Concentrations, optical properties and sources of humic-like substances (HULIS) in fine particulate matter in Xi'an, Northwest China

Humic-like substances ( HULLS) are ubiquitous in the atmospheric environment, which affects both human health and climate. We present here the mass concentration and optical characteristics of HULIS isolated from aerosol samples collected in Xi'an, China. Both mass concentration and absorption coefficient (Abs (385)) of HULIS show clear seasonal differences, with the highest average in winter (3.91 mu gC m(-3) and 4.78 M m(-1), respectively) and the lowest in summer (0.65 mu gC m(-3) and 0.55 M m(-1), respectively). The sources of HULIS _C and light absorption of HUUS were analyzed by positive matrix factorization (PMF) and four major sources were resolved, including secondary formation, biomass burning, coal burning, and vehicle emission. Our results show that secondary formation (i.e., gas-to-particle conversion from e.g., photochemical oxidation) was the major contributor to both HULIS _C (50%) and light absorption (55%) of HULIS in summer, biomass burning and coal burning were major sources of HULIS_C (similar to 70%) and light absorption (similar to 80%) of HULIS in winter. It is worth noting that biomass burning and coal burning had higher contribution to HUUS light absorption (47% in spring, 37% in summer, 73% in fall, and 77% in winter) than their corresponding contribution to HUUS_C concentration (41% in spring, 37% in summer, 54% in fall, and 69% in winter). However, vehicle emission had lower contribution to HUUS light absorption (26% in spring, 8% in summer, 18% in fall, and 11% in winter) than to HUUS_C concentration (24% in spring, 13% in summer, 28% in fall, and 18% in winter). These results suggest that HULIS from biomass burning and coal burning have higher light absorption ability than from vehide emission. (C) 2021 Elsevier B.V. All rights reserved