A preliminary study on humic-like substances in particulate matter in Malaysia influenced by Indonesian peatland fires

• Published in: The Science of the total environment Vol. 753; p. 142009
• Main Authors: Fujii, Yusuke, Tohno, Susumu, Ikeda, Kazuhiro, Mahmud, Mastura, Takenaka, Norimichi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20-01-2021
• Subjects: Biomass burning; EEM; HULIS; Peatland fire; WSOC; WSOC; EEM; Biomass burning; Peatland fire; HULIS
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.142009

In this paper, ambient total suspended particulates (TSP) with a focus on humic-like substances (HULIS) are characterized based on intensive ground-based field samplings collected in Malaysia during non-haze and haze periods caused by peatland fires on the Indonesian island of Sumatra. Furthermore, concentrations of water-soluble organic carbon (WSOC) and carbon content of HULIS (HULIS-C) were determined, and fluorescence spectra of the HULIS samples were recorded by excitation emission matrix (EEM) fluorescence spectroscopy. The concentrations of WSOC and HULIS-C over the entire period ranged from 4.1 to 24 and 1.3 to 18 μgC m−3, respectively. The concentrations of WSOC and HULIS-C during the peatland fire-induced strong haze periods were over 4.3 and 6.1 times higher, respectively, than the average values recorded during the non-haze periods. Even during the light haze periods, the concentrations of WSOC and HULIS-C were significantly higher than their averages during the non-haze periods. These results indicate that peatland fires induce high concentrations of WSOC, particularly HULIS-C, in ambient TSP at receptor sites. EEM fluorescence spectra identified fulvic-like fluorophores at the highest intensity level in the EEM fluorescence spectra of the haze samples. A peak at excitation/emission (Ex/Em) ≈ (290–330)/(375–425) nm is also observed at high intensity, though this peak is normally associated with marine humic-like fluorophores. It is shown that a peak at Ex/Em ≈ (290–330)/(375–425) nm is not derived from marine sources only; furthermore, peatland fires are shown to be important contributors to HULIS around this peak.
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•Humic-like substances in ambient TSP affected by peatland fires are characterized.•Peatland fires induce high concentrations of WSOC and HULIS-C at receptor sites.•Fulvic-like fluorophores at the highest intensity are identified in the haze days.