Scientists at Universidad Carlos III de Madrid are testing infrared (IR) remote sensing technology to evaluate the pollutant emissions associated with motor vehicle traffic. The technology could analyze all the gases of environmental interest with one instrument and one measurement.

The methodology has been used in this research in collaboration with the Universidad Europea de Madrid. It is based on the open-path Fourier transform IR technique, which takes advantage of specific properties of gases in order to detect them: the gases absorb radiation only in certain wavelengths which are always the same and particular to each gas. Many gases have absorption lines or bands in the IR, for which this area of the electromagnetic spectrum is very useful for remote detection, according to the researchers.

“With this technique, the gases that have absorption bands in the IR can be measured simultaneously — this includes almost all of the gases that are of environmental interest: carbon monoxide, carbon dioxide, nitrogen oxides, ozone, methane, hydrocarbons, sulfur dioxide, chlorhydric acid, etc.,” said Antonio de Castro, a professor and one of the leaders in the investigation.

The object of the research is to experimentally determine the concentration of the chief gas pollutants associated with motor vehicle traffic. For that purpose, the researchers developed a methodology that takes measurements outside of the concentration of different gases, mainly carbon monoxide and carbon dioxide.

“This technique offers the advantages inherent to a non-intrusive measurement technique, avoiding having to take gas samples in special recipients and providing average concentrations during a measurement line defined in real time,” said de Castro. In addition, the technique offers the capacity to simultaneously calculate the concentration of all the gases of interest taken from the same measurement.

This technique is highly valuable for resolving numerous environmental problems associated with atmospheric pollution, especially when the toxicity of the pollutants make simple in situ measurement dangerous. It is not necessary to go into the polluted area to carry out the measurement.

“The possibility of monitoring a wide spectrum of gases from a distance and observing wide areas in such a simple manner makes this technique a useful tool,” said the study’s co-author, Professor Susana Briz.

She further pointed out that the technique allows, in addition to the measurement of the concentration of pollutants, the calculation of emissions associated with different environmental issues, such as the characterization of emissions associated with forest fires, greenhouse-effect gas emissions from dumps and agriculture installations, and volcanic gases.

“You could say that this technique is useful for almost all of the problems associated with atmospheric pollution and in general with the detection of gases,” she said.

To take a measurement it is necessary to have an infrared source, such as a very hot object, and a spectrometer, an instrument that analyzes IR that comes from the origin with its wavelengths, just as a prism does when it separates white light into the colors of the rainbow, the researchers explained.

“If there is a certain gas between the infrared source and the spectrometer, its wavelength characteristic is absorbed and that is detected by the instrument,” Briz explained. “Afterwards, the analysis programs are also capable of determining the concentration of that gas.”

At the moment, various field experiments in the towns of Villaviciosa de Odón and Leganés have been carried out to test the validity of the method to calculate emissions based on concentration measurements with the open-path Fourier transform IR technique, verifying the methodology with standardized equipment (extractives).

The methodology proposed, based on dispersion models, has been proven in the opposite way: the emissions calculated independently (EMFAC2007) have been introduced, and the calculated concentrations have been compared with the experimental ones.

“In light of these results, we can assert that the proposed methodology is an effective tool to experimentally estimate the emission factors associated with a certain way,” said the researchers.

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