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. The frequent occurrence of severe air pollution episodesin China has been a great concern and thus the focus of intensive studies.Planetary boundary layer height (PBLH) is a key factor in the verticalmixing and dilution of near-surface pollutants. However, the relationshipbetween PBLH and surface pollutants, especially particulate matter (PM)concentration across China, is not yet well understood. We investigate thisissue at ∼1600 surface stations using PBLH derived fromspace-borne and ground-based lidar, and discuss the influence of topographyand meteorological variables on the PBLH–PM relationship. Albeit the PBLH–PMcorrelations are roughly negative for most cases, their magnitude,significance, and even sign vary considerably with location, season, andmeteorological conditions. Weak or even uncorrelated PBLH–PM relationshipsare found over clean regions (e.g., Pearl River Delta), whereas nonlinearlynegative responses of PM to PBLH evolution are found over polluted regions(e.g., North China Plain). Relatively strong PBLH–PM interactions are foundwhen the PBLH is shallow and PM concentration is high, which typicallycorresponds to wintertime cases. Correlations are much weaker over thehighlands than the plains regions, which may be associated with lighterpollution loading at higher elevations and contributions from mountainbreezes. The influence of horizontal transport on surface PM is consideredas well, manifested as a negative correlation between surface PM and windspeed over the whole nation. Strong wind with clean upwind air plays adominant role in removing pollutants, and leads to obscure PBLH–PMrelationships. A ventilation rate is used to jointly consider horizontal andvertical dispersion, which has the largest impact on surface pollutantaccumulation over the North China Plain. As such, this study contributes toimproved understanding of aerosol–planetary boundary layer (PBL) interactions and thus our abilityto forecast surface air pollution.

atmospheric chemistry and physics

Relationships between the planetary boundary layer height and surface pollutants derived from lidar observations over China: regional pattern and influencing factors