Unheard-of in Brazil and with rare similar representatives in the world, a system for measuring concentrations of pollutant gases in the atmosphere through a carbon dioxide (CO2) laser is in its final phase of development in the laboratories of the company Unilaser, in the city of Campinas. Named a photo acoustic spectrometer, it was projected by the physicist Edjar Martins Telles. The equipment is capable of detecting low concentrations of various pollutants monitored by the environmental control organizations, such as ozone, sulfur dioxide, ammonia and carbon dioxide.
The Unilaser company works with maintenance, recovery and the sale of laser equipment. The company was set up in 1986 by the physicist Artemio Scalabrin, a professor at the Gleb Wataghin Physics Institute of the State University of Campinas (Unicamp). It is installed in the Support Center for the Development of Technology Based Companies (Nade), of the Company for the Development of a High Technology Center of Campinas (Ciatec), a company incubator maintained by the city hall. The spectrometer project took up three years of research and had financial support through FAPESP’s Small Business Innovation Research (PIPE).
“Now we are in the final phase, working hard to improve the system and the automation of the tasks in order to simplify the integration between the user and the equipment”, explains Telles, a master’s and doctor through the Physics Institute of Unicamp and with his post doctorate at the National Institute of Standards and Technology (Nist) in Boulder, In Colorado State, in the United States.
Collision of molecules
The principle of the functioning of the system is the photo coustic effect, a technique which allows for the conversion of light into sound. In order to understand this one needs to begin with the type of laser chosen as a source for the optical excitement of the gaseous molecules. The choice was for a carbon dioxide (CO2) laser which has 90 emission lines within the spectrum of the infrared electromagnetic band, with wave lengths of approximately 10 microns (a one thousandth part of a millimeter). This type of laser allows the detection of various gases of interest, since they show the energy of their absorption frequency coinciding with the lines of the infrared band.
The heart of the system is the photo acoustic cell, a closed receptor where a flow of atmospheric air circulates or another gaseous mixture that is to be analyzed. The beam of the laser is aligned in the interior of the cell through a small window. “When the laser is synchronized on the same frequency of the gas molecules, they absorb the energy of the laser”, explains Telles. Before hitting the interior of the cell, the beam passes through a modulator, which interrupts and liberates the radiation in a constant rhythm, producing an effect similar to a car flashlight. When the beam is liberated, the molecules absorb the energy from the laser and reach the excitation level.
At the moment in which the radiation is interrupted, they fall back to the normal level, losing the excess of energy to the neighboring molecules through collisions, thus transforming the absorbed energy into movement energy, and generating heat. The variation of the temperature is followed by variations of pressure that generate acoustic waves in the interior of the cell detected by a microphone. The electrical signal generated in the microphone is directly proportional to the concentration of the molecules that absorb the energy of the specific frequency of the laser.
This signal is filtered, so as to eliminate undesirable noises, and amplified so that it can be analyzed by a computer, where the photo acoustic spectrum of the molecule is registered and interpreted by a piece of software also developed during the project. “Each molecule represents a unique photo acoustic spectrum, just as if it were a fingerprint” Telles explains. The equipment can detect one or various gases simultaneously. “All you have to do is to tune in the laser on the emission line of the infrared band with the molecule you want to analyze”, says the researcher.
The spectrometer permits the detection of small concentrations, in the order of parts per million (ppm), which is the level of concentration of the majority of the pollutant gases. Besides those gases monitored by environmental control organizations, the spectrometer detects ethylene, ethanol, methanol, nitrogen oxides, benzene and formic acid.
The discoverer of the photo acoustic effect was by the North American physicist of British origin Alexander Graham Bell (1847-1922), who invented the telephone. The discovery occurred in 1880, but for almost a century the possibility of converting light into sound was considered to be a mere curiosity. Only in the decade of the 30s, did the effect begin to awaken scientific interest when it was perceived that it could be used to analyze gases. So the photo acoustic spectroscope was born, a technique that gained even a bigger boost in the 70’s with the development of lasers and of progress in the field of electronics.
Few photo acoustic spectroscopes of the type built by Unilaser exist in the world, basically being restricted to academic institutions. “It is only produced at the Nijmegen University in Holland, which eventually attends to requests for orders for equipment that detects only ethylene” says Telles. The price is around US$ 110,000. However, the cost of the national model is estimated at around R$ 130,000, including the source of high tension for feeding the CO2 also developed during theproject, which the imported model doesn’t provide. Close to 90% of the pieces used to assemble the system and in the diagnostic appliances were produced in Brazil, a factor which reduced the cost of the equipment.
Cláudio Alonso, a manager at the Department of Environmental Control of the Company of Environmental Sanitation Technology (Cetesb in the Portuguese acronym), looks with optimism on the Unilaser initiative. “The country needs to begin to create a market with national technology”, he says. Currently, the monitoring centers of air quality are mounted using various pieces of equipment, one for each type of pollutant. All are imported from the United States and cost between US$ 10,000 and US$ 30,000. Throughout Brazil they are importing this type of equipment”, he says. Though the spectrometer is not able to measure all of the pollutants monitored by Cetesb, according to Alonso, the equipment could be an alternative to complement the system already implanted, as long as it respects the international technical norms of environmental control.
The demand exists. “Even in the state of São Paulo, which can count upon good coverage in terms of the control of air, there are still important regions which don’t have monitoring stations or which require some kind of re-enforcement”, says Alonso. Some examples are Guarulhos, in the metropolitan area of São Paulo, Ribeirão Preto, Jundiaí, São José dos Campos and Santos. “But most certainly the demand outside of the state is even higher”, he says.
Besides the air monitoring stations, both fixed and mobile, the spectrometer can also be an option for the companies that need to control their emission of gaseous pollutants, such as the petrochemical industry. “In the case of the São Paulo companies with high emission potential, self-monitoring is a Cetesb demand”, says Alonso.
Fruit and skin
Other potential clients are the research institutions in the environmental, farming and medical areas. “Many pieces of research about the of fruit, rely on the analysis of ethylene concentrations, a gas which accelerates the fruit ripening”, says Telles. Pioneer research into this area in Brazil is being carried out by professor Helion Vargas, at the State University of Norte Fluminesce (UENF), who makes use of a photo acoustic spectrometer imported from Holland. These studies allow the determination of more adequate methods for the fruit to arrive at its destination in good condition for commercialization.
In the area of medicine, the equipment could be used in studies that are monitoring the amount of ethylene exhaled through the skin under specific physiological conditions, such as excess heat, traumas, radiation and excessive exercising, making it a method with a quick response for monitoring stress processes. The prospect is that within a year the equipment will be ready to be commercialized. “This is the time necessary for us to conclude the phase of engineering of the product”, says the researcher.
In order to obtain the R$ 250,000 necessary for this phase and to place the equipment on the market, the company Unilaser is looking for partnerships with companies interested in investing in the project. The company also intends to obtain resources by making the equipment available for renting. Certainly, Unilaser has a wide market in front of it, in the monitoring of atmospheric pollutant in large parts of cities, a practice which has already made itself indispensable throughout the planet.
Development of a System for Measuring the Concentration of Pollutants in the Atmosphere using Infrared (CO2) Lasers by Photo Acoustic Spectroscope (nº 97/07445-3); Modality Program of Innovation Technology in Small Companies (PIPE); Coordinator Edjar Martins Telles – Unilaser; Investment R$ 115,381.31 and US$ 52,137.80