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Chemical Composition characterization of air pollution (aerosols and gases) on the basis of nonlinear multi-channel lidar experiments

Periodic Reporting for period 1 - CAPABLE (Chemical Composition characterization of air pollution (aerosols and gases) on the basis of nonlinear multi-channel lidar experiments)

Reporting period: 2017-02-01 to 2019-01-31

CAPABLE aimed at the development of a complex lidar spectrometer to measure vertically resolved profiles of chemically reactive trace gases, chemical components in particles, and bio-aerosols in atmospheric aerosol pollution. This information can be used for studies of the effect of the vertical distribution of aerosol and gas pollution on climate forcing, air quality, and human health. CAPABLE had four main interrelated objectives:
(i) Development of an end-to-end computer simulation program to model the processes of inelastic Photoluminescence and Raman scattering from aerosol particles and gases in the context of lidar remote sensing; (ii) Identify the luminescence and Raman scattering characteristics for a set of key natural and anthropogenic aerosols and gases by means of laser-based laboratory experiments; (iii) Performing test measurements and recording case studies under laboratory conditions; (iv) Define hardware specifications and build the hardware prototype of a complex inelastic lidar spectrometer.
A variety of actions were performed:
Preparation of a bibliographic database;
Development of software and a simulation program for identifying Raman and photoluminescence signal returns;
Simulations of Raman signals from gases considering various mixing conditions and components in cases of aerosol mixtures;
Identification of Raman cross sections of chemical components in the atmosphere with the simulation program and from available literature;
Development of equipment for laboratory experiments including a Raman/fluorescence microscope and a suite of gas chambers:
Definition of the hardware requirements for the complex lidar spectrometer;
Assembly and test of the complex lidar spectrometer;
Performing lidar measurements in the atmosphere.
The work performed from the beginning to the end of the project followed the initial plan, corresponding to the activities of all five work packages.
WP1 was aimed at developing a simulation program for identifying Raman signal returns from different chemical compounds. Raman scattering, and remote sensing theoretical models were selected from the available literature. The simulator was developed on base of lidar theory and methodology including Elastic, Raman, Polarization and Fluorescence lidar equations as well as approximations of single and multiple scattering. The basic equations and algorithms were summarized for the needs of the simulator. The simulator computed Raman lidar signals on the basis of given laser specifications (excitation wavelength, line width, pulse length) and realistic atmospheric conditions and various gas mixing conditions, and aerosol mixtures.
WP2 dealt with identification of Raman lines and cross sections of chemical compounds suitable for lidar measurements. Raman and fluorescence properties of more than 150 chemical compound were explored including gases, liquids and solid-state. As a result of the instigations cross sections of more than 30 Raman lines were selected as appropriative for detection by spectroscopic lidar. Examples of such lines are NO2 (754cm-1), C3H8 (867cm-1), O3 (1103cm-1), SO2 (1151cm-1), CO2 (1285cm-1and 1388cm-1), NO2 (1320cm-1) N2O (2223cm-1) N2 (2330cm-1), O2 (1556cm-1), H2O (liquid 1595cm-1 and vapour 3652cm-1), CH4 (2914cm-1).
WP3 was involved with the development of the laboratory experiments on the basis of the simulations results, definition of the lidar requirements, measurements of Raman lines and cross sections. A Raman/Fluorescence microscope was designed and assembled for testing of solid-state and liquid samples, as well as a suite of gas and aerosol chambers for tests of gases and aerosol particles in air. Raman/Fluorescence spectra of more than 50 samples were experimentally measured.
WP4 was focused on optimization work for the simulations and final design and specification of the spectroscopic lidar. Based on the results from WP2 and WP3 we optimized the design of the lidar spectrometer. Additional Zemax simulations were done for the lidar receiver and conjugation between lidar’s subsystems - telescopes, spectrometer, and detectors.
WP5 covered the prototyping of the spectroscopic lidar, set up and assembly, and performance testing. We developed not only a prototype, but a fully operational worldwide unique lidar system, capable of fulfilling a multitude of experiments used in lidar applications. The system is part of the newly established LITES (Lidar Innovations for Technologies and Environmental Sciences) spectroscopy facility. A number of tests were performed: the system measured for the first time ever range resolved entire pure rotational Raman spectrum of the air with better than 5cm-1.
CAPABLE pushed the limits of using lidar for observations and characterization of aerosol pollution. We provided ground-breaking technology that can be used for improving our understanding of the impact of particulate pollution on societal issues such as human health and ecology. CAPABLE’s results provide the next stage toward using lidar technology in highly important research areas such as food security and monitoring of ecosystems.
We developed a worldwide unique lidar system which can carry out all major experiments that can commonly only be covered by using a multitude of individual lidar systems. The system is part of the newly established LITES (Lidar Innovations for Technologies and Environmental Sciences) facility, inaugurated in November 2018 in the context of the final WP2 workshop meeting of the EC-project ACTRIS-2. LITES will play a fundamental part of future work in ACTRIS becoming a permanent European Research Infrastructure in 2025. CAPABLE’s achievements go far beyond its initial goals. In addition to a ground-breaking prototype lidar that exceeds currently existing lidar systems’ capabilities, we also developed a new Lidar Spectroscopy Instrument (LiSsI), now operational and forming the core of LITES. The other part of LITES, providing significant added value, consists of in-situ instruments such as a Raman and fluorescence microscope, and gas and aerosol particle chambers.
LiSsI allows for the profiling of trace gases, chemical components in particles, and bio-aerosols in atmospheric aerosol pollution in the troposphere through combining different non-linear spectroscopy techniques on a single measurement platform. It allows for the first time range-resolved observations of the entire pure rotational Raman spectrum with high spectral resolution up to several kilometers height above ground level. Compared to other systems and to the best of our knowledge LITES is a world-wide unique lidar system as it combines the most powerful Nd:YAG laser ever used in a lidar with an opto-parametric oscillator (OPO). LiSsI offers the best spectral resolution over a significant range of wavelengths (from deep UV to near IR) ever achieved by lidar. LiSsI as part of LITES provides for a unique design that allow easy sharing of the spectrometer by lidar, microscope and gas chambers through a unique modular design. LiSsI has been implemented in LITES such that we can profile simultaneously more than one species of atmospherically reactive trace gases. CAPABLE has made it possible to observe atmospheric composition in a significantly more comprehensive manner than ever before, as the system allows for simultaneous observations of the optical, chemical, and microphysical properties of atmospheric particulate pollution.