Remote sensing of air pollutants in China to study the effects of emission reduction policies on air quality

Air Quality (AQ) is determined by the concentrations of aerosols and trace gases. Aerosol concentration is measured by the mass concentration of particles smaller than 2.5 μm (PM2.5) or 10 μm (PM10), while trace gases include ozone (O₃), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), and carbon monoxide (CO). Ammonia (NH₃) and (biogenic) volatile organic compounds ((B)VOCs) also play an important role in atmospheric chemistry affecting the concentrations of trace gases and ultimately AQ. This study focuses on various aspects of AQ in China, utilizing remote sensing data from satellite and ground-based sensors to obtain information on PM emissions and concentrations and AQ-relevant trace gases. This research was conducted within the framework of the ESA/NRSCC MOST collaboration project Dragon 5, as part of the EMPAC (Exploitation of satellite remote sensing to enhance our comprehension of the Mechanisms and Processes influencing Air quality in China) project. It summarizes findings on four main topics: (1) Retrieval of trace gas concentrations and aerosol products from satellite data, validation using ground-based reference data, and interpretation of results in terms of AQ effects, such as the conversion of column-integrated properties to near-surface concentrations; (2) Determination of trace gases emissions relevant to AQ, using satellite data and models; (3) Analysis of time series data on trace gases and aerosols to assess the impact of emission reduction policies on AQ improvement; (4) Research contributing to a deeper understanding of mechanisms and processes affecting atmospheric composition about AQ.