Correlation between two different real time data acquisition systems: LIDAR Raman and Cavity Ringdown Laser Spectroscopy, for CH4 as a fugitive gas, in S?o Paulo Metropolitan Area

摘要

Fugitive emissions, defined as unintended or irregular leaks of gases and vapors, these are an important source ofpollutants to the atmosphere, which is difficult to monitor and control. These sources are present in different sites,including megacities like S?o Paulo that are growing in size and economic activity. At the same time, there is aremarkable growth in concerns about the environmental issues associated with these activities. In a constantly changingworld, with increasing concentrations of greenhouse gases (GHGs), among them methane (CH4) and volatile organiccompounds (VOC), mitigation of atmospheric emission of these gases to contain global warming, make field campaignsin the metropolitan region of S?o Paulo very relevant. Optical remote sensing techniques as lidar can attend the needfor real time and trustable information on fugitive emissions. The Cavity Ringdown Laser Spectroscopy (CRDS)technique was adopted because it is widely used in the detection of gas samples that absorb light at specific wavelengthsand also for their ability to detect mole fractions up to the parts per trillion level. The Raman lidar system used includesa commercial laser pulsed Nd:YAG Quantel S.A., model CFR 200, with wavelengths of 355 nm, 353 nm and 396 nm,120 mJ pulse power, with laser repetition rate of 20 Hz and pulse width of 20 s, with a spatial resolution of 7,5 m. Thesystem includes an ethernet interface, used together with LabView software to control the measurement and readout ofthe acquired data. The mixing ratio of CH4 can be observed within the planetary boundary layer. The measured methaneprofiles correlate with the acquisitions made with the CRDS, however, an additional contribution of control data inwhich the Raman lines detect with high sensitivity.