Atmospheric pollution is one of the worst threats to modern society. The consequences derived from different forms of atmospheric pollution vary from the local to the global scale, with deep impacts on climate, environment and human health. Several gaseous pollutants, even when present in trace concentrations, play a fundamental role in important processes that occur in atmosphere. Phenomena such as global warming, photochemical smog formation, acid rain and the depletion of the stratospheric ozone layer are strongly related to the increased concentration of certain gaseous species in the atmosphere. The transport sector significantly produces atmospheric pollution, mainly when diesel oil is used as fuel. Therefore, new methodologies based on selective and sensitive gas detection schemes must be developed in order to detect and monitor pollutant gases from this source. In this work, CO₂ Laser Photoacoustic Spectroscopy was used to evaluate ethylene emissions and electrochemical analyzers were used to evaluate the emissions of CO, NO_x and SO₂ from the exhaust of diesel powered vehicles (rural diesel with 5% of biodiesel, in this paper called only diesel) at different engine rotation speeds. Concentrations in the range 6 to 45 ppmV for ethylene, 109 to 1,231 ppmV for carbon monoxide, 75 to 868 ppmV for nitrogen oxides and 3 to 354 ppmV for sulfur dioxide were obtained. The results indicate that the detection techniques used were sufficiently selective and sensitive to detect the gaseous species mentioned above in the ppmV range.

The increase in greenhouse gas emissions is a serious environmental problem and has stimulated the scientific community to pay attention to the need for detection and monitoring of gases released into the atmosphere. In this regard, the development of sensitive and selective gas sensors has been the subject of several research programs. An important greenhouse gas is sulphur hexafluoride, an almost non-reactive gas widely employed in industrial processes worldwide. Indeed it is estimated that it has a radiative forcing of 0.52 W/m². This work compares two photoacoustic spectrometers, one coupled to a CO₂ laser and another one coupled to a Quantum Cascade (QC) laser, for the detection of SF₆. The laser photoacoustic spectrometers described in this work have been developed for gas detection at small concentrations. Detection limits of 20 ppbv for CO₂ laser and 50 ppbv for quantum cascade laser were obtained.

Brazil has abundant water resources and depends on them for hydroelectric power generation. In 2011, 81.9% of the electricity in the country was produced by hydropower. A significant change in the Brazilian hydrological cycle reduced this percentage to 64% in 2015. The scarcity of rain decreased the volumes in the reservoirs of the hydroelectric power plants located mainly in the Southeast, Center-West and Northeast regions. In this scenario, the National Operator System authorized the use in full load of thermoelectric plants powered by natural gas, biomass and coal. As a result, thermoelectric generation grew 329%, increasing carbon dioxide (CO₂) emissions. The intensification in the use of thermoelectric energy leads to a vicious energy–environment cycle, as it increases the CO₂ emissions. Brazilian government is aware of the necessity of electricity generation, and future uncertainties generated by the instabilities of hydrological cycles may jeopardize the country’s energy security. The country has proposed programs to encourage energy generation by other renewable sources (wind and solar) and avoid the use of thermoelectric plants, which increase the generation costs and environmental impacts. This could compromise the goals of reducing carbon emissions signed by Brazil at Paris Conference (COP21).

A method suitable for the thermal characterization of gases is described. It is based on thermal wave interference (TWI) in a cavity. A TWI device was constructed and the thermal diffusivity of different binary gas mixtures as a function of their relative concentration was measured. From these values, using a logarithm mixing model for the thermal conductivity of a two-phase gas system, the thermal properties of the corresponding pure gases were calculated. The data obtained for several test gases show good agreement with values reported in the literature.