Passive FTIR emission spectroscopy using a commercial medium resolution instrument with a telescope has been applied to analyze the hot exhaust gases of various combustion sources, such as industrial and building smoke stacks, aircraft engines, flares, and forest fires. To interpret the remotely measured spectra a multi-layer, line-by-line spectra retrieval software using the molecular spectral databases HITRAN and HITEMP has been developed, validated and successfully used to determine the exhaust gas temperatures and the concentrations of CO₂, H₂O, CO, N₂O, CH₄, NO, NO₂, SO₂, and HCl for different combustion conditions of the sources. In this paper the feasibility and the setup of passive IR measurements, the basic theory of radiative transfer and special features of the commercially available spectra analysis code are described. In addition, the results of the different measurement applications are summarized.

Concentration measurements of trace gases in the atmosphere require the use of highly sensitive and precise techniques. The UV-visible DOAS technique is one of them heavily used for tropospheric measurements. In order to assess the advantages and drawbacks of using a Fourier transform spectrometer, we have built a DOAS optical setup based on a Bruker IFS 120M spectrometer. The characteristics and capabilities of this setup have been studied and compared to those of the more conventional grating based instruments during several intercomparison campaigns. The main advantages of the FTS are: (i) the existence of a reproducible and precise wavenumber scale, which greatly simplifies the algorithms used to analyze the atmospheric spectra; and (ii) the possibility to record large spectral regions at relatively high resolution, enabling the simultaneous detection of numerous chemical species with better discriminating properties. The main drawback, on the other hand, is due to the fact that an FTS records high frequency signals and does not have the signal integration capabilities of the CCD based grating spectrographs. The FTS therefore needs fairly large amounts of light and is limited to short to medium absorption pathlengths.

Fourier transform IR (FTIR) spectroscopy for making non- intrusive measurements of gas turbine exhaust gases and laser induced incandescence for measuring soot content are being evaluated in EU Brite EuRam project AEROJET. Soot concentrations in modern aero-engine exhausts are very low with mean particle sizes < 100 nm. The standard extractive filter paper soot measurement gives results expressed in terms of SAE smoke number, typically < 10 SAE for modern engines.

Passive remote sensing with a Fourier transform IR (FTIR) spectrometer allows the detection and identification of pollutant clouds in the atmosphere. In this work the measurement technique and a data analysis method that does not require a previously measured background spectrum are described. Recent experimental results obtained with anew high sensitive FTIR remote sensor are presented. Many situations do not allow the measurement of a background spectrum prior to the measurement of pollutants in order to perform background removal. After a radiometric calibration of the FTIR spectrometer with IR reference sources the spectral radiance of the environment can be measured. With the inverse function of Planck's radiation law the brightness temperature is computed. The temperature spectrum has a constant baseline for many natural materials that serve as the background in field measurements because their emittance is high and almost constant in the spectral range 800-1200 cm^-2. The influence of environmental and instrumental parameters on the sensitivity of the method are discussed. Experimental results are presented to illustrate the enhancement of the signal to noise ratio that can be achieved by the alignment of the spectrometer to backgrounds with a high temperature difference to the environment.

A method for the non-intrusive determination of temperature and concentrations of the exhaust gases of aeroengines will be presented. A MIROR-type FTIR spectrometer is used to measure spectra of the IR radiation emitted by the hot gases in the exhaust. New evaluation software, specially developed for this application, is described. The software permits line-by-line radiative transfer modeling of the radiance emitted by the exhaust of these engines. Least squares fitting routines are then used to match the measured with the modeled spectrum, thereby determining the unknown quantities, i.e., temperature and species concentrations. Results of measurements aboard aircraft are presented. The achieved accuracy in temperature is estimated to be better than 1 percent. Comparison of the values determined for the NO_x emission index with results from correlation models show deviations of 15 to 20 percent and are thus within the accuracy limits claimed for both methods.

Fourier-transform IR spectroscopic (FTIS) measurements have been performed at natural gas production facilities to study their potential to release hydrocarbons form vented and diffuse sources into the atmosphere. The measurements were realized using a commercial, moderate-resolution, mobile Fourier spectrometer. Effluent concentrations in the post- combustion zone above a flare are determined applying a multicomponent air pollution software which is based on radiative transfer line-by-line calculations and least- squares fit procedures. Emission rates are calculated on the basis of measured concentrations and known fuel flow rates to the flare. Diffuse emissions of the processing area are examined on the basis of open-path absorption measurements and Gaussian dispersion modeling. The flare combustion efficiencies were generally above 99 percent and indicate a rather small local environmental impact of methane emissions due to natural gas flaring. Contrary, comparatively, high diffuse emissions due to site leakages were determined which exceed the flare emissions by a factor of about 25.

Multivariate quantitative analysis of FTIR-spectra requires that the spectral line shapes of sample spectrum and spectral reference, and hence, the respective instrumental line shape (ILS) functions, match as closely as possible. In open-path measurements, the ILS' generally differ because of the differences in the optical geometry of the setups, or in the case of synthetic reference spectra, because the ILS cannot exactly be determined from the measuring parameter. In particular, when using large field stop diameters the line shapes can deviate considerably. Therefore, a mathematical method to approximate the ILS based on a parametrical identification has been developed and integrated into an algorithm for quantitative multivariate analysis. This article gives an overview over the parametrical model of the ILS approximation and its integration in the spectral evaluation algorithm, and presents results of their application to transmission spectra of extractive and open-path exhaust gas measurements.

Passive emission spectroscopy using a line by line model carbon dioxide around band head region has been developed to determine the temperature and concentration fields of exhaust gases. Resulting is a model which takes into account the hot band parameter in the first CO₂ band head in the 2397 cm^-1 region. Modeling absorption spectra have been compared with measurement absorption spectra in a new tight high temperature gas cell. Error is less than 2 percent until 1 100 K. The solution of the radiative transfer equation, is found by least square fitting between measured spectra and line by line modeling spectra inversion software, uses a non-linear simplex algorithm and a procedure of random couple pulling of temperature and partial pressure for testing convergence. It allows a discretization in four elements of the gas flow. Measurements were performed with a FTIR spectrometer using a telescope form gas exhaust form a 100 KW engine through an ambient air of 7 meters path. The average value is in good agreement with the measure of a thermocouple, in the center of the flow positioned. Thermocouple maximum deviation is 23 K between the measures and the worst element calculation.

This work describes the use of a He:Ne laser based test rig, developed at NPL, and a low pressure gas cell containing CO to measure the instrument line shape (ILS) function of a Unicam Research Series FTIR spectrometer, which has been extensively used for the detection and measurement of fugitive gas emissions. During the ILS function measurements minor optical misalignments were introduced into the optical system, and their effect on the measured ILS function observed. The ILS functions obtained using the laser system and low pressure gas cell containing CO were in good agreement, both having a full width at half maximum of 0.3 cm^-1. The minor optical misalignments had a significant effect on the ILS function. The initially symmetric function became more asymmetric as the degree of misalignment was increased. Gas concentrations have been retrieved using a symmetric and an asymmetric ILS function, and the differences presented.

The quantification of benzene in FTIR spectra is restricted by the interference of benzene with carbon dioxide. In this paper different methods are presented to overcome these problems with a detector of medium resolution of 0.5 cm^-1. The experiments were performed either in a 10 m gas cell or as open path experiments. One method compares the peak at 673.76 cm^-1 with the strongest absorption band of benzene in the single beam spectrum to the neighboring peaks, one method analyzes the shape of the peak at 674 cm^-1. Another method works with an artificial background and the latest methods analyze the absorbance spectrum and serve as a reference. The results from all these methods agreed very well down to the level of 30 to 50 ppb.

NO₂ absorption cross-sections have been obtained at 220 K and 294 K at a resolution of 2 cm^-2 from a series of spectra recorded with pure NO₂ at pressures from 0.007 to 2 torr. The N₂O₄ absorption cross-section has been obtained at 220 K. The uncertainty in the NO₂ cross-sections is estimated to be less than 3 percent for the spectral region below 40000 cm^-1 at 294 K, 3 percent below 30000 cm^-1 at 220 K. Temperature and pressure effects have been observed. Comparison with literature data show good agreement between 37500 and 20000 cm^-1. O₂ absorption spectra have been recorded at high and low resolution in the UV. A re-analysis of the three Herzberg band systems has been performed, extending the rotational assignment up to N equals 31 and identifying several new vibrational bands. Determination of the integrated intensities and oscillator strengths of the bands has been performed. These values have been compared with data of the literature. Spectra recorded with increasing pressures of N₂ or Ar show that the structure d continuum overlapping the Herzberg bands cannot be explained by O₂-O₂ absorption, but comes from collision induced absorption. Low resolution spectra have also been recorded in the visible region in order to determine the (O₂)₂ absorption cross-section.

In this work, experimental results obtained with the first Spanish LIDAR-DIAL prototype are presented. This DIAL consists of the well-known configuration of a dye laser as the tuning element, pumped by a Nd:YAG laser. In order to evaluate the performance of this DIAL, parallel measurements of SO₂ from industrial point sources with a passive remote technique were carried out. The spectrometer used as reference instrument was a COSPEC V, widely used for SO₂ concentration measurements from natural and anthropogenic plumes. Due to the different nature of these remote techniques, it has been necessary to design several field experiments and to homogenize all data before comparison. In this sense, the SO₂ traceability, because of its high chemical stability in the atmosphere, has been important to assess the performance of the DIAL system by using this experimental strategy. Also, the data obtained from the continuous monitoring of the emissions in the stacks are in good agreement with those provided by the remote sensors. It can be concluded that the new DIAL system works properly in a 4 Km range. Quality control of industrial emission inventories can be considered as a promising line of application of this DIAL system.

Measurements of air pollutant concentrations made at monitoring stations are often used to validate dispersion calculations in urban areas. A problem arises here, because of monitoring stations provide readings at specific points, whereas dispersion calculations need average values taken over specific computation volumes. By using open-path equipment, a comparison can be made between monitoring measurements and path-averaged measurements. This was carried out in two city areas. In one area it can be assumed that there are no direct pollutant sources, and the emissions are homogeneously distributed in the air. The second area is an inner-city zone with the measurement path covering two roads of very different traffic load. A comparison between a UV-DOAS system and monitoring stations showed that very god correlation could be established in the first area between the readings for NO, NO₂ and O₃ from the different systems, both in their actual level and in the curve they followed. This was not the case in the second test set-up because of the different emissions situation. Thus the values form such monitoring stations are only suitable for validation purposes under certain conditions.

A sun-photometer designed for aerosol studies was built and it was installed permanently at San Luis City, Argentina. This instrument measures the attenuation of direct solar light at wavelengths were molecular absorption are minimal, 380 nm, 500 nm, 770 nm, and 1060 nm. It makes continuous measurements mounted on a solar tracker and data are filed every minute. An extra channel at 940 nm was introduced for water measurements. Results in San Luis confirm that aerosols normally present in that place are dust-like particles with a very shallow extinction spectrum. Such aerosols can not be represented by the standard form of the angstrom's formula where (alpha) equals 1.2 is normally assumed. This fact must be taken into account when radiative-transfer models are used, specially in the UV region. During two short periods of time, the meter was operated at different places: Las Cuevas, at 3200 m height at Los Andes mountains, and Pampa Amarilla, the site for a future cosmic ray observatory in Argentina. Typical results for these geographical regions corresponded to clean atmospheres with small quantity of large particles. The water channel was calibrated by simultaneous measurements with a Microtops II, a commercial sun-photometer; in the near future the radiometer will be contrasted against water-radiosonde measurements.

A ground-based spectrometer using the DOAS technique measuring at zenith was deployed at Izana Observatory during the 2nd CRISTA flight, in August 1997. CRISTA was flown on the ASTROPAS free-flying platform during the Space Shuttle mission STS-85, and among other species measured NO₂ profiles. The twilight measurements of NO₂ profiles. The twilight measurements of NO₂ total column over the station obtained by the ground-based spectrometer has been used to estimate the profile of this species in the subtropics for summer and to compare with the results of CRISTA during the overpassings. The results of both data sets, and the origin of the discrepancies are discussed in the paper.

The increment of the exploitable optical path represents one of the most important efforts in the differential optical absorption spectroscopy (DOAS) instruments improvement. The methods that allow long path measurements in the UV region are presented and discussed in this paper. These methods have been experimented in the new Italian DOAS instrument - SPOT - developed and manufactured by Kayser Italia. The system was equipped with a tele-controlled optical shuttle on the light source unit, allowing background radiation measurement. Wavelength absolute calibration of spectra by means of a collimated UV beam from a mercury lamp integrated in the telescope has been exploited. Besides, possible thermal effects on the dispersion coefficients of the holographic grating have been automatically compensated by means of a general non-linear fit during the spectral analysis session. Measurements in bistatic configuration have been performed in urban areas at 1300 m and 2200 m in three spectral windows from 245 to 380 nm. Measurements with these features are expected in the other spectral windows on path lengths ranging from about 5 to 10 km in urban areas. The DOAS technique can be used in field for very fast measurements in the 245-275 nm spectral range, on path lengths up to about 2500 m.

An evaluation of atmospheric turbidity parameters related with aerosols from ground-based broadband measurements of global and diffuse radiation is presented. First, an inversion of a direct-diffuse broadband radiation splitting model is applied to cloudless sky radiation data. The inversion requires diffuse fraction as the main input parameter. Subsequently we perform an empirical correction to the diffuse fraction in order to extended the previous method to scattered cloud conditions. The correction is based on temporal variations of global atmospheric transmissivity normalized with respect to the air mass. In order to test the applicability of the broadband method and our extension, concurrent measurements of spectral radiation were also taken. Spectra were taken by a spectroradiometer equipped with an integrating sphere and an occulting tube. Under scatted cloudy conditions, spectra were taken during direct shining episodes, that is between occultation intervals. Values of aerosol extinction and of angstrom's (beta) coefficient have been obtained. The latter were obtained through two procedures: a single wavelength evaluation, and a fit to the aerosol spectral extinction coefficients. Values of (beta) obtained from the cloudiness correcte diffuse fraction show a smooth daily evolution that would correspond to an equally turbid but cloudless atmosphere. Results suggest that cloudiness correction to the diffuse fraction can extend the inversion of cloudless broadband radiation models to scattered cloudy skies, in order to retrieve aerosol parameters.

A pollutant gas detector is presented. The sensor system detects simultaneously CO and SO₂ in a range from 0 to 200 ppm with a resolution of 7 ppm, however the system is bale to analyze up to 19 gases simultaneously. A new technique based on a multilayer filter array is proposed to prevent the use of moving parts. The central-wavelengths of filters were selected according to the position of the absorption band of interest for each gas. The CO and SO₂ central-wavelengths were measured and its transmission spectral response was also predicted by using the HITRAN database. Also a new conditioning circuit with high- performance is proposed using low-cost components. The circuit is based on shifting the measured signal to intermediate frequency. With this technique a reduction of 1/f noise is achieved. The new systems features reduction of moving parts, high acquisition speed and low-cost.

An optical modulator based on the Frustrated Total Internal Reflection represents an alternative to the optical modulation based on the classic chopping wheel. This alternative permits to eliminate the presence of moving parts within IR spectroscopy equipment. The proposed design of the modulator has two elements of dielectric material. These elements are separated by an air gap. The radiation passes through the air gap from the first element to the second one. The transmission coefficient present a non- linear dependence on the separation distance. Furthermore, the micro-movement has a non-sinusoidal waveform. Both effects result on a non-sinusoidal waveform of the intensity modulation and make the energy of the modulated radiation to be distributed among several harmonics. The quality of the modulation has been studied by means of the optical efficiency and the total harmonic distortion index. The modulator based on the Frustrated Total Internal Reflection, FTIR, and an ideal square chopper can be compared using the optical efficiency coefficient. The total harmonic distortion index shows the ratio of chopper energy that is not hold by the main harmonic does.

An IR absorption system for real-time measurement of pollutants in exhaust gases from moving vehicles is proposed. The system consists of an IR source at one side of the road, and a wheel with specific IR filters and a detector at the other side. We have, firstly, simulated the expected exhaust gases concentrations at different inspection conditions. The well-known HITRAN database has been used in order to estimate intensities, signal-to-noise ratio and threshold concentration levels. These results have then been verified by open-path Fourier transform IR (FTIR) spectroradiometry of the exhaust gases from both gasoline and Diesel vehicles. This confirms the feasibility of such a device by using some conventional filters -those of CO, CO₂ and NO₂ for example - some ultra-narrow sold state Fabry-Perot filters - that of NO for example. As the proposed system monitors all kinds of oxides and hydrocarbons in exhaust gases the stoichiometry of the combustion or 'lambda coefficient' may be also deduced and it is fully applicable for 'ministry of transport' test of vehicles.

A plasma shutter has been made for cutting nitrogen tail of energy pulse of TEA CO₂ laser. Studies to implement all set-ups has been done using preliminarily a TE CO₂ laser source. The system is described and the dependence of the gas break down by energy of the discharge is discussed.

In recent years the use of opto-chemical sensors has grown in very diverse fields, particularly in environmental control. Luminescence methods are being developed because they entail some advantages. Two multi-parametric measurement system of low light intensity based on a CCD are evaluated in this article. The light arrives through several optic fibers from the corresponding sample or chemical sensor phase, where the luminous phenomenon is produced. Possible applications of this system include fields like environmental control, biology or medicine. Two low-cost CCDs have been used with the aim of evaluating their performance in situations of low luminosity so as to justify their possible use in measurement of luminescence phenomena. Both systems are made up, firstly of a CCD sensor and an analogical state, where the signal is amplified and suitably sampled. The whole system is managed by the control stage, made up of a programmable logic device, so as to achieve flexibility and integration.

On the late nineties, recurrent episodes of odor nuisance were produced on the Besos river basic with special incidence on the nearby city of Montecada i Reixac, particularly during the dry summer season. In order to gain more information about the phenomenon, an appropriate H₂S emission survey program was designed, by means of two monitorization stations, one fixed and another mobile, equipped with continuous real-time analyzers. The H₂S was analyzed by previous oxidation to SO₂, followed by molecular fluorescence determination of this compound. During the 1994 summer period the measured levels of H₂S concentration, meteorologic conditions and occurrence of odor episodes was evident.

In 1992 an experimental campaign took place in Barcelona whose main goal was the study of the circulatory patterns of air pollutants in the region. An elastic-backscatter lidar operating at a wavelength of 1.064 micrometers , being mainly sensitive to changes in the distribution of aerosols was used. The study of temporal series of lidar vertical scans revealed a multilayer arrangement of the aerosols above the city. A few years after that experiment, the UPC started to develop its own lidar system. The first stadium of the project was the construction of an elastic-backscatter lidar. In 1997, in the frame of a meteorological situation very similar to the one present during the first campaign, the UPC lidar acquired vertical profiles of elastic- backscatter in the Barcelona's atmosphere. The study of the temporal series also showed the development of elevated layers of aerosols at similar altitudes to the ones observed during the first campaign. The second experiment seems to confirm that the formation of elevated layers in Barcelona is a typical behavior for the region during the summer period and not just a particular situation.

Up to now emission source strengths of diffuse and heterogenous emission of important VOCs are not well known especially from gas stations and gasoline tank farms. To estimate the total emission of these sources non-intrusive measurements were performed by a differential optical absorption spectroscopy (DOAS) system to determine the path- integrated concentrations of exhaust compounds downwind of the source through the whole exhaust plume. Simultaneously, the meteorological parameters were measured for modeling the dispersion of the plume inversely to obtain the emission source strengths of these compounds. The emissions by road traffic were determined by an additional open-path DOAS measurement. Measurement campaigns were performed during different wether conditions and at different sources which were characterized by well defined and easy air flow conditions. The emission source strengths were calculated with the Gaussian model PAL. The determined total emission of gas stations with gasoline vapor recovery system are about 20 mg benzene per kg refueled gasoline and the emission from refueling activities vary between 1 and 9 benzene per kg refueled gasoline depending on the technical behavior of the gasoline vapor recovery system. These values which were found from measurements during times with a and without refueling activities show a high amount of diffuse emissions. The emission rates from a gasoline taken farm were measured on an open path through the middle of that area and a maximum of 8 (mu) g/(m²s) was determined.

The DF laser's capabilities for monitoring natural gas and petroleum products in pipeline areas are considered. The absorption coefficients of methane, ethane, and propane were determine experimentally for 11 spectral lines in the 3.55- 3.75 micrometers range of the DF laser output. The criteria were formulated for selecting analytic and reference lines suitable for measuring atmospheric hydrocarbons by means of the differential absorption technique. Combinations of analytic and reference lines were chosen according to these criteria. The laboratory mock-up of hydrocarbon analyzer implemented around a DF laser was tested.

A CO₂ laser-based DIAL system has been developed for mapping vapor plumes. The DIAL system is composed of two home-made twin TEA CO₂ lasers in self filtering unstable resonator. The receiving system is based on a Newtonian telescope with a 40 cm diameter that acquires the backscattered signal with a cooled HgCdTe detector on the focal plane. The signal is acquired by a VXI system and stored in the memory of a personal computer. The laser pulse is transmitted and received by a scanner module. Our first measurements indicated some disagreement between theory an practice. To resolve these problems in our fixed station we had to modify many aspects relating to the optical emission and performance of the station. The measurement have been made on water vapor and ozone. After a careful study of the experimental result we have decided to build a mobile lidar station.

Some aspects of a new method of registrating radioactive ejections to the atmosphere from, for instance, nuclear power stations are discussed. The method based on the remote dejection of the optical flourescence of the air ionized by the radionuclides of the ejections. We propose to detect the three blue optical emission bands from the highly ionized molecules of oxygen. This will provide reliable selection of the ejection radiation from the radiation of other natural or artificial sources. The apparatus for remote detection of the regular ejections from nuclear power stations for the purpose of experimental testing the new method is developed in the framework of the proposal for International Science and Technology Center number 1240 'Development of the optical method of the remote registration of radioactive air ejections'.

The remote sensing of CO₂ plumes or clouds is made possible by a passive optical method: we analyze the measured radiation to find the plume temperature and concentration which are supposed to be constant in the plume along the measuring optical path. The optical axis is issued from the background which is considered as air at room temperature; the radiation first goes across the CO₂ cloud along an optical path a few meters long then across air volume between the detection apparatus and the CO₂ cloud. We have to take into account the absorptivity of the atmosphere air and the emissivity of the background. Three measuring wavelengths are necessary: one gives us the background luminance, the two others are two CO₂ absorption bands. The selection of these wavelengths requires a spectroscopic simulation of the CO₂ and H₂O molecules; consequently we have to model the spectroscopic product of the CO₂ emissivity and air transmittance line by line. After identifying the measured luminances from a database we can find the temperature and then the concentration of the CO₂ plume. We are also perfecting too a two wavelengths imaging system using an IR camera to visualize a CO₂ plume over a very short period of time.

This work describes how an IR DIAL system has been sued both to measure the emission rates of Volatile Organic Compounds (VOCs) from external floating roof tanks, and in addition, to map the concentration of VOCs over the roofs of tanks. The data presented shows concentration iso-surfaces resolved at 0.2 ppm intervals over an operating 50 m diameter tank. This data will be used to validate subsequent models of tank emissions. The data suggests that when the floating roof is sufficiently low inside the tank a re-circulating air flow is established that extends for several meters into the open air above the tank rim. In this instance the emission rate of product from the tank is the rate of bleed off from the re-circulation zone into the free air stream. As the tank roof height is increased, it is expected that a point will be reached where the re-circulating zone shrinks to a small region near the rim and the majority of the tank roof is exposed to the free stream air flow. The existence of a large re-circulation zone when the roof is low is confirmed by the preliminary results of flow measurements above a tank roof.

We present a novel method developed for the localization of leaks along natural gas pipelines. Methane distributions in the atmosphere around the leaky pipeline are detected and visualized by spectrally tuned IR imaging. In contrast to conventional techniques which utilize laser radiation sources or scanning, we irradiate the overall region under investigation by 1 kW halogen lamps. The scene background is subtracted by a real-time computer evaluation of the image. The methane gas emitted from the leak creates a flickering cloud in the image which is easily recognized. Methane concentrations as low as 0.03 percent by volume are visible. The method was successfully tested under realistic conditions on a buried pipeline by a natural gas provider.