Florin Caldararu

Autonomous system for real time air pollution monitoring using semiconductor toxic gas sensors

The measurement concentration range of SnO/sub 2/ semiconductor sensors for toxic and flammable gases (TGS) was extended for use in air pollution monitoring. A real time autonomous system for air pollution monitoring (NH/sub 3/, CO, R113 and R22 freons) using TGS sensors and an 80C552 INTEL microcontroller for data acquisition and management was tested. The air pollution concentrations measured in the industrial and residential areas of Bucharest fulfil the Romanian air pollution standards requirements as well as the US EPA ones. A simulator (SIMPA) for real time air pollution measurements was developed for the environment protection laboratories of scientific and technical universities.

The far to equilibrium time evolution of the ozone layer: steady-state and critical behaviour

Abstract The ozone layer stability in the far equilibrium conditions was studied in the framework of the irreversible thermodynamics. Following the Prigogines procedures concerning the Brusselator model, the phenomenological model of the ozone layer leads to a system of non-linear differential equations. The steady-state solution of the system outlines the fact that the ozone layer can reach a steady state in the far equilibrium conditions for any pollutant concentration values. Applying the Lyapounovs theorem of stability, it is demonstrated that all the steady-state solutions for the ozone layer are stable ones. The natural limit of the ozone concentration is calculated, as well as that of the pollutant concentrations (the upper limits). This procedure suggests a way of assessing the effect of the anthropogenetic activities. The transmission coefficients of the UV radiation are calculated establishing the lower limits of the “permitting” pollution. The error analysis shows that the prediction of the stability of the steady state of the ozone layer does not depend on the errors of the input data.

Ozone distribution in the stratosphere-troposphere system using the interdisciplinary physics modelling

A theoretical ozone distribution in the stratosphere-troposphere system is provided using the physical analogy between the stratosphere-troposphere system and the well-known illuminated semiconductor p-n junction. The equations of a 2D model of the illuminated p-n junction were rewritten for the ozone and pollutant particles in the altitude-latitude co-ordinates. A comparison between the calculated curves and the recent experimental achievements is also given.

Monitoring of volatile organic compounds using a single tin dioxide sensor

The paper describes a new and simple method for monitoring volatile organic compounds resulting from a specific industrial indoor process. The method is based on the characteristics of tin dioxide sensors to be sensitive and non-selective to a large variety of gases. We use these characteristics to determine an equivalent concentration of the volatile organic compound mixture, a method which has not been used in other studies or experiments. The value of the equivalent concentration shows the accuracy of the process and the air purity of an industrial environment. A system including a tin dioxide sensor with its conditioning circuits and a temperature compensation circuit, a microcontroller and a graphical interface, was built in order to obtain a versatile, online and user friendly monitoring tool. The system was used for monitoring the volatile organic compound concentrations resulting from leather finishing processes in the Romanian industry.

VOCs Monitoring System Simulation and Design

The designed and simulated system will be used in the tanning industry, for Volatile Organic Compound (VOC) measurements. In this industry, about 90% of the solvent contained in the emulsions evaporates during its application, giving rise to VOC, which are at the same time hazardous atmospheric pollutants and one of the sources of ground level photochemical ozone formation. It results that a monitoring system is necessary in a leather finishing process, in order to detect hazardous VOC concentration and conducting process in order of VOC concentration diminishing. The paper presents the design of a VOC monitoring system, which includes sensors for VOCs and temperature, the conditioning circuitry for these sensors, the suction system of the gas in the hood, the data acquisition and the computing system and graphic interface. The used sensor in the detection system is a semiconductor sensor, produced by Figaro Engineering Inc., characterized by a short response time, high sensitivity at almost all VOC substances. The design of the conditioning circuitry and data acquisition is done in order to compensate the sensor response variation with temperature and to maintain the low response time of the sensor. The temperature compensation is obtained by using a thermistor circuitry, and the compensation is done within the software design. A Mitsubishi PLC is used to receive the output signals of the circuits including the sensor and of the thermistor, respectively. The acquisition and computing system is done using Mitsubishi ALPHA 2 controller and a graphical terminal, GOT 1000.

Hardware simulator of a tin dioxide sensor array for urban pollution monitoring

The present paper presents a hardware simulator of an integrated array of microminiaturized SnO2 sensors and their preconditioning circuit for measurement of CO, NOx and VOC (Volatile Organic Compounds) pollutants emitted in urban traffic. The SnO2 sensor array is simulated by three discrete SnO2 sensors together with their conditioning circuitry and the power supply coupled to a microcontroller. SnO2 sensors are characterized by short response times and high fiability, but low discrimination. The design main goal is to surpass this problem through technological design of the sensors, electrical circuit optimization and special software for the measured data. The hardware simulator includes three low power sensors, obtained on SnO2 deposited on ceramic, analogue with the sensors which will be integrated in the array. Experimental calibration curves were obtained, using a special calibration chamber for each of above gases. The calibration and measured data are included in a special designed software, using Visual Basic 6.0 and a subroutine of Fortran Power Station Library. The hardware simulator presented in this paper was used to measure the concentrations of the pollutants emitted from the Bucharest urban traffic, and are in good agreement with those reported by the Romanian National Agency for Environmental Protection.

Coupling devices for smart transducers with optical fiber link used in automotive industry

The fiber optic transmission systems have been used extensively for obtaining communication and intercommunication links within the public telephonic network, but lately the fiber optics has entered the vehicles field. The cable method might imply low costs if the coupling of the transducers to the optical fiber is optimised from the point of view of cost and fiability. The paper presents several methods of the optical fiber coupling, implying a glass or a plastic optical fiber, based on modern optical devices produced by Infineon.

Hardware simulator for design and characterization of MOEMS for environmental applications

The MOEMS for enviromnental applications have a complex structure architecture: a sensitive layer for environment interface, optical devices for radiation beam processing (waveguides on semiconductor) and photodiodes. The sensor includes an electronic module, used as transimpedance amplifier and phase shift detector and a radiation source coupled to the waveguide. Each of these sensor modules have specific parameters which must be optimized in order to obtain the best sensitivity for MOEMS, as well as to determine the appropriate concentration domain. The optimization process involves a great number of parameters and boundary conditions, so that a mathematical model is not sufficient. In this paper a hardware simulator for MOEMS design and characterization is presented. The structure and dynamics of environmental signal, the beani radiation processing and the power transfer from the environmental signal to the photogenerated current are physically simulated. An application of this simulator for design and characterization of aimnonia measurement MOEMS is presented.

Chemo-optical sensor for toxic gases detection

Many applications in the field of toxicology and laboratory medicine as well as some air pollution applications require low concentrations levels for toxic gas detection and its real-time monitoring. The authors have designed and manufactured an experimental integrated chemo-optical sensor on silicon containing a sol-gel layer, a silicon nitride waveguide and a silicon photodiode. The first measurements realized on an experimental structure show a good correlation with the requirements of the Romanian standards in the fields as well as EPA standards

Natural and anthropogenetic pollution limits of the stratospheric ozone

Starting from the irreversible thermodynamics stability analysis of the ozone layer in the far equilibrium conditions, an analytical procedure for separating the natural and anthropogenetic ozone pollution channels was developed. In this way the upper and the lower limits of the ozone layer concentrations were calculated, as well as, the lower (natural) limits and the upper limits (permitted pollution) of the pollutants that destroy ozone. The results are important in practical applications allowing one to include the ozone layer depletion as statements on the NO/sub 2/ and freons F11 and F12 in the air quality standards.