Vertical distribution and seasonal variations of dicarboxylic acids in urban PM2.5: Insights from multi-level observations on 600 m Canton tower in Guangzhou

Abstract

Dicarboxylic acids are important constituents of organic aerosols, but the lack of their seasonal and vertical distribution hinders thorough knowledge of atmospheric physicochemical behavior. This study examines dicarboxylic acids at three heights (∼3, 118, and 488 m) on the 600 m high Canton Tower in urban Guangzhou, aiming to illustrate their primary sources and formation pathways across different seasons and heights. The concentration of dicarboxylic acids (678.7 ± 351.9 ng m⁻³) was lower or comparable to those in domestic cities but higher than in remote aeras. Oxalic acid had the highest concentration, with malonic, succinic, glyoxylic, and azelaic acids following. Most dicarboxylic acids peaked in autumn, following by winter, spring and summer. Higher dicarboxylic acids were observed at upper layers. The C₃/C₄ (1.5 ± 0.5) was relatively higher, and the proportion of C₂ in dicarboxylic acids increased with height. Our results showed that combustion and secondary conversion were primary sources of dicarboxylic acids in dry season, while biomass combustion and secondary formation processes dominated during wet season. Significant gas-phase oxidations were prevalent during summer, while aqueous-phase formations were prominent in spring. Aerosol aging process played an important role at higher atmospheric levels throughout the year, suggesting an enhanced atmospheric oxidation capacity in upper boundary layers. These vertical profiling measurements enable the identification of predominant origins and formation pathways of dicarboxylic acids across different seasons and boundary layer dynamics. The findings provide critical insights for understanding atmospheric chemical evolution processes, validating atmospheric models, and developing effective air pollution mitigation strategies.