lable at ScienceDirect

Atmospheric Environment 123 (2015) 18e24

Contents lists avai

Atmospheric Environment

journal homepage: www.elsevier .com/locate/atmosenv

Diurnal variations of carbonaceous components, major ions, andstable carbon and nitrogen isotope ratios in suburban aerosols fromnorthern vicinity of Beijing

Nannan He a, b, Kimitaka Kawamura a, *, Yugo Kanaya c, Zifa Wang d

a Institute of Low Temperature Science, Hokkaido University, N19 W8, Kita-ku, Sapporo 060-0819, Japanb Graduate School of Environmental Science, Hokkaido University, N10 W5, Kita-ku, Sapporo 060-0810, Japanc Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Japand LAPC, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

h i g h l i g h t s

� Diurnal changes of carbonaceous and ionic components were studied in northern Beijing.� d13C and d15N of total carbon and nitrogen in aerosols were determined.� We found diurnal changes of chemical constitutes with day/night air mass transport.� In daytime pollutants are transported from Beijing to northern vicinity.� During rainfall events, all chemical components declined with the depletion of nitrate.

a r t i c l e i n f o

Article history:Received 9 May 2015Received in revised form19 September 2015Accepted 19 October 2015Available online 23 October 2015

Keywords:AerosolsInorganic ionsOrganic carbonElemental carbonIsotope ratios

* Corresponding author.E-mail address: kawamura@lowtem.hokudai.ac.jp

http://dx.doi.org/10.1016/j.atmosenv.2015.10.0521352-2310/© 2015 Elsevier Ltd. All rights reserved.

a b s t r a c t

We report diurnal variations of organic carbon (OC), elemental carbon (EC), water-soluble organic carbon(WSOC) and major ions as well as stable carbon and nitrogen isotope ratios (d13C and d15N) in ambientaerosols at a suburban site (Mangshan), 40 km north of Beijing, China. We found that aerosol chemicalcompositions were largely controlled by the air mass transport from Beijing in daytime with southerlywinds and by relatively fresh air mass in nighttime from the northern forest areas with northerly winds.Higher concentrations of aerosol mass and total carbon were obtained in daytime. Further, higher OC/ECratios were recorded in daytime (4.0 ± 1.7) than nighttime (3.2 ± 0.7), suggesting that OC is formed byphotochemical oxidation of gaseous precursors in daytime. Contributions of WSOC to OC were slightlyhigher in daytime (38%) than nighttime (34%), possibly due to secondary formation of WSOC in daytime.We also found higher concentrations of Ca2þ in daytime, which was originated from the constructiondust in Beijing area and transported to the sampling site. d13C ranged from �25.3 to �21.2‰(ave. �23.5 ± 0.9‰) in daytime and �29.0 to �21.4‰ (�24.0 ± 1.5‰) in nighttime, suggesting thatMangshan aerosols were more influenced by fossil fuel combustion products in daytime and byterrestrial C3 plants in nighttime. This study suggests that daytime air mass delivery from megacityBeijing largely influence the air quality at the receptor site in the north together with photochemicalprocessing of organic aerosols during the atmospheric transport, whereas the Mangshan site is coveredwith relatively clean air masses at night.

© 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Carbonaceous aerosols are enriched with organic carbon (OC)

(K. Kawamura).

rather than elemental carbon (EC). Almost 50% of global EC areemitted from fossil fuel combustion. OC has primary (anthropo-genic or biogenic) and secondary sources via atmospheric oxidationof volatile organics (Galbally and Goldstein, 2007). The formation ofsecondary organic aerosol (SOA) increases atmospheric levels of OCand hence OC/EC ratios are enhanced (Cabada et al., 2004). OC/ECratio has been used as a tool for the source apportionment of

Fig. 1. Location of the sampling site and Beijing city.

N. He et al. / Atmospheric Environment 123 (2015) 18e24 19

carbonaceous aerosol (Gnauk et al., 2008; Plaza et al., 2011).Significant fraction (20e70%) of organic carbon (OC) or total

carbon (TC) is water-soluble (Duarte et al., 2007; Semp�er�e andKawamura, 1994). Water-soluble organic carbon (WSOC) plays animportant role in the wet scavenging of atmospheric particles,formation of haze, and the impact on human health (Dreher, 2000;Turpin, 1999), and also acts as cloud condensation nuclei (CCN)influencing the global climate (Kanakidou et al., 2005). The emis-sion sources of primary WSOC include biomass burning (Fine et al.,2002; Nolte et al., 2001; Rogge et al., 1998; Schauer et al., 2001),cooking (He et al., 2004; Rogge et al., 1991; Schauer et al., 1999),paved road dust (Nolte et al., 2002) and automobiles (He et al.,2006; Rogge et al., 1993). However, major fraction of WSOC isderived from atmospheric oxidation of volatile organic compounds(VOCs) emitted from the primary sources (Kondo et al., 2007) viachemical aging during atmospheric transport (Rudich et al., 2007).

Stable carbon (d13C) and nitrogen (d15N) isotope ratios havebeen successfully used to better understand the contributions ofvarious sources to organic aerosols (Cachier et al., 1986; Kawamuraet al., 2004; Narukawa et al., 1999; Turekian et al., 1998). Thecontribution of nitrate (NO3

�) and ammonium (NH4þ) ions to total

aerosol nitrogen could provide additional information on thesource types of aerosols (Kundu et al., 2010; Pavuluri et al., 2010).Water-soluble inorganic ions (e.g., Kþ, SO4

2�, NH4þ, Ca2þ and

NO3�) are often considered as indicators of different origins (e.g.,

biomass burning, coal combustion, agricultural emission, NOx, andsoil/dust) (Wang et al., 2005a,b). Secondary formation of inorganicaerosols and their contribution to fog and haze formation havebeen discussed. For example, Guo et al. (2010) reported that 55% ofsummertime fine aerosol mass (<1.8 mm) in Beijing was derivedfrom secondary inorganic aerosols (sum of NH4

þ, NO3� and SO4

2�),which were responsible to the regional-scale pollution.

Beijing city is generally considered more polluted than its sub-urban areas due to geographically closer situation to emissionsources, e.g., vehicle exhaust and industrial areas. With continuouseconomic growth, air quality in Beijing has been deterioratingseriously (Cao et al., 2014; Yu et al., 2013). However, our recentstudy on dicarboxylic acids in the ambient aerosols from back-ground vicinity site (Mangshan) of Beijing demonstrated that theirconcentrations were much higher than those previously reportedin Beijing (He et al., 2014). Here, we present comprehensive datasets on OC, EC, WSOC, major ions, and stable carbon and nitrogenisotopes in the ambient aerosols from Mangshan site. We discussaerosol chemical properties to elucidate the source differencefollowing the wind patterns during day and night. The photo-chemical aging of atmospheric aerosols will also be discussedduring the transport from Beijing to the receptor site.

2. Aerosol collection and analytical methods

2.1. Site description and aerosol sampling

Aerosol (TSP) sampling was carried out in a suburban site nearthe entrance of the Mangshan national forest park (40�160N,116�170E; elevation of 187 m above sea level). The sampling site is40 km north of the center of Beijing. Forest-surrounded areasexpand to the north of Mangshan, while populous, urbanized andindustrialized areas including Beijing, Tianjin and Hebei Provincesexpand in the south of the sampling site (Fig. 1).

We collected 3-h daytime samples (n ¼ 26), 9-h daytime sam-ples (n ¼ 12), and 15-h nighttime samples (n ¼ 20) together with 4field blanks from 15th September to 5th October 2007 using a high-volume air sampler and pre-combusted quartz fiber filters(20 � 25 cm). Before and after the sampling, filters were stored in aclean glass jar (150 ml) with a Teflon-lined screw cap. The filter

samples were stored at �20 �C in a dark freezer room prior toanalysis. Meteorological parameters including precipitation,ambient temperature, relative humidity, and wind direction wererecorded at the sampling site during the campaign period. Theaverage temperature and relative humidity at Mangshan were25 �C and 57% in daytime and 17 �C and 78% in nighttime. Thedominant wind pattern was characterized by southwesterly wind(205�, on average) during daytime and northeasterly wind (30�, onaverage) during nighttime, being consistent mostly with air massback trajectories (He et al., 2014). Rainfall was observed at night ofSeptember 17, evening of September 26, and daytime of Oct 1. Lightrain lasted from October 4 to the end of the field campaign.

2.2. Chemical analyses

We conducted the measurements of total carbon (TC), total ni-trogen (TN), organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), stable carbon and nitrogen iso-topes of TC and TN, and inorganic ions in the ambient aerosolsamples. For TC and TN and their stable isotopes, a filter cut (area3.14 cm2) was placed into a pre-cleaned tin cup and shaped into arounded ball, which was introduced to an elemental analyzer (EA;model: NA 1500 NCS, Carlo Erba Instruments) using an auto-sampler. The sample was oxidized in a combustion column topromote the intensive oxidation of sample materials in an atmo-sphere of pure oxygen. Excess oxygen is removed and nitrogenoxides coming from the combustion column are reduced to mo-lecular nitrogen (N2) in the reduction column. The N2 and CO2derived from the samples were isolated on-line using a gas chro-matograph and then measured with a thermal conductivitydetector.

Aliquots of the N2 and CO2 gases were then introduced into anisotope ratio mass spectrometer (Thermo Quest, Delta Plus)through an interface (Thermo Quest, ConFlo II). The isotopic com-positions of carbon (d13C) and nitrogen (d15N) were determinedusing acetonitrile as a standard and the following isotope conver-sion equations:

d13Cð‰Þ ¼� ð13C=12CÞsample

ð13C=12CÞstandard� 1

�� 1000 (1)

N. He et al. / Atmospheric Environment 123 (2015) 18e2420

d15Nð‰Þ ¼� ð15N=14NÞsample

ð15N=14NÞstandard� 1

�� 1000 (2)

OC and EC were measured using a semi-continuous OC/ECanalyzer (Sunset Laboratory Inc., Portland, USA). A punch of thefilter (F14 mm) was placed in a quartz boat inside the thermaldesorption chamber of the analyzer, and then stepwise heating(IMPROVE) was applied. The generated CO2 was determined using aNDIR detector (Wang et al., 2005a).

For the measurements of WSOC, aliquots of filter samples(3.14 cm2) were extracted with 10 mL Milli-Q water, and filtratedthrough a disc filter (0.45 mm, GL Science) to remove the particlesand quartz filter debris. The solution was then injected into a car-bon analyzer (Shimadzu, TOC-5000). For the determination ofinorganic ions (SO4

2�, NO3�, Cl�, NH4

þ, Naþ, Ca2þ, Kþ and Mg2þ),we used a Metrohm 761 ion chromatograph (IC) system (Herisau,Switzerland). The details of the methodologies are presented inKundu et al. (2010) and Agarwal et al. (2010).

Procedural blanks were carried out in parallel with real samplesto account for any contamination. The data presented here arecorrected for the blanks. The analytical uncertainties of ion ana-lyses, and WSOC and TC and TN analyses were roughly 10e15%.Uncertainties in the measurements of stable carbon and nitrogenisotope ratios werewithin 0.2‰ and 0.3‰, respectively (Kawamuraet al., 2004).

3. Results and discussion

3.1. Total aerosol mass, TC, TN, d13C, d15N and TC/TN ratio

Concentrations of major constitutes in both daytime andnighttime samples are summarized in Table 1. Throughout the 3-week observation at Mangshan site, we found distinct diurnalvariations in the concentrations of total aerosol mass (AM), TC, TN,fractions of TC/AM and TN/AM as shown in Fig. 2. The concentra-tions of TC ranged from 6 to 51 mg m�3 (ave. 25 ± 13 mg m�3) indaytime samples and ranged from 4 to 35 mg m�3 (17 ± 10 mg m�3)in nighttime samples. Higher concentrations of TC were observedin daytime, which are associated with strong emission from Beijing,followed by atmospheric transport to the north. Pollutants emittedfrom the industrial areas of Beijing are important sources as well as

Table 1Concentrations of major constitutes in daytime and nighttime aerosol samples from Ma

Constitutes Daytime (n ¼ 38)

Min. Max.

Bulk analysesAerosol mass (mg m�3) 47.8 603Total carbon (TC) (mg m�3) 5.8 51.3Total nitrogen (TN) (mg m�3) 0.8 33.5Isotope ratio of TC (‰) �25.3 �21.2Isotope ratio of TN (‰) 9.0 20.8Organic carbon (OC) (mg m�3) 5.8 38.5Elemental carbon (EC) (mg m�3) 1.9 10.3Water-soluble organic carbon (WSOC) (mg m�3) 2.2 12.9

Inorganic ions (mg m�3)Naþ N.D. 2.2NH4

þ 0.5 26.6Kþ 0.1 5.4Ca2þ 0.5 14.2Mg2þ 0.1 1.7Cl� 0.0 7.0NO3

� 1.0 58.9SO4

2� 1.3 78.4

N.D. ¼ Not Detected.Note: All the numerical data in this table, except integers, show one demical place.

automobile exhausts from the heavy traffic (Hao and Wang, 2005;Schipani, 2014).

TC accounted for 9 ± 2% (range 3e14%) of AM in daytime, and11 ± 3% (4e17%) in nighttime. Concentrations of TC and its pro-portions to AM are higher in the source region and lower in theoutflow region far from the sources. TC and its proportion to AM inMangshan are lower than those observed in Beijing (49 mg m�3,17%) (Sekine et al., 1992) and Tokyo (24 mg m�3, 21%) (Kawamuraand Yasui, 2005), but significantly higher than those from marineaerosols in the Pacific (0.38 mg m�3, 0.75%) (Kawamura andSakaguchi, 1999), suggesting that the proportion of TC to AM inthe Mangshan aerosols decreased along with the increase of inor-ganic components during the transport. The concentrations of TNranged from 1 to 33 mg m�3 (ave. 13 ± 10 mg m�3) in daytime, ac-counting for 4 ± 2% (range 1e10%) of AM. In contrast, they rangedfrom 0 to 26 mg m�3 (10 ± 9 mg m�3) in nighttime, accounting for6 ± 3% (1e10%) of AM. TC/TN ratios ranged from 1.0 to 14.6 (ave.3.2 ± 2.5) in daytime, and ranged from 0.7 to 9.5 (2.8 ± 2.2) innighttime, but they did not indicate distinct diurnal changes in theMangshan aerosols. The higher ratios in daytime suggest morecontributions of organic aerosols from Beijing area by southwest-erly wind.

d13C of TC and d15N of TN showed diurnal variations in most ofthe sampling days as shown in Fig. 3. d13C shows minimumin nighttime, whose values ranged from �25.3 to �21.2‰(ave. �23.5 ± 0.9‰) in daytime, and from �29.0 to �21.4‰(�24.0 ± 1.5‰) in nighttime (Fig. 3a). The d13C values in Mangshanaerosols indicate mixed sources of marine phytoplankton (�15to �28‰), natural gas (�21 to �90‰), fossil fuel combustion (coaland petroleum) (�25 to �31‰), and terrestrial C3 plants (�23to �30‰) (Deines, 1980; Mook et al., 1983; Rau et al., 1982).However, the sampling site is far from the ocean and located in thenational forest park, hence, fossil fuel combustion and terrestrial C3plants are considered as two major sources. Further, northeastwinds in nighttime probably bring organic matter of terrestrial C3plant origin from the forest areas to the receptor site. Diurnal var-iations of d15N will be discussed in Section 3.4.

3.2. OC and EC

Concentrations of OC and EC and OC/EC ratios in Mangshan

ngshan.

Nighttime (n ¼ 20)

Ave. S.D Min. Max. Ave. S.D

267 129 29.4 270 146 78.624.9 13.4 3.5 34.5 16.9 9.512.6 9.7 0.4 25.8 10.5 8.6

�23.5 0.9 �29.0 �21.4 �24.0 1.515.0 2.4 13.1 21.3 16.8 2.522.2 7.9 3.5 29.0 14.7 7.26.0 2.6 0.7 9.9 4.8 2.46.8 3.5 0.8 10.2 4.2 2.4

0.1 0.4 N.D. 1.9 0.2 0.49.8 8.0 0.3 21.4 8.1 7.11.8 1.2 0.3 4.6 1.5 1.16.9 3.7 0.2 7.6 2.9 1.80.7 0.4 0.0 1.2 0.4 0.30.9 1.2 0.1 6.1 0.9 1.3

23.5 19.4 0.7 47.2 18.2 14.722.0 19.8 1.2 66.1 20.1 19.5

Fig. 2. Concentrations of (a) aerosol mass (AM), (b) total carbon (TC), (c) total nitrogen(TN), (d) ratios of TC/AM, and (e) ratios of TN/AM in Mangshan aerosol samples. Hollowplots represent daytime samples and solid plots represent nighttime samples.

Fig. 3. Stable (a) carbon isotope ratios (d13C) of TC and (b) nitrogen isotope ratios(d15N) of TN in Mangshan aerosols. Hollow plots represent daytime and solid plotsrepresent nighttime samples.

N. He et al. / Atmospheric Environment 123 (2015) 18e24 21

samples show distinct diurnal variations. OC concentrations rangedfrom 6 to 39 mg m�3 (ave. 22 ± 8 mg m�3) in daytime and4e29 mgm�3 (15± 7 mgm�3) in nighttime (Table 1). Higher levels ofOC in daytime may be caused by the atmospheric transport ofpolluted air masses from Beijing and the photochemical productionof OC via the oxidation of anthropogenic hydrocarbons during the

transport in daytime. Average concentrations of EC were6 ± 3 mg m�3 (range: 2e10 mg m�3) in daytime, and 5 ± 2 mg m�3

(1e10 mgm�3) in nighttime. OC and EC concentrations of Mangshanaerosols are comparable to those reported in Hong Kong (12.4 and2.5 mg m�3, respectively), but lower than other Chinese cities (23.9and 4.2 mg m�3 in Guangzhou, and 23.7 and 4.6 mg m�3 in Xi'an,respectively) (Duan et al., 2007; Shen et al., 2009).

OC/EC ratios of Mangshan aerosols ranged from 2.1 to 9.3 with amean of 4.0 ± 1.7 in daytime, and 2.0 to 5.0 with a mean of 3.2 ± 0.7in nighttime. Generally, OC/EC ratios depend on emission sourcesand formation of secondary organic aerosols (SOA). The higher OC/EC ratios in daytimemay be attributed to different emission sourcesthat are rich in OC and are transported by the southerly wind indaytime. Another possibility may be a large production of SOA byphotochemical processing during the transport from the industrialarea of Beijing to Mangshan site in daytime. Interestingly, He et al.(2014) reported increased concentrations of dicarboxylic acids,which may serve as markers of photochemical production, andrelated compounds in daytime during the same campaign. Theproduction of dicarboxylic acids and related compounds in photo-chemical process should contribute to the increase of OC/EC ratiosin daytime.

3.3. Water-soluble organic carbon (WSOC)

In the present study, WSOC in daytime samples ranged from 2 to13 mg m�3 (ave. 7 ± 4 mg m�3), accounting for 21e54% (38 ± 7%) ofOC. In contrast, WSOC in nighttime samples ranged from 1 to10 mg m�3 (4 ± 2 mg m�3), accounting for 20e45% (34 ± 6%) of OC.Concentrations of WSOC in Mangshan aerosols generally showeddaytime maxima and nighttime minima as illustrated in Fig. 4a.WSOC/OC ratios also show similar diurnal trend (Fig. 4b). Based onthe enhanced WSOC/OC values in daytime, we emphasize thatsecondary chemical processes are more important in controllingthe aerosol composition in the northern vicinity of Beijing than

Fig. 4. Temporal variations in (a) the concentrations of WSOC, and (b) WSOC/OC ratiosin Mangshan aerosol samples. Open circles represent daytime and solid circlesrepresent nighttime samples.

Fig. 5. (a) Concentrations of total inorganic ions, and (b) proportions of each ion intotal ions measured in the Mangshan aerosol samples.

N. He et al. / Atmospheric Environment 123 (2015) 18e2422

primary sources in daytime. This can be further supported byrelatively high OC/EC ratios in daytime. Interestingly, Jaffrezo et al.(2005) reported that aged aerosols have higher fractions (>40%) ofWSOC in OC.

3.4. Water-soluble inorganic ions

Fig. 5a shows temporal variation of the concentrations of totalions during the campaign. Although total ions peaked in daytime inmost days, they dropped markedly when precipitation took placeespecially in September 17 and 26 (Fig. 5a). Fig. 5b presents thefractions of SO4

2�, NO3� and NH4

þ in total ions, which are alsosignificantly influenced by rainfall. SO4

2� and NO3� are the most

abundant ions in both day- and nighttime. The concentrations ofSO4

2� ranged from 1 to 78 mg m�3 (ave. 22 ± 20 mg m�3), ac-counting for 32 ± 9% of total ions in daytime, while its concentra-tions ranged from 1 to 66 mg m�3 (ave. 20 ± 20 mg m�3) innighttime, accounting for 36 ± 10%. Compared to SO4

2�, the relativehigher concentrations of NO3

� in daytime and the relative lowerconcentrations of it in nighttime are possibly due to: (1) differentconcentrations of their precursors in daytime. The southerly windcarried more precursors of NO3

�, which are emitted from vehicleand industry activities, rather than those of SO4

2�, which arederived from fossil fuel combustion; (2) in nighttime, there wereless sources of NO3

� than SO42�; besides, NO3 can serve as a main

oxidant in nighttime in the reaction with biogenic VOCs (such asisoprene and monoterpenes emitted in the forest area) to producemethyglyoxal and glyoxal (Warneke et al., 2004), which lead to theconsumption of NO3

�. It is of interest to note that SO42� and NO3

�

preferentially declined during the rainfall events (Fig. 5b), sug-gesting that the decrease of these two ions may have been due tocombined effects of wet removal (both in-cloud and below-cloud)and/or air mass changes. However, the data of wind direction did

not indicate any changes in air mass origins.Because SO4

2� is produced by photochemical oxidation of SO2(fossil fuel derived pollutant), its higher concentrations demon-strate that air quality of Mangshan is heavily polluted. Levels ofNO3

� show the similarity to those of SO42�. Concentrations of

NO3� ranged from 1 to 59 mg m�3 (ave. 24 ± 19 mg m�3) in daytime,

accounting for 31 ± 10% of total ions. In contrast, its nighttimeconcentrations ranged from 1 to 47 mg m�3 (av. 18 ± 15 mg m�3),accounting for 32 ± 10% of total ions. The third most abundant ionwas NH4

þ, whose daytime concentrations were 1e27 mg m�3 (ave.10 ± 8 mg m�3), accounting for 14 ± 3% of total ions. Their nighttimeconcentrations were 0e21 mg m�3 (ave. 8 ± 7 mg m�3), accountingfor 14 ± 4% of total ions. We obtained a good ion balance betweenanions and cations (R2 ¼ 0.97) for all samples during the campaign(the result is not shown as a figure). However, the R2 is 0.92 fordaytime samples and 0.98 for nighttime. During the samplingperiod, all nighttime samples were collected for 15 h (from 6pm to9am), while daytimes were partially collected from every 3 h (from9am to 12am, from 12am to 3pm, from 3pm to 6pm) and partiallycollected for 9 h (from 9am to 6pm). The difference of ion balancesbetween daytime and nighttime samples might be attributed tothat the numbers of daytime samples, which subjected to the sta-tistics of wet removal during rain event, are more than those ofnighttime samples. And the decrease in the concentrations of sul-fate and nitrate due to wet removal may cause the plots of daytimesamples in the figure of ion balance deviating from the trend lineand lead to the relatively lower value of R2 in daytime.

Most ions did not show clear diurnal variations. However, Ca2þ

showed a distinct diurnal variation with twice higher concentra-tions in daytime (range of 1e14 mg m�3, mean of 7 ± 4 mg m�3,relative abundance of 16 ± 11%) than nighttime (0e8 mg m�3,3 ± 2 mg m�3, 10 ± 9%). Zhang and Iwasaka (1999) reported thatCa2þ in Beijing aerosols is mostly derived from construction dust.From the year of 2005, widespread construction activities haveboomed in China, especially in Beijing and its vicinity. Theconstruction-emitted dusts may have enhanced the atmosphericlevels of Ca2þ in Beijing in daytime (Hu et al., 2005). As the wind

N. He et al. / Atmospheric Environment 123 (2015) 18e24 23

speed of daytime and nighttime samples in a same sampling daywas comparable during the sampling period, therefore, the relativemore abundant Ca2þ in daytime samples might have been deliv-ered from Beijing due to construction activities.

Strong correlations were found between WSOC and NO3� in

both daytime (R2 ¼ 0.68) and nighttime (R2 ¼ 0.67), while fairlygood correlations were obtained between WSOC and SO4

2�

(R2 ¼ 0.41 in daytime and R2 ¼ 0.40 in nighttime). The strongcorrelation between WSOC and NO3

� indicates that WSOC may belargely produced by photochemical oxidation of organic precursorsemitted with exhausts from industry activities and automobiles.We also found good correlations between NO3

� and TN (R2 ¼ 0.89in daytime, R2 ¼ 0.67 in nighttime) and NH4

þ and TN (R2 ¼ 0.93 indaytime, R2 ¼ 0.92 in nighttime) in Mangshan aerosols, demon-strating that aerosol nitrogen is largely associated with NO3

� andNH4

þ. Interestingly, at Mangshan site, NH4þeN is more abundant

than NO3�eN by 10e20% in the Mangshan aerosols. This result

suggests higher emissions of NH3 and lower emissions of NOx inthe northern vicinity of Beijing due to agricultural activities, whichis consistent with previous studies on NH4

þ and NO3� (Shen et al.,

2011; Zhang et al., 2008).It is also noteworthy that positive correlation between TN and

(NO3� þ NH4

þ)eN is very strong (R2 ¼ 0.96 in daytime andR2¼ 0.88 in nighttime) as shown in Fig. 6. Although some points arescattered somehow in the figure, the slope of regression line is closeto unity, indicating that combination of nitrate and ammoniumaccounts for most of aerosol nitrogen. This result means thatorganic nitrogen is negligible in the Manshan aerosols, being incontrast to the marine aerosols reported from Cape Hedo, OkinawaIsland in the western North Pacific Rim, an outflow region of Asiandusts and pollutants, in which organic nitrogen accounted for onethird of TN (Kunwar et al., 2015). In a deciduous broadleaf forestfrom Sapporo, Japan, high abundances of water-soluble organicnitrogen were reported especially in summer (Miyazaki et al.,2014).

As shown in Fig. 3b, diurnal variations in d15N of TN are char-acterized by smaller values in daytime samples and greater valuesin nighttime samples in most sampling dates. Higher d15N values innighttime samples may be associated with ammonium nitrogen(NH4

þeN) originated from the forest areas in the north of Man-gshan. During the transport, isotopic exchange between gaseousNH3 and aerosol NH4

þ may occur in the atmosphere, causing anisotopic enrichment of heavier nitrogen (15N) in aerosol phase

Fig. 6. Correlation plots between (NO3� þ NH4

þ)eN and total nitrogen (TN) in theMangshan aerosols. Open circles represent daytime and solid circles represent night-time samples.

NH4þ (Pavuluri et al., 2010).

4. Conclusions

This study reveals diurnal and temporal variations of major ionsin the aerosols collected in the vicinity of Beijing. Higher concen-trations of Ca2þ were found in daytime, suggesting thatconstruction-derived aerosols were delivered from Beijing to thenorthern vicinity. Based on the good correlation between nitric acid(NO3

�) and sulfuric acid (SO42�), we suggest that inorganic acids

are largely titrated by gaseous NH3 and particulate Ca2þ in the at-mosphere during the transport. Higher OC/EC ratios and WSOC/OCratios were observed in daytime, demonstrating that secondaryorganic aerosols are significantly produced in daytime during theatmospheric transport.

During the field campaign, several rainfall events happened overthe sampling site. We observed significant decreases in the con-centrations of aerosol mass, TC, TN, WSOC and major ions duringthe rain events.We also found the depletion of nitrate and sulfate inthe ambient aerosols during the rain events, suggesting that fineparticles enriched with these water-soluble ions may act as cloudcondensation nuclei. Within a few days after the rain events, theatmospheric levels of TC, TN,WSOC andmajor ions recovered in thesite both by the transports and secondary formation in theatmosphere.

Greater d15N values of TN in nighttime suggest that TN is largelyassociated with ammonium originated from the forest areas in thenorth, which is subjected to isotopic exchange between gaseousNH3 and aerosol NH4

þ during the transport, causing an enrichmentof 15N in aerosols. d13C (�23.5‰ on average) of TC suggests thatfossil fuel combustion and terrestrial C3 plants are two majorsources of aerosol carbon.

At Mangshan site, the aerosols coming from the southwest indaytime deliver more pollutants from the industrial regions inBeijing with photochemical processing during the transport to thesampling site.When thewind direction changed to northeasterly innighttime, organics emitted from the forest areas are mixed withurban aerosols.

This study on diurnal variations of ambient aerosols demon-strates that atmospheric transport of air pollutants from Beijing tothe northern receptor site is significant with photochemicaltransformation of both organic and inorganic components duringthe transport.

Acknowledgment

We appreciate K Okuzawa for the help of sample collection, andEri Tachibana for experimental support. We acknowledge thefinancial support by Japan Society for the Promotion of Science(JSPS) through grant-in-aid Nos. 19204055 and 24221001. Thefinancial support by the Global Environment Research Fund (B-051)of the Ministry of the Environment, Japan should also beacknowledged for the shipping of the sampling equipment to theMangshan site.

References

Agarwal, S., Aggarwal, S.G., Okuzawa, K., Kawamura, K., 2010. Size distributions ofdicarboxylic acids, ketoacids, a-dicarbonyls, sugars, WSOC, OC, EC and inorganicions in atmospheric particles over Northern Japan: implication for long-rangetransport of Siberian biomass burning and East Asian polluted aerosols. Atmos.Chem. Phys. 10 (13), 5839e5858.

Cabada, J.C., Pandis, S.N., Subramanian, R., Robinson, A.L., Polidori, A., Turpin, B.,2004. Estimating the secondary organic aerosol contribution to PM2.5 using theEC tracer method. Aerosol Sci. Technol. 38, 140e155.

Cachier, H., Buat-M�ENard, P., Fontugne, M., Chesselet, R., 1986. Long-range transportof continentally-derived particulate carbon in the marine atmosphere:

N. He et al. / Atmospheric Environment 123 (2015) 18e2424

evidence from stable carbon isotope studies. Tellus B 38B, 161e177.Cao, C., Jiang, W., Wang, B., Fang, J., Lang, J., Tian, G., Jiang, J.K., Zhu, T.F., 2014.

Inhalable microorganisms in Beijing's PM2. 5 and PM10 pollutants during asevere smog event. Environ. Sci. Technol. 48, 1499e1507.

Deines, P., 1980. The carbon isotopic composition of diamonds: relationship todiamond shape, color, occurrence and vapor composition. Geochim. Cosmo-chim. Acta 44, 943e961.

Dreher, K.L., 2000. Particulate matter physicochemistry and toxicology: in search ofcausality-A critical perspective. Inhal. Toxicol. 12, 45e57.

Duan, J., Tan, J., Cheng, D., Bi, X., Deng, W., Sheng, G., Fu, J., Wong, M.H., 2007.Sources and characteristics of carbonaceous aerosol in two largest cities in PearlRiver Delta Region, China. Atmos. Environ. 41, 2895e2903.

Duarte, R.M.B.O., Santos, E.B.H., Pio, C.A., Duarte, A.C., 2007. Comparison of struc-tural features of water-soluble organic matter from atmospheric aerosols withthose of aquatic humic substances. Atmos. Environ. 41, 8100e8113.

Fine, P.M., Cass, G.R., Simoneit, B.R.T., 2002. Chemical characterization of fine par-ticle emissions from the fireplace combustion of woods grown in the SouthernUnited States. Environ. Sci. Technol. 36, 1442e1451.

Galbally, A.H., Goldstein, I.E., 2007. Known and unexplored organic constituents inthe earth's atmosphere. Environ. Sci. Technol. http://dx.doi.org/10.1021/es072476p.

Gnauk, T., Müller, K., van Pinxteren, D., He, L.-Y., Niu, Y., Hu, M., Herrmann, H., 2008.Size-segregated particulate chemical composition in Xinken, Pearl River Delta,China: OC/EC and organic compounds. Original Research Article Atmos. Envi-ron. 42, 6296e6309.

Guo, S., Hu, M., Wang, Z.B., Slanina, J., Zhao, Y.L., 2010. Size-resolved aerosol water-soluble ionic compositions in the summer of Beijing: implication of regionalsecondary formation. Atmos. Chem. Phys. 10 (3), 947e959.

Hao, J., Wang, L., 2005. Improving urban air quality in China: Beijing case study.J. Air Waste Manag. Assoc. 55, 1298e1305.

He, L.-Y., Hu, M., Huang, X.-F., Yu, B.-D., Zhang, Y.-H., Liu, D.-Q., 2004. Measurementof emissions of fine particulate organic matter from Chinese cooking. Atmos.Environ. 38, 6557e6564.

He, L.-Y., Hu, M., Huang, X.-F., Zhang, Y.-H., Tang, X.-Y., 2006. Seasonal pollutioncharacteristics of organic compounds in atmospheric fine particles in Beijing.Sci. Total Environ. 359, 167e176.

He, N., Kawamura, K., Okuzawa, K., Pochanart, P., Liu, Y., Kanaya, Y., Wang, Z.F., 2014.Diurnal and temporal variations of water-soluble dicarboxylic acids and relatedcompounds in aerosols from the northern vicinity of Beijing: implication forphotochemical aging during atmospheric transport. Sci. Total Environ. 499,154e165.

Hu, M., Zhao, Y., He, L., Huang, X., Xiaoyan, T., Yao, X., Chan, C.K., 2005. Mass sizedistribution of Beijing particulate matters and its inorganic water-soluble ionsin winter and summer (in Chinese). Environ. Sci. 26, 1e6.

Jaffrezo, J.L., Aymoz, G., Delaval, C., Cozic, J., 2005. Seasonal variations of the watersoluble organic carbon mass fraction of aerosol in two valleys of the FrenchAlps. Atmos. Chem. Phys. 5 (10), 2809e2821.

Kanakidou, M., Seinfeld, J.H., Pandis, S.N., Barnes, I., Dentener, F.J., Facchini, M.C.,Van Dingenen, R., Ervens, B., Nenes, A., Nielsen, C.J., Swietlicki, E., Putaud, J.P.,Balkanski, Y., Fuzzi, S., Horth, J., Moortgat, G.K., Winterhalter, R., Myhre, C.E.L.,Tsigaridis, K., Vignati, E., Stephanou, E.G., Wilson, J., 2005. Organic aerosol andglobal climate modelling: a review. Atmos. Chem. Phys. 5, 1053e1123.

Kawamura, K., Kobayashi, M., Tsubonuma, N., Mochida, M., Watanabe, T., Lee, M.,2004. Organic and inorganic compositions of marine aerosols from East Asia:seasonal variations of water-soluble dicarboxylic acids, major ions, total carbonand nitrogen, and stable C and N isotopic composition. In: Hill, Ronald J.,Leventhal, J., Aizenshtat, Z., Baedecker, M.J., Claypool, G., Eganhouse, R.,Goldhaber, M., Peters, K. (Eds.), The Geochemical Society Special Publications.Elsevier, pp. 243e265.

Kawamura, K., Sakaguchi, F., 1999. Molecular distributions of water soluble dicar-boxylic acids in marine aerosols over the Pacific Ocean including tropics.J. Geophys. Res. Atmos. 104, 3501e3509.

Kawamura, K., Yasui, O., 2005. Diurnal changes in the distribution of dicarboxylicacids, ketocarboxylic acids and dicarbonyls in the urban Tokyo atmosphere.Atmos. Environ. 39, 1945e1960.

Kondo, Y., Miyazaki, Y., Takegawa, N., Miyakawa, T., Weber, R.J., Jimenez, J.L.,Zhang, Q., Worsnop, D.R., 2007. Oxygenated and water-soluble organic aerosolsin Tokyo. J. Geophys. Res. Atmos. 112, D01203.

Kundu, S., Kawamura, K., Andreae, T.W., Hoffer, A., Andreae, M.O., 2010. Diurnalvariation in the water-soluble inorganic ions, organic carbon and isotopiccompositions of total carbon and nitrogen in biomass burning aerosols from theLBA-SMOCC campaign in Rondonia, Brazil. J. Aerosol Sci. 41, 118e133.

Kunwar, Bhagawati, Torii, K., Zhu, C., Fu, Pingqing, Kawamura, Kimitaka, 2015.Springtime variations of organic and inorganic constituents in submicronaerosols (PM1.0) from Cape Hedo, Okinawa. Atmos. Environ. Special Issue(Chemical Characterization of SOA), (in press).

Miyazaki, Y., Fu, P., Ono, K., Tachibana, E., Kawamura, K., 2014. Seasonal cycles ofwater-soluble organic nitrogen aerosols in a deciduous broadleaf forest innorthern Japan. J. Geophys. Res. Atmos. 119.

Mook, W.G., Koopmans, M., Carter, A.F., Keeling, C.D., 1983. Seasonal, latitudinal, and

secular variations in the abundance and isotopic ratios of atmospheric carbondioxide: 1. Results from land stations. J. Geophys. Res. Oceans 88, 10915e10933.

Narukawa, M., Kawamura, K., Takeuchi, N., Nakajima, T., 1999. Distribution ofdicarboxylic acids and carbon isotopic compositions in aerosols from 1997Indonesian forest fires. Geophys. Res. Lett. 26, 3101e3104.

Nolte, C.G., Schauer, J.J., Cass, G.R., Simoneit, B.R.T., 2001. Highly polar organiccompounds present in wood smoke and in the ambient atmosphere. Environ.Sci. Technol. 35, 1912e1919.

Nolte, C.G., Schauer, J.J., Cass, G.R., Simoneit, B.R.T., 2002. Trimethylsilyl derivativesof organic compounds in source samples and in atmospheric fine particulatematter. Environ. Sci. Technol. 36, 4273e4281.

Pavuluri, C.M., Kawamura, K., Tachibana, E., Swaminathan, T., 2010. Elevated ni-trogen isotope ratios of tropical Indian aerosols from Chennai: implication forthe origins of aerosol nitrogen in South and Southeast Asia. Atmos. Environ. 44,3597e3604.

Plaza, J., Artí~nano, B., Salvador, P., G�omez-Moreno, F.J., Pujadas, M., Pio, C.A., 2011.Short-term secondary organic carbon estimations with a modified OC/EC pri-mary ratio method at a suburban site in Madrid (Spain). Original ResearchArticle Atmos. Environ. 45, 2496e2506.

Rau, G.H., Sweeney, R.E., Kaplan, I.R., 1982. Plankton 13C: 12C ratio changes withlatitude: differences between northern and southern oceans. Deep Sea Res. PartA. Oceanogr. Res. Pap. 29, 1035e1039.

Rogge, W.F., Hildemann, L.M., Mazurek, M.A., Cass, G.R., 1998. Sources of fineorganic aerosol. 9. Pine, oak, and synthetic log combustion in residential fire-places. Environ. Sci. Technol. 32, 13e22.

Rogge, W.F., Hildemann, L.M., Mazurek, M.A., Cass, G.R., Simoneit, B.R.T., 1991.Sources of fine organic aerosol. 1. Charbroilers and meat cooking operations.Environ. Sci. Technol. 25, 1112e1125.

Rogge, W.F., Mazurek, M.A., Hildemann, L.M., Cass, G.R., Simoneit, B.R.T., 1993.Quantification of urban organic aerosols at a molecular level: identification,abundance and seasonal variation. Atmos. Environ. Part A. General Top. 27,1309e1330.

Rudich, Y., Donahue, N.M., Mentel, T.F., 2007. Aging of organic aerosol: bridging thegap between laboratory and field studies. Annu. Rev. Phys. Chem. 58, 321e352.

Schauer, J.J., Kleeman, M.J., Cass, G.R., Simoneit, B.R.T., 1999. Measurement ofemissions from air pollution sources. 1. C1 through C29 organic compoundsfrom meat charbroiling. Environ. Sci. Technol. 33, 1566e1577.

Schauer, J.J., Kleeman, M.J., Cass, G.R., Simoneit, B.R.T., 2001. Measurement ofemissions from air pollution sources. 3. C1�C29 organic compounds fromfireplace combustion of wood. Environ. Sci. Technol. 35, 1716e1728.

Schipani, S., 2014. The red Zone: why Beijing's air pollution crisis is more compli-cated than you think. J. Sustain. Dev. 12, 76e81.

Sekine, Y., Hashimoto, Y., Makamura, T., Chen, Z., Mitsuzawa, S., 1992. Character-ization of atmospheric aerosol components at Beijing, China. J. Jpn. Soc. AirPollut. 27, 237e245.

Semp�er�e, R., Kawamura, K., 1994. Comparative distributions of dicarboxylic acidsand related polar compounds in snow, rain and aerosols from urban atmo-sphere. Atmos. Environ. 28, 449e459.

Shen, Z., Cao, J., Tong, Z., Liu, S., Reddy, L.S.S., Han, Y., Zhang, T., Zhou, J., 2009.Chemical characteristics of submicron particles in winter in Xi'an. Aerosol AirQual. Res. 9, 80e93.

Shen, J., Liu, X., Zhang, Y., Fangmeier, A., Goulding, K., Zhang, F., 2011. Atmosphericammonia and particulate ammonium from agricultural sources in the NorthChina Plain. Atmos. Environ. 45, 5033e5041. http://dx.doi.org/10.1016/j.atmosenv.2011.02.031.

Turekian, V.C., Macko, S., Ballentine, D., Swap, R.J., Garstang, M., 1998. Causes of bulkcarbon and nitrogen isotopic fractionations in the products of vegetation burns:laboratory studies. Chem. Geol. 152, 181e192.

Turpin, B.J., 1999. Peer reviewed: options for characterizing organic particulatematter. Environ. Sci. Technol. 33, 76Ae79A.

Wang, H., Kawamura, K., Shooter, D., 2005a. Carbonaceous and ionic components inwintertime atmospheric aerosols from two New Zealand cities: implications forsolid fuel combustion. Atmos. Environ. 39, 5865e5875.

Wang, Y., Zhuang, G., Tang, A., Yuan, H., Sun, Y., Chen, S., Zheng, A., 2005b. The ionchemistry and the source of PM2.5 aerosol in Beijing. Atmos. Environ. 39,3771e3784.

Warneke, C., de Gouw, J.A., Goldan, P.D., Kuster, W.C., Williams, E.J., Lerner, B.M.,Fehsenfeld, F.C., 2004. Comparison of daytime and nighttime oxidation ofbiogenic and anthropogenic VOCs along the New England coast in summerduring New England Air Quality Study 2002. J. Geophys. Res.: Atmos.(1984e2012), 109(D10).

Yu, L., Wang, G., Zhang, R., Zhang, L., Song, Y., Wu, B.B., Li, X.F., An, K., Chu, J.H., 2013.Characterization and source apportionment of PM2. 5 in an urban environmentin Beijing. Aerosol Air Qual. Res. 13, 574e583.

Zhang, D., Iwasaka, Y., 1999. Nitrate and sulfate in individual Asian dust-stormparticles in Beijing, China in spring of 1995 and 1996. Atmos. Environ. 33 (19),3213e3223.

Zhang, Y., Liu, X.J., Fangmeier, A., Goulding, K.T.W., Zhang, F.S., 2008. Nitrogen inputsand isotopes in precipitation in the North China Plain. Atmos. Environ. 42,1436e1448. http://dx.doi.org/10.1016/j.atmosenv.2007.11.002.