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