Aerosol-PBL relationship under diverse meteorological conditions: Insights from satellite/radiosonde measurements in North China

The planetary boundary layer height (PBLH) plays crucial roles in regulating air pollution levels; however, its relationships with PM 2.5 (fine particulate matter with diameter ≤ 2.5 μm) under diverse meteorological conditions, as well as potential causes, are not yet well understood. This study leverages approximately three years of satellite/radiosonde derived PBLH to investigate PBLH-PM 2.5 relationships under six typical circulation patterns in North China, and some novel physical explanations for the varying PBLH-PM 2.5 relationship are proposed. The six circulation patterns are dominated by three high- and three low-pressure systems, with significantly negative PBLH-PM 2.5 correlations exhibited in high-pressure patterns, while weak or even insignificant relationships in low-pressure patterns. Meteorological factors , particularly humidity and vertical winds, can largely explain the varying PBLH-PM 2.5 relationships across different synoptic patterns. Under high-pressure patterns, elevated PM 2.5 aligns well with high humidity within boundary layer, which restricts the magnitude of the PBLH and thus the negative PBLH-PM 2.5 correlation. However, under low-pressure patterns, humidity in boundary layer and in free atmosphere exert conflicting effects on PBLH-PM 2.5 relationship. Higher PM 2.5 is observed when only the boundary layer is moist, whereas when thewhole column is moist or supersaturated, nucleation, transitions, and wet scavenging lead to reduced PM 2.5 and lower PBLH, thereby the positive PBLH-PM 2.5 correlation. Additionally, the column feature of vertical wind within boundary layer can also help explain the positive PBLH-PM 2.5 relationship. These findings provide deeper insights into understanding boundary layer processes and pollution dynamics. • The PBLH-PM 2.5 relationships vary with diverse circulation patterns. • Low-pressure patterns show weak or insignificant PBLH-PM 2.5 relationship. • Column features of humidity and vertical wind can explain the weak relationship.