Volatile organic compounds (VOCs) affect ozone formation and air quality. However, our understanding is limited due to insufficient measurements, especially for oxygenated VOCs. This study combines land, ship, and satellite data in Hong Kong, showing that oxygenated VOCs make up a significant portion of total VOCs. Despite their importance, many are underestimated in current models. These findings highlight the need to improve VOC representation in models to enhance air quality management.

This study presents the humidity measurements with a synergistic algorithm combining Raman lidar,  microwave radiometer, and satellite. The results from 47 sites in China show the best correlation over 0.9 concerning the radiosonde measurements. This validates the relative humidity (RH) accuracy with various data integrations. Three representative sites present the different seasonal characteristics, indicating the geographic and height influences on the RH vertical distribution.

Long-term field testing across diverse climatic environments is conducted to identify the optimized calibration conditions for NO₂, NO, CO and O₃ electrochemical sensors. The results uncovered three factors that influence calibration performance: calibration period, concentration range and time averaging. We developed a comprehensive framework for the best sensor calibration practices, which serves as a valuable reference for calibrating various sensor types used in air quality monitoring.

A full suite of radical measurements (OH, HO₂, RO₂, and k_OH) was established to accurately elucidate the limitations of oxidation in a chemically complex atmosphere. Sensitivity tests revealed that the incorporation of complex processes enabled a balance in both radical concentrations and coordinate ratios, effectively addressing the deficiency in the ozone generation mechanism. The full-chain radical detection bridged the gap between the photochemistry and the intensive oxidation level.

This study developed a nested machine learning model to convert the GEMS NO₂ column measurements into ground-level concentrations across China. The model directly incorporates the NO₂ mixing height (NMH) into the methodological framework. The study underscores the importance of considering NMH when estimating ground-level NO₂ from satellite column measurements and highlights the significant advantages of new-generation geostationary satellites in air quality monitoring.