An injection method for measuring the carbon isotope content of soil carbon dioxide and soil respiration with a tunable diode laser absorption spectrometer

We present a novel technique in which the carbon isotope ratio (δ¹³C) of soil CO₂ is measured from small gas samples (<5 mL) injected into a stream of CO₂‐free air flowing into a tunable diode laser absorption spectrometer (TDL). This new method extends the dynamic range of the TDL to measure CO₂ mole fractions ranging from ambient to pure CO₂, reduces the volume of sample required to a few mL, and does not require field deployment of the instrument. The measurement precision of samples stored for up to 60 days was 0.23‰. The new TDL method was applied with a simple gas well sampling technique to obtain and measure gas samples from shallow soil depth increments for CO₂ mole fraction and δ¹³C analysis, and subsequent determination of the δ¹³C of soil‐respired CO₂. The method was tested using an artificial soil system containing a controlled CO₂ source and compared with an independent method using the TDL and an open soil chamber. The profile and chamber estimates of δ¹³C of an artificially produced CO₂ flux were consistent and converged to the δ¹³C of the CO₂ source at steady state, indicating the accuracy of both methods under controlled conditions. The new TDL method, in which a small pulse of sample is measured on a carrier gas stream, is analogous for the TDL technique to the development of continuous‐flow configurations for isotope ratio mass spectrometry. While the applications presented here are focused on soil CO₂, this new TDL method could be applied in a number of situations requiring measurement of δ¹³C of CO₂ in small gas samples with ambient to high CO₂ mole fractions. Copyright © 2010 John Wiley & Sons, Ltd.     

Analysis of nitrated polycyclic aromatic hydrocarbons by liquid chromatography with fluorescence and mass spectrometry detection: air particulate matter, soot, and reaction product studies

Polycyclic aromatic hydrocarbons (PAH) and their nitrated derivatives (nitro-PAH) are environmental pollutants which pose a threat to human health even at low concentration levels. In this study, efficient analytical methods for the analysis of nitro-PAH and PAH (extraction, clean-up, chromatographic separation, and spectrometric detection) have been developed, characterized, and applied to aerosol samples. The separation and quantification of 12 nitro-PAH was carried out by reversed-phase high performance liquid chromatography (HPLC), on-line reduction, and fluorescence detection. The detection limits were in the range of 0.03–0.5 g L^–1 (6–100 pg in the investigated sample aliquots), and the recovery rates from soot samples were 70–90%. Nitro-PAH and PAH concentrations have been determined for different types of soot and for urban, rural, and alpine fine air particulate matter (PM2.5). For the first time, trace amounts of nitro-PAH have been detected in a high-alpine clean air environment. The on-line reduction and fluorescence technique has been complemented by atmospheric pressure chemical ionization time-of-flight mass spectrometry (APCI-TOF-MS). The MS detection allowed the analysis of partially nitrated and oxygenated PAH in laboratory studies of the heterogeneous reaction of PAH on soot and glass fiber substrates with gaseous nitrogen oxides and ozone. It led to the tentative identification of a previously unknown nitrated derivative of the particularly toxic PAH benzo[a]pyrene (BaP-nitroquinone), and provides the first experimental evidence that PAH-nitroquinones can be formed by reaction of PAH with atmospheric photooxidants.     

Single particle excitations in Ba from a ( , t) reaction study

The ¹³⁰Ba( ¹²⁹Ba reaction was studied with 25 MeV deuterons and excellent energy resolution. About 50 excited states have been observed up to E_x = 2.0 MeV and for 42 of them transferred ℓ values and/or J^π values were assigned on the basis of the measured angular distributions and asymmetries. The level scheme of ¹²⁹Ba, the neutron pickup strength distribution and the known electromagnetic decay scheme are compared with results of calculations with the interacting boson-fermion model. These simple multi-shell IBFM-1 calculations describe well the main features of the experimental data.     

Possibilities and Perspective of Photovoltaic Conversion in Organic Materials

The aim of the paper is to give the present state of the art in solar cells based on organic solid-state films. After short outline of the history of the field, the main trends in development of plastic solar cells are presented. The main obstacles, facing the field of photovoltaic conversion in solid films systems with organic semiconductors to be solved in future, are slow transport of charge-carriers, difficulties in contacts forming and stability towards ambient and UV radiation.     

Accuracy and resolution issues in NO/acetone PLIF measurements of gas-phase molecular mixing

Under-resolved passive-scalar measurements in liquid and gaseous shear layers have been known to over-predict mixed-fluid quantities as a result of sub-resolution stirring. In recent studies, simultaneous cold-chemistry (nitric oxide) and passive-scalar (acetone) planar laser-induced fluorescence have been employed for the measurement of sub-resolution molecular mixing. In the current work, the theory and experimental approach of this technique are reviewed, and new analyses of quenching corrections, differential diffusion errors, and imaging resolution are presented. Results from both experimental work and direct numerical simulations indicate that this technique provides a successful means of quantifying macro- and micro-scale turbulent molecular mixing in gaseous shear flows. Received: 20 December 2000/Accepted: 24 September 2001