Environmental trace gas monitoring instrument (EMI) onboard GaoFen-5 was launched in May 2018 and has successfully operated on-orbit for more than a year. EMI contains four grating spectrometers, covering wavelengths in the range 240-710 nm with a spectral resolution of 0.3-0.5 nm, and enables one-day global coverage. For EMI on-orbit calibration, two onboard solar diffusers (SD), one surface reflectance aluminum diffuser, and one quartz volume diffuser (QVD) are used to measure solar spectra. The solar spectra are used to perform accurate spectral and radiometric calibrations. EMI on-orbit spectral calibration contains wavelength calibration and instrument spectral response function (ISRF), both of which are the key quantities in trace gas retrievals based on differential optical absorption spectroscopy (DOAS) analysis. The wavelength calibration is performed using the Fraunhofer lines in the solar spectrum, and the ISRF parameters are obtained by fitting high-resolution and EMI-measured solar spectra. Based on the known solar irradiation and characteristic of SD, SD radiance can be calculated and is used for EMI on-orbit radiometric calibration. The radiometric calibration also determines the absolute Earth reflectance spectra that are used as inputs for atmospheric retrieval algorithms. For EMI on-orbit radiometric monitoring, aluminum diffuser is used as reference SD to monitor QVD degradation. An internal white light source is used to detect pixel performance and monitor radiometric throughput.

A homemade portable no-blind zone laser detection and ranging (lidar) system was designed to map the three-dimensional (3D) distribution of aerosols based on a dual-field-of-view (FOV) receiver system. This innovative lidar prototype has a space resolution of 7.5 m and a time resolution of 30 s. A blind zone of zero meters, and a transition zone of approximately 60 m were realized with careful optical alignments, and were rather meaningful to the lower atmosphere observation. With a scanning platform, the lidar system was used to locate the industrial pollution sources at ground level. The primary parameters of the transmitter, receivers, and detectors are described in this paper. Acquiring a whole return signal of this lidar system represents the key step to the retrieval of aerosol distribution with applying a linear joining method to the two FOV signals. The vertical profiles of aerosols were retrieved by the traditional Fernald method and verified by real-time observations. To effectively and reliably retrieve the horizontal distributions of aerosols, a composition of the Fernald method and the slope method were applied. In this way, a priori assumptions of even atmospheric conditions and the already-known reference point in the lidar equation were avoided. No-blind-zone vertical in-situ observation of aerosol illustrated a detailed evolution from almost 0 m to higher altitudes. No-blind-zone detection provided tiny structures of pollution distribution in lower atmosphere, which is closely related to human health. Horizontal field scanning experiments were also conducted in the Shandong Province. The results showed a high accuracy of aerosol mass movement by this lidar system. An effective quantitative way to locate pollution sources distribution was paved with the portable lidar system after validation by the mass concentration of suspended particulate matter from a ground air quality station.

The achievement of the targets of coordinated control of PM_2.5 and O₃ and the carbon peaking and carbon neutrality depend on the development of pollution and greenhouse gas monitoring technologies. Optical monitoring technology, based on its technical characteristics of high scalability, high sensitivity and wide-targets detection, has obvious advantages in pollution/greenhouse gases monitoring and has become an important direction in the development of environmental monitoring technology. At present, a system of environmental optical monitoring technology with differential optical absorption spectroscopy (DOAS), cavity ring-down spectroscopy (CRDS), light detection and ranging (LIDAR), laser heterodyne spectroscopy (LHS), tunable diode laser absorption spectroscopy (TDLAS), fourier transform infrared spectroscopy (FTIR) and fluorescence assay by gas expansion (FAGE) as the main body has been established. However, with the promotion of “reduction of pollution and carbon emissions” strategy, there have been significant changes in the sources of pollution/greenhouse gases, emission components and emission concentrations, which have put forward new and higher requirements for the development of monitoring technologies. In the future, we should pay more attention to the development of new optical monitoring techniques and the construction of stereoscopic monitoring system, the interdisciplinarity (among mathematics, physics, chemistry and biology, etc.), and the monitoring of greenhouse gases and research on atmospheric chemistry.