Gasoline Evaporation Research Articles

Combined-phase source apportionment of ambient PM2.5, PAHs and VOCs from an industrialized environment: Consequences of photochemical initial concentrations

Air pollutants in the particulate (PM2.5 species, PAHs) and gaseous phases (VOCs) collected between 2013 and 2019 once every three or six days for a period of 24 hours in an industrialized city in Ontario were analyzed to apportion their common sources. The consequences of using these species jointly for receptor modelling were assessed via combined-phase source apportionment that used the data as is, and in a protocol that factored in the potential for photochemical losses of gas-phase species. Thus, photochemically corrected initial concentrations (PIC) were calculated. Analyses of the inputs followed either with positive matrix factorization or its dispersion-normalized variant (DN-PMF). Comparisons of applying PMF to the originally observed input data (BASE) and DN-PMF on data with PIC corrections were made. When the inputs consisted only of VOCs, three factors were resolved with BASE PMF: natural gas, vehicular emissions, and industrial emissions co-emitted with summertime gasoline evaporation. A fourth factor was obtained, representing reactive VOCs when DN-PIC PMF was used. When the combined phase input data were analyzed, nine factors were resolved for both BASE and DN-PIC PMF. These factors in order of diminishing average PM mass contributions were: particulate sulphate, secondary organic aerosol (SOA), particulate nitrate (pNO3), biomass burning with natural gas, crustal matter, winter blend of gasoline, coking/coal combustion, steelmaking, and summer blend/light duty vehicular emissions. When BASE and DN-PIC PMF results are compared, the average PM mass contribution of the summer gasoline fuel factor increased from 2% in BASE case to 5%, suggesting severe underestimation of this source's contributions without DN-PIC. Also, substantial increases of reactive VOCs in the SOA factor, and PAHs with ≥four rings in the pNO3 and steelmaking factors were observed with DN-PIC PMF compared to the BASE PMF case, indicating that for SOA, reactive VOCs at this location contributed to SOA sources.

Mutagenic atmospheres generated from the photooxidation of NOx with selected VOCs and a complex mixture: Apportionment of aromatic mutagenicity for reacted gasoline vapor

The interaction of sunlight with volatile organic compounds (VOCs) emitted from various sources results in mutagenic photooxidation products that contribute substantially to air pollution. Evaporation of gasoline is one such source of VOCs; however, no studies have evaluated the mutagenicity of the photooxidation products of gasoline vapors or of many of the non-aromatic constituent VOCs of gasoline. Here we determined the mutagenicity in Salmonella TA100 of atmospheres generated in a steady-state atmospheric simulation chamber by irradiating gasoline and individual non-aromatic VOCs in the presence of nitrogen oxides (NOX) in air. In addition to gasoline, we evaluated α-pinene; 2-pentene; ethanol; isobutanol; isoprene; and 2,2,4-trimethylpentane (isooctane). Cells were exposed at the air-agar interface to the atmospheres for 1, 2, 4, 8, or 16 h. Atmospheres generated in the dark were not mutagenic. However, under irradiation all atmospheres other than that of 2,2,4-trimethylpentane were mutagenic, with mutagenic potencies spanning 8.6-fold. The mutagenicity was due exclusively to direct-acting, late-generation photooxidation products. The non-aromatic VOCs studied here contributed little to the mutagenic potency of the photooxidation products of gasoline. However, the sum of the mutagenic potencies of these atmospheres plus those from the photooxidation of some aromatic VOCs in gasoline measured here and elsewhere (Riedel et al., 2018) accounted for 71% of the mutagenic potency of the photooxidation products of gasoline vapor. In photochemical mixtures with strong biogenic contributions, isoprene products may also contribute significantly to mutagenic potency. Strategies to reduce the emissions of gasoline and those VOCs whose photooxidation products are most mutagenic would reduce VOC-associated air pollution and improve public health.

Characteristic, source apportionment and effect of photochemical loss of ambient VOCs in an emerging megacity of Central China

During the transportation from emission sources to sampling site, volatile organic compounds (VOCs) undergo photochemical losses which have significant effects for tropospheric ozone (O3) formation and VOCs source apportionment. In this study, based on hourly speciated VOC data from May 23, to July 8, 2019 with high O3 concentrations, the concentration level, chemical composition, and diurnal variation of observed VOCs were studied, and the initial concentration of VOCs was obtained by combining the local emission inventory in Zhengzhou, Central China. The impact of photochemical loss on source apportionment was evaluated using the Positive Matrix Factorization/Multilinear Engine 2-Species Ratio (PMF/ME2-SR) model based on observed and initial VOCs concentration (OC-PMF and IC-PMF). Results suggest that during the observed period, the average concentration of total VOCs (TVOCs) was 23.74 ± 9.20 ppbv, and alkanes (3.92 ± 2.40 ppbv) were the predominant component. The photochemical losses of TVOCs were approximately 10.15 ± 7.13 ppbv, with an average loss rate of 29.9%. The ozone formation potential (OFP) based on the initial VOCs concentration was 2.2 times higher than that observed VOCs concentration. Alkenes contributed the most to OFP and were also the largest contributors to photochemical losses. TVOC concentrations increased by 5.0% during O3 pollution compared to non-O3 pollution. Seven sources of VOCs were determined, including biomass burning, liquefied petroleum gas (LPG), vehicle emission, industrial emission, solvent usage, gasoline evaporation, and biogenic emission. Compared to the results of IC-PMF, the contributions of these sources in OC-PMF were underestimated by 15.4%, 14.4%, 13.0%, 11.7%, 31.5%, 7.6%, and 4.7%, respectively. This study still exhibits certain limitations in calculation method, and further exploration can be conducted in the future.

Elucidating the unexpected importance of intermediate-volatility organic compounds (IVOCs) from refueling procedure

Evaporative emissions release organic compounds comparable to gasoline exhaust in China. However, the measurement of intermediate volatility organic compounds (IVOCs) is lacking in studies focusing on gasoline evaporation. This study sampled organics from a real-world refueling procedure and analyzed the organic compounds using comprehensive two-dimensional gas chromatography coupled with a mass spectrometer (GC×GC-MS). The non-target analysis detected and quantified 279 organics containing 93 volatile organic compounds (VOCs, 64.9 ± 7.4 % in mass concentration), 182 IVOCs (34.9 ± 7.4 %), and 4 semivolatile organic compounds (SVOCs, 0.2 %). The refueling emission profile was distinct from that of gasoline exhaust. The b-alkanes in the B12 volatility bin are the most abundant IVOC species (1.9 ± 1.4 μg m−3) in refueling. A non-negligible contribution of 17.5 % to the ozone formation potential (OFP) from IVOCs was found. Although IVOCs are less in concentration, secondary organic aerosol potential (SOAP) from IVOCs (58.1 %) even exceeds SOAP from VOCs (41.6 %), mainly from b-alkane in the IVOC range. At the molecular level, the proportion of cyclic compounds in SOAP (12.1 %) indeed goes above its mass concentration (3.1 %), mainly contributed by cyclohexanes and cycloheptanes. As a result, the concentrations and SOAP of cyclic compounds (>50 %) could be overestimated in previous studies. Our study found an unexpected contribution of IVOCs from refueling procedures to both ozone and SOA formation, providing new insights into secondary pollution control policy.

Experimental research and estimation model of gasoline evaporative emissions from vehicles in China

Evaporative emission is an important source of vehicle pollutant emission and volatile organic compounds (VOCs), causing serious environmental pollution. Carbon canisters are used to store fuel vapor in evaporative emission control (EVAP) system, but canisters are prone to saturation, leading to the direct release of fuel vapor into the atmosphere. Therefore, accurate estimation of fuel vapor generation is crucial for EVAP system. Gasoline evaporation rate is mainly influenced by vapor-liquid interface area, gasoline saturated vapor pressure, filling level and temperature. The quantitative relation between different parameters and gasoline evaporation rate has rarely been reported, and a gasoline evaporative emission estimation model suitable for China needs to be proposed urgently. In this study, gasoline evaporative emission tests have been carried out in VT-SHED, and the effects of vapor-liquid interface area, filling level and temperature on gasoline evaporative emissions have been analyzed under the premise of consistent gasoline temperature and ambient temperature. Some valuable conclusions are obtained. The results show that different from expectation, gasoline evaporative emissions are not positively correlated with the vapor-liquid interface area. There is an approximately exponential relationship between the headspace volume and gasoline evaporative emissions. The widely used Reddy equation and Hata equation underestimate the gasoline vapor generation in China. Based on China VI test program and gasoline, accurate estimation of mass transfer coefficient has been conducted, and a new semi-empirical estimation model for vapor generation has been proposed. The model can accurately estimate the fuel evaporation of vehicles in China, providing guidance for the matching and optimization of EVAP system.

Characterization and source apportionment of volatile organic compounds in Hong Kong: A 5-year study for three different archetypical sites

Initial success has been achieved in Hong Kong in controlling primary air pollutants, but ambient ozone levels kept increasing during the past three decades. Volatile organic compounds (VOCs) are important for mitigating ozone pollution as its major precursors. This study analyzed VOC characteristics of roadside, suburban, and rural sites in Hong Kong to investigate their compositions, concentrations, and source contributions. Here we show that the TVOC concentrations were 23.05 ± 13.24, 12.68 ± 15.36, and 5.16 ± 5.48 ppbv for roadside, suburban, and rural sites between May 2015 to June 2019, respectively. By using Positive Matrix Factorization (PMF) model, six sources were identified at the roadside site over five years: Liquefied petroleum gas (LPG) usage (33%–46%), gasoline evaporation (8%–31%), aged air mass (11%–28%), gasoline exhaust (5%–16%), diesel exhaust (2%–16%) and fuel filling (75–9%). Similarly, six sources were distinguished at the suburban site, including LPG usage (30%–33%), solvent usage (20%–26%), diesel exhaust (14%–26%), gasoline evaporation (8%–16%), aged air mass (4%–11%), and biogenic emissions (2%–5%). At the rural site, four sources were identified, including aged air mass (33%–51%), solvent usage (25%–30%), vehicular emissions (11%–28%), and biogenic emissions (6%–12%). The analysis further revealed that fuel filling and LPG usage were the primary contributors to OFP and OH reactivity at the roadside site, while solvent usage and biogenic emissions accounted for almost half of OFP and OH reactivity at the suburban and rural sites, respectively. These findings highlight the importance of identifying and characterizing VOC sources at different sites to help policymakers develop targeted measures for pollution mitigation in specific areas.

Ozone Pollution in Suzhou During Early Summertime: Formation Mechanism and Interannual Variation

This study investigated the concentrations of atmospheric pollutants in the urban area of Suzhou from May to June, 2017-2021. The variation characteristics and annual changes of ozone (O3), nitrogen oxide (NOx), total oxidant (Ox), carbon monoxide (CO), and volatile organic compounds (VOCs) were analyzed. The O3 formation mechanism and its annual changes were studied using an Observation-Based Model (OBM), and VOCs source apportionments and their trends were discussed. The results indicated that ① The volume fractions of Ox and the concentrations of NOx and CO have decreased in the urban area of Suzhou in recent years, while the volume fractions of VOCs have increased, and sufficient photochemical conditions for O3 formation still existed during polluted days. ② The O3-NOx-VOCs sensitivity in Suzhou was in the VOCs-limited regime. The long-term reduction ratio between VOCs and NOx should not be less than 5:1, and aromatics and alkenes were the critical VOCs for mitigating O3 pollution. ③ The results of VOCs source apportionment revealed that industrial emissions, gasoline vehicle exhaust, and diesel engine exhaust were the major sources of VOC emissions in Suzhou. Industrial emissions and solvent usage declined from 2017 to 2021; however, gasoline vehicle exhaust and gasoline evaporation, which possess higher O3 formation potential(OFP), increased significantly. ④ The OFP source apportionments results indicated that controlling VOC emissions from solvent usage and gasoline vehicle exhaust is crucial for O3 pollution control in Suzhou.

Characteristics and Health Risk Assessment of Volatile Organic Compounds in Different Functional Zones in Baoji in Summer

The situation of air pollution in Guanzhong Plain has been increasing in recent years; hence, it is very important to study the characteristics of volatile organic compounds (VOCs) and their health risks in urban functional zones. We analyzed 115 VOCs using gas chromatography-mass spectrometry/hydrogen ion flame detector (GC-MS/FID) and high performance liquid chromatography (HPLC) at four sampling sites in the traffic, comprehensive, industrial, and scenic zones of Baoji. We analyzed the main components and key species in the different functional zones. Ozone formation potential (OFP),·OH consumption rate (L·OH), and secondary organic aerosol formation potential (SOAFP) were used to evaluate the environmental impact, and the hazard index (HI) and lifetime cancer risk (LCR) methods were employed. The results revealed that the mean values of φ(TVOCs) in the traffic, comprehensive, industrial, and scenic zones were (59.63±23.85)×10-9, (42.92±11.88)×10-9, (60.27±24.09)×10-9, and (55.54±7.44)×10-9, respectively. The dominant contributors at the traffic zone were alkanes, and those at the other functional zones were OVOCs. Acetaldehyde, acetone, n-butane, and isopentane were abundant at different functional zones. According to the characteristic ratios of VOCs, the average ratio of toluene to benzene (T/B) at the traffic, comprehensive, industrial, and scenic zones were 1.84, 2.39, 1.28, and 1.64, respectively, and the ratio of iso-pentane to n-pentane (i/n) was mainly between 1 and 4. The results indicated that VOCs in Baoji were significantly affected by vehicle emissions and gasoline evaporation, biomass and coal combustion, and industrial coatings and foundry. The ratio of m/p-xylene to ethylbenzene (X/E) was lower than 2 at the four functional zones, and the minimum was 1.79 at the scenic zones; the results revealed that X/E was small, and the aging degree of air masses was high, indicating the influence of regional transport. According to the ratio of formaldehyde to acetaldehyde (C1/C2) and the ratio of acetaldehyde to propanal (C2/C3), it was suggested that there may have been evident anthropogenic emission sources, and the photochemical reaction had an important effect on aldehydes and ketones. Environmental impact assessment results revealed that OVOCs and alkenes contributed significantly to OFP and OFP from large to small was as follows:industrial zone>scenic zone>traffic zone>comprehensive zone. The range of L·OH in each functional zone was 8.77-15.82 s-1, with isoprene contributing the most in the industrial zone and acetaldehyde contributing the most at other functional zones. The SOAFP of each functional zone was as follows:scenic zone>comprehensive zone>traffic zone>industrial zone. Toluene, m/p-xylene, and isoprene were the notable species. According to the health risk assessment of EPA, the HI of toxic VOCs in all functional zones was lower than 1, which was at an acceptable level. However, the number of days with HI>1 in industrial zones accounted for 42.86% of the total sampling days, indicating a high risk. The lifetime carcinogenic risk (LCR) of the traffic, comprehensive, industrial, and scenic zones were 1.83×10-5, 1.21×10-5, 1.85×10-5, and 1.63×10-5, respectively, which were all in grade Ⅲ of the rating system, indicating a high probability of cancer risk. Species with LCR greater than 10-6 were formaldehyde; acetaldehyde; 1,2-dibromoethane; 1,2-dichloroethane; 1,2-dichloropropane; and chloroform.

Source apportionment and ozone formation mechanism of VOCs considering photochemical loss in Guangzhou, China

Understanding the sources and impact of volatile organic compounds (VOCs) on ozone formation is challenging when the traditional method does not account for their photochemical loss. In this study, online monitoring of 56 VOCs was carried out in summer and autumn during high ozone pollution episodes. The photochemical age method was used to evaluate the atmospheric chemical loss of VOCs and to analyze the effects on characteristics, sources, and ozone formation of VOC components. The initial concentrations during daytime were 5.12 ppbv and 4.49 ppbv higher than the observed concentrations in the summer and autumn, respectively. The positive matrix factorization (PMF) model identified 5 major emission sources. However, the omission of the chemical loss of VOCs led to underestimating the contributions of sources associated with highly reactive VOC components, such as those produced by biogenic emissions and solvent usage. Conversely it resulted in overestimating the contributions from VOC components with lower chemical activity such as liquefied petroleum gas (LPG) usage, vehicle emissions, and gasoline evaporation. Furthermore, the estimation of ozone formation may be underestimated when the atmospheric photochemical loss is not taken into account. The ozone formation potential (OFP) method and propylene-equivalent concentration method both underestimated ozone formation by 53.24 ppbv and 47.25 ppbc, respectively, in the summer, and by 40.34 ppbv and 26.37 ppbc, respectively, in the autumn. The determination of the ozone formation regime based on VOC chemical loss was more acceptable. In the summer, the ozone formation regime changed from the VOC-limited regime to the VOC-NOx transition regime, while in the autumn, the ozone formation regime changed from the strong VOC-limited regime to the weak VOC-limited regime. To obtain more thorough and precise conclusions, further monitoring and analysis studies will be conducted in the near future on a wider variety of VOC species such as oxygenated VOCs (OVOCs).

Source apportionment of consumed volatile organic compounds in the atmosphere

Conventional source apportionments of ambient volatile organic compounds (VOCs) have been based on observed and initial concentrations after photochemical correction. However, these results have not been related to ozone (O3) and secondary organic aerosol (SOA) formation. Thus, the apportioned contributions could not effectively support secondary pollution control development. Source apportionment of the VOCs consumed in forming O3 and SOA is needed. A consumed VOC source apportionment approach was developed and applied to hourly speciated VOCs data from June to August 2022 measured in Laoshan, Qingdao. Biogenic emissions (56.3%), vehicle emissions (17.2%), and gasoline evaporation (9.37%) were the main sources of consumed VOCs. High consumed VOCs from biogenic emissions mainly occurred during transport from parks to the southwest and northwest of study site. During the O3 pollution period, biogenic emissions (46.3%), vehicle emissions (24.2%), and gasoline evaporation (14.3%) provided the largest contributions to the consumed VOCs. However, biogenic emissions contribution increased to 57.1% during the non-O3 pollution period, and vehicle emissions and gasoline evaporation decreased to 16.5% and 9.01%, respectively. Biogenic emissions and the mixed source of combustion sources and solvent use contributed the most to O3 and SOA formation potentials during the O3 pollution period, respectively.

Differences in compositions and effects of VOCs from vehicle emission detected using various methods

Vehicle exhaust and oil fuel evaporation emit volatile organic compounds (VOCs). The differences in VOC compositions and their effects determined using different methods have not been addressed sufficiently. In this study, VOC samples are obtained from single gasoline and diesel vehicle exhausts using a portable emission measurement system, from a tunnel in Yichang City, and from gasoline and diesel evaporation at gas stations. A total of 107 VOCs are analysed. The calculated VOC source profiles (based on VOC source profiles of single-vehicle type and vehicle fleet composition in the tunnel) and the tested source profiles (from a tunnel test) are compared. The results show that gasoline burning can reduce alkenes from a mass fraction of 53.1% (for evaporation) to 3.6% (for burning), as well as increase the mass fraction of alkenes from 1.3% (for diesel evaporation) to 34.0% (for diesel burning). The calculated VOC source profiles differed from the tested VOC source profiles, with a coefficient of divergence of 0.6. Ethane, ethylene, n-undecane, and n-dodecane are used to distinguish VOCs in gasoline and diesel exhausts. Cis-2-butene, 2-methylpentane, m/p-xylene, o-xylene, and n-decane can be used to separate gasoline from diesel. The xylene/ethylbenzene ratios accurately reveal the photochemical age. Gasoline burning increases health risks associated with VOCs compared with gasoline evaporation. Furthermore, it modifies the main contributor to ozone formation potential. This study is expected to facilitate refined VOC source apportionment and studies pertaining to speciated emission inventories.

Identify the key emission sources for mitigating ozone pollution: A case study of urban area in the Yangtze River Delta region, China

Ozone (O3) has become the most critical air pollutant in the Yangtze River Delta (YRD) region of China. Research on the O3 formation mechanism and its precursor sources (including nitrogen oxides (NOX) and volatile organic compounds (VOCs)) could provide a theoretical basis for mitigating O3 pollution in this region. In this study, simultaneous field experiments were conducted for air pollutants in a typical urban area (Suzhou) in the YRD region in 2022. The capacity of in-situ O3 formation, O3-NOX-VOCs sensitivities and sources of O3 precursors were analyzed. The results showed that in-situ formation contributed 20.8 % of the O3 concentration in the warm season (April to October) of the Suzhou urban area. Compared with the warm season average, the concentrations of various O3 precursors increased on pollution days. The O3-NOX-VOCs sensitivity was the VOCs-limited regime based on the average concentrations during the warm season. O3 formation was most sensitive to anthropogenic VOCs, of which oxygenated VOCs, alkenes and aromatics were the key species. There was a VOCs-limited regime in spring and autumn, while a transitional regime in summer due to the changes in NOX concentrations. This study considered NOX emission from VOCs sources and calculated the contribution of various sources to O3 formation. The results of VOCs source apportionment showed that diesel engine exhaust and fossil fuel combustion had a dominant proportion, but O3 formation presented significant negative sensitivities to the above two sources because of their high NOX emissions. There were significant sensitivities of O3 formation to gasoline vehicle exhaust and VOCs evaporative emissions (gasoline evaporation and solvent usage). The contribution of VOCs evaporative emissions during the O3 pollution episode was significantly higher than the average; therefore, controlling VOCs evaporative emissions during the O3 pollution episode is critical. These results provide feasible strategies to mitigate O3 pollution.

Analysis of Temperature Effect on the Gasoline Evaporation in Fire Investigation by HS-GC-MS

ABSTRACT The aim of the research is to determine changes in the composition of selected gasoline compounds in cotton carpet samples due to different weathering times. EVO 95 gasoline was used as a fire accelerant and a cotton carpet was used as a matrix. The samples were exposed to various weathering durations (0–360 min) in laboratory conditions. We investigated samples that were unburnt (only weathered) and samples that were burned and subsequently subjected to further weathering. Residual gasoline compounds in carpet samples were determined by gas phase extraction (headspace – HS) coupled with gas chromatography (GC) and mass spectrometry (MS). We focused on the comparison of selected gasoline compounds; toluene, ethylbenzene, p-xylene, 1,2,3-trimethylbenzene (TMB), 1,3,5-trimethylbenzene and naphthalene. The biggest changes were determined in the reduction of the intensity of most volatile compounds (alkylalkanes), where toluene decreased by 11.92%. A similar but not so pronounced trend, occurred in the burned samples, where toluene decreased by 7.40%. Minor changes occurred in alkyl derivatives of benzene, where some of the total 15 gasoline markers also occur, e.g. (1,2,3-trimethylbenzene, 1,3,5-trimethylbenzene). On the contrary, naphthalene as a heavier compound showed an increase in intensity about 0.42%. For burnt samples, the increase was 1.31%. The results show that largest changes can be observed after four or five hours of weathering, which implies the need for rapid sampling and subsequent timely analysis.

Characteristics and Source Apportionment of Volatile Organic Compounds in Zhanjiang in Summer

Ozone pollution is intensifying in China, and its related studies are weak in non-focus regions and non-focus cities. Here, we investigated the characteristics and sources of volatile organic compounds (VOCs) at three sampling sites in Zhanjiang. We analyzed 101 VOCs using a gas chromatography-mass spectrometry/hydrogen ion flame detector (GC-MS/FID) and high-performance liquid chromatography (HPLC) using a Summa canister and DNPH adsorption tube. We calculated the ozone formation potential (OFP) of VOCs and used the positive matrix factorization (PMF) model for source apportionment. The results showed that the mean φ(TVOCs) was 1.28×10-7, and the dominant contributors were OVOCs (52%), followed by alkanes (36%), alkenes (7%), halogenated hydrocarbons (2.42%), aromatic hydrocarbons (1.61%), and alkynes (0.78%). The diurnal variation in VOCs was influenced by photochemical reactions; the ratio of aromatic hydrocarbons and alkanes was high in the morning and evening and low at noon, whereas OVOCs had a low ratio in the morning and noon and high in the evening, influenced by primary emissions and the upwind transport of pollutants. The OFP was 3.28×10-7, and the dominant species were formaldehyde, butene, n-butane, butanone, and acetaldehyde.The analysis of X/E values (characterizing the aging degree of air masses) and backward trajectories of air masses showed that during the sampling, when influenced by air masses from the south or southwest, X/E was small, and the aging degree of air masses was high, indicating the influence of regional transport; when influenced by air masses from the east or southeast direction, X/E was large, and the air masses were fresh, and VOCs were mainly from local emissions. Six emission sources of VOCs, including industrial emissions, gasoline vehicle exhaust and gasoline evaporation, regional background and transport sources, biomass combustion, diesel vehicles and marine shipping emissions, and solvent use emission sources, were resolved using the PMF model, with contributions of 36.05%, 28.99%, 13.84%, 10.13%, 7.05%, and 3.95%, respectively.Zhanjiang should strengthen the supervision of formaldehyde, butene, n-butane and butanone, industry sources, and mobile sources as the focus of control.

Characteristics of volatile organic compounds (VOCs) at an urban site of Delhi, India: Diurnal and seasonal variation, sources apportionment

This study reports the measurements of 25 volatile organic carbon compounds (VOCs) in the ambient air at an urban location of Delhi, India. The air samples were collected in stainless steel canisters following the standard recommended practice of Environmental Protection Agency (EPA) and analysing using a gas chromatograph with Flame Ionization Detector (GC-FID) from January 2018 to June 2019. The most abundant are alkene (39%) followed by Alkane (36%), and aromatic (16%). Alkyne (9%) is observed in a very limited number of samples. Alkanes and aromatic compounds show a gradual decrease in concentration from morning to evening, whereas, the concentration of alkenes increased from morning to day time. Higher mixing height (m) during the day (0800–1800 h) and emissions from several sources have controlled the diurnal variation. VOCs show a strong seasonal cycle for alkanes (24–47%), alkenes (31–46%), Alkynes (4–18%), and aromatic compounds (14–20%). PCA/APCS-MLR analysis has been resolved 6 factors with 18 VOCs which are mostly dominated by gasoline evaporation (27.1%) and biomass burning (26.7%) followed by LPG (16.7%), and vehicular emissions (16.4%). PMF analysis shows gasoline vehicular emission + gasoline emission+ organic solvent (39.9%) followed by biomass burning (20.7%), LPG (15.8%), diesel vehicular emission (13.4%), and painting (10.1%).

Molecular simulation of the effects of activated carbon structure on the adsorption performance for volatile organic compounds in fumes from gasoline

AbstractImproving the adsorption performance of activated carbon can effectively reduce the emission of volatile organic compounds (VOCs). In this paper, the influences of pore size, functional groups, and water molecular content on the adsorption for four gasoline evaporation VOCs (n‐butane, n‐hexane, p‐xylene, and ethanol) were investigated in terms of equilibrium adsorption capacity and threshold pressure by molecular simulation. The simulation results show that capillary condensation can increase the equilibrium adsorption capacity of gas, while functional groups and water molecules will reduce the effective adsorption volume of activated carbon. On the other hand, the threshold pressure depends primarily on the interaction energy and the number of adsorption sites. The superposition effect of the adsorption force field makes the lowest threshold pressure of four VOCs. The threshold pressure of n‐butane, n‐hexane, and p‐xylene is increased by the presence of functional groups and water molecules, while functional group modification and a certain amount of water molecules can improve the adsorption capacity of ethanol at low pressure. The results of the study can provide a reference for the selection of activated carbon in vehicle carbon canisters and the development of high‐performance activated carbon.

Changes in O3-VOCs-NOx Sensitivity and VOCs Sources at an Urban Site of Nanjing Between 2020 and 2021

The synergistic control of PM2.5 and ozone (O3) are the focus of air quality improvement during the 14th Five-Year Plan in China. The production of O3 shows a highly nonlinear relationship with its precursors volatile organic compounds (VOCs) and nitrogen oxides (NOx). In this study, we conducted online observations of O3, VOCs, and NOx at an urban site in downtown Nanjing from April to September of 2020 and 2021. The average concentrations of O3 and its precursors between these two years were compared, and then the O3-VOCs-NOx sensitivity and the VOCs sources were analyzed using the observation-based box model (OBM) and positive matrix factorization (PMF), respectively. The results showed that the mean daily maximum O3 concentrations, VOCs, and NOx concentrations decreased by 7% (P=0.031), 17.6% (P<0.001), and 14.0% (P=0.004) from April to September of 2021 compared with those from the same period in 2020, respectively. The average relative incremental reactivity (RIR) values of NOx and anthropogenic VOCs during the O3 non-attainment days in 2020 and 2021 were 0.17 and 0.14 and 0.21 and 0.14, respectively. The positive RIR values of NOx and VOCs indicated that O3 production was controlled by both VOCs and NOx. The O3 production potential contours (EKMA curves) based on the 50×50 scenario simulations also supported this conclusion. The PMF results showed that industrial and traffic-related emissions were the main sources of VOCs. The five PMF-resolved factors were identified as industrial emissions, including industrial liquefied petroleum gas (LPG) use, the benzene-related industry, petrochemistry, toluene-related industry, and solvent and paint use, which contributed 55%-57% of the average mass concentration of total VOCs. The summed relative contributions of vehicular exhaust and gasoline evaporation were 43%-45%. Petrochemistry and solvent and paint use showed the two highest RIR values, suggesting that VOCs from these two sources should be reduced with priority to control O3. With the implementation of VOCs and NOx control measures, the O3-VOCs-NOx sensitivity and VOCs sources have changed, and therefore we still need to follow their variations in the future to timely adjust O3 control strategies during the 14th Five-Year Plan.

VOCs sources and roles in O3 formation in the central Yangtze River Delta region of China

Surface ozone (O3) pollution has become a prominent air quality problem in the Yangtze River Delta (YRD) region of China in recent years. Since O3 is non-linearly related to its precursors (volatile organic compounds (VOCs), nitrogen oxides (NOx)), identifying the characteristics of VOCs is significant for the control of O3 pollution. In this study, online observation of ambient VOCs from August to October 2018 was conducted at 2 sites in Changzhou, an industrial city located in the central YRD region, to investigate the O3 pollution characteristics, sources of VOCs, and their roles in O3 formation. The average concentration of VOCs in Changzhou during the observational period was 39.52 ± 23.14 ppb. Alkanes, oxygenated VOCs (OVOCs), and halocarbons were the main contributors to the total VOCs concentration, with the average relative contributions of 39.4%, 23.1%, and 16.1%, respectively. An observation-based model (OBM) was used to investigate the sensitivity of O3 formation to VOCs and NOx. Results of relative incremental reactivity (RIR) of individual VOC and empirical kinetics modeling approach (EKMA) showed that the O3 formation in Changzhou was within the VOCs-limited regime. Anthropogenic VOCs with the largest RIR values were xylenes and propene, respectively. The positive matrix factorization (PMF) model was applied to quantitatively identify the sources of VOCs. Six factors were resolved, including vehicle exhaust, gasoline evaporation, paint and solvent usage, electronic manufacturing, petrochemical industry, and biogenic source & secondary formation. The average relative contribution of traffic-related emissions to the total VOCs mass concentration was about 49.5%, followed by electronic manufacturing (22.9%), paint and solvent usage (14.7%), and petrochemical industry (7.1%). The average relative contributions of individual sources for xylenes and propene were further compared. Xylenes were mainly emitted from paint and solvent usage (60%), electronic manufacturing (17%), and vehicle exhaust (16%). Petrochemical industry (67%) and vehicle exhaust (30%) were the major sources of propene. Therefore, VOCs from industrial emissions and traffic-related emissions should be given priority for the control of O3 pollution in the central YRD region.

Characteristics of summertime ambient volatile organic compounds in Beijing: Composition, source apportionment, and chemical reactivity

Comprehensive observations of ambient volatile organic compounds (VOCs) were conducted in Beijing (the capital of China) in the summer of 2018 with high temporal resolution, and the compositions, sources, ozone formation potential (OFP), and secondary organic aerosol formation potential (SOAP) were examined. A high mixing ratio of total VOCs (TVOCs) (26.6 ± 9.5 ppbv) was observed in this study, which was similar to that obtained in 2014 and 2016 in Beijing. The dominant components were alkanes (51.1% of TVOCs), alkenes (24.1%), and aromatics (19.5%). According to backward trajectories and potential source contribution function analysis, medium-distance transport from the south of the sampling region contributed more than 50% of the trajectories, and the potential source regions were mainly located in Shandong and Hebei Provinces. The seven sources identified by the positive matrix factorization receptor model included natural/liquified petroleum gas (NG/LPG) usage and gasoline evaporation (21.68%), solvent usage (20.14%), combustion sources (16.07%), industrial emissions (15.24%), diesel exhaust (14.89%), gasoline exhaust (6.05%), and biological emissions (5.92%). Alkenes (50.05%) and aromatics (36.20%) contributed the most to the total OFP, whereas aromatics contributed more than 90.00% to the total SOAP. The source with the greatest contribution to OFP and SOAP was solvent usage, the contribution of which exceeded 50%. The results of this study are favorable for the development of control strategies for VOCs and for reducing the formation of photochemical smog and secondary particulate matter.

Competitive adsorption characteristics of gasoline evaporated VOCs in microporous activated carbon by molecular simulation

The activated carbon in the vehicle's carbon canister needs to adsorb a variety of VOCs (Volatile Organic Compounds) emitted by gasoline evaporation, while the difference in gas adsorption capacity can lead to adsorption competition phenomena. In this study, three typical VOCs (toluene, cyclohexane, and ethanol) were selected to study the adsorption competition characteristics between multi-component gases at different pressures by molecular simulation method. In addition, the effect of temperature on adsorption competition was also investigated. The results show that the selectivity of activated carbon to toluene is negatively correlated with the adsorption pressure, but the opposite is true for ethanol, and the change of cyclohexane is not significant. The competitive order of the three VOCs is toluene > cyclohexane > ethanol at low pressure, which becomes ethanol > toluene > cyclohexane at high pressure. With increasing pressure, the interaction energy decreases from 12.87 kcal/mol to 11.87 kcal/mol, where the electrostatic interaction energy increases from 1.97 kcal/mol to 2.54 kcal/mol. In microporous activated carbon, the competition is mainly manifested in that ethanol preempts the low-energy adsorption sites of toluene in the pore size of 10 Å to 18 Å, while gas molecules near the surface of activated carbon or in smaller pore sizes are stably adsorbed without competition. Despite the fact that high temperature decreases the total adsorption capacity, activated carbon selectivity for toluene increases instead, while the competitiveness of polar ethanol decreases significantly.