Factors influencing the relationships between hourly visibility and aerosol optical depth in China—implications for hourly aerosol optical depth retrievals using automatic visibility observations

Abstract

Aerosol optical depth (AOD) is a key parameter for evaluating climate change and air quality, yet ground-based AOD observations in China remain limited, and satellite data often suffer from acquisition gaps due to cloud cover. Surface visibility (VIS) offers a promising alternative for AOD retrieval, but the relationship between VIS and AOD is complex and shaped by multiple factors such as meteorological conditions, the vertical distribution of aerosols, topography, and population density. This study systematically explored the influence of these factors on the hourly VIS–AOD relationship, using over ∼2300 automatic VIS measurements and Himawari-8 satellite-retrieved AOD data collected across China from 2016 to 2021. The results reveal significant spatiotemporal variations in the VIS–AOD relationship, with stronger diurnal aerosol fluctuations in eastern China compared to the west, and a consistent inverse correlation between VIS and AOD. The correlation peaks in the late afternoon and reaches a seasonal maximum during winter. These relationships are influenced not only by regional meteorological thresholds but also by constraints from aerosol vertical distribution patterns and geographical conditions. Crucially, adjusting the AOD by incorporating the planetary boundary layer height markedly improves its correlation with VIS, underscoring the importance of daily planetary boundary layer dynamics. These findings offer valuable insights for refining hourly AOD retrieval methods from VIS, thereby enhancing the understanding of aerosol behavior across China.