Humic Acid, Kerogen, and Black Carbon Isolated from Atmospheric Total Suspended Particulate from Guangzhou, China

The organic macromolecules in total suspended particulate (TSP) are complex and have not been thoroughly investigated. In this article, six composite TSP samples were collected from urban, suburban, and forest sites of Guangzhou. Organic macromolecules in the TSP were separated into humic acids (HA), kerogen and black carbon (KB), and black carbon (BC) by chemical treatment with sodium hydroxide, hydrochloric acid/hydrofluoric acid, and potassium dichromate/sulfuric acid. Note that the BC isolated is part of KB. To obtain sufficient amounts of HA, KB, and BC for subsequent analyses, 1.5 g TSP were used for each sample. The isolated fractions were characterized by elemental analysis, solid-state 13C crosspolarization and magic angle spinning nuclear magnetic resonance spectroscopy, Fourier transformed infrared spectroscopy, stable carbon isotopic ratio, and radiocarbon ratio mass spectrometry. Total carbon content in TSP ranged from 12.8 to 19.0%, and HA, KB, and BC were accounted for 2.39-14.8, 37.4-53.5, and 16.0-32.1% of total carbon, respectively. Isolated HAs were characterized by high H/C and N/C atomic ratios; KB showed high H/C but low N/C atomic ratios; BC was low in H/C, indicating a predominance of aromatic units in its carbon skeleton. The δ13C and radiocarbon data showed that all macromolecular fractions were mixtures of components having biogenic and fossil-fuel origins. The contribution of biogenic material to HA, KB, and BC, estimated by radiocarbon ratios, are 44.2-61.5%, 17.5-24.8%, and 3.3-17.2%, respectively. The atmospheric optical properties and hygroscopicity of kerogen are not known at present and warrant investigation because of the high content of kerogen in TSP. Copyright © American Association for Aerosol Research.