Removal of gaseous benzene by a fixed-bed system packed with a highly porous metal-organic framework (MOF-199) coated glass beads.

The utility of nanomaterial adsorbents is often limited by their physical features, especially fine particle size. For example, a large bed-pressure drop is accompnied inevitably, if fine-particle sorbents are used in a packed bed system. To learn more about the effect of adsorbent morphology on uptake performance, we examined the adsorption efficiency of metal-organic framework 199 (MOF-199) in the pristine (fine powder) form and after its binding on to glass beads as an inert support. Most importantly, we investigated the effect of such coatings on adsorption of gaseous benzene (0.1-10 Pa) in a dry N2 stream, particularly as a function of the amount of MOF-199 loaded on glass beads (MOF-199@GB) (i.e., 0,% 1%, 3%, 10%, and 20%, w/w) at near-ambient conditions (298 K and 1 atm). A 1% MOF-199 load gave optimal performance against a 0.1 Pa benzene vapor stream in 1 atm of N2, with a two-to five-fold improvement (e.g., in terms of 10% breakthrough volume [BTV] (46 L atm [g.MOF-199)-1], partition coefficient at 100% BTV (3 mol [kg.MOF-199]-1 Pa-1), and adsorption capacity at 100% BTV (20 mg [g.MOF-199]-1 (areal capacity: 8.8 × 10-7 mol m-2) compared with those of 3%, 10%, and 20% loading. The relative performance of benzene adsorption was closely associated with the content of MOF-199@GB (e.g., 1% > 3% > 10% > 20%) and the surface availability (m2 [g.MOF-199]-1) such as 291 > 221 > 198 > 181, respectively. This study offers new insights into the strategies needed to expand the utility of finely powdered MOFs in various environmental applications.

The feasibility and temporal storability of gas phase standards of volatile organic compounds prepared through liquid phase vaporization in polyester aluminum bags at room temperature.

Currently, the presence of many classes of volatile organic compounds (VOCs) in indoor air is well recognized. There is an impetus to accurately quantify airborne VOCs for the proper assessment of their human health risks. VOC standards prepared in a solvent are often vaporized in N2 gas-filled sampling bags for external calibration as the use of grab sampling bags is a common practice for the collection of real ambient air samples. Such practices can nontheless be subject to many sources of biases in their calibration (e.g., VOC chemical reaction with the solvent, adsorption on the bag interior surface, or leakage). The main goal of this work is to measure the temporal stability of 11 VOC targets (benzene, toluene, o-xylene, styrene, propionaldehyde, n-butyraldehyde, isovaleraldehyde, valeraldehyde, acrylonitrile, isoprene, and methyl ethyl ketone) selected in this research over 24 h which started 10 min after the injection and vaporization of liquid-phase standards (all prepared in methanol solvent) into polyester aluminum (PEA) bags containing 1 atm N2. Although all tested VOCs showed gradual decreases of their concentrations (e.g., >17% in 24 h), the aromatic hydrocarbon VOCs (namely BTXS) yielded the best relative recoveries (e.g., decreases of 11%-30% in 24 h) and relative errors (e.g., relative standard error (RSE) = 2.14-3.59%) in 5 replicate tests. A good linear relationship was established between the 24 h VOC relative recovery and molecular weight (R2 > 0.81). The results of this study offers valuable clues to properly reduce the bias in the calibration of gas-phase VOC standards when calibrating the system through the vaporization of liquid-phase VOC standards prepared in a solvent.

Proof of concept for CUK family metal-organic frameworks as environmentally-friendly adsorbents for benzene vapor.

The utility of metal-organic frameworks (MOFs) such as the CUK family (CUK - Cambridge University-KRICT) has been explored intensively for adsorption/separation of airborne volatile organic compounds (VOCs). In this article, three M-CUK analogs (M = Mg, Co, or Ni) were synthesized hydrothermally under similar conditions to assess the effects of their isostructural properties and metal centers on adsorption of benzene vapor (0.05-1 Pa). A list of performance metrics (e.g., breakthrough volume (BTV) and partition coefficient (PC)) were used to assess the role of the metal type (in M-CUK-1s) in the adsorption of VOCs. Specifically, Co-CUK-1 (average pore size of 8.98 nm) showed 2-3 times greater performance (e.g., in terms of 10% BTV (2012 L atm g-1) and PC (6 mol kg-1 Pa-1)) over other analogs when exposed up to 0.05 Pa benzene vapor. The superiority of mesoporous Co-CUK-1 (e.g., enhanced adsorption diffusion mechanism through favorable metal-π and π- π interactions) can be attributed to the presence of cobalt metal centers (e.g., in reference to Mg- or Ni-CUK-1).

Utilization of metal-organic frameworks for the adsorptive removal of an aliphatic aldehyde mixture in the gas phase.

Considerable efforts have been undertaken in the domain of air quality management for the removal of hazardous volatile organic compounds, particularly carbonyl compounds (CCs). In this study, the competitive sorptive removal of six CCs (namely, formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isovaleraldehyde, and valeraldehyde) was assessed using selected metal-organic frameworks (MOFs: MOF-5, MOF-199, UiO-66, and UiO-66-NH2) and inexpensive commercial activated carbon as a reference sorbent. The sorption experiments were conducted using a mixture of the six CCs (formaldehyde and acetaldehyde at ∼1 Pa and propionaldehyde, butyraldehyde, isovaleraldehyde, and valeraldehyde at ∼0.2 Pa) together with 15 Pa water and 2.6 Pa methanol in 1 bar nitrogen. For all of the carbonyl compounds other than formaldehyde, MOF-199 showed the best 10% breakthrough performance ranging from 34 L g-1 and 0.14 mol kg-1 Pa-1 for acetaldehyde to 1870 L g-1 and 7.6 mol kg-1 Pa-1 for isovaleraldehyde. Among all the sorbents tested, UiO-66-NH2 exhibited the best 10% breakthrough performance metrics towards the lightest formaldehyde which remains to be one of the most difficult targets for sorptive removal (breakthrough volume: 285 L g-1 and partition coefficient: 1.1 mol kg-1 Pa-1). Theoretical density functional theory (DFT)-based computations were also conducted to provide better insights into the adsorbate-adsorbent interactions. Accordingly, the magnitude of adsorption energy increased with an increase in the CC molar mass due to an enhancement in the synergetic interaction between C[double bond, length as m-dash]O groups (in adsorbate molecules) and the MOF active centers (open metallic centers and/or NH2 functionality) as the adsorbent. Such interactions were observed to result in strong distortion of MOF structures. In contrast, weak van der Waals attraction between the hydrocarbon "tail" of CC molecules and MOF linkers were seen to play a stabilizing role for the sorbent structure. The presence of the NH2 group in the MOF structure was suspected to play a key role in capturing lighter CCs, while such an effect was less prominent for heavier CCs. Overall, the results of this study provided a basis for the establishment of an effective strategy to enhance the sorption capacity of MOFs against diverse carbonyl species.

The effects of continuous- and stop-flow gas streams on adsorptive removal of benzene vapor using type - II covalent organic polymers.

Various materials have been investigated for the adsorptive removal of volatile organic compounds (VOCs, such as benzene). However, most materials proposed for the adsorptive removal of gaseous benzene (and other VOCs) perform relatively poorly (e.g., an impractically low-service 10% breakthrough volume [BTV10] at < 100 ppm). The adsorbent uptake rate (mg g-1 min-1) can also be assessed as a function of the gas-stream flow rate (or space velocity). The main aim of this study is to explore the effect of two different gas-stream supply modes - stopped flow (at a fixed stream flow rate of 330 mL atm min-1) vs. continuous flow (a variable-stream flow rate of 100, 200, or 330 mL atm min-1) on the adsorption metrics of gaseous benzene on 5 mg of two types of - II covalent organic polymers (COPs: CBAP-1 [DETA], CD; or CBAP-1 [EDA], CE). The sorbent tube outlet stream was sampled by two respective sampling methods (i.e., a large-volume injector [LVI] for stopped flow vs. syringe injection [SI] for continuous flow) for sample quantitation by gas chromatography flame-ionization detection (GC-FID). The observed BTV10 values in the two sampling modes were similar when tested using 10 ppm benzene, irrespective of sorbents: 56/60 (CD) vs. 620/624 L atm g-1 (CE). BTV10 values increased systematically with decreasing stream-flow rates to reflect the importance of space velocity in adsorptive removal of benzene. The overall assessment of adsorption performance between stopped flow (LVI) and continuous flow (SI) revealed that the performance of the adsorbent is independent of flow mode (e.g., when performance was compared at flow rate of 330 mL min-1).

Evidence of inter-species swing adsorption between aromatic hydrocarbons.

In this research, the competitive adsorption characteristics between aromatic hydrocarbons were investigated. It is well-known that an industrial effluent may contain a mixture of pollutants. The composition of effluents is usually highly variable in nature to depend upon the feedstock. Hence, one of the pollutants that is present in larger amounts may have the potential to dominate the sorption processes. Although many studies have investigated the competitive adsorption of volatile organic compounds (VOCs) onto activated carbon (AC) in detail, little is known about how the overall process is influenced when a fresh incoming VOC molecule encounters a sorbent bed pre-loaded with other VOCs. Consequently, the objective of the present study was to investigate the stability of pre-adsorbed VOC molecules in the presence of other potentially competitive VOCs in the influent stream. In this regard, the sorbent bed of AC was first preloaded with benzene (50 ppm (0.16 mg L-1)) and subsequently challenged by either high purity nitrogen or a stream of xylene (at 10, 50, or 100 ppm (0.043, 0.22, or 0.43 mg L-1)). The desorption rate of preloaded benzene and uptake rate of challenger xylene were assessed simultaneously. The maximum desorption rates of benzene (Rb) against two challenge scenarios (e.g., 100 ppm (0.43 mg L-1) xylene and pure N2) were very different from each other, i.e., 663 vs. 257 g kg-1 h-1, and their final benzene recoveries were 84% and 42%, respectively. The initially high desorption rate for the former quickly decreased with decreasing benzene residual capacity (C, mg g-1). Interestingly, the adsorption capacity of xylene increased considerably after the preloading of benzene (relative to no preloading). As such, 10% breakthrough volumes (BTV10) of 100, 50, and 10 ppm (0.43, 0.22, and 0.043 mg L-1) xylene challenge scenarios increased significantly from 100 to 186, 43.4 to 694, and 600 to 1000 L atm g-1, respectively. The prevalent mechanisms were analyzed using density functional theory (DFT)-based modelling approaches. The results demonstrated effective replacement of pre-adsorbed molecules with weaker affinity (e.g., benzene) when challenged by molecules with stronger affinity (e.g., xylene) toward the sorbent; this was accompanied by noticeable synergistic enhancement in the adsorption capacity of the latter.

Utilization of activated carbon as an effective replacement for a commercialized three-bed sorbent (Carbopack) to quantitate aromatic hydrocarbons in ambient air.

The potential use of activated carbon (AC) as an inexpensive and effective alternative sorbent material in thermal desorption is presented and validated for the analysis of aromatic volatile organic compounds (VOCs) such as benzene, toluene, m-xylene, and styrene (BTXS) in air. The optimum desorption conditions of an AC sampling tube (2 mg AC bed) were determined and compared with a commercial three-bed (Carbopack; C + B + X) tube sampler as a reference. The AC sampler exhibited good linearity (R2 > 0.99) and reproducibility (RSE of 2.38 ±â€¯0.21%) for BTXS analysis. The AC tube sampler showed good storability (up to 3 d) and excellent recyclability (up to 50 cycles). An analysis of BTXS in ambient air showed excellent agreement between AC and CBX (bias < 5%). The 1% breakthrough volume values for 2 mg AC, when tested at 100 ppb of benzene as a sole component or in a BTXS mixture, were 10,000 or 5000 L g-1, respectively. The results of this study support the performance of AC as a suitable medium for sampling VOCs as reliable as high-cost commercial sorbent products.

The retrograde adsorption phenomenon at the onset of breakthrough and its quantitation: An experimental case study for gaseous toluene on activated carbon surface.

The adsorption dynamics of common solid sorbents against various pollutant species are yet poorly understood with respect to the retrograde phenomenon in which the relationship between breakthrough vs. pulled volume is characterized by an early unusual trend (initial increase followed by a decrease to a minimum) and by a normal trend of finally increasing to 100% (or equilibrium). If such trend is expressed in terms of the partition coefficient (PC), a reversed trend of adsorption processes becomes more evident. Retrograde has been previously observed in the initial breakthrough (<10%) isotherms in continuous flow gas-phase adsorption processes. However, retrograde has been neglected/overlooked and not discussed at all in the main stream literature even when it is explicitly observed from isotherm datasets. To properly describe the various aspects of such process, a stop-flow technique was developed to measure the adsorption isotherm of a model volatile organic compound (i.e., toluene in this study) onto a commercial low-cost sorbent (activated carbon: AC). Accordingly, a 10% breakthrough volume of 762 L atm g-1 (corresponding adsorption capacity of 142 mg g-1) was determined (at an inlet stream 5 Pa of toluene in 1 atm of N2 and 5 mg of AC). This automated method was effective to generate a detailed breakthrough profile at high stream-flow rates (or high space velocities) to specifically detect the retrograde phenomenon at the breakthrough onset. This study offers a practical approach towards establishing an in-depth monitoring protocol for the rare retrograde phenomenon.

The unique features of non-competitive vs. competitive sorption: Tests against single volatile aromatic hydrocarbons and their quaternary mixtures.

The adsorption characteristics of four aromatic hydrocarbons (i.e., benzene, toluene, xylene, and styrene) onto ground-activated carbon were investigated both independently and as a mixture of the four at <10 Pa partial pressures (e.g., 0-100 ppm concentration range). The maximum sorption capacities for benzene, toluene, styrene, and xylene were measured both as a sole component and as a mixture (at 10 Pa). In the former, the values were approximately 123, 184, 272, and 238 mg g-1, respectively. In contrast, the latter values were 5, 52, 222, and 248 mg g-1 respectively, showing dramatic reduction in lighter compounds (below C7) relative to heavier ones (above C8). The mechanistic detail of sorption has been explained in terms of Henry's law and Langmuir, Freundlich, Dubinin-Radushkevich, and Elovich isotherm models. The linearized Langmuir adsorption isotherm analysis showed three sorption pressure regions: low (<1 Pa, retrograde), intermediate (1-4 Pa), and high (4-10 Pa). As such, the outcome of this study offers a unique opportunity to acquire detailed information on the dramatic and dynamic effects of the sorptive interaction between competing sorbates, along with a common sorption process between sorbent and sorbate at 298 K.

Competitive adsorption of gaseous aromatic hydrocarbons in a binary mixture on nanoporous covalent organic polymers at various partial pressures.

Covalent-organic polymers (COPs) are recognized for their great potential for treating diverse pollutants via adsorption. In this study, the sorption behavior of benzene and toluene was investigated both individually and in a binary mixture against two types of COPs possessing different -NH2 functionalities. Namely, the potential of COPs was tested against benzene and toluene in a low inlet partial pressure range (0.5-20 Pa) using carbonyl-incorporated aromatic polymer (CBAP)-1-based diethylenediamine (EDA) [CD] and ethylenetriamine (DETA) [CE]. The maximum adsorption capacity and breakthrough values of both COPs showed dynamic changes with increases in the partial pressures of benzene and toluene. The maximum adsorption capacities (Amax) of benzene (as the sole component in N2 under atmospheric conditions) on CD and CE were in the range of 24-36 and 33-75 mg g-1, respectively. In contrast, with benzene and toluene in a binary mixture, the benzene Amax decreased more than two-fold (range of 2.7-15 and 6-39 mg g-1, respectively) due to competition with toluene for sorption sites. In contrast, the toluene Amax values remained consistent, reflecting its competitive dominance over benzene. The adsorption behavior of the targeted compounds (i.e., benzene and toluene) was explained by fitting the adsorption data by diverse isotherm models (e.g., Langmuir, Freundlich, Elovich, and Dubinin-Radushkevich). The current research would be helpful for acquiring a better understanding of the factors affecting competitive adsorption between different VOCs in relation to a given sorbent and across varying partial pressures.

The effect of diverse metal oxides in graphene composites on the adsorption isotherm of gaseous benzene.

The effective removal technique is necessary for the real world treatment of a hazardous pollutant (e.g., gaseous benzene). In an effort to develop such technique, the adsorption efficiency of benzene in a nitrogen stream (5 Pa (50 ppm) at 50 mL atm min-1 flow rate and 298 K) was assessed against 10 different metal oxide/GO composite materials (i.e., 1: graphene oxide Co (GO-Co (OH)2), 2: graphene oxide Cu (GO-Cu(OH)2), 3: graphene oxide Mn (GO-MnO), 4: graphene oxide Ni (GO-Ni(OH)2), 5: graphene oxide Sn (GO-SnO2), 6: reduced graphene oxide Co (rGO-Co(OH)2), 7: reduced graphene oxide Cu (rGO-Cu(OH)2), 8: reduced graphene oxide Mn (rGO-MnO), 9: reduced graphene oxide Ni (rGO-Ni(OH)2), and 10: reduced graphene oxide Sn (rGO-SnO2)) in reference to their pristine forms of graphene oxide (GO) and reduced graphene oxide (rGO). The highest adsorption capacities (at 100% breakthrough) were observed as ~23 mg g-1 for both GO-Ni(OH)2 and rGO-SnO2, followed by GO (~19.1 mg g-1) and GO-Co(OH)2 (~18.8 mg g-1). Therefore, the GO-Ni(OH)2 and rGO-SnO2 composites exhibited considerably high capacities to treat streams containing >5 Pa of benzene. However, the lowest adsorption capacity was found for GO-MnO (0.05 mg g-1). Alternately, if expressed in terms of the 10% breakthrough volume (BTV), the five aforementioned materials showed values of 0.50, 0.46, 0.40, 0.44, and 0.39 L g-1, respectively. The experimental data of target sorbents were fitted to linearized Langmuir, Freundlich, Elovich, and Dubinin-Radushkevich isotherm models. Accordingly, the non-linear Langmuir isotherm model revealed the presence of two or more distinct sorption profiles for several of the tested sorbents. Most of the sorbents showed type-III isotherm profiles where the sorption capacity proportional to the loaded volume.

A comparison of figure of merit (FOM) for various materials in adsorptive removal of benzene under ambient temperature and pressure.

To effectively remove gaseous pollutants from air using sorbents, a thorough knowledge of the actual sorption performance is needed at ambient conditions rather than at unrealistically high-pressure conditions, as is commonly presented in the literature. To this end, the sorbent capacities of gaseous benzene were evaluated at a constant sorbent bed inlet pressure (50 ppm or ~5 Pa) in 1 atm of N2, room temperature (298 K), a fixed flow rate (50 mL min-1), and equal outlet sampling intervals (5 min). The benzene adsorption patterns were investigated against six sorbent types in a total of 17 different forms: 1- zeolite in five forms: beads (ZB), ground to 212 µm (ZG212), beads ground to 300 µm (ZG300), coarsely ground/washed zeolite (ZWc), and coarsely ground/washed/thermally treated zeolite (ZTc), 2- activated carbon in two forms: 212 µm (ACd212) and granular (ACdg), 3- Carbopack-X (CX), 4- Tenax TA (TA), 5- used black tea leaves of 150 or 300 µm in three forms: dry (TD150/TD300), wet (TW150/TW300), and wet dust (TWd), and 6- used ground coffee in either dry (CD) or wet forms (CW). Accordingly, the largest adsorption capacities at 5 Pa (e.g., >10 mg g-1) were observed for ACd212 (79.1) and ACdg (73.6). Moderate values (e.g., 5 < < 10 mg g-1) were obtained for ZG212 (7.98), CX (6.79), ZG300 (5.70), and ZB (5.58), while the remainder were far lower at < 5 mg g-1 (e.g., tea leaves, ground coffee, TA, ZWc, and ZTc). The experimental benzene capacities of the tested sorbents were further assessed by the Langmuir, Henry's law, Freundlich, Dubinin-Radushkevich, and Elovich isotherm models. The linearized Langmuir adsorption isotherms of ACd212, ACdg, and CX showed the presence of more than one adsorption site (i.e., retrograde at the lowest pressures and two others at higher pressures). However, TA, zeolite, tea leaves, and ground coffee exhibited a type-V isotherm, wherein the sorption capacity continued to increase with loaded volume (i.e., multilayer adsorption). Thus, ACd212 has the best figure-of-merit based on a high 10% breakthrough volume (BTV) and low cost for real-world applications.

Sorptive process and breakthrough behavior of odorous volatile compounds on inert surfaces.

The use of glass impinger is an important device for sampling and handling when measuring volatile organic compounds (SVOCs). Thus, it is important to check for possible analyte losses to the inner glass surface when carrying out sample analysis with the aid of impinger system. In this research, we evaluated the sorptive loss patterns of vapor-phase semi-volatile organic compounds [SVOCs (n = 10): acetic acid (ACA), propionic acid (PPA), i-butyric acid (IBA), n-butyric acid (BTA), i-valeric acid (IVA), n-valeric acid (VLA), phenol (PhAl), p-cresol (p-C), indole (ID), and skatole (SK)] on inert surfaces of an impinger in reference to sampling bags. The gaseous standard of these SVOCs (48-406 ppb) in polyester aluminum (PEA) bags was passed through an empty impinger in 1 L steps. The exiting SVOCs were collected on three-bed sorbent tubes for subsequent analysis by thermal desorption-gas chromatography-mass spectroscopy (TD-GC-MS). Impinger wall sorption capacities ranged from 2.0 to 21.0 ng cm-2. The 10% breakthrough adsorption capacities on the impinger wall for acids, phenols, and indoles ranged from 1.21 ± 0.15 to 5.39 ± 0.79, 0.92 ± 0.12 to 13.4 ± 2.25, and 4.47 ± 0.42 to 5.23 ± 0.35 ng cm-2, respectively. The observed sorptive patterns suggest that the sorptive losses of the volatile fatty acids, phenols, and indoles can occur very effectively at low ppb levels onto a glass surface.

The effect of flavor content in e-liquids on e-cigarette emissions of carbonyl compounds.

The effect of flavors on carbonyl compound (CC) emission factors (EF) from electronic cigarettes (ECs) vaping was investigated at the default vaping (voltage) setting in all experiments using a total of 21 lab-made e-liquid samples (five different types of retail flavorant bases: beverage/dessert/fruit/mint/tobacco). Each flavorant base was added to a separate unflavored base composed of a 1:1 mixture of propylene glycol/vegetable glycerol (PG/VG) at four levels (5/10/30/50% (v/v)). The e-liquid CC levels increased linearly with flavorant base content, 1.3-10.5 times (R2: 0.762-0.999). The vaping CC EFs increased linearly with flavorant base content (if ≥ 10%) from 1.0 to 92 times (R2: 0.431-0.998). For flavorant base content of 0%, 5%, and 10%, the EFs ranged from undetected to 0.11 µg puff-1 (acetone). The 40-year cancer risk due to formaldehyde (70 kg EC user inhaling 5% flavorant base content e-liquid: 120 puffs day-1) is estimated to be 2.0E-06 (highest) compared to 1.0E-06 for the 1:1 PG:VG base. Most formaldehyde vaped from the fruit flavored e-liquid was the flavorant base. The CC concentrations in EC liquids (before vaping) were approximately linear with e-liquid flavorant base content. Retail e-liquid product information labels should be guided to provide a complete list of all ingredients, their concentrations, and carbonyl compound EFs.

Determination of carbonyl compounds in electronic cigarette refill solutions and aerosols through liquid-phase dinitrophenyl hydrazine derivatization.

In this study, we report a 2,4-dinitrophenylhydrazine (DNPH) derivatization HPLC/UV method to quantify carbonyl compounds (CCs) either in electronic cigarette (EC) refill solutions or in vaped aerosols. Vaped aerosol samples were entrained in a 1 L atm min-1 ambient lab air stream and pulled through an impinger containing a DNPH solution for derivatization. The mass change tracking (MCT) approach was used to check mass balance. Refill solution samples were diluted (2, 4, and 10 times) in a DNPH/acetonitrile solution for derivatization. EC vaping samples were collected for 5, 10, or 15 puffs (2-s puff duration) with a 10-s interpuff interval. The DNPH derivatization method was used successfully for the estimation of both EC liquid CCs concentrations and vaping emission factors. The results for formaldehyde (FA), acetaldehyde (AA), and butyraldehyde (BA) were determined as 10.4 ± 3.10 µg mL-1 (27.6 ± 7.43 ng puff-1), 1.9 ± 0.83 µg mL-1 (4.4 ± 1.98 ng puff-1), and 4.4 ± 2.82 µg mL-1 (12.0 ± 7.43 ng puff-1), respectively.

Airborne volatile aromatic hydrocarbons at an urban monitoring station in Korea from 2013 to 2015.

The concentrations of C6-C10 volatile aromatic hydrocarbons (AHCs) in air were measured at an urban air quality monitoring station in Jong-Ro, Seoul, Korea, between 2013 and 2015. Their temporal patterns (e.g., diurnal, intraweek, daily) were assessed individually and collectively as groups of benzene, toluene, ethylbenzene, styrene, and xylene (BTESX); total aliphatic hydrocarbon (TALHC: C2-C12); total aromatic hydrocarbon (TARHC: C6-C10); and total hydrocarbon (THC: C2-C12). The highest mean AHC concentrations over the 3-year study (in ppb (v/v)) were observed for toluene (6.0 ±â€¯4.3), followed by the xylenes (1.5 ±â€¯1.3), ethylbenzene (0.85 ±â€¯0.93), benzene (0.73 ±â€¯0.77), and styrene (0.16 ±â€¯0.30) nL/L. The mean ppbC ((v/v), nL∙atm∙C/nL∙atm) values for BTESX, TALHC, TARHC, and THC were 65.8, 113, 77.7, and 191 ppbC, respectively. For most AHC species (e.g., toluene, styrene, and BTESX), only weak seasonal trends were observed in contrast to temporally varying species like nitric oxide (NO) (e.g., 26.3 ppb (January-February) vs. 8.5 ppb (July-August) during weekdays in 2013). Furthermore, toluene and NO concentrations were much higher (up to a factor 3) on weekdays than on Sunday for most weeks. This might reflect reduced anthropogenic activities on Sunday.

Long-term trends in airborne SO2 in an air quality monitoring station in Seoul, Korea, from 1987 to 2013.

Atmospheric concentration of sulfur dioxide (SO2) was intermittently measured at an air quality monitoring (AQM) station in the Yong-san district of Seoul, Korea, between 1987 and 2013. The SO2 level was compared with other important pollutants concurrently measured, including methane (CH4), carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO2), ozone (O3), and particulate matter (PM10). If split into three different periods (period 1, 1987-1988, period 2, 1999-2000, and period 3, 2004-2013), the respective mean [SO2] values (6.57 ± 4.29, 6.30 ± 2.44, and 5.29 ± 0.63 ppb) showed a slight reduction across the entire study period. The concentrations of SO2 are found to be strongly correlated with other pollutants such as CO (r = 0.614, p = 0.02), which tracked reductions in reported emissions due to tighter emissions standards enacted by the South Korean government. There was also a clear seasonal trend in the SO2 level, especially in periods 2 and 3, reflecting the combined effects of domestic heating by coal briquettes and meteorological conditions. Although only a 16% concentration reduction was achieved during the 27-year study duration, this is significant if one considers rapid urbanization, an 83.2% increase in population, and rapid industrialization that took place during that period. IMPLICATIONS: Since 1970, a network of air quality monitoring (AQM) stations has been operated by the Korean Ministry of Environment (KMOE) for routine nationwide monitoring of air pollutant concentrations in urban/suburban areas. To date, the information obtained from these stations has provided a platform for analyzing long-term trends of major pollutant species. In this study, we examined the long-term trends of SO2 levels and relevant environmental parameters monitored continuously in the Yong-san district of Seoul between 1987 and 2013. The data were analyzed over various time scales (i.e., monthly, seasonal, and annual intervals). The results obtained from this study will allow us to assess the effectiveness of abatement strategy and to predict future concentrations trends in association with future abatement strategies and technologies.

Air ionization as a control technology for off-gas emissions of volatile organic compounds.

High energy electron-impact ionizers have found applications mainly in industry to reduce off-gas emissions from waste gas streams at low cost and high efficiency because of their ability to oxidize many airborne organic pollutants (e.g., volatile organic compounds (VOCs)) to CO2 and H2O. Applications of air ionizers in indoor air quality management are limited due to poor removal efficiency and production of noxious side products, e.g., ozone (O3). In this paper, we provide a critical evaluation of the pollutant removal performance of air ionizing system through comprehensive review of the literature. In particular, we focus on removal of VOCs and odorants. We also discuss the generation of unwanted air ionization byproducts such as O3, NOx, and VOC oxidation intermediates that limit the use of air-ionizers in indoor air quality management.

Toward a better understanding of the impact of mass transit air pollutants on human health.

Globally, modern mass transport systems whether by road, rail, water, or air generate airborne pollutants in both developing and developed nations. Air pollution is the primary human health concern originating from modern transportation, particularly in densely-populated urban areas. This review will specifically focus on the origin and the health impacts of carbonaceous traffic-related air pollutants (TRAP), including particulate matter (PM), volatile organic compounds (VOCs), and elemental carbon (EC). We conclude that the greatest current challenge regarding urban TRAP is understanding and evaluating the human health impacts well enough to set appropriate pollution control measures. Furthermore, we provide a detailed discussion regarding the effects of TRAP on local environments and pedestrian health in low and high traffic-density environments.

Airborne foliar transfer of PM bound heavy metals in Cassia siamea: A less common route of heavy metal accumulation.

In order to investigate possible foliar transfer of toxic heavy metals, concentrations of Cd, Pb, and Fe were measured in samples of: Cassia siamea leaves (a common tree) Cassia siamea foliar dust, nearby road dust, and soil (Cassia siamea tree roots) at six different sites in/around the Bilaspur industrial area and a control site on the university campus. Bilaspur is located in a subtropical central Indian region. The enrichment factor (EF) values of Pb and Cd, when derived using the crustal and measured soil Fe data as reference, indicated significant anthropogenic contributions to Pb and Cd regional pollution. Based on correlation analysis and scanning electron microscopy (SEM) observations, it was evident that Pb and Cd in foliar part of Cassia siamea were largely from airborne sources. The SEM studies of leaf confirmed that leaf morphology (epidermis, trichome, and stomata) of Cassia siamea helped accumulate the toxic metals from deposited particulate matter (PM). There is a line of evidence that the leaf of Cassia siamea was able to entrap PM in respirable suspended particulate matter (RSPM) range (i.e., both in fine and coarse fractions). The overall results of this study suggest that Cassia siamea can be a potential plant species to control the pollution of PM and PM-bound metals (Pb and Cd) in affected areas.