·m-3, in which the contribution rate of aromatic hydrocarbons was the highest (88.00%), and the solvent use source was the emission source with the highest contribution rate.

Pollution Characteristics and Health Risk Assessment of VOCs in Jinghong

In order to investigate the seasonal variation in chemical characteristics of VOCs in the urban and suburban areas of southwest China, we used SUMMA canister sampling in Jinghong city from October 2016 to June 2017. Forty-eight VOC species concentrations were analyzed using atmospheric preconcentration gas chromatography–mass spectrometry (GC–MS), Then, regional VOC pollution characteristics, ozone formation potentials (OFP), source identity, and health risk assessments were studied. The results showed that the average concentration of total mass was 144.34 μg·m−3 in the urban area and 47.81 μg·m−3 in the suburban area. Alkanes accounted for the highest proportion of VOC groups at 38.11%, followed by olefins (36.60%) and aromatic hydrocarbons (25.28%). Propane and isoprene were the species with the highest mass concentrations in urban and suburban sampling sites. The calculation of OFP showed that the contributions of olefins and aromatic hydrocarbons were higher than those of alkanes. Through the ratio of specific species, the VOCs were mainly affected by motor vehicle exhaust emissions, fuel volatilization, vegetation emissions, and biomass combustion. Combined with the analysis of the backward trajectory model, biomass burning activities in Myanmar influenced the concentration of VOCs in Jinghong. Health risk assessments have shown that the noncarcinogenic risk and hazard index of atmospheric VOCs in Jinghong were low (less than 1). However, the value of the benzene cancer risk to the human body was higher than the safety threshold of 1 × 10−6, showing that benzene has carcinogenic risk. This study provides effective support for local governments formulating air pollution control policies.

Emission Characteristics of PM (PMtotal, PM10, PM2.5), NOx, CO and VOCs Emitted from LNG-fired Gas Turbine and Small Domestic Boiler

In recent years, natural gas is increasingly being used in the heating and power generation sectors as a clean fuel with an aim to reduce air pollution. In this study, a standard test method was used to measure air pollutants and identify emission characteristics for gas turbines and small domestic boilers, which use LNG as fuel. For gas turbines, the air pollutants were measured at 14 sites, whereas for small domestic boilers, six of them were installed in a laboratory to run tests due to limitations in on-site measuring and testing. However, the small domestic boilers were all new machines and were operated for long consecutive hours for testing, meaning that the results could vary from that of on-site boilers. The results show that gas turbines and small domestic boilers not only emit PM2.5, but also particulate matters larger than PM2.5. According to the measurements, the average concentration level of PMtotal, PM10, and PM2.5 generated from gas turbines are 51.8, 38.5, and 28.1 µg/m3 (@O2 15%), respectively. Those generated from small domestic boilers were 31.3, 26.2, and 20.0 µg/m3 (@O2 4%), respectively. The NOx concentration levels complied with the emission limits. Especially where a NOx control device was in place, both the NOx and CO concentration levels were relatively low. However, the NOx and CO concentration levels were generated from small domestic boilers were relatively high, since the emission limits were not applied. VOCs were measured at 10 facilities where 28 samples were collected. The compounds that were identified were Aromatics, Oxygenated VOCs, Alkanes, in that order, which were consistent across the samples. Aromatics consisted mostly of toluene, o,m,p-xylenes, benzene, and ethylbenzene. Among oxygenated VOCs, ethyl acetate, vinyl acetate, and isopropyl alcohol, etc. were identified. In other words, gas turbines generated a wider range and higher concentration levels of VOCs compared to small domestic boilers. The emission factors of gas turbines and small domestic boilers were derived from the measurements, and then compared with the standard emission factors of other countries (NAER, U.S. EPA AP-42, EMEP/EEA). PM emission factors calculated in this study were lower than that of existing emission factors and the calculated NOx emission factors (uncontrolled) for the small boilers were also lower. The CO emission factor for gas turbines was lower than that of existing emission factors, but higher for the small domestic boilers. Emission factors of benzene, toluene, and xylenes, which are hazardous air pollutants, were lower than those of U.S. EPA AP-42.

The Characteristics of Heavy Ozone Pollution Episodes and Identification of the Primary Driving Factors Using a Generalized Additive Model (GAM) in an Industrial Megacity of Northern China

Tropospheric ozone is the only normal pollutant with a continuously increasing annual average concentration worldwide. In this study, data were monitored at the Nankai University Air Quality Research Supersite (NKAQRS) (38.99° N, 117.33° E) between 1 April, and 31 August from 2018 to 2020, 33 O3 episodes from 2018 to 2020 were analyzed to reveal the characteristics of O3, VOCs and OFP during O3 episodes and to evaluate the driving factors. The O3 episodes showed a decreasing trend in terms of pollution frequency, days, heavy pollution duration and peak concentration. Ethane, acetylene, cyclopentane, and methylcyclopentane were the major types in 2020, while 1-hexene was the main component in 2019. The main ozone-contributing species in 2020 were propene cyclopentane methylcyclopentane and ethylene. Alkenes were important contributors to ozone formation. Using generalized additive models (GAMs), the explanatory variables in the study are divided into environmental and meteorological factors, and 16 impact factors are selected as explanatory variables. We found that the influence of these meteorological factors on O3 pollution was nonlinear and impacted by the interaction between variables. O3 episodes were mainly driven by meteorological and precursor (NO) factors in 2018, while meteorological conditions (T), followed by precursor (NO2) were the driving factors in 2019 and 2020, suggesting that O3 episodes were mainly driven by meteorological conditions.

Emission Characteristics and Environment Impacts of VOCs from Typical Rubber Manufacture

The emission characteristics of VOCs from three typical rubber manufacture industries were studied by GC-MS/FID. Maximum incremental reactivity(MIR) and fractional aerosol coefficient(FAC) were employed to evaluate the ozone formation potential(OFP) and secondary organic aerosol(SOA) formation potential. The results show that the VOC types emitted from the manufacturing of rubber products mainly include alkanes, ketones, aldehydes, alcohols, and benzene series. For traditional rubber products manufactured through rubber mixing and vulcanization, the main pollutants are ketones and alcohols, whereas for production processes involving gluing and painting, the main pollutants belong to the benzene series. In terms of ozone impact, the traditional processes contribute to ozone formation mainly through oxygenated hydrocarbons. In industries that utilize adhesives and paints, the extensive use of these organic solvents lead to a significantly higher contribution of the benzene series than other VOC species to ozone formation; the benzene series account for 82.9% of the total contribution. In terms of SOA impact, the benzene series are the main contributor to SOA, whereas the contribution of VOCs from traditional processes is small; hence, SOA primarily originates from the gluing and painting processes. Therefore, in traditional production of rubber products through rubber mixing and vulcanization, the emission of oxygenated hydrocarbons should be preferentially controlled, whereas for rubber industries utilizing gluing and painting processes, the emission of benzene series should be preferentially controlled.

Characterization of ambient volatile organic compounds, source apportionment, and the ozone–NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt;–VOC sensitivities in a heavily polluted megacity of central China: effect of sporting events and emission reductions

Abstract. The implementation of strict emission control during the 11th National Minority Games (NMG) in September 2019 provided a valuable opportunity to assess the impact of such emission controls on the characteristics of VOCs and other air pollutants. Here, we investigated the characteristics of VOCs and the O3–NOx–VOC sensitivity comprehensively in Zhengzhou before, during, and after the NMG by delivering field measurements combined with WRF-CMAQ (Weather Research and Forecasting Community Multiscale Air Quality) model simulations. The average mixing ratios of VOCs during the control periods were 121 ± 55 µg m−3 and decreased by about 19 % and 11 % before and after emission reduction. The ozone precursors (NOx) also decreased significantly during the control period; however, the ozone pollution was severe during the entire observation period. Positive matrix factorization analysis indicated seven major sources of ambient VOCs, including coal combustion, biomass burning, vehicle exhausts, industrial processes, biogenic emissions, solvent utilization, and liquefied petroleum gas (LPG). The results show that the major source emissions, such as coal combustion and solvent utilization, were significantly reduced during the control period. As for ozone formation potential (OFP), the value during the control period was 183 ± 115 µg m−3, which was 0.23 and 0.17 times lower than before and after the control period, respectively. Solvent utilization and combustion controls were the most important measures taken to reduce OFP during the NMG period. Control policies can effectively reduce carcinogenic risk. However, non-cancer risks of ambient VOC exposures were all exceeding the safe level (hazard quotient = 1) during the sampling periods, and emphasis on the reduction of acrolein emissions was needed. In addition, the WRF-CMAQ model simulation indicated that O3 formation was controlled by VOCs in Zhengzhou. The results of the Empirical Kinetic Modeling Approach showed that the NOx reduction in Zhengzhou might lead to higher ozone pollution. It is suggested that reduction ratios of the precursors (VOCs : NOx) should be more than 2, which can effectively alleviate ozone pollution.

Chemical surface modification of beaded activated carbon: A strategy to inhibit heel accumulation from VOC

This study elucidates the factors responsible for the deterioration of beaded activated carbon (BAC), used in the abatement of volatile organic compounds that stem from painting processes in industries. In practice, continuous use of adsorbents during periodic adsorption–desorption results in the formation of heel (non-desorbable polymeric complex) in its pore structures, rendering the adsorbent eventually unusable. Here, the adsorption–desorption characteristics of VOCs from porous BAC are investigated, and an effective surface modification strategy is developed to impede heel formation and extend the operational life of the BAC. This modification protocol increases porosity by up-to 55 % and modifies the functional groups on the BAC surface without altering its structural integrity. Consequently, the adsorption capacity of the BAC increased by nearly 38% while decreasing the peak desorption temperature by as much as 50 °C due to lowered adsorption strength. Additionally, to provide mechanistic insights, the resultant changes in porosity, surface morphology, and adsorption–desorption characteristics of the BAC are investigated by N2 physisorption, SEM, TGA, and DRIFTS. Finally, cyclic adsorption–desorption studies conducted under conditions mirroring the industrial setup proved that the percentage heel accumulation in surface modified BAC is significantly lower (≤ 3%) compared to unmodified BAC.

Source Profiles and Impact of VOCs Based on Production Processes in Foundry Industries

The characteristics of the VOCs species in foundry industries based on the production processes were analyzed through gas chromatography-mass spectrometry (GC-MS) after sampling the emissions of VOCs in 9 typical foundry enterprises using air packages and absorption tubes. The source profiles of the VOCs species in foundry industries based on production processes were established for the first time in China. In addition, the emission characteristics of VOCs and the contribution of VOCs emitted by various production processes to ozone generation were also studied. The results showed that the characteristic components of the VOCs in foundry industries were predominantly aromatic hydrocarbons, halogenated hydrocarbons, and oxygenated hydrocarbons. The average concentrations were 50.9%, 20.8%, and 12.6%, respectively. In general, aromatic hydrocarbons, such as toluene, benzene, and m/p-xylene; halogenated hydrocarbons, such as trichloroethylene and dichloromethane; oxygenated hydrocarbons, such as acetone, ethyl acetate, cyclopentanone, and some alkanes, were the primary VOCs species of the foundry industries. The emission characteristics of different production processes were related to the solvents and surface treating agents used by each process. The results also demonstrated that painting was the largest contributor of VOCs concentrations among all the production processes, followed by the modeling procedure and the silica sol and pouring processes. The OFP values for the different production processes ranged from 0.29-96.09 mg·m-3. Painting was the largest contributor to OFP, followed by the modeling procedure and the melting and pouring processes. Aromatic hydrocarbons and oxygenated hydrocarbons were the dominant contributors to OFP, and 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, toluene, and m/p-xylene were the main active components in the foundry industry, with a total contribution to the ozone generation potential of nearly 60%. It is suggested that the painting process should be prioritized regarding control measures to reduce its emissions and impact, while the waste gas from the modeling procedure and the melting and pouring processes should be collected efficiently and treated properly before being discharged to the environment.