History

The experience in basic optical spectroscopy and related measurement techniques acquired during these 30 years enabled its application to worldwide concern issues such as ozone depletion measurements and atmospheric gas pollution detection.

Since mid 80s and all through the 90s, these problems have been both of scientific and popular interest, mainly due to the growth of global environmental-protection awareness. Spectroscopic and optical methods can be readily used for the determination of ozone depletion and atmospheric pollution measurements. We developed low-cost, user-friendly techniques based on open column differential optical absorption. The two papers selected here show the main activities carried out in this line of research.

The first one deals with ground-based ultraviolet radiation measurements during spring in the southern-hemisphere part of the American Continent, using a network of optical devices deployed in 9 locations in Argentina and Chile.

The devices built for this purpose have been designed to be of low cost and easy to manipulate, in order to implement an extended UV network. The device consists of two EGG detectors (type DF) incorporating blue silicon photodiodes (spectral response 250-900 nm) and integrated interferential filters (centered at 313 nm and 300 nm, with 10 nm bandwidth). Two quartz based telescopic assemblies and an equatorial mounting (ALSTAR) allow Sun tracking for direct solar-radiation measurement. The relative response of the devices has been carefully calibrated at CIOp.

Due to the great difference (a factor of six) in the absorption cross-section at the selected wavelengths (313 and 300 nm), changes in the irradiance ratio at these wavelengths clearly indicate a decrease in the total ozone amount. Ozone data obtained from the ground stations are compared with total ozone values supplied by the satellite showing a very good agreement.

The second paper exemplifies the work carried out for measurement of atmospheric pollutant gases such as SO₂ and NO₂. Similarly to those developed for ozone, non dispersive UV (NDUV) devices with appropriate interference filters were constructed and run in a laboratory-based industrial chimney, with very good sensitivity. For urban air quality measurements, differential optical absorption spectroscopy (DOAS) was used. A collimated white light beam is launched, at one end, through a several hundred-meter long atmospheric column and analyzed with a spectrograph at the other end.
The absorption bands found and their deepness provide accurate information about the gas species and its concentration through the direct application of Lambert-Beer (LB) law. In particular, the paper shows a novel application of LB to the determination of the concentration of interfering gases.

Back