Subscriber access provided by Weizmann Institute of Science
Article
Fossil and Non-Fossil Sources of Organic and Elemental Carbon Aerosols in the Outflow from Northeast China Yanlin Zhang, Kimitaka Kawamura, Konstantinos Agrios, Meehye Lee, Gary Salazar, and Soenke Szidat Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b00351 • Publication Date (Web): 20 May 2016 Downloaded from http://pubs.acs.org on May 23, 2016
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 33
Environmental Science & Technology
1
1
Fossil and Non-Fossil Sources of Organic and Elemental Carbon Aerosols in the
2
Outflow from Northeast China
3
Yan-Lin Zhang1,2 ,*, Kimitaka Kawamura2,*, Konstantinos Agrios3,4, Meehye Lee5,
4
Gary Salazar3, Sönke Szidat3
5
1Yale-NUIST
6
Information Science and Technology, Nanjing10044, China
7
2Institute
8
Sapporo 060-0819, Japan
9
3
Center on Atmospheric Environment, Nanjing University of
of Low Temperature Science, Hokkaido University, N19 W08, Kita-ku,
Department of Chemistry and Biochemistry & Oeschger Centre for Climate Change
10
Research, University of Bern, Bern 3012, Switzerland
11
4
Paul Scherrer Institute (PSI), Villigen-PSI 5232, Switzerland
12
5
Department of Earth and Environmental Sciences, Korea University, Seoul 136-701,
13
South Korea
14
*
15
[email protected]) or Kimitaka Kawamura
16
(
[email protected])
17
Phone: 81-11-706-5457; fax: 81-11-706-7142
Correspondence to: Yan-Lin Zhang (
[email protected] or
18
ACS Paragon Plus Environment
Environmental Science & Technology
Page 2 of 33
2
19
Abstract
20
Source quantification of carbonaceous aerosols in the Chinese outflow regions still
21
remains uncertain despite their high mass concentrations. Here, we unambiguously
22
quantified fossil and non-fossil contributions to elemental carbon (EC) and organic
23
carbon (OC) of total suspended particles (TSP) from a regional receptor site in the
24
outflow of Northeast China using radiocarbon measurement. OC and EC
25
concentrations were lower in summer, representing mainly marine air, than in other
26
seasons, when air masses mostly travelled over continental regions in Mongolia and
27
Northeast China. The annual-mean contribution from fossil-fuel combustion to EC
28
was 76±11% (0.1-1.3 µg m-3). The remaining 24±11% (0.03-0.42 µg m-3) was
29
attributed to biomass burning with slightly higher contribution in the cold period
30
(~31%) compared to the warm period (~21%) because of enhanced emissions from
31
regional biomass combustion sources in China. OC was generally dominated by non-
32
fossil sources with an annual average of 66±11% (0.5-2.8 µg m-3), approximately half
33
of which was apportioned to primary biomass burning sources (34±6%). In winter,
34
OC almost equally originated from primary (POC) emissions and secondary OC
35
(SOC) formation from fossil fuel and biomass burning sources. By contrast,
36
summertime OC was dominated by primary biogenic emissions as well as secondary
37
production from biogenic and biomass burning sources, but fossil-derived SOC was
38
the smallest contributor. Distinction of POC and SOC was performed using primary
39
POC/EC emission ratios separated for fossil and non-fossil emissions.
40
ACS Paragon Plus Environment
Page 3 of 33
Environmental Science & Technology
3
41
TOC
42
43
44 45
46
ACS Paragon Plus Environment
Environmental Science & Technology
Page 4 of 33
4
47
1 Introduction Carbonaceous aerosols contribute 10-70% to the atmospheric fine particulate
48
1, 2
49
matter
and have multiple and significant impacts on air quality, atmospheric
50
visibility, human health and the Earth’s climate 3-5. The total content of carbonaceous
51
aerosols (i.e., total carbon, TC) is operationally classified into two major fractions,
52
namely organic carbon (OC) and elemental carbon (EC) or black carbon (BC) 6. OC
53
can be directly emitted as primary OC (POC) or formed as secondary OC (SOC) via
54
gas-particle conversion resulting from atmospheric oxidation of anthropogenic and
55
natural precursors 6, 7. OC can affect the Earth’s climate forcing by directly reflecting
56
incoming sunlight and indirectly by altering the ability of organic aerosols to act as
57
cloud condensation nuclei (CCN) 5. EC almost exclusively derives from incomplete
58
combustion of fossil fuel (e.g. coal and petroleum) or biomass 6, 8, leading overall to a
59
warming effect by either absorbing incoming solar radiation or by reducing the albedo
60
of the Earth’s surface (i.e., snow and ice) 5.
61
High mass concentrations of carbonaceous particles have been reported in the
62
outflow regions of Chinese pollutants, such as Japan and Korea, due to long-range
63
atmospheric transport
64
source regions of China often differ in their origins and formation processes, which
65
may complicate the source identification of aerosols from downwind areas. Therefore,
66
there is an urgent need to get a better understanding of the sources of OC and EC in
67
outflow regions of China. Radiocarbon (14C) analysis is a powerful and unambiguous
68
tool for quantitatively determining fossil versus non-fossil sources of carbonaceous
69
aerosols, especially if such analysis is conducted separately for different carbonaceous
70
fractions such as OC, EC and/or water-soluble OC (WSOC)
71
source apportionment study showed that fossil sources contribute on average 80% to
9-11
. Previous studies have also revealed that OC and EC in
ACS Paragon Plus Environment
12-14
. A recent 14C-based
Page 5 of 33
Environmental Science & Technology
5
72
EC at Gosan site, which is higher than suggested by bottom-up approaches due to less
73
constrains on emission ratios in various fuel types and combustion efficiencies
74
However, such source constraints are only limited to shorter campaigns or specific
75
seasons.
15
.
76
In this study, 14C measurement combined with the Latin-Hypercube Sampling
77
(LHS) model was applied to aerosol samples from an East Asian receptor site (Gosan
78
supersite at Jeju Island, Korea) in order to obtain fruitful information on regionally
79
integrated sources and formation processes of carbonaceous aerosols from China. To
80
the best of our knowledge, this is the first time that
81
was carried out on both EC and OC aerosols in East Asian continental outflow
82
regions, covering a full seasonal cycle.
14
C-based source apportionment
83
84
2 Experimental
85
2.1 Sampling
86
Field sampling was conducted at the Korea Climate Observatory at Gosan, an
87
East Asian Supersite (33.17°N, 126.10°E, see Figure 1), which is located on the
88
western edge of Jeju Island facing the Asian Continent (~100 km south of the Korean
89
Peninsula, ∼500 km east of China, ∼200 km west of Kyushu Island, Japan), and the
90
sampling site is far away from local residential areas of the island. This sampling site
91
has been used in several multinational projects for aerosol studies such as ABC
92
(Atmospheric Brown Clouds) Project
93
Experiment–Asia) project
94
Asian Continent 14, 17-19. Total suspended particles (TSP) were collected on preheated
16
10
and ACE-Asia (Aerosol Characterization
as a downwind site of air pollution outflow from the
ACS Paragon Plus Environment
Environmental Science & Technology
Page 6 of 33
6
95
(450 °C for at least 6 h) quartz fiber filters (20 cm × 25 cm, Pallflex) using a high
96
volume air sampler (Kimoto AS-810, ~65 m3 h−1) near-continuously from April 2013
97
to April 2014 on the roof of a trailer house (∼3 m above the ground). Similar TSP
98
sampling approaches (instead of finer cut-offs, such as PM2.5 or PM10) have been
99
previously reported in South Asia and Northeast/East Asia to assess the sources of 11, 14, 20, 21
100
carbonaceous particles in full size range
101
detection limits for microscale
102
fractions (see Sec 2.3), a sampling collection interval of 10-14 days was used. After
103
sampling, filters were put in a pre-combusted glass jar (150 mL) with a Teflon-lined
104
screw cap to avoid contaminations and stored in a dark freezer room at −20°C before
105
analysis. Three field blank filters were collected, shipped, stored and measured in the
106
same way as the samples.
107
2.2 Carbon Aerosol Mass Concentration
14
. To fulfill the requirement of
C measurements in different carbonaceous aerosol
108
Concentrations of OC and EC were measured by a thermal-optical
109
transmittance method with OC/EC Carbon Aerosol Analyzer (Sunset Laboratory Inc.
110
USA) following the NIOSH protocol
111
showed an analytical precision with relative standard deviations of 5.8%, 12.0%, and
112
6.0% for OC, EC and TC, respectively. All reported OC and TC were blank
113
subtracted using an average filter blank (1.8±1.0 µg cm-2; n = 3). The EC blank is
114
smaller than the limit of detection and thus blank correction of EC is not necessary.
115
2.3 Radiocarbon Analysis
116
22
. The triplicate analysis of samples (n = 8)
14
C of TC was measured by online coupling of an elemental analyzer with a
117
MIni CArbon Dating System (MICADAS) equipped with a gas ion source and a
118
versatile gas interface
23
at University of Bern, Switzerland 24, as described in detail
ACS Paragon Plus Environment
Page 7 of 33
Environmental Science & Technology
7 25
119
elsewhere
. In order to remove carbonate carbon, the filters were exposed to HCl
120
fuming in a desiccator overnight (~12 hours). 14C analysis of EC was carried out by
121
online coupling the MICADAS with a Sunset Lab OC/EC analyzer where OC was
122
removed from the filter sample (1.5 cm2) by thermal-optical Swiss_4S protocol 26 and
123
CO2 evolved from the EC peak is subsequently separated 27. 14
C results were expressed as fractions of modern (fM), i.e., the fraction of the
124 125
14
C/12C ratio of the sample related to that of the reference year 1950
28
126
each sample was further corrected by EC loss (30±8% on the average) during the OC
127
removal steps and possibly positive EC artifact from OC charring (10±6% of EC on
128
the average) as described by
129
of the initial attenuation (ATN) as monitored by the laser signal of the (OC/EC)
130
analyzer and the ATN before isolating EC for
131
Charring of OC relative to EC is estimated for each thermal step as the difference of
132
the max. ATN and the initial ATN normalized to the initial ATN assuming that
133
50%±15% of the charred OC is co-evolved in the EC step. The determination of EC
134
yield and charred OC from the laser signal was conservatively assigned with a relative
135
uncertainty of 33%, which resulted in an overall uncertainty of fM(EC) of 4% on the
136
average from correction for these parameters based on error propagation. fM(TC) was
137
corrected for field blanks.
138
according to an isotope mass balance 13.
. fM(EC) for
26, 29
. For each sample, the EC yield is quantified as ratio
14
14
C measurement (i.e., EC step).
C results in OC (fM(OC)) were calculated indirectly
139
Non-fossil fractions of OC and EC (i.e., fNF(OC) and fNF(EC), respectively)
140
were determined from their corresponding fM values and reference values for pure
141
non-fossil sources by fNF=fM(sample)/fM(REF). These reference values are estimated
142
as 1.07±0.04 and 1.10±0.05 for OC and EC, respectively by a tree-growth model with
143
a long term 14CO2 measurement
30
and by assuming biomass burning contribution to
ACS Paragon Plus Environment
Environmental Science & Technology
Page 8 of 33
8
144
non-fossil OC and EC is 50% and 100%, respectively. The fraction of fossil-fuel
145
sources was calculated by: fFF=1-fNF. Uncertainties were determined by error
146
propagation of all individual uncertainties including mass determination in OC and
147
EC,
148
field blanks, EC recovery and charring. The overall uncertainties of fNF were
149
estimated to be on average 4% (i.e., ranging from 3% to 5%) for OC and 7% (i.e.,
150
ranging from 3% to 10%) for EC, and the most important contribution to their
151
uncertainties were generally from blank corrections and EC yield corrections for OC
152
and EC, respectively.
153
2.4 Back Trajectory Analysis
14
C results in OC and EC, reference values (fM(REF)) as well as corrections for
154
Five-day back trajectories were calculated every 6 h for the entire campaign
155
period using the HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory)
156
Model
157
(http://ready.arl.noaa.gov/HYSPLIT.php). All individual trajectories were then
158
clustered into 3 or 4 clusters for each season using HYSPLIT to provide seasonal
159
specific information about major air mass origins. The seasonal variation of back
160
trajectories was clearly characterized with the summertime air masses mostly
161
originating from the ocean and in other seasons from continental regions in Northeast
162
China and Mongolia (Figure 1).
163
3 Results and Discussion
164
3.1 Overview of OC and EC Concentrations
access
provided
by
NOAA
ARL
READY
Website
165
The mass concentrations of OC and EC ranged from 0.6 to 4.1 µg m-3 and 0.2
166
to 1.5 µg m-3, with a mean value of 2.2±1.0 µg m-3 and 0.7±0.4 µg m-3, respectively
167
(Figure 2). OC and EC mass concentrations were similar to or lower than those
ACS Paragon Plus Environment
Page 9 of 33
Environmental Science & Technology
9
168
reported at the same site during spring and fall of 2008-2012 (excluding 2010, 3.3 µg
169
m-3 for OC and 0.7 µg m-3 for EC) 31 and the ACE-Asia program during the spring of
170
2011 (7.00 µg m-3 for OC and 1.29 µg m-3 for EC) 32; however, our results were also
171
much higher than those from remote sites in the North Pacific Ocean (