Cold Trap Research Articles

A simple Peltier cold trap aperture for protection of vacuum UV optics against hydrocarbons and reliable calibration of VUV spectrometers using D2 lamps

A simple Peltier cooled cold trap aperture is presented to minimize the flux of hydrocarbons on optics in vacuum UV systems. The system can be cooled down to −40 °C under vacuum. To test the effect of the cold trap, the aperture is placed in front of a high-intensity D2 lamp used for calibration in the range of 116 nm to 300 nm which is flanged to a VUV spectrometer. The influence of the aperture temperature is monitored by measuring the intensity loss rate of the Lyman-alpha emission line at 121.6 nm due to the formation of carbon contamination on the MgF2 window of the lamp depending on the Peltier temperature. The application of the aperture significantly reduced the intensity loss from approx. 20% h−1 to less than 2% h−1 and enables the reliable use of a D2 lamp for the relative intensity calibration of the spectrometer.

Effects of transition metal oxides on pyrolysis properties of PVC

Polyvinyl chloride (PVC) produces a large amount of solid wastes because of its wide use. How to dispose quickly and harmlessly of the PVC solid wastes and turn into a resource is currently a major problem. In this paper, the experimental material was PVC. Thermogravimetric analyzer (TG) and pyrolysis-gas chromatography-mass spectrometer (Py-GC–MS) were used to study the pyrolysis characteristics of PVC with transition metal oxide. The effect of in-situ pyrolysis of PVC in N2 on transition metal oxides was studied in a SX3−4-10A muffle furnace. The composition of tars captured by the cold trap was analyzed by GC–MS. The residual carbon after pyrolysis was analyed by scanning electron microscope (SEM) and XRD. The results of PY-GC–MS and GC–MS showed that the two stages of PVC pyrolysis were advanced with the transition metal oxide.The decomposition peak temperature increased to make PVC pyrolysis more complete. The transition metal oxide reduced significantly the production of benzene, toluene, indene, naphthalene, anthracene and other compounds during the pyrolysis of PVC. The results of SEM and XRD showed that transition metal oxides absorbed HCl produced by pyrolysis and increased the amount of residual carbon in the system. These studies provided a theoretical basis for the pyrolysis rapidly of PVC.

Mercury biogeochemistry over the Tibetan Plateau: An overview

Since the beginning of the 21st century, our knowledge of the sources and fate of Hg over the Tibetan Plateau (TP), the “Roof of the World,” has been greatly enhanced with growing literature. Here, we reviewed the available literature to obtain a comprehensive understanding of Hg biogeochemistry over the TP. The biogeochemical Hg cycling is characterized by the following features: (1) There are existing but limited local emission sources of anthropogenic Hg in the TP. The Indian Summer Monsoon is an important transporter of atmospheric Hg pollution into the inland TP; (2) “Cold trapping effect” plays an important role in the atmospheric Hg deposition over the TP. Glacier, vegetation, and soil act as important “sinks” of atmospheric Hg pollution; (3) Enhanced anthropogenic activities around the TP, climate warming and glacier melting have the potential impacts to affect the behavior and distribution of Hg; (4) Significant bioaccumulation of MeHg (>100 ng/g) has been found in the Tibetan aquatic food chains. Considering that transboundary transport is responsible for the widespread Hg pollution in the TP, international/regional collaborations regarding Hg emission regulations are needed to reduce the migration of Hg and to mitigate adverse Hg pollution impacts on the TP.

Cryocooled cold trap system for the SuperCDMS dilution refrigerator

Operating 6,800 feet underground at the SNOLAB facility in Sudbury, Ontario, Canada, the dilution refrigerator-cooled SuperCDMS SNOLAB (Super Cryogenic Dark Matter Search at the Sudbury Neutrino Observatory Laboratory) experiment has been designed for maximum cryogenic up-time and remote operations. A key element in achieving these goals is a pair cold traps in the helium circulation stream of the dilution refrigerator; the first operating near liquid nitrogen temperatures and the second operating near liquid helium temperatures. Previous experience with the CDMS experiment, located underground at the Soudan Under-ground Laboratory, has given significant operational experience with dilution refrigerator cold traps and has solidified the demand of a system of dual cold traps. Unlike the CDMS-era system, the new SuperCDMS system will feature a cryocooler powered liquid nitrogen re-liquefying system (as opposed to regular under-ground re-filling of cold trap dewars using portable nitrogen dewars) and a cryogen-free 4 K cold trap, which eliminates the need for a bath of liquid helium.

Stabilization of Dayside Surface Liquid Water via Tropopause Cold Trapping on Arid Slowly Rotating Tidally Locked Planets

Abstract Terrestrial-type exoplanets orbiting nearby red dwarf stars (M dwarfs) are among the best targets for atmospheric characterization and biosignature searches in the near future. Recent evolutionary studies have suggested that terrestrial planets in the habitable zone of M dwarfs are probably tidally locked and have limited surface water inventories as a result of their host stars’ high early luminosities. Several previous climate simulations of such planets have indicated that their remaining water would be transported to the planet’s permanent nightside and become trapped as surface ice, leaving the dayside devoid of water. Here we use a three-dimensional general circulation model with a water cycle and accurate radiative transfer scheme to investigate the surface water evolution on slowly rotating tidally locked terrestrial planets with limited surface water inventories. We show that there is a competition for water trapping between the nightside surface and the substellar tropopause in this type of climate system. Although under some conditions the surface water remains trapped on the nightside as an ice sheet, in other cases liquid water stabilizes in a circular area in the substellar region as a wetland. Planets with 1 bar N2 and atmospheric CO2 levels greater than 0.1 bar retain stable dayside liquid water, even with very small surface water inventories. Our results reveal the diversity of possible climate states on terrestrial-type exoplanets and highlight the importance of surface liquid water detection techniques for future characterization efforts.

PAH sampling and quantification from woody biomass fast pyrolysis in a pyroprobe reactor with a modified tar sampling system

The present work focuses on the sampling procedure and quantification of the PAH yield from the fast pyrolysis of waste softwood. In particular, fast pyrolysis experiments were conducted using a CDS Pyroprobe 5200 at temperatures between 500 °C and 1000 °C, at a heating rate of 600 °C/s for a sample size of 30 mg. High performance liquid chromatography (HPLC) was used for the determination of the PAH compounds present in the liquid sample fraction, while a micro – GC was employed for the analysis of the main gaseous products (CO, CO2, CH4 and H2). An alternative tar sampling protocol was proposed, which employed the use of a cold trap (50 °C) and an isopropanol filled impinger bottle for the collection of the condensable products. The experiments were compared to heated foil reactor based pyrolysis tests within the same temperature range and heating rate, except for a slightly lower sample size (10 mg).The Pyroprobe and adapted sampling system proved to be more efficient regarding PAH capture and quantification compared to the heated foil reactor. Naphthalene, acenaphthylene and phenanthrene were the main PAH compounds detected. The PAH yields increased with pyrolysis temperature, up to values corresponding to roughly 0.2 wt% of the overall yield at 1000 °C. From the results it was derived that PAH evolution is mainly a product of secondary decomposition of primary tar, since the char yield stabilized for higher temperatures and the yields of CO, H2 and CH4 increased. Overall mass balance closure values were around 80 wt% on average. Char and gas yields were determined with high reproducibility, however gravimetric liquid analysis lacked due to the inability to gravimetrically measure the yield condensing in the impinger bottle. Future work is aimed on improving on this particular aspect. Overall, the alternative tar sampling system proposed was successful in the quantification of PAH from biomass fast pyrolysis experiments offering increased flexibility, accuracy and practicality of use.

High-rate sputter deposition of chromium oxide thin films using water vapor as a reactive gas

The use of water vapor as a reactive gas under metallic mode for high rate sputter deposition of chromium oxide thin films have been studied in the course of this research. Chromium oxide (Cr2O3) thin films were deposited by an RF magnetron sputtering system with chromium metal as a target and argon (Ar) and water vapor (H2O) as the sputtering gas. Water was injected to the target or substrate surface at an H2O flow ratio of H2O/(H2O + Ar), varied from 0 to 100%. A liquid nitrogen cold trap was placed in the sputtering chamber to adsorb non-reacted H2O molecules.When the cold trap was inactive, the deposition rate and discharge voltage dropped and the transmittance of the films increased above an H2O flow ratio of 10%. Discharge voltage and plasma emission measurements showed that Cr2O3 films were deposited under compound target mode. In contrast, when the cold trap was active, the deposition rate increased with increase in H2O flow ratio and also a gradual increase in the transmittance of the films was observed. Hence, the target surface was considered to be almost in a metallic state and the oxidation proceeded gradually. Results of this study indicate that H2O sputtering using cold trap is a promising method for the formation of chromium oxide thin films at high deposition rates under metallic target mode.

Assessment of Cu, Zn, Mn, and Fe enrichment in Mt. Kenya soils: evidence for atmospheric deposition and contamination.

Mountains are the preferred sites for studying long-range atmospheric transportation and deposition of heavy metals, due to their isolation and steep temperature decrease that favors cold trapping and condensation of particulate forms of heavy metals. Any enrichment of heavy metals in mountains is presumed to primarily occur through atmospheric deposition. In this particular study, we assessed the status of 27 subsurface soils collected along two elevation gradients of Mt. Kenya using enrichment factors (EFs) as the ecological risk assessments. The collected soils were analyzed for total organic carbon, zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu). The mean concentration of Mn, Fe, Zn, and Cu was 0.376mg/kg, 47.6mg/kg, 12.3mg/kg, and 4.88mg/kg in Chogoria and 0.560mg/kg, 113mg/kg, 12.7mg/kg, and 2.70mg/kg in Naro Moru respectively. These concentrations were below the US-EPA maximum permissible levels for soils, implying that the levels recorded had low toxicity. Meanwhile, the mean enrichment factors for Mn, Cu, and Zn were 0.447, 131, and 78.8 in Chogoria and 0.463, 38.9, and 53.0 in Naro Moru respectively. This implied that Zn and Cu in Chogoria sites were extremely enriched, while in Naro Moru, enrichment levels ranged from significant to extreme. However, Mn was found to have minimal enrichment in all the sites. Lower montane forest and bamboo zone recorded relatively high enrichment due to distance from source of pollution. Ericaceous zone also had high mean enrichment due to influence of wind which favors higher deposition at mid-elevations.

Thermogravimetric-mass spectrometric characterization of thermal decomposition of lignite with attention to the evolutions of small molecular weight oxygenates

Thermogravimetry coupled with electron impact mass spectrometry (TG-EI MS) was used to investigate the evolutions of gases and small molecular weight oxygenates during the pyrolysis of a raw lignite and a potassium (K)-impregnated lignite. By clarifying the effects of ionization on the fragmentations of various compounds, it was found that a low ionizing energy of 20 eV was better for detecting oxygenates. The study further proposed a unique approach of the installment of a cold trap between the TG-MS interfaces. This vapor trapping approach is useful to distinguish between some compounds of equal mass in terms of their different boiling points. The real-time release of various oxygenates during the pyrolysis of the raw lignite and the K-impregnated lignite were detected. It was found that some highly volatile oxygenates such as formic acid (46 m/z), acetone (58 m/z) and butanone (72 m/z) started to release at a temperature of 200 °C or lower. Many oxygenates such as furan (68 m/z), methylfuran (82 m/z), cyclopentenone (82 m/z), cyclopentanone (84 m/z), furfural (96 m/z), dimethylfuran (96 m/z), cyclohexenone (96 m/z) and dimethoxyphenol (154 m/z) could be explained as the products degraded from the preserved woody components in this low-maturity lignite. The K impregnation overall facilitated the formations of oxygenates, while it had an inhibitory effect on the formation of CO and an insignificant effect on the formations of some oxygenates such as acetic acid and phenol. The curves of differential thermogravimetry (DTG) were deconvoluted to correspond to the staged release characteristics of main gases and various oxygenates.

Uranus in Northern Midspring: Persistent Atmospheric Temperatures and Circulations Inferred from Thermal Imaging

Abstract We present results from mid-infrared imaging of Uranus at wavelengths of 13.0 and 18.7 μm, sensing emission from the stratosphere and upper troposphere, acquired using the VISIR instrument at the Very Large Telescope, 2018 September 4–October 20. Using a combination of inverse and forward modeling, we analyze these northern midspring (L s ∼ 46°) images and compare them to archival data to assess seasonal changes since the 1986 southern solstice and subsequent equinox. We find the data are consistent with little change (<0.3 K) in the upper tropospheric temperature structure, extending the previous conclusions of Orton et al. well past equinox, with only a subtle increase in temperature at the emerging north pole. Additionally, spatial-temporal variations in 13 μm stratospheric emission are investigated for the first time, revealing meridional variation and a hemispheric asymmetry not predicted by models. Finally, we investigate the nature of the stratospheric emission and demonstrate that the observed distribution appears related and potentially coupled to the underlying tropospheric emission six scale heights below. The observations are consistent with either midlatitude heating or an enhanced abundance of acetylene. Considering potential mechanisms and additional observations, we favor a model of acetylene enrichment at midlatitudes resulting from an extension of the upper tropospheric circulation, which appears capable of transporting methane from the troposphere, through the cold trap, and into the stratosphere for subsequent photolysis to acetylene.

High-Sensitivity Measurement of Cr Isotopes by Double Spike MC-ICP-MS at the 10 ng Level.

High-sensitivity and high-precision (2 SD ≤ 0.06‰) measurement of chromium (Cr) isotopes at the 10 ng level was successfully carried out using double spike multiple-collector inductively couple plasma mass spectrometry (MC-ICP-MS). To enhance the signal sensitivity and stability, the Aridus II desolvating nebulizer system was improved by placing its waste gas trap bottle in an ice chamber (5 °C cold trap). This setup, beyond Cr isotope analysis, can be applied to most heavy metal isotope measurements. The sensitivity of the 52Cr signal is ≥300 V mg-1 L (with a 1011Ω amplifier and a 110 μL min-1 uptake rate), an enhancement of ≥1.5 times compared to the Aridus II without the cold trap. In addition, the relative standard deviation of the 52Cr signal varied ≤4% over 8 h, demonstrating high stability. The δ53Cr values of common geological reference materials determined using 10 ng of Cr are in excellent agreement with results measured at 25 ng and 50 ng and are consistent with previous determinations, validating the accurate and precise Cr isotope ratio measurements. An empirical method is proposed to correct for the residual (after subtraction) effect of Fe interference on δ53Cr determination. This method relies on a linear relationship between the [Fe]/[Cr] and δ53Cr shift within one analytical session. Finally, we report the δ53Cr values of 19 new reference materials, ranging from -0.44‰ to 0.49‰. Among them, GSS-7 (-0.44 ± 0.02‰, 2 SD, n = 5), GSS-4 (0.48 ± 0.02‰, 2 SD, n = 5), and GSD-10 (0.49 ± 0.05‰, 2 SD, n = 5) can be used as candidate reference materials for interlaboratory comparisons to complement existing ones that are mostly isotopically unfractionated from the bulk silicate earth.

Burn-up determination and accident testing of HTR-PM fuel elements irradiated in the HFR Petten

The current paper reports the results of gamma spectroscopic burn-up determination and KüFA safety testing at JRC Karlsruhe on spherical high-temperature reactor fuel elements, which were fabricated by the Institute of Nuclear and New Energy Technology of the Tsinghua University, Beijing. The fuel elements were irradiated in the High Flux Reactor, Petten, in the frame of the HFR-EU1 and HTR-PM campaigns and transported to JRC Karlsruhe for post-irradiation examination and accident testing in the KüFA device in the frame of a bilateral safety research study. Burn-up determination was performed on seven fuel elements based on the quantitative measurement of their Cs-137 inventories using an established gamma spectroscopy set-up in the JRC hot cell facilities. Accident testing was conducted on three HTR-PM fuel elements in several phases at simulated accident temperatures between 1620 °C and 1770 °C for 150 h to simulate hypothetical depressurization and loss-of-forced circulation accidents. The release of Kr-85 was measured during the tests in a cold trap and solid fission product release was determined by gamma spectroscopic analyses of exchangeable cold plates in a low background environment. After successful completion of the KüFA tests the fuel elements are currently undergoing further post-irradiation examinations including profile disintegration as well as ceramography and scanning electron microscopy of individual coated particles.

Bioenergetic potential of Ponkan peel waste (Citrus reticulata) pyrolysis by kinetic modelling and product characterization

The purpose of this study is to investigate the kinetic and products of the pyrolysis of Ponkan peel waste (Citrus reticulata) to determine its bioenergy potential. Pyrolysis runs were performed under an inert environment at 5, 10 and 15 °C min−1 in a macro-TGA coupled to a GC-FID/TCD for analysis of non-condensable gases (CO, CO2, CH4 and H2), while the condensable gases were collected by a cold trap and analyzed in a GC/MS. The kinetic study was performed by a multi-step mechanism using the Vyazovkin method, compensation effect and master plot. Pyrolysis occurred mainly between temperatures of 130–400 °C, where the release of a high amount of CO2 and CO was observed, while CH4 and H2 were detected at temperatures >400 °C. The condensable fraction is represented mainly by furan, acids, ketones and phenol compounds, which account for 84.68% of the condensable gases. The kinetic parameters (Ea, A and f(α)) fit the reaction model for geometrical contraction and n-order, which satisfactorily described the pyrolysis of Ponkan peel waste.

Footprints of Non-Inflationary Cosmology in Programs OLIMPIA and Synthesis of Heavy Elements

In this work we are going to apply one of main ideas of “Non-Inflationary Cosmology”, established by author as an alternative theory of cosmology – the analogue of the phenomenon of 6-photonic capture of Higgs bosons in Bose-Einstein condensate in the early Universe – as a possible scenario for the implementation and further possible development of two Russian programs “OLIMPIA” and “Synthesis of heavy elements”. Offered by us and thoroughly discussed phenomenon of “the cold trapping of baryons within 6-photonic potential well” may be additional or even possible alternative mechanism to the well-known “mechanism of cold synthesis of nuclei”.

Stir bar sorptive extraction and automatic two-stage thermal desorption-gas chromatography-mass spectrometry for trace analysis of the byproducts from diphenyl carbonate synthesis

In this study, a fast and sensitive method based on stir bar sorptive extraction (SBSE) and two-step thermal desorption coupled with online gas chromatography-mass spectrometry was established to simultaneously analyse six trace byproducts [phenyl salicylate (PS), xanthone (XA), methyl o-hydroxybenzoate (MS), 2-methyl diphenyl carbonate (PTC), methyl o-methoxybenzoate (MSME) and phenyl o-methoxybenzoate (PSME)] generated in the process of diphenyl carbonate (DPC) synthesis. Analytes were enriched with multiple sorptive stir bars simultaneously, followed by thermal desorption, cryo-focusing, and instantaneous injection, effectively solving such problems as long adsorption time and small sample volumes compared with conventional stir bars. The main factors influencing SBSE and thermal desorption were studied. Optimized stir bar extraction conditions are as follows: the volume fraction of methanol is 10%, the extraction time is 6 min, and the stirring rate is 1200 rpm at room temperature (25 °C). Optimized two-step thermal desorption conditions are as follows: in the first desorption step, the desorption temperature is 300 °C, the desorption time is 10 min, and the valve and transmission line temperature is 200 °C; in the second desorption step, the cold trap temperature is −10 °C, which is increased at a rate of 100 °C/s to 320 °C and held for 5 min. A splitless mode and a split mode with a split ratio of 20:1 are used in the first and the second desorption step, respectively. Under the optimal conditions, the six byproducts generated in the synthesis of DPC via transesterification were quantitatively analyzed by external standard method. The results showed that, within the range of 1.0−100 ng/L for all of the six transesterification byproducts, this method revealed good linearity with correlation coefficients (r) ≥0.997. The limits of detection (LODs) were between 0.054 ng/L and 0.253 ng/L, the relative standard deviations (RSD) were from 5.2% to 11.5%, and the recoveries were 81.6%−102.6% (n = 3). The method is simple, rapid and has a wide linear range, high accuracy, and sensitivity, as well as good stability. It is suitable for simultaneous, rapid and selective analysis of six trace byproducts in the process of DPC synthesis. It can also provide vigorous data support and industrialization guidance for the selection of transesterification conditions and research on the formation mechanisms, distribution regularity, and even control of transesterification byproducts.

Seasonal Polar Temperatures on the Moon

AbstractThe Diviner Lunar Radiometer Experiment on the Lunar Reconnaissance Orbiter has been acquiring visible and infrared radiance measurements of the Moon for nearly 10 years. These data have been compiled into polar stereographic maps of temperatures poleward of 80° latitude at fixed local times and fixed subsolar longitudes to provide an overview of diurnal temperatures of the polar regions. The data have been divided into winter and summer seasons, defined by the times of year when the subsolar latitude is above or below the equator, to characterize the variations in seasonal temperatures that result from the 1.54° angle between the Moon's spin pole and the ecliptic plane. Since the illumination in the polar regions is perpetually at grazing angles, topography plays a dominate role in surface temperatures. Consequently, the surface and near‐surface thermal environment can vary in complex ways with time of day and season, which produces areas that are seasonally shadowed for prolonged periods and that are much more extensive than the permanently shadowed regions (PSRs). We find that surfaces below 110 K capable of cold trapping water over 1 Gyr increases by factors of 2.8 and 4.3 in the winter for the south and north polar regions, respectively, with seasonal residence times of adsorbed water molecules occurring at higher temperatures and thus larger areas.

Effects of Model, Method of Collection, and Topography on Chemical Elements and Metals in the Aerosol of Tank-Style Electronic Cigarettes

Our purpose was to examine the effect of model, puffing topography (voltage, air-flow, puff interval), and method of collection on 19 elements/metals in aerosols from six tank-style electronic cigarettes (EC). Aerosols were collected from six brands using a cold trap or impinger and various puffing topographies. 19 elements were quantified using inductively coupled plasma optical emission spectroscopy. 16 elements/metals were present and quantified in the aerosols. The total concentrations of elements/metals ranged from 43 to 3,138 µg/L with the impinger method of collection and 226 to 6,767 µg/L with the cold trap method. The concentrations of individual elements were often similar across brands and across topographies. Some elements (e.g., zinc) were present in most aerosols, while others (e.g., cadmium, titanium, vanadium) were rarely found. Concentrations of some elements (e.g., lead) increased in aerosols as voltage/power increased. The model with fewest metal parts in the atomizer had the fewest metals in its aerosols. Most elements/metals in the aerosols have been found previously in the atomizers of EC. All tank-style aerosols had elements/metals that appeared to originate in the atomizers, and concentrations increased with increasing power. Concentrations of some elements were high enough to be a health concern.

Controlled separation of coal tar based on different temperature

An online condensation system was designed to separate coal tar during cooling process. Traditional method use room temperature ammonia water to cool hot pyrolysis gas by quenching for tar collection, and then follow by dehydration and distillation process for tar separation. This method will cause a lot of wastewater, repetitive energy cost and make system far more complex. On the basis of applying cleaner production idea, we put forward this online indirect heat exchange separation system, which can separate while cooling. The system consist of two high temperature oil bath and a cold trap as three condensers to realize an online cooling separation. 120, 240 ℃ is selected temperature for two oil bath as cut points for light, middle and heavy coal tar fraction. −20 ℃ is selected temperature for cold trap for a complete condensation. The results showed that this system give a high yield of the light fraction tar, which has a higher commercial value. In addition, the influence of pyrolysis temperature for tar separation was also examined for this system.

Lunar polar water resource exploration – Examination of the lunar cold trap reservoir system model and introduction of play-based exploration (PBE) techniques

Driven by a need to find low-cost energy solutions to meet anticipated demands arising from increased robotic and human cislunar activities, the extraction and utilization of naturally occurring volatiles found on the lunar surface is an area of growing interest to both the private and public space sectors. The use of hydrogen and oxygen extracted from accumulations of water is viewed as particularly promising. Several lines of evidence point to the presence of water, possibly in the form of water ice, stored within cold trap reservoirs in the permanently shadowed regions (PSRs) of the northern and southern poles of the Moon. The type and spatial resolution of available datasets however prevent evaluation of resource potential on a scale relevant to address geological uncertainties and assess the technological and economic feasibility of water resource extraction for use by an in-space market. Surface field exploration is required to reduce investment risk; however the success of resource exploration activities will depend on the selection of appropriate exploration methods. To address this we introduce the application of play-based exploration (PBE) techniques, a resource exploration approach commonly used by the terrestrial petroleum and geothermal energy industries to direct decision making regarding high-risk ventures. Applied to the Moon this method seeks to identify locations where exploration activities are most likely to encounter an economically/commercially viable quantity of water guided by the geological concepts of delivery, trapping, and storage of water molecules within a reservoir. In this study we examine the critical geological uncertainties in the reservoir system model and provide recommendations for resource exploration approach, data collection, and analysis techniques.

Assessment of polychlorinated biphenyls (PCBs) in the Himalayan Riverine Network of Azad Jammu and Kashmir

The emission of polychlorinated biphenyls (PCBs) in South Asian countries is one of the great environmental concerns and has resulted in the contamination of surrounding high altitude regions such as Azad Jammu and Kashmir (AJK), Pakistan. This first investigation of Polychlorinated Biphenyl (PCBs) concentrations in the ambient air, water and surface soil was conducted along the extensive stream network in the AJK valley of the Himalayan Region. In 2014, surface soil samples were taken and passive air and water samplers were deployed along the four main rivers, namely Jhelum, Neelum, Poonch and Kunhar, and analysed for PCBs (33 congeners) using GC-MS/MS. The ∑33PCBs concentrations ranged from 31.17 to 175.2 (mean ± SD: 81 ± 46.4 pg/L), ND to 1908 (1054 ± 588.5 pg/g), and 29.8 to 94.4 (52.9 ± 22.7 pg/m3) in surface water, soil and air matrices, respectively. The levels of dioxin-like PCBs (∑8DL-PCBs) contributed considerably towards the total PCBs concentrations: 60.63% (water), 43.87% (air) and 13.76% (soil). The log transformed air-water fugacity (log fa/fw) ratios ranged from −9.37 to 2.58; with 86.3% of the sampling sites showing net volatilization of selected PCB congeners. Similarly, the fugacity fractions for air-soil exchange exhibited narrow variation (0.8 to < 1) indicating net volatilization of PCBs. The ecological risk assessment showed low potential ecological risks (Eri = 1.58–7.63) associated with PCB contamination. The present findings provide baseline data that suggest cold trapping of POPs in the remote mountainous areas of Pakistan and can support environmental management of POPs at the regional level.This pioneer investigation campaign to assess the PCBs concentrations in Himalayan Riverine Network of Azad Jammu and Kashmir, Pakistan helps to develop baseline data of PCBs from the strategically important riverine environment that would help in future regional as well as global ecological studies. However, the effects of temperature variations on the sampling rates of chemicals across a wide spectrum of volatility along the elevation gradient were not taken under consideration for PCBs atmospheric concentrations.