Subscriber access provided by University of Sydney Library
Article
Structural and light-absorption characteristics of complex water-insoluble organic mixtures in urban submicron aerosols Qingcai Chen, Fumikazu Ikemori, Yuua Nakamura, Petr Vodicka, Kimitaka Kawamura, and Michihiro Mochida Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 22 Jun 2017 Downloaded from http://pubs.acs.org on June 22, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 37
Environmental Science & Technology
1
Structural and light-absorption characteristics of
2
complex water-insoluble organic mixtures in urban
3
submicron aerosols
4
Qingcai Chen1,2, Fumikazu Ikemori1,3, Yuua Nakamura1, Petr Vodicka4, Kimitaka Kawamura4,
5
Michihiro Mochida*1
6
1 Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan
7
2 School of Environmental Science and Engineering, Shaanxi University of Science and
8
Technology, Xi’an 710021, China
9
3 Nagoya City Institute for Environmental Sciences, Nagoya 457-0841, Japan
10
4 Chubu Institute for Advanced Studies, Chubu University, Kasugai 487-8501, Japan
11
*Corresponding author e-mail:
[email protected] 12
Phone/fax: 052-788-6157
13
Address: Department of Earth and Environmental Sciences, Graduate School of Environmental
14
Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
15 16
1 Environment ACS Paragon Plus
Environmental Science & Technology
17
ABSTRACT: Submicrometer aerosols in the urban atmosphere of Nagoya, Japan, were
18
collected in late winter and early spring, and the water-insoluble organic matter (WISOM) in the
19
samples were fractionated into six subfractions based on their polarities by using solvent and
20
normal-phase solid-phase extractions: non-polar (F1), low-polar (F2 and F3), and medium-polar
21
(F4, F5, and F6) fractions. The overall structural characteristics of these subfractions were then
22
analyzed using Fourier transform infrared spectroscopy, nuclear magnetic resonance
23
spectroscopy, and high-resolution aerosol mass spectrometry. Quantitative information related to
24
the overall chemical characteristics of the WISOM in the different polarity fractions, including
25
their elemental compositions, the relative abundances of different functional groups and their
26
fragments from electron impact ionization, was obtained. These water-insoluble fractions
27
accounted for half of the total light absorption by the extracted aerosol matter at 400 nm. The
28
contributions of the medium-polar fractions to both the total organic carbon and light absorption
29
by the extracts were dominant among the contributions from the six subfractions. Large
30
molecules with aromatic and heteroatomic (O and N) groups, including charge transfer
31
complexes, might have greatly contributed to the light absorption by the fraction F4, which is the
32
largest fraction of the extracted water-insoluble organic matter.
33
KEYWORDS: water-insoluble organic matter, brown carbon, chemical structure, aerosol mass
34
spectrometry, Fourier transform infrared spectroscopy
35 36 37 38
2 Environment ACS Paragon Plus
Page 2 of 37
Page 3 of 37
38
Environmental Science & Technology
INTRODUCTION
39
Submicrometer aerosol particles in the atmosphere contain abundant organic compounds (20–
40
90%).1,2 Their presence influences the properties of these aerosols and thereby affects the roles
41
of the aerosols in the climate and in human health.3 The chemical characterization of these
42
organic compounds is important to understand and predict these roles. However, the organic
43
aerosol components remain poorly characterized because of the highly complex nature of their
44
composition.4-6 The brown carbon (BrC) in organic aerosols can absorb light at visible and near-
45
ultraviolet (UV) wavelengths. Hence, BrC potentially plays important roles in the photoinitiated
46
reactions of organic aerosols and thus in the radiative balance of the Earth. The characterization
47
of BrC is important to gain insight into their source and formation processes and to evaluate the
48
effects of BrC on the climate.7,8
49
Over the past decade, much of the work on the characterization of organic aerosol components
50
has focused on water-soluble organic matter (WSOM).9-13 However, the overall characteristics of
51
the remaining organic matter, i.e., the water-insoluble organic matter (WISOM), have not
52
received much attention14 even though the remaining organic matter constitutes a large fraction
53
of the organic carbon in urban and marine aerosols (26%–94% in OC; 19%–92% in OM).14-17
54
Aerosol WISOM is a complex organic matter that is composed of not only hydrocarbons but also
55
N- and O-containing compounds.16,18,19 WISOM also contains high-molecular-weight
56
oligomers.20-22 The analysis of the chemical composition of aerosol WISOM has generally been
57
performed using gas chromatography (GC) or two-dimensional GC (2D-GC) in combination
58
with mass spectrometry.19, 23, 24 However, the composition of a large mass fraction of the organic
59
matter, including unresolved complex mixtures (branched and cyclic compounds) and
60
nonvolatile or thermally unstable compounds (oxygenated compounds with high molecular
3 Environment ACS Paragon Plus
Environmental Science & Technology
61
weights), has not been well characterized.6,
19, 23, 24
62
fractions, and recent studies have shown that WISOM has a significant light absorptivity that is
63
stronger than that of WSOM.9,25 The light absorption by the methanol-extracted matter from the
64
ambient aerosols in Los Angeles was ~3 (365 nm) and 21 (532 nm) times higher than that
65
extracted by water.9 Among the organic compounds in WISOM, unsaturated compounds, such as
66
polycyclic aromatic hydrocarbons (PAHs) and oxygenated and nitrated PAHs, have electron-
67
conjugated systems and absorb light at near-ultraviolet and -visible wavelengths.26-28 It is
68
important to clarify which classes or structures of the organic compounds contribute largely to
69
the light absorption of WISOM.
BrC is in both the WSOM and WISOM
70
In this study, we employed Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic
71
resonance (NMR) spectroscopy and high-resolution aerosol mass spectrometry (HR-AMS) to
72
characterize the structures of a WISOM comprised of a wide variety of organics. These
73
analytical techniques are suitable to obtain the overall structural information of complex organic
74
matter.6 A normal-phase solid-phase extraction (SPE) method was employed to separate the
75
WISOM into six subfractions, i.e., non-polar (F1), low-polar (F2 and F3), and medium-polar (F4,
76
F5 and F6) fractions. The fractions were quantified, and the characteristic compound classes
77
were identified using the above analytical techniques. Furthermore, the light-absorption
78
characteristics of the WISOM and its subfractions were investigated using the UV-visible spectra.
79
The major organic compound groups contributing to light absorption in the WISOM were
80
identified, and their relationship to the chemical structures is discussed.
81
EXPERIMENTAL SECTION
82
Collection, extraction and separation of aerosol components
4 Environment ACS Paragon Plus
Page 4 of 37
Page 5 of 37
Environmental Science & Technology
83
Submicrometer urban atmospheric particles (aerodynamic diameter:
