First Chinese ultraviolet–visible hyperspectral satellite instrument implicating global air quality during the COVID-19 pandemic in early 2020

Abstract

In response to the COVID-19 pandemic, governments worldwide imposed lockdown measures in early 2020, resulting in notable reductions in air pollutant emissions. The changes in air quality during the pandemic have been investigated in numerous studies via satellite observations. Nevertheless, no relevant research has been gathered using Chinese satellite instruments, because the poor spectral quality makes it extremely difficult to retrieve data from the spectra of the Environmental Trace Gases Monitoring Instrument (EMI), the first Chinese satellite-based ultraviolet–visible spectrometer monitoring air pollutants. However, through a series of remote sensing algorithm optimizations from spectral calibration to retrieval, we successfully retrieved global gaseous pollutants, such as nitrogen dioxide (NO2), sulfur dioxide (SO2), and formaldehyde (HCHO), from EMI during the pandemic. The abrupt drop in NO2 successfully captured the time for each city when effective measures were implemented to prevent the spread of the pandemic, for example, in January 2020 in Chinese cities, February in Seoul, and March in Tokyo and various cities across Europe and America. Furthermore, significant decreases in HCHO in Wuhan, Shanghai, Guangzhou, and Seoul indicated that the majority of volatile organic compounds (VOCs) emissions were anthropogenic. Contrastingly, the lack of evident reduction in Beijing and New Delhi suggested dominant natural sources of VOCs. By comparing the relative variation of NO2 to gross domestic product (GDP), we found that the COVID-19 pandemic had more influence on the secondary industry in China, while on the primary and tertiary industries in Korea and the countries across Europe and America.

Ultraviolet Exciton-Polariton Light-Emitting Diode in a ZnO Microwire Homojunction

“…Ultraviolet (UV) light sources, including light-emitting diodes (LEDs) and laser diodes (LDs), are of fundamental interest in a wide range of applications, e.g., bioanalytical, material processing, water purification, plant lighting, free-space optical communication, disinfection, and medical diagnostics. − Traditionally, UV light sources are mainly based on semiconductors with bandgap energies larger than 3.0 eV, such as SnO 2 , ZnO, GaN, etc. − Among these, GaN-based materials are the most commercially used in the design and fabrication of UV LEDs and LDs due to the successful manufacture of light emitters with reasonable p-type conductive characteristics. ,,− However, when working at high current injection levels, these optoelectronic devices would suffer a severe reduction of the internal quantum efficiency (IQE), the so-called efficiency droop. , That is caused by high in-plane strain, strong piezoelectric polarization fields, inevitable carrier leakage, and so forth. ,, Moreover, the realistic applications of GaN-based micro/nanoscale LEDs and LDs are hindered by the synthesis of high-quality nano/micromaterials, which are commonly based on time-consuming and expensive single-crystal synthesis techniques; high vacuum and high temperature are necessary for these synthesis techniques. − Briefly speaking, the achievement of low-cost and high-quality single-crystalline nano/micromaterials, especially for commercial manufacture of low-dimensional UV LEDs and LDs, still remains a long-term and arduous task.…”

Exciton–polariton light-emitting diode based on a single ZnO superlattice microwire heterojunction with performance enhanced by Rh nanostructures

“…Low-dimensional semiconductor micro/nanostructures, which simultaneously possess self-constructed cavities, superior gain characteristics, and unique optical and electrical properties, have been expected to feature as prospective building blocks for optoelectronic devices in the future. 1–8 Among these fascinating micro/nanostructures, one-dimensional (1D) superlattice semiconductor micro/nanostructures can provide a platform to modulate photon transport coherently with a defined direction in the shape of an optical waveguide, and they have been widely studied due to their captivating optoelectronic properties and electronic confinement properties. 9–13 In particular, the optical cavities formed along the axial direction of the wire-like structures, which exhibit well-defined confinement of photons and controlled modulation of electronic transport characteristics, have been employed to construct coherent light sources.…”

Problems with and Improvement of HCHO/NO2 for Diagnosing Ozone Sensitivity—A Case in Beijing

“…According to Rfn determined on the basis of satellite data, China is overall VOC-limited; more specifically, urban cities are mostly VOC-limited, while rural and remote areas are NOx-limited [9]. However, when considering of the vigorous NOx emission reductions, megacities, such as Beijing, Shanghai and Guangzhou, have shown an increasing NOx sensitivity in recent years [10][11][12][13][14].…”

“…Nevertheless, VOCs have different sources in different areas [13]. Studies have found that HCHO mainly comes from natural sources, among which isoprene oxidation accounts for the largest contribution, reaching 50% in strong source areas [15,16].…”