第七届青年地学论坛

Gaseous dicarboxylic acids (di-acids) are suggested to participate in atmospheric new particle formation via bonding with sulfuric acid (SA), ammonia (NH₃), amines, and other molecules. However, there is a lack of observational evidence for the involvement of di-acids in particle nucleation. Comprehensive measurements were conducted at a rural site of the North China Plain in winter, and unexpectedly high nucleation rates (J_OBS, 30.5−839.7 cm⁻³ s⁻¹) were observed under low SA levels (0.7 × 106 to 4.4 × 106 cm⁻³). Neither SANH3 nor SA-dimethylamine (DMA) mechanisms could fully explain the JOBS. Gaseous di-acid monomers and dimers and di-acid-SA-DMA clusters were identified in this study. The J_OBS values were enhanced by a factor of 5 to 10 as the signal intensities of di-acids increased 4-fold. Products of di-acid signals and SA concentrations showed a positive correlation with the J_OBS (Pearson’s correlation coefficient = 0.72). Experimental evidence was found that succinic acid competes with the second SA molecule for addition to the SA·DMA cluster. The concentrations of di-acids were estimated to be 1−3 orders of magnitude higher than those of SA. We propose that di-acids could actively participate in particle nucleation and may dominate the initial steps under high [di-acids]/[SA] ratios.