| 05 Mar 2026
Vertical Structure and Driving Mechanism of PM2.5 and PM10 Aerosols in Hefei Based on LiDAR Observations (2021–2023)
Abstract. Aerosol pollution remains a significant environmental concern in China. However, the vertical structure and evolution of particulate matter are poorly understood due to the lack of long-term, high-resolution observations. In Hefei, the aerosols during the study period were dominated by a mixture of fine particulate matter (PM2.5) and coarse particulate matter (PM10), mainly originating from urban traffic emissions, industrial activities, and regional transport, with significant contributions from secondary inorganic aerosols and occasional dust events. To address the knowledge gap in aerosol vertical distribution during different pollution episodes, this study employed an aerosol LiDAR system with 532 nm band to investigate the vertical profile characteristics of aerosols, with a focus on comparing the stratification differences of optical properties between PM2.5 and PM10 pollution events over Hefei across different periods and altitudes. The seasonal and diurnal variations of aerosol profiles were investigated, and vertical structures were compared on polluted and clean days. The relationship between near-surface particulate matter concentrations and aerosol stratification was analyzed, alongside the dynamic evolution of aerosol layers during typical pollution events. Our results demonstrated that the extinction coefficient (532 nm) of PM2.5-polluted days below 0.6 km was approximately three times that of PM10-polluted days. In contrast, the depolarization ratio of PM10-polluted episodes remains consistently higher than that of PM2.5-polluted cases throughout the entire observed altitude range. The differences in extinction between polluted and clean days for PM2.5 were most pronounced below 0.9 km and subsequently decreased as altitude increased, whereas the differences in PM10 remained significant below 1.2 km. For PM2.5, the strongest enhancement appeared between 7:00 and 14:00 (Beijing time, BJT). A subtle lifting with height was observed around midday. PM10-polluted days were characterized by a greater vertical extension of high aerosol extinction (reaching up to ~1.2–1.4 km) but a shorter duration of strong extinction, in contrast to PM2.5-polluted days, which exhibited a more persistent but vertically confined aerosol layer. PM10 pollutant tended to accumulate within the altitude range of 0.4–1.2 km on polluted days. The vertical wind shear (VWS) was weaker on PM2.5-polluted days compared to clean days. On PM10-polluted days, the VWS in the near-surface layer (1000–900 hPa) was significantly stronger than that on clean days, especially during the early morning and evening periods. The PM2.5 pollution in Hefei was mostly contributed by temperature inversion and high relative humidity, while PM10 pollution was driven by long-range transport of aerosol particles under the cold front system and dry conditions. These findings highlight the complex interactions between aerosol optical properties, boundary-layer dynamics, and synoptic-scale meteorology, providing new insights into the vertical processes governing air quality in eastern China.
General comments
This study investigates the vertical distribution characteristics of atmospheric aerosols in Hefei using a ground-based aerosol lidar system. It effectively compares optical properties between PM2.5 and PM10 pollution events with sufficient data support. The authors systematically present on the advantages and limitations of the aerosol LiDAR. The integration of LiDAR observations with surface particulate matter monitoring and meteorological data (e.g., vertical wind shear, temperature inversion, relative humidity) strengthens the rigor of the analysis, allowing for a comprehensive exploration of the links between aerosol vertical properties and pollution formation mechanisms.
The research design is reasonable, and the conclusions are scientific and reliable. The results reveal the formation mechanisms of the two types of pollution and fill the research gap in aerosol vertical distribution, providing valuable insights for air quality research in eastern China. This studycould enhance our understanding of how vertical aerosol dynamics regulate surface air quality, which is critical for improving air quality forecasting and formulating targeted pollution control strategies. In the context of increasingly frequent regional air pollution events in eastern China, the detailed vertical profile data and comparative analysis of PM2.5 and PM10 presented here provide a new perspective for distinguishing the distinct drivers of fine and coarse particulate pollution.
The supplementary materials are highly valuable for readers to further understand the observational data and analytical results. Nevertheless, several minor issues still need to be addressed to improve readability. The font size in some figures is too small to distinguish clearly, which affects reading efficiency. In addition, a few technical terms are used inappropriately in certain contexts, and some descriptions are unnecessarily repetitive across different sections. These redundant expressions can be further condensed and polished to enhance the conciseness and fluency of the manuscript. I favor publishing this manuscript in Atmospheric Measurement Techniques after minor revisions.
Specific comments