Namgoo Kang

Characteristics of perchlorate formation via photodissociation of aqueous chlorite

Environmental context. Perchlorate, a well-known thyroid disruptor with both man-made and natural sources represents a major environmental problem in the United States but little information is available concerning the source of natural perchlorate. Previous research has demonstrated that perchlorate can be produced from exposure of some chlorine compounds to ultraviolet radiation, but no information was available how quickly or comparatively how much perchlorate was formed. The results of the present study can be used to evaluate the potential impact of ultraviolet processes on the overall occurrence of perchlorate in the environment. Abstract. The present study provides new and important information on perchlorate (ClO4–) formation through ultraviolet (UV) photodissociation of unbuffered chlorite (ClO2–) solutions from the standpoint of kinetics under three different wavelength regimes having maximum emissions, λe,max, at 235.7, 300 and 350 nm. ClO4– production rates and yields were in general found to be inversely related, with higher yields and lower rates at higher wavelengths, and vice versa. A simple kinetic model for ClO4– production as a function of the ClO2– first-order decay constant and starting concentration was fitted to the experimental data, resulting in the calculation of a rate constant, k2, which is a function of light-source characteristics. Further, a conceptual scheme for ClO4– formation via photochemical reactions between oxychlorine species was proposed based on the experimental results and available literature. The present study is a further step towards understanding the formation of ClO4– from the photolysis of its precursors.

Direct determination of arsine in gases by inductively coupled plasma-dynamic reaction cell-mass spectrometry.

Reliable determination of arsine (AsH(3)) in gases is of great importance due to stringent regulations associated with health, safety and environmental issues. It is, however, challenging for an analyst to determine trace airborne arsine concentrations without specifically designed collection procedures using adsorption, desorption, dissolution or impinging techniques. To circumvent such technical barrier, we have newly developed a direct analytical method, characterized by introduction of an arsine gas sample into stable plasma stream, followed by gas-phase oxidation of arsine with molecular oxygen in a dynamic reaction cell (DRC) equipped within the inductively coupled plasma-mass spectrometry (ICP/MS) system, followed by subsequent detection of AsO(+) ion. This preliminary work used trace arsine concentrations (161 microg m(-3), 322 microg m(-3), and 645 microg m(-3)) gravimetrically prepared in N(2) balance. The proposed method was optimized for the important experimental parameters such as the flow rates of the reaction gas, the arsine sample, and the carrier gas. This method was then validated by demonstrating good figure-of-merits including the low limit of detection (0.10 microg m(-3)), good linearity (r(2)>0.9915), low measurement uncertainty (0.66%), and high speed of analysis (<6 min). The proposed method is expected to be potentially applicable to the determination of arsine in real workplace air after appropriate modifications are made.

Different elution modes and field programming in gravitational field-flow fractionation: Effect of channel angle

Gravitational field-flow fractionation (GrFFF) has been shown to be useful for separation and characterization of various types of micrometer-sized particles. It has been recognized however that GrFFF is less versatile than other members of FFF because the external field (Earths gravity) in GrFFF is relatively weak and is not tunable (constant), which makes the force acting on the particles constant. A few approaches have been suggested to control the force acting on particles in GrFFF. They include (1) changing the angle between the Earths gravitational field and the longitudinal axis of the channel, and (2) the use of carrier liquid having different densities. In the hyperlayer mode of GrFFF, the hydrodynamic lift force (HLF) also act on particles. The existence of HLF allows other means of changing the force acting on the particles in GrFFF. They include (1) the flow rate programming, or (2) the use of channels having non-constant cross-section. In this study, with polystyrene latex beads used as model particles, the channel angle was varied to study its effect on elution parameters (such as selectivity, band broadening and resolution) in the steric or in the hyperlayer mode of GrFFF. In addition, the effects of the channel thickness and the flow rate on the elution parameters were also investigated. It was found that, in the steric mode, the resolution decreases as the flow rate increases due to increased zone broadening despite of the increase in the selectivity. At a constant volumetric flow rate, both the zone broadening and the selectivity increase as the channel thickness increases, resulting in the net increase in the resolution. It was also found that the retention time decreases as the channel angle increases in both up- and down-flow positions. The zone broadening tends to increase almost linearly with the channel angle, while no particular trends were found in selectivity. As a result, the resolution decreases as the channel angle increases.

Determination of Cd and Cr in an ABS candidate reference material by instrumental neutron activation analysis

In order to practically better cope with technical barriers to trade (TBT) of a great number of resin goods, our research presents first-ever results for the determination of Cd and Cr in acrylonitrile butadiene styrene (ABS) candidate reference material using instrumental neutron activation analysis (INAA) recently recognized as a candidate primary ratio method with a particular attention to the estimation of involved measurement uncertainties.

Instrumental neutron activation analysis of mass fractions of toxic metals in plastic

It is very challenging to decompose a plastic product for the purpose of analysis of hazardous elements contained. To circumvent such technical problem, it is imperative that an analyst employ a nondestructive analytical method free of any pretreatments. The analytical results of the concentrations of toxic metals such as Cd and Cr in polypropylene for seven samples at two different levels were obtained using the instrumental neutron activation analysis. This work was intended ultimately to establish certified reference materials (CRMs) of these metals in the polypropylene, traceable to the SI. The uncertainties associated with the analytical procedures were estimated in accordance with the ISO guideline. The results were subsequently validated by a comparison with those for CRM-680 and -681 of the Bureau Communautaire de Reference (BCR), which demonstrated acceptable agreement within their uncertainty ranges.

Effect of variation in argon content of calibration gases on determination of atmospheric carbon dioxide.

Carbon dioxide (CO(2)) is a greenhouse gas that makes by far the largest contribution to the global warming of the Earths atmosphere. For the measurements of atmospheric CO(2) a non-dispersive infrared analyzer (NDIR) and gas chromatography are conventionally being used. We explored whether and to what degree argon content can influence the determination of atmospheric CO(2) using the comparison of CO(2) concentrations between the sample gas mixtures with varying Ar amounts at 0 and 18.6 mmol mol(-1) and the calibration gas mixtures with Ar at 8.4, 9.1, and 9.3 mmol mol(-1). We newly discovered that variation of Ar content in calibration gas mixtures could undermine accuracy for precise and accurate determination of atmospheric CO(2) in background air. The differences in CO(2) concentration due to the variation of Ar content in the calibration gas mixtures were negligible (<+/-0.03 micromol mol(-1)) for NDIR systems whereas they noticeably increased (<+/-1.09 micromol mol(-1)) especially for the modified GC systems to enhance instrumental sensitivity. We found that the thermal mass flow controller is the main source of the differences although such differences appeared only in the presence of a flow restrictor in GC systems. For reliable monitoring of real atmospheric CO(2) samples, one should use calibration gas mixtures that contain Ar content close to the level (9.332 mmol mol(-1)) in the ambient air as possible. Practical guidelines were highlighted relating to selection of appropriate analytical approaches for the accurate and precise measurements of atmospheric CO(2). In addition, theoretical implications from the findings were addressed.

International comparison CCQM-K82: methane in air at ambient level (1800 to 2200) nmol/mol

The CCQM-K82 comparison was designed to evaluate the degrees of equivalence of NMI capabilities for methane in air primary reference mixtures in the range (1800 to 2200) nmol/mol. The balance gas for the standards was either scrubbed dry real air or synthetic air. CH4 in air standards have been produced by a number of laboratories for many years, with more recent developments focused on standards at atmospheric measurement concentrations and aimed at obtaining agreement between independently produced standards. A comparison of the differences in primary gas standards for methane in air was previously performed in 2003 (CCQM-P41 Greenhouse gases. 1 and 2) with a standard deviation of results around the reference value of 30 nmol/mol and 10 nmol/mol for a more limited set of standards. This can be contrasted with the level of agreement required from field laboratories routinely measuring atmospheric methane levels, set by Data Quality Objectives (DQO) established by the World Meteorological Organization (WMO) to reflect the scientifically desirable level of compatibility for CH4 measurements at the global scale, currently set at 2 nmol/mol (1 sigma). The measurements of this key comparison took place from May 2012 to June 2012. Eight laboratories took part in this comparison coordinated by the BIPM and NIST. Key comparison reference values were calculated based on Cavity Ring Down Spectroscopy Measurements performed at the BIPM, combined with participants gravimetric values to identify a consistent set of standards. Regression analysis allowed predicted values for each standard to be calculated which acted as the KCRVs. In this comparison reported standard uncertainties by participants ranged from 0.50 nmol/mol to 2.4 nmol/mol and the uncertainties of individual KCRVs ranged from 0.68 nmol/mol to 0.71 nmol/mol. The standard deviation of the ensemble of standards about the KCRV value was 1.70 nmol/mol. This represents a greater than tenfold improvement in the level of compatibility of methane in air standards compared to that demonstrated in 2003. Further improvements in the compatibility of standards will require improved methods and uncertainties for the measurement of trace level methane in balance gases. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

CO2 Outgassing from an Urbanized River System Fueled by Wastewater Treatment Plant Effluents

Continuous underway measurements were combined with a basin-scale survey to examine human impacts on CO2 outgassing in a highly urbanized river system in Korea. While the partial pressure of CO2 (pCO2) was measured at 15 sites using syringe equilibration, 3 cruises employing an equilibrator were done along a 30 km transect in the Seoul metropolitan area. The basin-scale survey revealed longitudinal increases in surface water pCO2 and dissolved organic carbon (DOC) in the downstream reach. Downstream increases in pCO2, DOC, fluorescence index, and inorganic N and P reflected disproportionately large contributions from wastewater treatment plant (WWTP) effluents carried by major urban tributaries. Cruise transects exhibited strong localized peaks of pCO2 up to 13 000 μatm and 13CO2 enrichment along the confluences of tributaries at an average flow, whereas CO2 pulses were dampened by increased flow during the monsoon period. Fluctuations in pCO2 along the eutrophic reach downstream of the confluences reflected environmental controls on the balance between photosynthesis, biodegradation, and outgassing. The results underscore WWTP effluents as an anthropogenic source of nutrients, DOC, and CO2 and their influences on algal blooms and associated C dynamics in eutrophic urbanized river systems, warranting further research on urbanization-induced perturbations to riverine metabolic processes and carbon fluxes.

Evaluation of changes in cylinder volume due to gas filling and subsequent release

This paper provides useful and important information in gas metrology especially where high-precision gas mixtures are essential. Buoyancy effects due to cylinder expansion are taken into account as a source of uncertainty in weighing for the preparation of primary or standard gas mixtures by gravimetric methods. Potential effects of cylinder construction materials, nominal volumetric capacity and filling gas species on cylinder volume during the preparation of primary standard gas mixtures remain unknown in the current literature. It is also difficult to find experimental evidence to demonstrate the theory that cylinder expansion upon pressurization is linear. We therefore devised an indirect measurement method to measure apparent volume changes and ultimately estimate changes in the volume of highly pressurized cylinders. We found that changes in the volumes of some gas cylinders varied significantly with construction material and nominal volumetric capacity. The relative volume changes for aluminium alloy cylinders were about 30% higher than those for manganese steel cylinders regardless of the nominal volumetric capacity and the filling gas species. We also provide experimental evidence verifying that changes in cylinder volume follow nearly linear patterns within the pressure range from 12?MPa to 0.1?MPa. Our estimate for the volume expansion of an aluminium alloy cylinder of 5?dm3 capacity with a pressure difference of 15?MPa is (15???2)?cm3. The reported value of about 20?cm3 in ISO 6142?:?2001 would be regarded as a rough estimate.

International comparison CCQM-K119 liquefied petroleum gas

M L Downey, P J Brewer, E Atkins, R J C Brown, A S Brown, E T Zalewska, A M H van der Veen, D E Smeulders, J B McCallum, R T Satumba, Y D Kim, N Kang, H K Bae, J C Woo, L A Konopelko, T A Popova, A V Meshkov, O V Efremova and Y Kustikov National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK. Van Swinden Laboratorium, Chemistry Group, Thijsseweg 11, 2629 JA Delft, the Netherlands. National Measurement Institute, 36 Bradfield Rd, Lindfield NSW, 2070, Australia. Korea Research Institute of Standards and Science, 267 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea. D.I. Mendeleyev Institute for Metrology, 19 Moskovsky Prospekt, 198005 St-Petersburg, Russia.