Methane detection in the lower troposphere related to the burning of biomass and leakage in a petrochemical pole, using raman lidar technique

Abstract

Fugitive emissions, defined as unintended or irregular leaks of gases and vapors, are an important source of pollutants to the atmosphere, which is difficult to monitor and control. These sources are present in different sites, especially in regions that are growing in size and economic activity. In this study, we present the results of the capability to detect methane profiles at low troposphere combining data retrieval correlations between a rotacional/vibracional Raman lidar (RVRL) and a cavity ring-down spectrometer (CRDS). The measurements were made at two different sites, metropolitan area of São Paulo (MSP) and industrial area of Cubatão (IC). The lidar is based on a tripled Nd:YAG laser with a 20 Hz repetition rate, operating on the 355 nm wavelength elastic channel, the 353 nm and 396 nm wavelength inelastic channels. A measurement protocol was established, considering acquisition time for signal accumulation, climatic conditions and data above and below the planetary boundary layer. The idea was to establish specific measurement procedures for situations related to product leakage in the oil process and natural events, such as biomass burning. With over 150 hours of data acquisition, the results pointed the possibility of analyzing data from distances up to 1500 m with an initial resolution of 7.5 m which was extended to 100 - 300 m after data smoothing for obtaining final results. The concentration was calculated from the ratio between the methane Raman backscatter signal and the nitrogen signal, at 396 nm and 353 nm, respectively. The temporal variation of methane concentrations was correlated with CRDS data, in order to obtain a first degree calibration.