Chemical characteristics and source of size-fractionated atmospheric particle in haze episode in Beijing

    Chemical characteristics and source of size-fractionated atmospheric particle in haze episode in Beijing Jihua Tan, Jingchun Duan, Naijia Zhen, Kebin He, Jiming Hao PII: DOI: Reference:

S0169-8095(15)00190-8 doi: 10.1016/j.atmosres.2015.06.015 ATMOS 3437

To appear in:

Atmospheric Research

Received date: Revised date: Accepted date:

2 April 2015 12 June 2015 17 June 2015

Please cite this article as: Tan, Jihua, Duan, Jingchun, Zhen, Naijia, He, Kebin, Hao, Jiming, Chemical characteristics and source of size-fractionated atmospheric particle in haze episode in Beijing, Atmospheric Research (2015), doi: 10.1016/j.atmosres.2015.06.015

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ACCEPTED MANUSCRIPT Chemical characteristics and source of size-fractionated atmospheric particle in haze episode in Beijing Jihua Tan 1,3, Jingchun Duan2,*, Naijia Zhen 1, Kebin He3, Jiming Hao3

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1. University of Chinese Academy of Sciences, Beijing 100049, China

2. State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of

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Environmental Sciences, Beijing 100012, China. E-mail: [email protected]

3. State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex,

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School of Environment, Tsinghua University, Beijing 100084, China,

Abstract:The abundance, behavior and source of chemical species in size-fractionated

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atmospheric particle were studied with a 13-stage low pressure impactor (ELPI) during high polluted winter episode in Beijing. Thirty three elements (Al, Ca, Fe, K, Mg, Na, Si, Sc, Ti, V,

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Cr, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Zr, Mo, Ag, Cd, In, Sn, Sb, Cs, Ba, Hg, Tl and Pb)

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and eight water soluble ions (Cl-, NO3-, SO42-, NH4+, Na+, K+, Ca2+ and Mg2+) were determined by ICP/MS and IC, respectively. The size distribution of TC (OC + EC) was

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reconstructed. Averagely, 51.5±5.3% and 74.1±3.7% of the total aerosol mass was distributed in the sub-micron (PM1) and fine particle (PM2.5), respectively. A significant shift to larger fractions during heavy pollution episode was observed for aerosol mass, NH4+, SO42−, NO3−,

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K, Fe, Cu, Zn, Cd and Pb. The mass size distributions of NH4+, SO42−, NO3− and K were dominated by accumulation mode. Size distributions of elements were classified into four main types: (I) elements was enrich within the accumulation mode (<1µm, Ge, Se, Ag, Sn, Sb, Cs, Hg, Ti and Pb);(II) those mass (K, Cr, Mn, Cu, Zn, As, Mo and Cd) was resided mainly within the accumulation mode, ranged from 1-2µm; (III) Na, V, Co, Ni and Ga were distributed among fine, intermediate and coarse modes; and (IV) those which were mainly found within particles larger than 2.7μm (Al, Mg, Si, Ca, Sc, Tl, Fe, Sr, Zr and Ba). [H+]cor showed an accumulation mode at 600 - 700 nm and the role of Ca2+ should be fully considered in the estimation of acidity. The acidity in accumulation mode particles suggested that generally gaseous NH3 was not enough to neutralize sulfate completely. PMF method was applied for source apportionment of elements combined with water soluble ions. Dust, vehicle, aged coal combustion and sea salt were identified and the size resolved source

ACCEPTED MANUSCRIPT apportionments were discussed. Aged coal combustion was the important source of fine particles and dust contributed most to coarse particle.

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Key words:source apportionment; elements; PM2.5; water soluble ion; Haze

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Introduction

Epidemiological studies have shown that increasing levels of atmospheric particulate matter are associated not only with exacerbations of respiratory diseases but also with

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increased morbidity and mortality from cardiovascular conditions (Dockery and Pope, 1994; Chen et al., 2011; Vanos et al., 2014). The size distribution of atmospheric particulate matter

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can provide chemical and physical information in understanding its effects on human health, dry deposition, light extinction, sources and formation processes (Trijonis 1983; Pakkanen et

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al., 2001; Salma et al., 2005; Tang et al., 2006; Duan et al., 2005, 2007, 2012; Tan et al.,

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2009a; Tao, et al., 2012a, b). Size-fractionated results revealed that roughly 60-90% of PAHs were distributed in the accumulation mode (0.1-1.8um) (Duan et al., 2005) and most

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atmospheric heavy metals were existed in PM2.5 and 44-62% of these metals can breakthrough into pulmonary alveoli (Duan and Tan, 2013; Duan et al., 2014). Size distribution of chemical species would also be helpful to solve the collinearity problem in

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source apportionment (Duan et al., 2012; Tan et al., 2014). Size-fractionated data were also used to analyze the formation of haze successfully, suggesting the yield of SOA (Secondary Organic Aerosol) in PM smaller than 0.49um showed strong dependent on the aerosol acidity on the haze days (Zhang et al., 2007; Tan et al., 2009). Size-fractionated characteristics of hygroscopic components such as sulfate and nitrate would be much important to understand their impacts on light scattering and haze formation (Tao et al., 2012a; Liu et al., 2012; Yang et al., 2015). It might be particularly important in the Beijing area, which is characterized by complex meteorology that favors the ageing of pollutants and influenced by the transportation of anthropogenic and natural pollutants from neighbor area as a consequence of its geographic location. Beijing is the capital of China, is one of the world’s largest metropolises comprising a

ACCEPTED MANUSCRIPT resident population of more than 21.14 million (Statistical bulletin for national economic and social development 2014). With the substantial economic development, large amounts of pollutants were emitted into this area, which led to a rapid deterioration of air quality in and

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around this region. Great efforts have been made to improve the air quality in Beijing since

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1998. The air pollution type in Beijing has shifted from simple type of coal smoke pollution

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to regional complex air pollution by the adjustments of industrial and energy structure, usage of clean energy including nature gas and clean coal (Zhang et al, 2011). In recent years, many researches have been investigation on the air pollution in Beijing (Wei et al., 2014, Yang et al.,

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2011, Zhang et al., 2013). However, few studies have focused on the physical and chemical characteristics, formation mechanism and source apportionment of Size-fractionated

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atmospheric particles.

In this study, the objectives of this work were to characterize the size distributions of

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atmospheric particle (PM0.1, PM1, PM2.5 and PM10), water soluble inorganic species, elements

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and reconstructed carbonaceous species in an urban background site in Beijing. Furthermore, the size-segregated data were used to perform source apportionment. The samples were

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collected with a 13 stage low pressure impactor (ELPI). Positive Matrix Factorization (PMF) receptor model base on size segregated data was employed to investigate the differences in the source contribution to the size ranges from 0.028μm to 10μm.The size segregated acidity

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of PM and enrichment factor of elements were also evaluated. The results would be helpful for studies on health effect and policy making.

1 Materials and methods 1.1 Study area and sampling A thirteen-stage low pressure cascade impactor (LPI, Dekati, Finland) was used to collect particles with PTFE filter in the range of 0.028–10μm at a flow rate of 10 L/min (Table 1). There are no 50% cut off diameters (D50, μm) at 0.1, 1.0, 2.5 and 10μm, so cut off diameters at 0.095, 0.948, 2.390 and 9.92μm were used to calculate the mass concentration of PM0.1, PM1.0, PM2.5 and PM10. Sampling site is located on the rooftop of a building (5 m above the ground) within Tsinghua University at an urban area, which is located 20 km in the North West direction from the center of Beijing and 2 km from 4th Ring Road. Samples were

ACCEPTED MANUSCRIPT collected during 4th - 27th, Dec. 2006. Sampling duration lasted for 24-hour and filter were replaced daily at 9:00 am Beijing time through the whole sampling period. Meteorological data during the sampling periods were also recorded. The filters were weighed before and

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after sampling, and were equilibrated in an RH (40±5%) and temperature (20±1°C) constant

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environment for 24 h before gravimetric analysis.

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Table 1 Cutpoints of stages of ELPI

1.2 Chemical analysis

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Half of each filter were placed in Teflon tubes with a 4 mL mixture of hydrochloric and nitric acid at volume ratio of 3:1, and then microwaved for 58 min to ensure the complete

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digestion of particles. The first step is to ramp temperature to 120°C from room temperature in 5 min and hold 5 min; the second is to ramp to 155°C in 8 min and hold 8 min; the third is

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180°C in 5 min and to hold 5 min; and the last step is to ramp to 195°C and hold 12 min. The

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digested solution was diluted to 10 mL by using ultra-pure water to perform the analysis by ICP-MS (Thermo, X serial) and ICP-AES (Thermo, IRIS Intrepid II XSP). The calibration

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was made by using multi-element standards (certified reference materials (CRMs); National Analysis Center for Iron and Steel, China) in a 3% (V=V) HNO3 solution. Six blank filters were treated and analyzed in the same way. In addition, the approximate detection limits were

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listed in Table 2.

Water-soluble inorganic ions were analyzed by ion chromatography system (ICS-1400, Dionex, USA) at Analysis and Testing Center of Beijing Normal University. The filter was submerged in a vial with 5 mL ultra-pure water and ultrasonically extracted for 20 min. The extraction was processed twice and then merged to determine the concentrations of water soluble inorganic ions. The contributions to water soluble inorganic ions (F-, Cl-, NO3-, SO42-, NH4+, Na+, K+, Ca2+ and Mg2+) in the field blanks were 0.22, 0.11, not detected (nd), 0.21, nd, 0.32, nd, 0.35 and 0.21μg/m3, respectively. The details were given elsewhere (Tan et al., 2009b).

1.3 Acidity The estimation of H+ molar concentrations (in nmol m-3) was based on two methods. The

ACCEPTED MANUSCRIPT conventional method was based on the difference between the concentrations of NH4+ measured and NH4+ required to fully neutralize the measured concentrations of NO3-, SO42-, and Cl-. The other method is corrected with Ca2+, for atmospheric calcium is important in

(1)

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[H+] =2 × SO42-/96 + NO3-/62 + Cl-/35.5 - NH4+/18

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north China:

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[H+]cor=2 × SO42-/96 + NO3-/62 + Cl-/35.5 - NH4+/18 –2 × Ca2+/40

(2)

Where, [H+] denotes the H+ molar concentrations (in nmol m-3); NH4+, SO42-, NO3-, Ca2+, and Cl- denote the mass concentrations of the species and the denominators correspond to

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their molecular weights.

The degree of stoichiometric neutralization for the ensemble of measured particles is

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obtained from the normalized ratio of the measured NH4+ molar concentration to the NH4+ molar concentration required for full neutralization of the anions: (3)

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NH4+mea/NH4+neu = (NH4+/18) / (2 × SO42-/96 + NO3-/62 + Cl-/35.5)

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NH4+mea/NH4+neu (corrected) = (NH4+/18) / (2 × SO42-/96 + NO3-/62 + Cl-/35.5 - 2 ×Ca2+/40) (4)

The ratio of NH4+mea to NH4+neu was used to identify “neutralized particle periods”

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(NH4+meas/NH4+neu) =1) and “more acidic particle” (NH4+meas/NH4+neu<0.75). The ratio of NH4+mea/NH4+neu(corrected) was based on the correction of Ca2+.

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1.4 Enrichment Factor

Enrichment factor (EF) can be used to differentiate between the metals originating from human activities and natural procedure, and assess the degree of anthropogenic influence. The EFCrust of element E in aerosols is defined as below: EFCrust= [E/R]Air /[E/R]Crust

(5)

Where R is a reference element of crustal material and [E/R]Air is the concentration ratio of E to R in aerosol, and [E/R]Crust is the mass concentration ratio of E to R in crust. The titanium is selected as the reference element, which is relatively stable in the crust, and its distribution is not affected by human activities (Chen et al., 2008).

1.5 The reconstruction of carbonaceous species Teflon filter couldn’t be analyzed for carbonaceous species; thus, size segregated

ACCEPTED MANUSCRIPT carbonaceous species (TC = OC + EC) were estimated based on the subtraction of crustal material and water soluble inorganic species from PM in this study. The concentration of

Crustal material =SiO2 + Al2O3 + CaO + Fe2O3 + K2O + Na2O + MgO

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crustal material is calculated as below: (6)

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=1.89[Al] + 1.66[Mg]n + 1.21[K] + 1.40[Ca]n + 1.43[Fe]n + 1.35[Na－ss-Na+] + 2.14[Si]

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[SS-Na+] refers to water-soluble Na+ in sea salt. [Si], [Fen], [Can] and [Mgn] were calculated based on the ratio to Al in the crustal materials. The calculation method for crustal

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materials can be found in Kunwar (2014).

1.6 PMF analysis

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EPA PMF is one of the receptor models that the US EPA's Office of Research and Development has developed. In this study, the size segregated concentrations and

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equation-based uncertainties of mass, seventeen elements and eight ions were included in the

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PMF 5.0. Data with unusually high concentrations of a few chemical species was excluded to avoid distortion. The equation-based uncertainty included detection limits and error fractions

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(5%). If the concentration is less than or equal to the method detection limit (MDL) provided, the uncertainty (Unc) is calculated using the following equation (Polissar et al., 1998; Tan et al., 2014).

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5 Unc   MDL 6

(7)

If the concentration is greater than the MDL provided, the calculation is

Unc  ( ErrorFraction  concentrat ion) 2  (MDL) 2

(8)

2 Results and discussion 2.1 levels of PM, elements and water soluble ions Some epidemiological evidences suggest mortality in urban areas may be linked to particulate material (Lippmann, 1998). As shown in Table 3, the averaged ultra-fine articles (PM0.1), sub-micrometer particles (PM1), Fine particles (PM2.5) and respirable particulate (PM10) were 4.5±2.2 μg/m3, 99.7±29.1 μg/m3, 142.3±46 μg/m3 and 193.4±57.3 μg/m3, respectively, during sampling period. PM2.5 and PM10 were much higher than the National

ACCEPTED MANUSCRIPT Ambient Air Quality Standard (NAAQS-2012) of China for PM2.5 (35μg/m3) and PM10 (70μg/m3). During sampling period, water soluble species in PM2.5 accounted for 51% of the total

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mass of PM2.5, and SO42− was the dominant species in fine particles. Secondary inorganic

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species of SO42−, NO3− and NH4+ were the major water soluble ions and accounted for 68% of

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total water soluble ions. Ca2+ (7.77±3.23μg/m3) and Cl− (5.34±1.42μg/m3) were also the important water soluble ions and couldn’t be ignored in Beijing area. Secondary inorganic species (SO42−, NO3− and NH4+) and water soluble ions from combustion (Such as Cl− and K+)

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were mostly distributed in PM1, and the ratios of their mass concentrations in PM1 to PM2.5 were in the range of 79%-89%. Ca2+, Mg2+ and Na+ contributed approximately 43%, 35% and

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25% of particles larger than 2.5μm, respectively, indicating that these crustal water soluble ions were also mainly associated with fine particles, however, crustal elements such as Al,

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Mg, and Ca were mainly distributed in coarse particles. The averaged TC in PM0.1, PM1,

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PM2.5 and PM10 were 0.63μg/m3, 30.9μg/m3, 51.2μg/m3 and 61.9μg/m3, respectively, during sampling period, which indicated that carbonaceous species were also important components

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of the fine particulate.

The 33 trace elements accounted for approximately 12.5% of the total aerosol mass. The mean elemental compositions are given in Table 3. In general, the most important elements

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accounted for 93.6% of the sum concentration of total elements and in the order of: Ca > Si> Fe > Al > K > Mg > Na, which was consistent with the previous result in Beijing (Li et al., 2013).The crustal elements of Ca, Si, Fe, Al, and Mg were mainly present in coarse mode and the proportions of their concentrations of coarse mode particles to the total mass concentration were 70%, 65%, 65%, 68% and 73.1%, respectively. Trace elements components represented only 1.1% of the total mass. Atmospheric heavy metals such as Pb, Zn, Cu, Ni etc. were of great concern because of their high toxicity. The average concentration of atmospheric Pb is 10.44±5.82ng/m3, 212.86±73.33ng/m3, 266.81±101.05ng/m3 and 281.4±105.15ng/m3 in PM0.1, PM1, PM2.5 and PM10 in Beijing. Pb in PM2.5 is comparable with the average concentration of Pb (261.0±275.7 ng m3) in China (Duan and Tan, 2013) which fall below the annual limits of current of NAAQS (GB3095-2012, 500ng/m3) and the WHO guideline of 500 ng/m3. This

ACCEPTED MANUSCRIPT can be mainly attributed to the nationwide prohibition of leaded gasoline in China since July 1, 2000.The concentration of As is 0.89±0.57ng/m3, 27.17±11.96ng/m3, 42.04±25.4 ng/m3 and 46.32±28.97 ng/m3 in PM0.1, PM1, PM2.5 and PM10, which is similar to the reported average

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concentration of 51.0 ng/m3 in China (Duan and Tan, 2013), and much higher than the limit of

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the new NAAQS (GB3095-2012) in China (6 ng/m3) and the limit of WHO (6.6 ng/m3).

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Table3. Mass concentrations of elements and water soluble ions in total, fine, sub-micrometer and ultra-fine particles

2.2 Size Distribution

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A good understanding has been acquired on the size distribution of three main components (water soluble inorganic species, element and carbonaceous species). Generally,

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typical aerosol has three modes. Nucleation and accumulation particles tend to be produced either directly from combustion emission or by secondary formation of sulfate, nitrate,

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ammonium and organics. Coarse mode particles tend to be mechanically generated such as

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soil dust, construction dust and road dust. The ratios of PM1/PM10 and PM2.5/PM10 for elements and water soluble ions were also

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shown in Table 3. PM2.5/PM10 ranged from 67% to 76% with an average of 74.1±3.7%, and PM1/PM10 from 48% to 54% with an average of 51.5±4.3%. It indicated ambient particles were dominated by sub-micron and fine particles. SO42-, NO3-,Cl-, Na+, K+, Mg2+, Cr, Ni, Cu,

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Zn, Ga, Ge, As, Se, Mo, Ag, Cd, Sn, Sb, Cs, Hg, Tl and Pb were dominated by sub-micron particles (PM1/PM10>50%); NH4+, Ca2+,Ti, V, Mn, Zr and Ba were dominated in fine particles (PM2.5/PM10>50%); Si, Fe, Al, Ca, Mg, Sc, Co and Sr were dominated in coarse particles (PM2.5/PM10<50%). The size distribution modes of the individual chemical elements were presented in Fig.1. In this study, size distributions of elements were classified into four main types: (I) elements whose mass was enrich mainly within accumulation mode (<1µm, Ge, Se, Ag, Sn, Sb, Cs, Hg, Ti and Pb): Ti, Pb and Cs peaks appeared in the <0.3µm；Sn and Hg were in the range of 0.3-0.4µm, Ag, Sb, Se and Ge were in the range of 0.4-0.7µm, respectively;(II) those elements (K, Cr, Mn, Cu, Zn, As, Mo and Cd) were resided mainly within the accumulation mode, ranged from 1-2µm; (III) Na, V, Co, Ni and Ga were distributed among fine, intermediate and coarse modes; and (IV) those which were mainly found within particles

ACCEPTED MANUSCRIPT larger than 2.7μm (Al, Mg, Si, Ca, Sc, Tl, Fe, Sr, Zr and Ba). Crustal elements: Al, Mg, Si, Ca, Sc, Tl, Fe, Sr, Zr and Ba, exhibited a single modal size distribution, and their highest mass

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peaks appeared in the range of 3.2–5.6µm.

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Fig. 1 Four types of size distributions of elements

Fig. 2 presented the size distribution of water soluble ions. The average size distributions of water soluble ions was mainly distributed in accumulation mode and have a relatively small

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contribution in coarse particles, and the peaks were similar with that of air mass. The mass size distributions of SO42−, NO3−, NH4+, Cl- and K+ were dominated in accumulation mode.

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SO42− showed a predominant droplet mode and its size distribution characteristics and formation pathways are well discussed. Droplet SO42− is generally formed through aqueous

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conversion of SO2 in clouds (Seinfeld and Pandis, 2006; Wei et al., 2015). Condensation

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SO42− was enhanced from gas phase photochemical oxidation of SO2 (Seinfeld and Pandis, 2006). Coarse SO42− could be attributed to heterogeneous reactions of SO2 on crustal particles

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(Pakkanen et al., 1996; Zhuang et al., 1999). The size distribution of NH4+ was very similar to SO42−. Compared to normal days, secondary inorganic species (SNA, SO42−, NO3− and NH4+) increased dramatically during haze periods and the contribution of SNA to PM2.5 in normal

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and haze days were 20.1% and 34.2%, respectively, suggested the important influence of secondary inorganic pollution to haze formation. SNA was dominated at condensation mode (0.263-0.382μm) and droplet mode (0.613-0.948μm) in normal and haze days, respectively, implying that in-cloud process was a major path to form sulfate in haze days. Cl- was dominated by droplet mode and a very minor coarse mode. On the contrary, Na+ was dominated by coarse mode and a very minor droplet mode, which could be well explained by their respective sources. Most of Cl¬ in PM2.5 is known to be the important constituent of particulate matter from coal burning and briquettes used in Chinese cities (Bond et al., 2002). High level of droplet Cl- associated with fine particle in winter is a distinctive feature in Beijing and even around inland China, which is ascribed to coal combustion (Zhang et al., 2013). Coarse mode Na+ and Cl- were associated with sea salt particles (Ye et a., 2003). Mg2+ and Ca2+ were dominated by coarse mode. Coarse Ca2+ was derived from the

ACCEPTED MANUSCRIPT reactions of crustal CaCO3 with acidic gases and had been frequently used as tracers for suspended crustal particles (Pakkanen et al., 1996; Zhuang et al., 1999). This mechanism was

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consistent with the observation of a high correlation between Ca2+ and NO3− in coarse mode.

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Fig. 2 The size distributions of water soluble inorganic species

The size distributions of particle mass during heavy haze (Visibility <5Km) and normal days (5Km< Visibility <10Km) were both bimodal but slightly different (Fig. 3). These mode

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peaks were within the range of 0.32–1.0 μm and 3.2–5.6 μm, similar to previous results (Tan et al., 2009). However, the peak of accumulation mode shifted toward larger size during

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heavy haze periods from 0.32μm to 1.0μm and coarse mode peak was relatively constant. The enhancement and shift of accumulation mode was similar to the previous study (Duan et al.,

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2006; Tan et al., 2009) and was generally thought to dominate light scattering due to their

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high scattering efficiency.

The chemical closure of size distribution of main chemical components (elements, SO42−,

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NO3−, NH4+, Cl−, and TC) were given in Fig 3. SO42−, NO3− and TC were the main chemical species of ultra-fine particle. With the increase of particle size, the percentage of TC was nearly double and Cl- decreased significantly within the range of 0.1-1μm. The percentage of

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other main chemical components such as elements, SO42−, NO3− and NH4+ showed slightly decrease in the range of 0.1-1μm. Elements, dominated by the crustal elements, increased most from 1μm to 2.5μm, mainly from natural emissions.

Fig. 3 The size distributions of mass in haze and normal days (left) and size distribution of main chemical components (right) 2.3 Acidity Size resolved [H+], particle mass and total water soluble inorganic species, and the ratios of NH4+meas/NH4+neu were presented in Fig.4. Size resolved [H+] were estimated from NH4+, SO42- and NO3- based on equation (1) and equation (2). The levels of [H+] in the range of 0.028-10μm were higher than 0, suggested PM10 was acidic. When particle was less than

ACCEPTED MANUSCRIPT 2μm, [H+] increased with the increases of particle size and reached a maximum at 2μm, then slowly decreased, but continued to be acidic. In consideration of the effect of Ca2+ (Equation 2), the size distribution of [H+] (<0.7μm) was similar with the result from the conventional

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method; however, the size distribution of [H+] (>0.7μm) was total different between the two

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methods. When particle size was larger than 0.7μm, [H+] decreased significantly with the

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increase of size and particle was tended to be alkaline, indicted that Ca2+ was particularly important in the calculation of acidity and couldn’t be negligent in the estimation of [H+] for PM2.5 and PM10 in Beijing area. The ratio of NH4+mea to NH4+neu was used to identify

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neutralized particle when NH4+mea/ NH4+neu was equal one and more acidic when this ratio was less 0.75 (Zhang et al., 2007). The significantly difference between two methods was also

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found when particle size was larger than 1μm. Thus, the role of Ca2+ should be fully considered in the estimation of acidity.

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Base on Equation (2), the average size distribution of [H+] peaked at the diameter (600 -

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700 nm) as those of water soluble inorganic species and particle mass (Fig. 4). This was consistent with the facts that [H+] correlated well with SO42-, and the mass concentration of

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SO42- in 600 - 700 nm increased during heavy haze periods compared to normal days. There was strong evidence that the formation and growth of new particles were tightly linked to the conversion of SO2 to H2SO4. Since accumulation mode (600 - 700 nm) is largely made up of

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aged secondary aerosol, which rich in SO42- and SOA, [H+] peak in this mode indicated that there was generally not enough gaseous NH3 to neutralize SO42- completely, which was also consistent with the results that aerosol from high SO42- periods tend to be more acidic.

Fig. 4 Average size distributions of (above) H+, total mass and total water soluble inorganic concentrations, and NH4+meas/NH4+neu ratio (below)

2.4 Enrichment Factor Enrichment factors were calculated according to the formula (5). Fig. 5 showed the size distribution of enrichment factors of elements. As, Zn, Sn, Pb, Ag, Cd and Se had the highest EFs (>400) among 32 elements and were ascribed to coal combustion (Zhang et al., 2013), which was the predominant source of aerosols over China (Yao et al., 2009). The EFs of Fe,

ACCEPTED MANUSCRIPT Zr, Co, Mg and Ba within ranges of 0.018–10µm were all less than 10, implying these elements were from natural sources. However, the EFs of Cu, Ge, Mo, Tl, As, Zn, Sn, Pb, Ag, Cd, Se and Pb within ranges of 0.018–10 µm were all much higher than 10, indicating these

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elements came from anthropogenic resources. The EFs of Cs, Sr, Ga, Cr and Sb in coarse

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mode particles were less than 10, but were extremely high (> 20) in fine and ultra-fine

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particles (<2.5µm), implying that these elements could be easily enriched in ultra-fine and fine particles. EFs of crustal elements within ranges of 0.018–10 µm were low and relatively constant, and anthropogenic elements (Cu, Ge, Tl, As, Zn, Sn, Pb, Ag, Cd, Se and Pb) had

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two peaks, with the primary peak within the range of 0.1–0.3µm and secondary peak within the range of 0.56–1.0 µm, which were different from those values in Shanghai city (Lv et al.,

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2012), which with primary peak in 3.2–5.6µm and secondary peak in 0.56–1.0 µm. The EF of another anthropogenic element group (Mo, and Sn) showed three peaks in 0.018–0.032 µm,

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0.1–0.3µm and 0.56–1.0 µm, respectively.

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Fig. 5 The size distributions of enrichment factors of different chemical elements

2.5 Source apportionment

Size segregated elements and ions as good source markers and with low uncertainties were

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included in the PMF model. Al and Ca are good indicators of crustal dust (Duan et al., 2012); K is a good marker for biomass burning (Duan et al., 2004); Coal combustion release more toxic air pollutants such as arsenic and Se (Duan et al., 2012; 2014); SO42-, NO3- and NH4+ are indicator of secondary inorganic aerosol and long-range transportation, and Tan et al. (2009) reported these ions are significantly higher during haze periods. Four Sources were identified and factor profiles were illustrated in Fig. 6. Source 1 (dust) was identified to be crust dust, road dust and construction dust, indicated by high loadings of Al, Ca, Fe, Mg and Ba. Source 1 was the important source of PM and crustal elements, and contributes less to secondary aerosol and trace atmospheric heavy metals. Construction and demolition activities are very common in China, and effective measures for dust control should be implemented. Source 2 (vehicle exhaust) was related with vehicle emission with high loadings of Mn, Cu, Zn, Arsenic, Cd and Pb (Johansson et al., 2009). Source 3 (aged

ACCEPTED MANUSCRIPT coal combustion) was associated with a mixture source of coal combustion, biomass burning and secondary aerosol, indicated by prominent loadings of K, Arsenic, Se, Pb and secondary inorganic ions of SO42-, NH4+ and NO3-. Liu et al. (2005) suggested that when wind from

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southern and southwestern directions prevails in Beijing, high concentrations of vapor and air

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pollutants from power plant, industry and biomass burning were brought in, which would

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enhance the concentration of aerosol. Na+ and Cl- are tracers for sea salt aerosols. Ni is often used as tracers of ship emissions (Kuang et al., 2015). So, the fourth source belongs to sea salt

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aerosol mixed with ship emissions, as it is indicated by the dominance of Cr, Ni, Na and Cl.

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Fig. 6 percentage values for the source profiles

The source contribution of chemical species strongly relies on the size distribution (Fig. 7).

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Generally, Source 1 (dust) contributed more to coarse mode and little in nucleation and

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accumulation mode; Source 2 (vehicle) contributed more to accumulation mode and a little coarse mode; Source 3 (aged coal combustion) contributed most to accumulation mode and

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was the important source of fine particles; Source 4 (sea salt) contributes to all of the three mode, but more to coarse mode.

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Fig.7 Size distribution of atmospheric elements reconstructed by source contributions

3 Conclusions

A study on size distributions of atmospheric elements and water soluble inorganic ions was carried out during haze period in winter in Beijing, China. The levels, size distributions and sources of elements and water soluble inorganic ions were discussed. Averagely, 51.5±5.3% and 74.1±3.7% of the total ambient aerosol mass was distributed in the sub-micron and fine particle, respectively. A significant shift to larger fractions during heavy pollution episode was observed for aerosol mass. The shifting was also found for the following species: NH4+, SO42-, NO3−, K, Fe, Cu, Zn, Cd and Pb. [H+]cor shows an accumulation mode at 600 700 nm and the role of Ca2+ should be fully considered in estimation of acidity. The acidity suggests that generally gaseous NH3 is not enough available to neutralize sulfate completely

ACCEPTED MANUSCRIPT in accumulation mode particles. Four types of elements were identified according to the distributions pattern of size distribution of elements. Furthermore, anthropogenic chemical species were substantially accumulated in coarse mode, which suggested that particles with a

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diameter larger than 2.5μm couldn’t be neglected during severe haze events. Four factors

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(dust, vehicle, aged coal combustion, and sea salt) are identified and their size distributions

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are discussed base on the PMF method.

Acknowledgments

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This study is supported by the National Natural Science Foundation of China (No. 41105111, 41275134, 41475116), State Environmental Protection Key Laboratory of Sources

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and Control of Air Pollution Complex（No. SCAPC201401）and the Research Found of

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CRAES (No. 2012ysky09).

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China. Presented at the Sixth International Aerosol Conference, Taipei,Taiwan on September

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Coefficients Using Chemical Compositions of PM2.5 in Winter in Urban Guangzhou, China, Adv Atmos Sci 29(2012a), pp. 359-368. Tao, J., Shen, Z.X., Zhu, C.S., Yue, J.H., Cao, J.J., Liu, S.X. et al., Seasonal variations and chemical characteristics of sub-micrometer particles (PM1) in Guangzhou, China, Atmos Res 118(2012b), pp. 222-231. Trijonis, J., Development and Application of Methods for Estimating Inhalable and Fine Particle Concentrations from Routine Hi-Vol Data, Atmos Environ 17(1983), pp. 999-1008. Vanos, J.K., Hebbern, C., Cakmak, S., Risk assessment for cardiovascular and respiratory mortality due to air pollution and synoptic meteorology in 10 Canadian cities, Environ Pollut 185(2014), pp. 322-332. Wei, L.F., Duan, J.C., Tan, J., H,, Ma, Y.L., He, K.B., Wang, S.X., Huang, X.F., Zhang, Y.X. Gas-to-particle conversion of atmospheric ammonia and sampling artifacts of ammonium in spring of Beijing. Sci China Ser D-Earth Sci 58(2015),pp. 345-355. Wang, X.M., Chen, J.M., Cheng, T.T., Zhang, R.Y., Wang, X.M., Particle number concentration, size distribution and chemical composition during haze and photochemical smog episodes in Shanghai, J Environ Sci-China 26(2014), pp. 1894-1902. WHO, 2000.World Health Organization.Guidelines for Air Quality Geneva. Yang, F., Tan, J., Zhao, Q., Du, Z., He, K., Ma, Y. et al., Characteristics of PM2.5 speciation in representative megacities and across China, Atmos Chem Phys 11(2011), pp. 5207-5219. Yang, Y.R., Liu, X.G., Qu, Y., Wang, J.L., An, J.L., Zhang, Y. et al., Formation mechanism of continuous extreme haze episodes in the megacity Beijing, China, in January 2013, Atmos Res 155(2015), pp. 192-203. Yao, Q., Li, S.Q., Xu, H.W., Zhuo, J.K., Song, Q., Studies on formation and control of combustion particulate matter in China: A review, Energy 34(2009), pp. 1296-1309. Yao, X., Lau, A. P., Fang, M., Chan, C. K., Hu, M. Size distributions and formation of ionic species in atmospheric particulate pollutants in Beijing, China: 1-inorganic ions. Atmos Environ 37 (2003),pp, 2991-3000. Ye, B., Ji, X., Yang, H., Yao, X., Chan, C. K., Cadle, S. H., Mulawa, P. A. Concentration and chemical composition of PM2.5 in Shanghai for a 1-year period. Atmos Environ 37 (2003),pp,499-510. Zhang, J., Ouyang, Z.Y., Miao, H., Wang, X.K., Ambient air quality trends and driving factor analysis in Beijing, 1983-2007, J Environ Sci-China 23(2011), pp. 2019-2028. Zhang, Q., Jimenez, J.L., Worsnop, D.R., Canagaratna, M., A case study of urban particle acidity and its influence on secondary organic aerosol, Environ Sci Technol 41(2007), pp. 3213-3219. Zhang, R., Jing, J., Tao, J., Hsu, S.C., Wang, G., Cao, J. et al., Chemical characterization and source apportionment of PM2.5 in Beijing: seasonal perspective, Atmos Chem Phys 13(2013), pp. 7053-7074.

ACCEPTED MANUSCRIPT Table captions Table 1 Cutpoints of stages of ELPI Table 2 the approximate detection limits of elements (ppb)

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Table 3 Mass concentrations of elements and water soluble ions in total, fine, sub-micrometer and

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ultra-fine particles (unit: ng/m3 for elements; μg/m3 for PM and water soluble ions)

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stage

1

2

3

4

5

6

7

8

9

10

11

12

13

Size/ μm

0.028

0.056

0.095

0.157

0.263

0.382

0.613

0.948

1.600

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Table 1 Cutpoints of stages of ELPI

4.000

6.680

9.920

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2.390

ACCEPTED MANUSCRIPT Table 2 the approximate detection limits of elements (ppb) Ca

Si

S

Pb

Ba

Mg

Fe

Se

Na

K

Al

Ti

Detection limits

221

216

92

1.11

1.43

40

40

0.22

55

102

33

5.14

Elements

V

Cr

Mn

Co

Ni

Cu

Zn

Ga

As

Sr

Zr

Mo

Detection limits

0.083

0.93

1.14

0.71

0.41

0.74

2.85

0.16

0.77

0.57

0.09

Elements

Ag

Cd

Sc

Sb

Tl

0.15

0.14

0.10

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0.11 0.027

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Detection limits

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0.17

ACCEPTED MANUSCRIPT Table3. Mass concentrations of elements and water soluble ions in total, fine, sub-micrometer and ultra-fine particles (unit: ng/m3 for elements; μg/m3 for PM and water soluble ions) Ultra-fine

sub-micrometer

Fine particles

articles(PM0.1)

particles(PM1)

（PM2.5）

PM

4.5±2.2

99.7±29.1

142.3±46

193.4±57.3

Sulfate

0.88±0.54

16.37±6.2

20.85±9.72

22.64±10.13

0.54±0.04

0.74±0.12

Nitrate

1.01±0.79

14.04±3.54

17.27±5.16

18.86±5.18

0.78±0.06

0.93±0.02

Ammonia

0.62±0.37

11.3±3.96

12.76±5.3

12.85±5.33

0.27±0.02

0.65±0.07

0.98±0.3

2.54±0.58

4.34±1.42

9.41±2.3

0.27±0.02

0.56±0.03

0.76±0.41

6.42±2.78

7.77±3.23

8.73±3.08

0.90±0.09

0.99±0.07

0.36±0.08

1.71±0.42

2.36±0.71

3.13±0.57

0.72±0.06

0.88±0.06

0.16±0.05

2.57±0.67

3.14±1.03

3.35±1.08

0.74±0.07

0.91±0.04

0.07±0.01

0.23±0.06

0.57±0.16

0.88±0.19

0.75±0.1

0.91±0.06

Al

41.4±55.9

293±106.2

1112.5±282.1

3475.5±602

0.09±0.04

0.32±0.04

Ca

31.5±63

411.8±152.7

2482.8±556.4

8168.8±1518.2

0.07±0.04

0.30±0.03

K

35.2±44.9

1740.7±505.2

2313.5±811.8

2801.1±931.1

0.63±0.04

0.82±0.03

Mg

22.2±27.6

184.9±53.9

677.6±118.6

1980.4±327.1

0.13±0.05

0.32±0.02

Na

27.7±39.9

735.6±211.2

1058.6±281.4

1470.6±341.9

0.5±0.09

0.72±0.08

Si

60±120

721.2±394.9

2073±245.1

5913.5±641

0.16±0.09

0.35±0.05

Sc

0.05±0.06

0.14±0.06

0.8±0.18

1.78±0.36

0.08±0.04

0.45±0.04

Ti

1.4±2.7

35.3±15.2

100.1±20.4

195.1±27.8

0.18±0.07

0.51±0.05

V

0.34±0.23

3.97±1.38

6.86±1.78

10.73±2.04

0.37±0.08

0.63±0.07

Cr

5.6±3.3

22.8±9.5

32.9±8

40.6±10.5

0.55±0.08

0.81±0.05

Mn

2.3±1.6

77.7±16.1

127.1±33.2

164±41

0.48±0.05

0.77±0.03

Fe

55±63

607.6±99.7

1504.2±166.6

4528.2±434.1

0.18±0.05

0.35±0.04

Co

0.15±0.31

0.44±0.62

1.01±0.69

1.77±0.98

0.22±0.34

0.46±0.32

Ni

2.9±2

13.2±2.9

17.6±1.8

22.4±3.3

0.59±0.07

0.79±0.05

Cu

2.2±1.4

43.5±17.3

61.6±27.6

71±29.4

0.62±0.07

0.86±0.04

Zn

10±5.9

317.4±107.9

462.8±174.1

502.1±184.4

0.64±0.1

0.92±0.03

Ga

0.74±0.54

10.13±2.91

13.31±3.72

16.5±4.19

0.61±0.06

0.8±0.03

Ge

0.42±0.28

4.33±1.76

5±1.88

5.53±1.94

0.78±0.06

0.9±0.03

As

0.89±0.57

27.17±11.96

42.04±25.4

46.32±28.97

0.64±0.16

0.91±0.03

Se

0.41±0.29

6.72±2.74

7.83±3.53

8±3.74

0.86±0.08

0.98±0.02

Sr

0.23±0.46

4.95±0.72

25.1±4.57

52.39±10.46

0.1±0.03

0.48±0.04

Zr

1.49±1.24

1.79±1.21

4.92±0.96

8.63±1.33

0.21±0.12

0.57±0.05

Mo

0.89±0.54

3.38±0.54

4.69±0.68

5.7±1.14

0.61±0.14

0.83±0.06

Ag

0.01±0.03

1.02±0.4

1.29±0.54

1.37±0.54

0.75±0.03

0.93±0.04

Cd

0.09±0.07

3.64±1.35

5.31±1.6

5.7±1.61

0.64±0.14

0.93±0.04

Sn

8.36±16.72

26.93±33.57

35.76±36.98

38±36.12

0.7±0.32

0.93±0.15

Sb

0.48±0.25

12.42±5.47

14.96±6.09

15.93±6.26

0.78±0.07

0.94±0.02

Cs

0.02±0.02

1.08±0.32

1.41±0.51

1.62±0.57

0.67±0.05

0.86±0.02

Ba

0.36±0.72

9.14±1.36

37.18±6.93

74.68±14.83

0.13±0.04

0.5±0.03

Hg

0.01±0.01

0.18±0.16

0.23±0.2

0.25±0.22

0.83±0.24

0.96±0.06

Mg

2+

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PM1/PM10 0.52±0.04

IP

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NU

K

+

MA

Na

D

+

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Cl

-

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Ca

AC

2+

PM10

PM2.5/PM10 0.73±0.04

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3.3±0.98

3.74±1.2

3.93±1.27

0.85±0.05

0.95±0.01

Pb

10.44±5.82

212.86±73.33

266.81±101.05

281.4±105.15

0.76±0.07

0.95±0.01

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Tl

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Fig. 1 Four types of size distributions of elements Fig. 2 The size distributions of water soluble inorganic species

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Fig. 3 The size distributions of mass in haze and normal days (left) and size distribution of

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main chemical components (right)

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Fig. 4 Average size distributions of (above) H+, total mass and total water soluble inorganic concentrations, and NH4+meas/NH4+neu ratio (below)

Fig. 5 The size distributions of enrichment factors of different chemical elements

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Fig. 6 Percentage values for the source profiles

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Fig.7 Size distribution of atmospheric elements reconstructed by source contributions

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Fig. 1 Four types of size distributions of elements

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Fig. 2 the size distributions of water soluble inorganic species

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Fig. 3 the size distributions of mass in haze and normal days (left) and size distribution of

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main chemical components (right)

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Fig. 4 average size distributions of (above) H+, total mass and total water soluble inorganic

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concentrations, and NH4+meas/NH4+neu ratio (below)

ACCEPTED MANUSCRIPT 300

300

250

Fe

zr

Co

Mg

SC

V

Mn

sr

Ba cs

ga

Cr

Ni

Sb

250

200

EFs

200

EFs

100

100

50

50

0

2

0.01

3

4

5 6 7 89

2

3

4

2

5 6 7 89

0.1 Dp [µm]

3

4

0

5 6 7 89

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150

10

3000

0.01

2

3

4

5 6 7 89

25000

mo

Tl

As

Zn

sn

Pb

20000

2000

EFs

EFs

15000 1500

10000 1000

2

3

4

5 6 7 89

2

3

0.1 Dp [µm]

4

2

5 6 7 89

1

3

4

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5000

0.01

3

4

0

5 6 7 89

10

5 6 7 89

2

3

4

5 6 7 89

1

Cd

10

Se

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ge

2500

0

2

0.1 Dp [µm]

Ag

Cu

500

IP

150

0.01

2

3

4

5 6 7 89

2

0.1 Dp [µm]

3

4

2

5 6 7 89

1

3

4

5 6 7 89

10

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Fig. 5 the size distributions of enrichment factors of different chemical elements

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% of Species

10 40%

1

20%

0.1

Vehicle

0% 100%

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80% 60% 40%

0% 100% 80%

0.01 1000

20% 0%

Al Ca Fe

K

Mg

V

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40%

Cr Mn Ni Cu Zn As Se Cd Sb Ba Pb Na

1 0.1 0.01

Sea salt

CE P

100 10 1 0.1 0.01

K

Mg Ca NH4 Cl SO4NO3 PM

Fig. 6 percentage values for the source profiles

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100 10

D

60%

0.1

aged coal combustion

MA

20%

1

Concentrations

20%

10

Concentrations

40%

100

Concentrations

IP

60%

0.01 1000

SC R

% of Species

80%

% of Species

1000 100

60%

0% 100%

% of Species

Concentrations

10000

Dust

80%

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% of Species

100%

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Fig.7 Size distribution of atmospheric elements reconstructed by source contributions

ACCEPTED MANUSCRIPT Highlights

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

A significant shift to larger fractions was observed for many species during heavy episode Size distributions of elements were classified into four types Ca2+ should be fully considered in the estimation of acidity NH3 is not enough to neutralize sulfate in accumulation mode Secondary aerosol and long-range transportation was the important source of PM2.5

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  