Anne-Marie Gomes

Development of an apparatus for the detection and measurement of the metallic aerosol concentrations in atmospheric air in situ and in real time: preliminary results

Abstract An apparatus for monitoring the air quality with regard to metallic aerosol concentrations (ultra-fine powders of metal, dust, flying ash) on-line and in real time is decribed. It is similar to those used in classical optical spectroanalysis: pollutants are atomized, excited and ionized in an inductively coupled plasma and they are identified for their optical spectrum. The problems related to calibration and detection limits obtained with this apparatus are discussed. The first results concerning the detection of some metals (Be, Co, Cd and Pb) are shown. The detection limits obtained for the metals in this preliminary study are lower than the actual threshold limit values, which are considered as upper concentration limits for human health and environment.

Continuous emission monitoring of metal aerosol concentrations in atmospheric air

Improvements of an apparatus for continuous emission monitoring (CEM) by inductively coupled plasma atomic emission spectrometry (ICP-AES) of metal aerosols in air are described. The method simultaneously offers low operating costs, large volume of tested air for valuable sampling and avoids supplementary contamination or keeping of the air pollutant concentrations. Questions related to detection and calibration are discussed. The detection limits (DL) obtained for the eight pollutants studied are lower than the recommended threshold limit values (TLV) and as satisfactory as the results obtained with other CEM methods involving air-argon plasmas.

Spectroscopic method for the determination of the electron temperature in quasi-thermal air discharges. Application to an inductively coupled air plasma at atmospheric pressure

A method for the approximation of the electron temperature, θe, in quasi-thermal air discharges, based on measurements of the relative emissivities of the weakly resolved OH and NO vibrational bands in the 210–320 nm spectral range, is described. The method is very sensitive and particularly suitable between 2000 and 6000 K, where intensities emitted by atomic lines cannot be easily distinguished from the molecular vibrational bands. It is shown that departures from thermodynamic equilibrium induced by radiative losses or by a difference between the electron temperature, θe, and the heavy particle temperature, θg, cannot lead to large systematic errors as long as the ratio X=θe:θg stays below 1.2. The uncertainty of the temperature determination is discussed together with an application to an inductively coupled air plasma at atmospheric pressure.

Measurement of heavy particle temperature in a radiofrequency air discharge at atmospheric pressure from the numerical simulation of the NO γ system

An optical diagnostic method particularly suitable for studying cold (2500–6000 K) air plasma properties when atomic line intensities are too weak to allow accurate measurements is presented. The method is based on a comparison between numerically simulated and experimental spectra of bands of the NO γ system. It was applied to an air inductively coupled plasma at atmospheric pressure. This method allows the determination of the plasma temperature by measuring, on emission spectra, the widths of a rotationally non-resolved band at different heights; the uncertainty on such measured temperature values is about 250 K.

Transport coefficient calculation in air-argon mixtures: explanation of the improvement of detection limits of pollutants in air inductively coupled plasmas by argon addition

Abstract To explain the improvement of detection limits of some atmospheric pollutants that result from the addition of a small quantity of argon to air inductively coupled plasmas, transport coefficients of air-argon mixtures were calculated. These coefficients are introduced in a simplified energy balance equation: as a general rule, introduction of a small amount of argon in an air discharge introduces an increase of the temperature due to the decrease of energy losses by thermal conduction; the intensity of spectral lines of the analyte is then increased.

Temperature Determination in Air Plasmas with Chlorofluorocarboned Molecules in the Range 2500 K < T < 6000 K: Application to Quantitative Analysis of Elemental Pollutants

The diagnosis by emission spectroscopy of quasi-thermal air plasmas mixed with pollutants was performed for temperatures lower than 6000 K at atmospheric pressure. The applications concern monitoring of the destruction of chlorofluorocarbons (CFC) and the measurement of very low concentrations (some ppb) of heavy metals (copper) in air. The proposed methods are based on the simulation of the absolute intensity of the most intense molecular systems of the spectra (systems Gamma of NO, A-X of OH and NH, Schumann–Runge of O2 and violet of CN). The plasma composition of the mixtures (air+x% H2O+y% Cu+z% CCl2F2) and spectra simulation takes into account non-thermal equilibrium (Tg and Te kinetic temperatures of gas and electrons with X=Te/Tg). Six methods were selected and the conditions for their use were discussed. They were applied to the diagnosis of an air Inductively Coupled Plasma (64 MHz, 2.4 kW). Excellent agreement was obtained among them. Temperature variations lower than 50 K were able to be revealed and temperatures lower than 2600 K were measured. In a spectroanalysis context, it was shown that the partial pressure of metal nebulized in the discharge is uniform and that its excitation temperature TCu=Tg. The copper concentration was measured with an uncertainty which does not exceed 7%.

Behaviour of a low temperature argon plasma at atmospheric pressure seeded with some metallic aerosols under thermodynamic non-equilibrium conditions

Abstract The behaviour of an argon plasma at atmospheric pressure seeded with a metallic aerosol was studied using a collisional-radiative model under temperature conditions similar to those encountered at “analytical” observation heights in an inductively coupled plasma. Beryllium was chosen as an example. Ambipolar diffusion and charge exchange processes were introduced in the rate equations in a parametric form to generalize the relationships for application to other analytes. From this modelling, some experimental results can be explained such as the overestimation of the temperature when a relative argon line intensity diagnostic method is used, the non-linearity effects observed for high analyte concentrations, and the departures from local thermodynamic equilibrium correlations between atomic and ionic line intensities.