Science and Technology

Group creates portable and economical method to measure air pollution by ozone

Formed by the air pollutants released by cars, O3 is also produced by a new generation of appliances

In the stratosphere, 15 km high, the gas ozone protects us from excessive ultraviolet radiation emitted by the sun. Already here in the troposphere, where we live, this molecule composed of three oxygen atoms reveals a villain pollutant, quite toxic to our respiratory system and that worries environmentalists, organs that monitor the air quality in large cities, as well as scientists, as Arnaldo Alves Cardoso, Institute of Chemistry, UNESP at Araraquara.

To measure the amount of O3 we breathe, the bodies responsible for monitoring air quality in the case of São Paulo, Cetesb use sophisticated equipment, large and heavy, making the real-time analysis. Cardoso has one of these in his laboratory in Araraquara. It cost about $ 10,000, he says. The method he and his group have developed is a cheaper option and portable. Can be an alternative for monitoring also places far from major centers, since the problem of ozone is no longer exclusive to metropolises says.

Formed in the air mainly from pollutants released by car exhausts, O3 can also be produced by a new generation of appliances. One day I opened the newspaper and saw ads to air purifiers, fans and even washing machines that generate ozone, Cardoso recalls. The reason is simple: powerful sterilant gas eliminates micro-organisms from air and water. It is also produced by so-called germicidal lamps. It is increasingly easy to generate it at home today, says the researcher.

In moderate concentrations, ozone is beneficial to the environment, the air acting as a kind of detergent. As a strong oxidant it breaks large organic molecules such as petroleum products, making them soluble in water, allowing them to be swept away by rain water. In large concentrations, however, becomes responsible for the gray fog late afternoon, a phenomenon typical of large cities.

In Araraquara, São Paulo municipality distant 277 km from the capital, with just over 200,000 inhabitants, he found, at peak times, concentrations of ozone in the air up to 85 parts per billion (ppb). The Resolution 3/1990 CONAMA (National Environment Council) states that to be considered of acceptable quality, the air of a city can exceed 81 ppb ozone only once a year. To have an idea, in São Paulo, in 2012 it was exceeded 36 times in Ibirapuera Park (one of the greenest areas of the city), according to data from Cetesb.

Dispensing large equipment, the method of Cardoso requires little more than a piece of paper. Is based on the chemical reaction of ozone with one of the oldest dyes used by man: the strong indigo blue color. Of circular shape and with only 2 cm in diameter, the role is small enough to fit in a syringe, where the reaction occurs (with a substance that serves to make the environment more humid). In the presence of ozone, the indigo is oxidized and hence the piece of paper was impregnated in which it clears. Thus, the more ozone in the air, the role will be clearer after eight hours of exposure to the environment, time required for completion of the test.

The final color of the paper is then compared with a disk with 30 shades of blue, which indicate the respective concentrations of ozone in the air. The core of the work was to transform each of these tones in a numerical code (using the RGB color system, the same used by computers) and relate mathematically the dye concentration in the role of the content of ozone in the air, explains doctoral student Gabriel Garcia, coauthor of the study.

Each scale range of blue is a variation of just over 3 ppb ozone, the student continues. In practice, this means that the difference between the color of the paper and the final correspond to 20 tones of the disc, the gas concentration in air is approximately 60 ppb. The technique has proven effective in determining ozone in any environment at concentrations ranging from 2 ppb and 97 ppb. We want to popularize this type of analysis and propose a field test kit to dispense any depth technical knowledge and physical structure of the laboratory, explains Garcia. Last year, the work was presented at the 35th Annual Meeting of the Brazilian Chemical Society, in Águas de Lindoia (SP).

<i> Analysis by phone </ i>

For now, the results provided by the test developed by the group of Araraquara require visual inspection only. That is, the user checks the color of the paper with the default color scale and infers the ozone concentration. Obviously, this can lead to different results depending on the beholder. The color blind, for example, would probably have trouble performing the task. However, the researchers envisage the possibility of automating the technique causing a computer program to analyze the final color of the paper, which certainly would increase the reliability of the result. According to them, you can create mobile applications to perform the calculation of the concentration of ozone in the air based on a sample photo.

Besides the portability of the method, one of the main advantages highlighted by Cardoso is in being a technology that uses no energy. The kit can be used to control activities and environmental education, he adds.

For him, it is also important to educate the population about the indiscriminate use of appliances ozone generators. I am not against this usage, which in fact is extraordinary, but it is important that people be guided and there is some kind of regulation of the amount of ozone released by these devices, so we can avoid the bad consequences for the environment.

<i> information UNESP Science </ i>