Fugitive emissions, defined as unintended or irregular leaks of gases and vapors, these are an important source of pollutants to the atmosphere, which is difficult to monitor and control. These sources are present in different sites, including megacities like São Paulo that are growing in size and economic activity. At the same time, there is a remarkable growth in concerns about the environmental issues associated with these activities. In a constantly changing world, with increasing concentrations of greenhouse gases (GHGs), among them methane (CH4) and volatile organic compounds (VOC), mitigation of atmospheric emission of these gases to contain global warming, make field campaigns in the metropolitan region of São Paulo very relevant. Optical remote sensing techniques as lidar can attend the need for 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 wavelengths and also for their ability to detect mole fractions up to the parts per trillion level. The Raman lidar system used includes a 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. The system includes an ethernet interface, used together with LabView software to control the measurement and readout of the acquired data. The mixing ratio of CH4 can be observed within the planetary boundary layer. The measured methane profiles correlate with the acquisitions made with the CRDS, however, an additional contribution of control data in which the Raman lines detect with high sensitivity.
The physical optics approximation is applied to calculate the backscattering Mueller matrix and the depolarization and color ratios for quasi-horizontally oriented hexagonal ice plates of cirrus clouds in the case of a tilted lidar. It is shown that the backscatter reveals some features caused by the corner reflection effect that is inherent to the pristine hexagonal ice plates. In particular, the backscatter creates sharp peaks of both the backscattering cross section and depolarization ratio at the lidar tilts of about 30 degrees off zenith. The experimental results obtained recently by Veselovskii et al. JQSRT, 2017;202:74–80 at the lidar tilt of 43 degrees have been interpreted as a partial manifestation of the corner reflection effect.
This study presents an overview of the recently results obtained by a novel concept of a lidar to remotely monitor methane and volatile organic compound including aerosols and fugitive gas emissions from pipelines, waste disposal areas and tankages. The system works based on Raman and fluorescence scattering principles by emission of a 355 nm beam (3rd Nd:YAG harmonic) and detection of the wavelengths at 355 nm (elastic), 353 nm (oxygen + nitrogen rotational Raman) and 396 nm (methane vibrational Raman) and alternatively the system can be switched to a uorescence lidar based on a 32-channel PMT coupled to an spectrometer to be able to observe fluorescence scattering caused by VOC's and aerosols. This paper shows a summary of the results obtained in the preliminary campaigns, which were carried out under different conditions to be adopted as benchmark for the system performance regarding detection limits, calibration capabilities, and time vs range resolution, in order to optimize the system performance.
This work focuses on the statistical analysis of day and night hourly pattern of columnar aerosol properties. To that end, we use the large database of star-photometry measurements at the University of Granada station (37.16°N, 3.60°W, 680 m a.s.l; South-East of Spain) for nighttime characterization, and co-located AERONET measurements for the daytime. The aerosol properties studied are the aerosol optical depth (AOD), Angstrom parameter (α(440-870)), aerosol optical depths of fine (AODfine) and coarse mode (AODcoarse) through the Spectral Deconvolution Algorithm (SDA). Microphysical properties are calculated by inverting AOD spectra and include the effective radius (reff) and volume concentration (V) of the total size distribution, and also the effective radius of the fine mode (rfine). The initial analysis for the different air masses that reach the study area reveals that generally day and night values of AOD and α(440-870) are not different statistically. Nighttime values of AODfine, reff and rfine do however, present larger values. The influence of North African air masses is remarkable both during the day and night, with high particle loads and low values of the Angstrom parameters and also with large contribution of coarse particles as AODcoarse and reff values are almost the double than for other air masses. The analyses of day-to-night hourly values reveal an increase in AOD, AODfine and AODcoarse during the day and a decrease during the night. Such a pattern could be explained by the different emission rates, accumulation, aging and deposition of particles. Changes in particle radius are also observed as part of the day-tonight particle evolution process, being rfine variations important mainly at daytime while for reff variations are more important at nighttime. Results of day-to-night evolution were found to be independent of air mass origin, and seem to be mainly associated with local processes.
In this study, a mapping of the soot extinction coefficient in an oil refinery flare using a three-wavelength elastic backscatter lidar system is presented. A log-normal aerosol size distribution was assumed for the flare, and a homogenous refractive index was assumed along the nearly horizontal beam path through the atmosphere, excluding the flare volume. The optical depth was estimated for each wavelength and from this the Angstr¨om exponent was calculated. The results were comparable with the literature, demonstrating that it is possible to distinguish small from large particles by this technique in low wind conditions.
The results of investigation of injection-locked KrF laser Raman conversion in deuterium are presented. Photon conversion efficiencies of 23% to the second Stokes order and of 27% to the third Stokes order at deuterium pressure of 35 atm are obtained. The described excimer- Raman laser system may be used for the ozone sounding in stratosphere and troposphere.
The powerful sources of UV radiation on a base of discharge excimer lasers find wide application in scientific research and technology. Short wavelengths, high peak and mean powers, and the possibility of quick working mixture exchange are making this type of laser extremely attractive for photochemistry, lithography, and laser medicine. Nevertheless, it is known that without taking special measures, excimer lasers possess bad spectral and spatial coherence. Further progress in the growing field of excimer laser application is impossible without flexible control of radiation parameters: linewidth, divergence, and laser pulse duration. The authors investigate different approaches to producing radiation with high spectral and spatial brightness as well as with variable pulse duration from commercial excimer lasers. The experiments were carried out on a commercial excimer laser Model 1701 developed in the Physics Instrumentation Center of the General Physics Institute. The laser discharge volume was 1 X 2 X 60 cm3, the output energy is 200 mJ at 248 nm and 100 mJ at 308 nm. Maximal repetition rate is 50 Hz.
This paper presents a novel application of UV laser radiation: fabrication of soft or apodized apertures (AA)I-3 with transmission profiles decreasing smoothly from the center to the edges for high-power single-pulse visible and near-IR lasers. Such units are used both outside and inside the cavity for beam shaping, for avoiding hard-edge Fresnel diffraction ripples in laser amplifiers, for increasing the second harmonic conversion efficiency, and for the brightness enhancement of master oscillators in single-mode lasing.
Waveform conjugation of narrowband KrF lasers with linewidth 0.02 cm-1 and divergence 10-4 rad was investigated. By means of Brillouin scattering in SF6 gas, the 12 ns duration pump pulse was compressed up to 1.5 ns with energy efficiency about 80% and the laser beam divergence retention. The waveform conjugation under thermal Raleigh scattering in hexane, heptane and hot water was also investigated. The maximum efficiency in hexane was about 10% and scattered pulse duration 2.5 ns. Waveform conjugation in a wide region of liquid absorption coefficients was also observed.
The laser system ''oscillator-amplifier'1' was developed to provide the high
spectral brightness (linewidth < 0.02 cm ) and diffraction limited divergence of
radiation. Spectral narrowing was achieved by the use of dispersive intracavity
elements. The oscillator radiation was amplified by double pass amplifier with phase
conjugate SBS mirror. Oscillator and amplifier were separated with etalon, tuned on
Brillouin shifted wavelength reflection. As a Brillouin scattering medium both
liquid n-hexane and quartz-polymer fiber were utilized. In contrast with n-hexane
the use of fiber decreased the SBS threshold more than two order of magnitude.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.