Aliphatic Volatile Organic Compounds Research Articles

Enigma of Urban Gaseous Oxygenated Organic Molecules: Precursor Type, Role of NOx, and Degree of Oxygenation.

Oxidation of volatile organic compounds (VOCs) forms oxygenated organic molecules (OOMs), which contribute to secondary pollution. Herein, we present measurement results of OOMs using chemical ionization mass spectrometry with nitrate as the reagent ion in Shanghai. Compared to those in forests and laboratory studies, OOMs detected at this urban site were of relatively lower degree of oxygenation. This was attributed to the high NOx concentrations (∼44 ppb), which overall showed a suppression on the propagation reactions. As another result, a large fraction of nitrogenous OOMs (75%) was observed, and this fraction further increased to 84% under a high NO/VOC ratio. By applying a novel framework on OOM categorization and supported by VOC measurements, 50 and 32% OOMs were attributed to aromatic and aliphatic precursors, respectively. Furthermore, aromatic OOMs are more oxygenated (effective oxygen number, nOeff = 4-6) than aliphatic ones (nOeff = 3-4), which can be partly explained by the difference in initiation mechanisms and points to possible discrimination in termination reactions. This study highlights the roles of NOx in OOM formation in urban areas, as well as the formation of nitrogenous products that might show discrimination between aromatic and aliphatic VOCs.

Discriminative Detection of Aliphatic, Electron‐Rich and Electron‐Deficient Aromatic Volatile Organic Contaminants Using Conjugated Polymeric Fluorescent Nanoaggregates with Aggregation Induced Emission Characteristics

AbstractDiscrimination of aromatic, aliphatic volatile organic compounds (VOCs) with high sensitivity and easy operational techniques is important due to related environmental implications. Herein the development of fluorescent conjugated polymers is reported, consisting of donor–acceptor pairs and their nanoaggregates as fluorophores with differential emission behavior in the presence of aromatic, aliphatic VOCs and electron‐deficient VOCs both in aqueous solution and solid state. The polymeric network consists of fluorene moiety with dangling alkyl groups as donors and aggregation‐induced emission (AIE) active tetraphenylethylene (TPE) unit as an acceptor. The corresponding fluorescent nanoaggregates exhibit enhancement in the emission intensity owing to restriction in intramolecular motion of AIE unit in the presence of aliphatic VOCs, whereas the fluorescence enhancement is accompanied by a bathochromic shift in emission maxima in the case of aromatic VOCs owing to the conformational change in the phenyl rings of TPE unit. On the other hand, the fluorescence of nanoaggregates quenches in the presence of an electron‐deficient VOC through a possible nonradiative electron transfer. Detailed mechanistic studies are corroborated through a variety of spectroscopic, density functional theory calculations, and theoretical simulations. The discriminatory response of the polymeric nanoaggregates toward a different kind of VOCs can also be observed visually in the thin‐film state.

Rate coefficients for reactions of OH with aromatic and aliphatic volatile organic compounds determined by the multivariate relative rate technique

Abstract. The multivariate relative rate method was applied to a range of volatile organic compound (VOC) reactions with OH. This previously published method (Shaw et al., 2018) was improved to increase the sensitivity towards more slowly reacting VOCs, broadening the range of compounds which can be examined. A total of 35 room temperature relative rate coefficients were determined, eight of which have not previously been reported. Five of the new reaction rate coefficients were for large alkyl substituted mono-aromatic species recently identified in urban air masses, likely with large ozone production potentials. The new results (with kOH (296 K) values in units of 10−12 cm3 molec.−1 s−1) were n-butylbenzene, 11 (±4); n-pentylbenzene, 7 (±2); 1,2-diethylbenzene, 14 (±4); 1,3-diethylbenzene, 22 (±4); and 1,4-diethylbenzene, 16 (±4). Interestingly, whilst results for smaller VOCs agreed well with available structure–activity relationship (SAR) calculations, the larger alkyl benzenes were found to be less reactive than the SAR prediction, indicating that our understanding of the oxidation chemistry of these compounds is still limited. kOH (296 K) rate coefficients (in units of 10−12 cm3 molec.−1 s−1) for reactions of three large alkanes with OH were also determined for the first time: 2-methylheptane, 9.1 (±0.3); 2-methylnonane, 11.0 (±0.3); and ethylcyclohexane, 14.4 (±0.3), all in reasonable agreement with SAR predictions. Rate coefficients for the 27 previously studied OH + VOC reactions agreed well with available literature values, lending confidence to the application of this method for the rapid and efficient simultaneous study of gas-phase reaction kinetics.

Formation of highly porous electrochemically etched silicon carbide: A novel reusable adsorbent for air purification technology

In this study, carbon-rich mesoporous silicon carbide (CRP-SiC: thickness of 1.3 μm and surface area of 77.3 m2/g) was obtained by electrochemical etching of polycrystalline SiC using HF/acetonitrile (1:5.6 ratio) at an optimum current density of 30 mA/cm2. The selective etching of Si from SiC was validated by Raman and X-ray diffraction analyses. High resolution-transmission electron microscope and atomic force microscope analysis showed the mesoporous structure (range: 10–100 nm) and a valley-and-peak form on the surface of CRP-SiC, respectively. The potential utility of CRP-SiC as an ideal adsorbent for commercial application was investigated against the low-molecular aliphatic volatile organic compounds (VOCs) like glutaraldehyde (GA) and formaldehyde (FA) as model target compounds. The maximum specific adsorption capacity of CRP-SiC, when measured for the GA and FA at the initial concentration 30 ppm, were 89.1 and 79.2 mg/g, respectively. The total adsorption capacity of this adsorbent was above 90%, when reused up to five times. The adsorption performance of CRP-SiC was also remarkably high in terms of partition coefficient relative to many other types of common sorbents (e.g., powder or granular activated carbon). The potential of carbon-rich surface on a stable and hard SiC semiconducting material is investigated in depth to help find the better alternative for the conventional or other well recognized adsorbent for treating VOCs.

Sensing and capture of toxic and hazardous gases and vapors by metal-organic frameworks.

Toxic and hazardous chemical species are ubiquitous, predominantly emitted by anthropogenic activities, and pose serious risks to human health and the environment. Thus, the sensing and subsequent capture of these chemicals, especially in the gas or vapor phase, are of extreme importance. To this end, metal-organic frameworks have attracted significant interest, as their high porosity and wide tunability make them ideal for both applications. These tailorable framework materials are particularly promising for the specific sensing and capture of targeted chemicals, as they can be designed to fit a diverse range of required conditions. This review will discuss the advantages of metal-organic frameworks in the sensing and capture of harmful gases and vapors, as well as principles and strategies guiding the design of these materials. Recent progress in the luminescent detection of aromatic and aliphatic volatile organic compounds, toxic gases, and chemical warfare agents will be summarized, and the adsorptive removal of fluorocarbons/chlorofluorocarbons, volatile radioactive species, toxic industrial gases and chemical warfare agents will be discussed.

Atmospheric OH reactivity in central London: observations, model predictions and estimates of in situ ozone production

Abstract. Near-continuous measurements of hydroxyl radical (OH) reactivity in the urban background atmosphere of central London during the summer of 2012 are presented. OH reactivity behaviour is seen to be broadly dependent on air mass origin, with the highest reactivity and the most pronounced diurnal profile observed when air had passed over central London to the east, prior to measurement. Averaged over the entire observation period of 26 days, OH reactivity peaked at ∼ 27 s−1 in the morning, with a minimum of ∼ 15 s−1 during the afternoon. A maximum OH reactivity of 116 s−1 was recorded on one day during morning rush hour. A detailed box model using the Master Chemical Mechanism was used to calculate OH reactivity, and was constrained with an extended measurement data set of volatile organic compounds (VOCs) derived from a gas chromatography flame ionisation detector (GC-FID) and a two-dimensional GC instrument which included heavier molecular weight (up to C12) aliphatic VOCs, oxygenated VOCs and the biogenic VOCs α-pinene and limonene. Comparison was made between observed OH reactivity and modelled OH reactivity using (i) a standard suite of VOC measurements (C2–C8 hydrocarbons and a small selection of oxygenated VOCs) and (ii) a more comprehensive inventory including species up to C12. Modelled reactivities were lower than those measured (by 33 %) when only the reactivity of the standard VOC suite was considered. The difference between measured and modelled reactivity was improved, to within 15 %, if the reactivity of the higher VOCs (⩾ C9) was also considered, with the reactivity of the biogenic compounds of α-pinene and limonene and their oxidation products almost entirely responsible for this improvement. Further improvements in the model's ability to reproduce OH reactivity (to within 6 %) could be achieved if the reactivity and degradation mechanism of unassigned two-dimensional GC peaks were estimated. Neglecting the contribution of the higher VOCs (⩾ C9) (particularly α-pinene and limonene) and model-generated intermediates increases the modelled OH concentrations by 41 %, and the magnitude of in situ ozone production calculated from the production of RO2 was significantly lower (60 %). This work highlights that any future ozone abatement strategies should consider the role that biogenic emissions play alongside anthropogenic emissions in influencing London's air quality.

Copper(I) Metal-Organic Framework: Visual Sensor for Detecting Small Polar Aliphatic Volatile Organic Compounds.

A porous Cu(I)-MOF [H2O⊂Cu2(L)2I2; L = 1-benzimidazolyl-3,5-bis(4-pyridyl)benzene], which can be a visual and luminescent sensor for detecting small polar aliphatic volatile organic compounds (VOCs), such as alcohols, ketones, and halocarbons, is reported. The naked-eye and luminescent detection limitations for these VOCs are 5 and 1 ppm, respectively.

Ambient levels of volatile organic compounds in the vicinity of petrochemical industrial area of Yokohama, Japan.

Urban ambient air concentrations of 39 aromatic (including benzene, toluene, and xylenes) and aliphatic volatile organic compounds (VOCs) were measured in Yokohama city, Japan. Yokohama city was selected as a case study to assess the amount of VOC released from Industrial area to characterize the ambient air quality with respect to VOC as well as to know the impact of petrochemical storage facilities on local air quality. For this purpose, ambient air samples were collected (from June 2007 to November 2008) at six selected locations which are designated as industrial, residential, or commercial areas. To find out the diurnal variations of VOC, hourly nighttime sampling was carried out for three nights at one of the industrial locations (Shiohama). Samples were analyzed using gas chromatographic system (GC-FID). Results show strong variation between day and nighttime concentrations and among the seasons. Aliphatic fractions were most abundant, suggesting petrochemical storage facilities as the major source of atmospheric hydrocarbons. High concentrations of benzene, toluene, ethyl benzene, and xylene (BTEX) were observed at industrial locations. BTEX showed strong diurnal variation which is attributed to change in meteorology. During our campaign, low ambient VOC concentrations were observed at the residential site.

Distribution of volatile organic compounds around a polluted river

The objectives of this study were to investigate the species and the concentration distribution of volatile organic compounds around a heavily polluted river. Air samples were collected seasonally at different locations near the polluted river. Samples were then analyzed by gas chromatography (electron capture detector for chlorinated organic compounds and flame ionization detector for ordinary hydrocarbons). The data was then analyzed by the statistical product and service solutions software. The results showed that total of 26 species of volatile organic compounds were identified. Each individual had its own concentration distribution pattern at different seasons and aliphatic volatile organic compounds displayed much higher concentrations than most benzenoic volatile organic compounds. In aliphatic volatile organic compounds, 1,2-dibromo-3-chloropropane, hexachlorobutadiene and 1,2-dibromoetane had much higher concentrations at the nearby environment of the river and they have been claimed to be carcinogenic to some experimental animals and possibly to human. Therefore, It is in doubt that for a long term, the volatile organic compounds evaporating out of the stream may threat the health of the residents living very close to the river. The concentrations of tetrachloroethene, 1,1,2,2-tetrachloroethane, hexachlorobutadiene, dibromoetane, dichlorobenzene and sec-butylbenzene appeared at the nearby environment of the river had significant correlations (P < 0.05) with those of each other or many other volatile organic compounds.

Volatile Organic Compounds Emission from Contaminated Soil During Surfactant Washing

The emission characteristics of aromatic and aliphatic volatile organic compounds (VOCs) produced by two kinds of surfactants, nonionic Triton X-100 (TX-100) and cationic domiphen bromide (DB), washing high and low soil organic matter (SOM) soils were evaluated with two mass-balance equations. The influential factors on volatilization mass were primarily related to the affinity of the VOCs to the soils and to the surfactant solutions. The results show that the VOC emissions are a function of Koc, the surfactant properties and the Sw and P of the VOC. Nonionic surfactants could more effectively wash the VOCs away from the soil, leading to relatively higher emissions. When the surfactant concentrations exceeded the critical micelle concentrations (CMCs), VOC partitioning into the surfactant sorbed on the soil surface to reduce the VOC emissions. Whether the VOC can freely dissolve in the solution is the key point in determining the volatilization parameters. The emission of dissolved VOC is dependent on KOL and Sw. The P is the major parameter governing the emission of VOCs in an insoluble state. The solution properties can strongly affect the emissions of low Sw compounds due to solubility enhancement effects. The main effects on higher Sw compound emissions were the amounts of the surfactants adsorbing on the soil surface.