Hefei Research Institute comprehensively analyzes the technical progress of spectroscopy in the field of environmental monitoring

[ Instrument R & D of Instrumentation Network] Recently, the Liu Wenqing team of Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences Hefei Institute of Material Science published an invited review of the 40th anniversary of the inauguration of the Journal of Optics to comprehensively analyze the technical progress of spectroscopy in the field of environmental monitoring.

For more than half a century, with the advancement and deepening of human understanding of the nature of light, great advances in optical technology, especially the invention of lasers and the application of laser technology, the understanding of the interaction between light and matter has fundamentally improved And development. At the same time, people's awareness of environmental pollution issues has also continued to improve, began to use modern technical means, especially optical technology to study some environmental physical and chemical phenomena and processes, and gradually developed modern environmental spectroscopy.

Environmental spectroscopy is not only an innovative development of classic optics, but also a new development of environmental science. Environmental spectroscopy monitoring is an important part of environmental optics. It uses the methods of absorption, emission, scattering and atmospheric radiation transmission in optics to obtain the characteristics of trace gases by establishing a characteristic factor fingerprint spectrum database and quantitative analysis algorithm, which can be used for Automatic monitoring of air quality, fixed and mobile pollution sources has the advantages of real-time, dynamic, fast, non-contact telemetry, telemetry, wide monitoring range, low cost, etc. It is the development direction and leading technology of today's international environmental monitoring.

Using methods such as absorption spectrum, emission spectrum, light scattering, and atmospheric radiation transmission in optics, the Liu Wenqing team proposed to carry out innovative research on the cross science of optics and the environment. At present, differential optical absorption spectroscopy (DOAS) technology, Fourier Transformed infrared spectroscopy (FTIR) technology, non-dispersive infrared (NDIR) technology, tunable semiconductor laser absorption spectroscopy (TDLAS) technology, laser radar (LIDAR) technology, fluorescence spectroscopy technology, laser induced breakdown spectroscopy (LIBS) technology, optical cavity Environmental optical monitoring technology system with Cavity Ring-Down Spectroscopy (CRDS), light scattering measurement technology, photoacoustic spectroscopy technology, etc. as the main body, realizes on-site rapid detection and multi-dimensional detection of environmental trace components / multi-elements Multi-platform monitoring has been successfully applied to the monitoring of atmosphere, water and soil.

In conventional gas monitoring, various optical technology routes are mainly used: for SO2, NO2, O3 and THC, CH4, NMHC, BTX and other pollutants, the DOAS technology uses the absorption characteristics of gas molecules to identify the components, and according to the narrow-band absorption intensity Reverse the concentration of trace gases; for the greenhouse gas CO2, CRDS uses a relatively narrow absorption window to avoid interference with other components and achieve higher accuracy detection; for CO, uses the wavelength tuning characteristics of TDLAS and scans with a single narrow-band laser frequency One or several gas characteristic absorption lines of gas molecules to achieve qualitative or quantitative analysis of CO;

In the monitoring of atmospheric oxidizability, the gas expansion laser-induced fluorescence technology can be used to obtain the most important oxidant in the atmosphere-HOx (OH, HO2) radicals. The 308-nanometer laser excites OH radicals to an electronically excited state and detects the excited state OH The fluorescence emitted by free radicals determines the concentration of OH radicals in the atmosphere; if you want to measure HO2 radicals, you need to pass a certain concentration of NO into the conversion device to convert HO2 radicals into OH radicals, and then measure OH radicals; In the monitoring of particulate matter, the vertical distribution of particulate matter in the atmosphere is uneven, and the vertical migration of high altitude will affect the pollution concentration near the ground.

The lidar system uses aerosol back-meter scattering echo signals to detect the aerosol optical characteristics such as the spatial and temporal distribution of the backscattering coefficient / extinction coefficient, which can realize the vertical distribution of particulate matter detection; in the monitoring of surface water quality, the use of water Most organic pollutants belong to macromolecular organic compounds containing fluorophores. Under the action of excitation light of the appropriate wavelength, the principle of characteristic fluorescence spectrum is emitted. Laser-induced fluorescence technology is used to achieve remote measurement of the pollution of organic substances in large areas of water. In terms of soil heavy metal monitoring , LIBS technology can be used to analyze the surface plasma radiation spectrum of soil samples to achieve rapid on-site monitoring of soil organic pollutants.

In practical application, the combination of environmental spectroscopy and remote sensing technology is usually applied. Through the study of systemic, regional and composite pollution and the fusion of multiple information, online monitoring of environmental composite pollutants, three-dimensional and mobile online monitoring can be achieved. The sky-ground integrated environmental composite pollutant observation, research and demonstration platform laid the technical foundation.

With the advancement of technology in the related fields of optics, electronics, information, biology, etc., environmental spectroscopy technology is developing towards the trend of high precision, high sensitivity, multi-component, multi-platform, and intelligent networking.

Problems such as low detection limits and low time resolution in the field monitoring of atmospheric oxidization, on-line measurement of nano-scale particulate matter, monitoring of ultra-low emission pollution sources, and online detection of heavy metals in water, soil, and soil also need to be further investigated. Improve detection accuracy and sensitivity, and apply optical monitoring technology to photochemical reaction mechanism research, industrial process control, and production safety monitoring; the rapid development of industry has led to a rapid increase in the types of pollutants monitored and more complex components. Detection of component organics, heavy metals, bioaerosols, secondary organic aerosol tracers, water bacteria, phytoplankton, and residual pesticides and other organic pollutants in the soil; development of multi-platform, intelligent, networked, and Special and selective environmental monitoring instruments, real-time acquisition of environmental multi-element monitoring data, through in-depth mining and model analysis of massive data, using big data to analyze the corresponding relationship between regional and watershed pollution sources and environmental quality, building an intelligent management decision-making platform to enable the environment Management Excellence Technology, precision transition for proactive foresee, large data scientific decision-making has become a new trend.