A beam of light scanning the sky may revolutionize the methods used in the measurement of pollution in Brazil. Watchful observers were able to see it in mid-October near the campus of the University of São Paulo (USP) in the State capital, during testing carried out by a group from the Energy and Nuclear Research Institute (Ipen) of the National Nuclear Energy Commission. It is a laser radar beam, part of a pioneering development developed in Brazil since 1995, by the Remote Sensoring System for Atmospheric Pollutants in São Paulo Development Program, financed by FAPESP under the Young Researchers program and coordinated by the nuclear physicist Eduardo Landulfo, of the Ipen, and which should be completed in July.
The purpose of the laser radar or Lidar -( light detection and ranging) is to measure the particle pollutants in the atmosphere (such as dust, smoke, and soot), using a laser light beam by the method called back mirroring. This technique enables the laser signal to return to its starting point after encountering a particle or any target. The equipment that Landulfo is proposing was presented in July last year at the 20th International Laser Radar Conference.
Ipen’s Lidar has various functions, already set into its assembly. It supplies data on suspended particles, warns of the need to take emergency measures in periods of still air, when the level of pollutants represents a public health risk – and this may be decisive to finding more efficient solutions in for the environment in large urban centers.
Companies that monitor pollution nowadays work with air quality stations, fitted with what are essentially filters, that collect data for analysis several times a day and supply information for air quality bulletins, as is done in Greater São Paulo, for example.
This job becomes more dynamic with the laser radar, since it instantly checks the pollutants in the air. In addition, it enables frequent monitoring of more polluted areas. Based on the emissions of the laser, the composition of particles and suspended gases can be established.
Tests and adjustments
The equipment used in the project undertaken by Ipen works with the kind of laser called Nd:YAG, made up of the chemical element neodymium (Nd) and a synthetic crystal called YAG made up of yttrium and aluminum oxide. This combination emits a laser beam on being triggered by a specific type of bulb. So far, the laser has been borrowed from the Spectroscopy group of Ipen’s Laser and Applications Center. The Brazilian group is waiting for the purchase of a new piece of equipment to complete the assembly of the system, which will be installed on Ipen’s premises. The laboratory where it will be installed looks like an ordinary room except for an opening in the roof, through which the laser’s emission/reception telescope will be pointed. Moving the equipment to the outside the laboratory is not ruled out, but it depends on buying a utility vehicle adapted for transporting the equipment, and this is not part of the project.
“The results we have accomplished so far show that we are on the right track”, says Landulfo. He says that when the work is complete, measurements will be able to be taken more often over longer periods. “The idea is to carry out tests lasting around eight hours, to obtain broader assessments of the behavior of pollutants in the region”, he explains. He points out that the time remaining to the completion of the project, expected in July, will be spent on adjustments and simulations.
The tests were done for a week in October, with seven hours of measuring, and a researcher from the National Institute for Space Research (Inpe) took part. The results enabled comparisons to be made with data from the State Technology and Basic Sanitation Company (Cetesb) which is the São Paulo State pollution authority and from USP’s Air Pollution Study Group. “The tests were very important, because they enabled us to judge the entire performance of the system”, says Landulfo. The next step will be for an international organization to validate the data and then to publish them.
The research is being monitored by Alexandros Papayannis, head of research at Lidar at Athens Technical University, in Greece. He is in charge of supervising the data produced by the Brazilian experiment. The Lidar project was approved in1998 and it is being developed by a multidisciplinary group of ten people. “The greatest difficulty our team has come up against so far has been to calibrate the equipment to operate according to the peculiarities of our air”, says Landulfo. He tells that a good part of the pollution in São Paulo is made up of particles and unbreathable matter.
Besides measuring pollution quicker, the equipment will also be able to predict in advance the thermal inversions that occur in winter”. Thermal inversion happens when a layer of hot air prevents pollutants from dispersing.
The Lidar developed by Ipen has the capacity to measure the distribution of the particulate matter in a vertical profile over a radius of 5 to 6 kilometers. “With this capacity, we are able to exceed a layer limit, located between 200 meters and 2,000 meters above the ground. This is the part of the atmosphere where there is the most interaction between man and the concentration of particulate pollutants”, says Landulfo. Besides this characteristic, the new Lidar can cover the area of four conventional measuring stations.
Investment of around US$ 65,000 was required to build the Lidar, spent on the purchase of equipment such as the telescope imported from France, a digital oscilloscope, detectors, and optical material. To complete the equipment only the laser is missing, bought for US$ 23,000. “We are awaiting the arrival of the laser to complete the laboratory”, says the researcher.
He has already lost track of how many hours he has spent in the Ipen laboratories doing simulations, to adjust the equipment to São Paulo’s environmental conditions. The tests, up to now, have used the Ipen laser (expect for the French item), which means that a break of almost two hours is necessary so the equipment won’t be damaged and a technician has to be employed to handle the device .
The potential users of the Lidar are environmental agencies, like, for example, the Green and Environment Secretariat (SVMA) of the municipality of São Paulo. “Even before finishing, the results of our work are creating considerable expectation in the Brazilian and international scientific community”, he says. The Brazilian Lidar project has also attracted the attention of the National Scientific and Technological Development Council (CNPq), which awarded a productivity grant to Landulfo.
The project, which should result in a patent, has been stirring the interest of companies in the field of environmental instrumentation. The first Brazilian Lidar is expected to be handed over to an air pollution agency of the city of São Paulo. It will continue to pierce the skies of the State capital with its beams of light.
The distance between the Earth and the Moon
The discovery of the laser (light amplification by stimulated emission of radiation) took place in the 60s and the most famous use of the Lidar apparatus was in 1969, when the Apollo 11 mission team, the first to land of the moon, set up a reflector on the satellite. By sending a laser beam from earth, it was possible to measure the distance between the two bodies accurately.
Currently, the laser radar is employed, among other things, to detect oil deposits, oil leaks, and shoals of fish. Scientists also use a Lidar to calculate the size of the hole in ozone layer. Prototypes of a laser pollution meter came out in Germany and France in the 70s. The United States and Japan have measured environmental pollution. However, it was the development of a more compact, solid state, laser-emitting device, that enabled smaller pieces of equipment to be built and simplified the move of these machines outdoors.
In Europe, Asia, and America there are a hundred similar pieces of equipment to the one the Ipen is developing, while in Latin America, there is only one in the category (as high as 10 kilometers), operating in Buenos Aires. Some Brazilian companies have even imported the finished equipment for the task of measuring pollutants, but this initiative has been given up. The reason was the difficulty of adapting the equipment to Brazil’s climatic and atmospheric conditions. The National Space Research Institute (Inpe) uses a Lidar to measure the concentration of sodium ions, this is done at an altitude that exceeds 80 kilometers.
In 2003, NASA, the US space agency, is expected to do a scan of the entire atmosphere of the earth with a Lidar, to observe the climate, the clouds, and suspended aerosol components. Countries already using the Lidar may be invited to take part.
Remote Sensoring System for Atmospheric Pollutants in São Paulo Development Program (nº 98/14891-2); Type Young Researchers Program; Coordinator Eduardo Landulfo – Ipen; Investment R$ 31,790.25 and US$ 68,650.70