Chemical composition, structural properties, and source apportionment of organic macromolecules in atmospheric PM in a coastal city of Southeast China.

Particulate matter (PM) associated with the fractions of organic macromolecules, including humic acid (HA), kerogen + black carbon (KB), and black carbon (BC), was determined during summer and winter at urban and suburban sites in a coastal city of southeast China. The organic macromolecules were characterized by elemental analysis (EA), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR), and their sources were identified by using stable carbon/nitrogen isotope (δC/δN) and the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) Model. The results showed that HA, kerogen (K), and BC accounted for the range of 3.89 to 4.55 % in PM, while they were the dominant fractions of total organic carbon (TOC), ranging from 64.70 to 84.99 %. SEM analysis indicated that BC particles were porous/nonporous and consisted of spherical and non-spherical (i.e., cylindrical and elongate) structures. The FTIR spectra of HA, KB, and BC exhibited similar functional groups, but the difference of various sites and seasons was observed. HA in PM contained a higher fraction of aliphatic structures, such as long-chain fatty and carbohydrates with a carboxylic extremity. The C/N ratio, SEM, and δC/δN values provided reliable indicators of the sources of HA, K, and BC in PM. The results suggested that HA and K majorly originated from terrestrial plants, and BC came from the mixture of combustion of terrestrial plants, fossil fuel, and charcoal. The air masses in winter originated from Mongolia (4 %), the northern area of China (48 %), and northern adjacent cities (48 %), suggesting the influence of anthropogenic sources through long-range transport, while the air masses for the summer period came from South China Sea (34 %) and Western Pacific Sea (66 %), representing clean marine air masses with low concentrations of organic macromolecules.