Fine particle measurements at two background sites in Korea between 1996 and 1997

1Present address: Department of Environmental Sciences,Rutgers University, USA.

*Corresponding author. Present address: Department of En-vironmental Science and Engineering, Ewha Womans Univer-sity, Seoul 120-750, South Korea. Tel.: #82-2-3277-2832; fax:#82-2-3277-3275.

E-mail address: [email protected] (Y.P. Kim).

Atmospheric Environment 35 (2001) 635}643

Fine particle measurements at two background sites in Koreabetween 1996 and 1997

Jong Hoon Lee!,",1, Yong Pyo Kim!,*, Kil-Choo Moon!,Hui-Kang Kim", Chong Bum Lee#

!Global Environmental Research Center, Korea Institute of Science and Technology, 39-1 Hawolkokdong Sungbukku, PO Box 131,Cheongryang, Seoul 136-791, South Korea

"Department of Environmental Engineering, Konkuk University, 93-1 Mojindong Kwangjinku, Seoul 143-701, South Korea#Department of Environmental Science, Kangwon National University, Chunchon 200-701, South Korea

Received 9 February 2000; accepted 12 July 2000

Abstract

Five intensive "eld measurements were carried out at two background sites in Korea; Kosan and Kangwha duringspring, fall, and winters of 1996 and 1997 to investigate the characteristics of long-range transport of air pollutants innortheastern Asia. Fine particles (PM

2.5) were collected by low-volume samplers and the concentrations of major ions,

organic and elemental carbons, and nitric acid were quanti"ed. The concentrations of anthropogenic species in PM2.5

measured at both sites were generally higher than those at other background areas, Nagano, Japan and San Nicolas Is.,USA due to continental out#ow of air pollutants, but lower than those at an urban background site, Qingdao, China.The major components of PM

2.5were sulfate, organic carbon (OC), and ammonium for Kosan and sulfate, OC,

ammonium, and nitrate for Kangwha. The major fractions of sulfate at both sites are non-sea-salts (nss) sulfate. Based onthe relationship among major anthropogenic species, analysis of the nss sulfate to total nitrate molar ratios, andbackward air parcel trajectories, it was found that "ne particles measured at both sites during the measurement periodsare mainly coming from China. At Kosan, the concentrations of anthropogenic species were higher when air parcels werecoming from southern China than when air parcels were from northern China. At Kangwha, however, the di!erences ofthe concentrations were not statistically signi"cant since most air parcels were from northern China and local e!ects areprominent. ( 2001 Elsevier Science Ltd. All rights reserved.

Keywords: PM2.5

; Ammonium to nss sulfate ratio; Nss sulfate to nitrate ratio; Long-range transport; Northeastern Asia

1. Introduction

Emissions of anthropogenic air pollutants in north-eastern Asia have been increasing drastically in the pastdecade. Table 1 shows the recent emission amounts ofsulfur dioxide and nitrogen oxides in the region along

with those of USA. China emits most of the sulfur dioxideand a major fraction of the nitrogen oxides in the region.Since the prevailing winds in the region except summerare westerly, it is expected that the anthropogenic airpollutants emitted from China be transported to Korea,Japan, the North Paci"c, and as far as North America.

A few studies have been carried out in Korea in rela-tion with long-range transport of air pollutants in theregion. These studies have focused on measurements ofeither air pollutants at Cheju Island or total suspendedparticles (TSP). Kim et al. (1998a) observed high concen-tration of non-sea-salt (nss) SO2~

4in TSP at Cheju Island

during spring 1994 and reported that most air parcelsarriving at the site were from China. Chen et al. (1997)

AEA=3117=Durai=Venkatachala=BG

1352-2310/01/$ - see front matter ( 2001 Elsevier Science Ltd. All rights reserved.PII: S 1 3 5 2 - 2 3 1 0 ( 0 0 ) 0 0 3 7 8 - 2

Table 1Emissions of SO

2and NO

xin northeastern countries and USA

(unit: 1000 ton yr~1)!

SO2

NOx

Reliability

China 18,908" 9700# Low31,220$

Korea (1996) 1500 1258 HighNorth Korea 407# 429# Low

332% 470%Japan (1987) 986 1935 HighRussia (1990)& 400 420 MiddleMongolia (1987) 101 72 MiddleUSA (1997) 21,365 18,456 High

!Emission data from Kim (1999) except USA (US EPA, 1998)."Emissions from 70,177 industries in 1995.#Emissions in 1994.$Emissions from various sources including straw burning in

1994.%Emissions in 1987.&Northeastern Asia region of Russia (103}139.53E, 30}623N).

Fig. 1. Site map of the measurement sites.

reported that Cheju Island was under the in#uence ofcontinental out#ow nearly 70% of the year between 1992and 1995. Kim et al. (1998b) measured PM

2.5at Cheju

Island during summer 1994 when the prevailing windwas southerly. However, the characteristics of long-rangetransport of "ne particles in the middle Korean peninsulahave not been well understood.

Five "eld measurements were carried out simulta-neously at two sites, one at the southern part of Koreaand the other at the middle part of Korea between 1996and 1997 by Global Environmental Research Center,Korea Institute of Science and Technology (KIST) andKonkuk University. In this study, compositions of "neparticles at two background sites in Korea are presentedand their transport characteristics are discussed on thebasis of the chemical composition data and backward airtrajectory analyses.

2. Measurement

The site map is given in Fig. 1. The Kosan site(126310@E, 33317@N) is located at the western tip of ChejuIsland, Korea. The site is about 70 m above sea level (asl)and 100m southwest from the Cheju upper air meteoro-logical station from which meteorological parameterswere measured. Kosan is one of the cleanest areas inCheju Island in which emission amounts and concen-trations of anthropogenic air pollutants are quite lowcompared to those at urban areas in Korean peninsula.The emission amounts of SO

2and NO

xat Cheju Island

in 1997 were 0.5 and 0.9% of the total SO2

andNO

xemissions of Korea, respectively (MOE, 1998). The

average concentrations of SO2

and NO2

at Kosan in1992 were 1.42 and 4.91 ppbv, respectively (Park et al.,1994). Also the average concentrations of SO

2and NO

2in the spring of 1994 were 0.97 and 3.50 ppbv, respectively(Kim et al., 1998a). Thus, the Kosan site can be consideredas a background site of Korea and several "eld studieshave been carried out at Kosan (Arimoto et al., 1996;Carmichael et al., 1997; Chen et al., 1997; Kim et al.,1998a, b, 1999, 2000). Detailed descriptions of the site aregiven elsewhere (Kim et al., 1998a).

The Kangwha site (126322@E, 37337@N) is located at thewest coast of Korean peninsula and is about 340km eastfrom Shandong peninsula, China. This site is 45 km westfrom Seoul, the capital city of Korea with 10 millionpeople in the area of 605 km2. The site is about 100mfrom the seashore and surrounded by an agriculturalarea. The sampler is located at the top of a tower at about10m asl. There are no data on the amount of localemissions of SO

2and NO

xaround the Kangwha site.

The average concentrations of SO2

and NO2

at a placeabout 3 km from the site in October of 1999 were 2 ppbv,for both species (MOE, 1999). Thus, the site can beconsidered as a background site for the MetropolitanSeoul Area (MSA) with about 20 million inhabitants.Detailed descriptions for Kangwha site are given else-where (Lee et al., 1997).

Five intensive time series measurements were carriedout between 1996 and 1997. Measurements were carriedout except during summer to observe the e!ects of conti-nental out#ow of air pollutants. Sampling periods areshown in Table 2. Daily sampling started at 0900 LSTand lasted for 24 h. A sampler has a vacuum pump(Dayton, USA) and two sampling trains. Each sampling

Aea=3117=Durai=VVC

636 J.H. Lee et al. / Atmospheric Environment 35 (2001) 635}643

Table 2Summary for the mean concentrations and standard errors of major components of "ne particles (PM

2.5) and nitric acid measured at

Kosan and Kangwha during "ve intensive measurements between 1996 and 1997 (unit: lgm~3)!

Kosan Mar/96(N"7)

Dec/96(N"4)

Jan/97(N"9)

Sep/97(N"10)

Dec/97(N"10)

Overall

SO2~4

5.38$1.45 4.91$1.50 5.48$1.29 5.94$0.80 3.93$0.56 5.13$0.47NO~

31.26$0.47 1.26$0.38 0.29$0.07 0.44$0.10 0.40$0.09 0.67$0.13

Cl~ 0.70$0.32 0.21$0.02 0.22$0.03 0.55$0.08 0.74$0.26 0.55$0.10NH`

41.26$0.32 1.55$0.43 1.34$0.31 1.95$0.28 1.25$0.22 1.48$0.13

Na` 0.95$0.14 0.39$0.13 0.45$0.06 0.68$0.11 0.68$0.10 0.64$0.06K` 0.33$0.11 0.33$0.17 0.23$0.05 0.24$0.05 0.20$0.05 0.26$0.04Ca2` 0.30$0.10 0.21$0.10 0.08$0.02 0.19$0.07 0.05$0.01 0.15$0.03Mg2` 0.09$0.01 0.03$0.01 0.03$0.01 0.07$0.02 0.03$0.01 0.05$0.01OC 2.97$0.53 4.41$0.75 3.31$0.55 3.56$0.43 2.60$0.52 3.26$0.24EC 0.32$0.08 0.43$0.10 0.23$0.04 0.42$0.06 0.34$0.06 0.34$0.03HNO

30.45$0.13 1.02$0.21 0.61$0.12 1.50$0.10 0.39$0.10 0.77$0.08

Mass 18.3$3.64 23.2$5.96 15.5$2.74 16.8$1.50 13.6$1.97 16.6$1.23Total N"40

Kangwha Mar/96(N"14)

Dec/96(N"6)

Jan/97(N"11)

Sep/97(N"9)

Dec/97(N"10)

Overall

SO2~4

5.27$0.54 9.96$2.42 6.16$1.45 3.77$1.21 6.39$0.98 5.98$0.58NO~

32.99$0.68 7.34$1.88 3.63$1.20 1.03$0.33 3.27$0.82 3.35$0.47

Cl~ 0.58$0.13 0.85$0.15 0.67$0.11 0.53$0.25 0.35$0.11 0.57$0.07NH`

43.34$0.35 5.07$0.93 2.69$0.54 2.03$0.53 5.30$0.97 3.61$0.34

Na` 0.40$0.09 0.86$0.09 0.70$0.05 0.73$0.56 0.32$0.15 0.56$0.10K` 0.55$0.15 1.56$0.35 0.58$0.12 0.26$0.06 0.34$0.07 0.58$0.09Ca2` 0.19$0.02 1.39$0.54 0.29$0.10 0.06$0.03 0.25$0.07 0.37$0.09Mg2` 0.06$0.01 0.20$0.04 0.07$0.01 2.19$0.46 0.04$0.01 0.46$0.15OC 5.16$0.50 11.0$1.70 7.58$1.05 4.28$0.93 6.23$0.76 6.45$0.48EC 0.56$0.07 2.45$0.50 0.95$0.15 0.79$0.22 0.90$0.16 0.98$0.12HNO

31.15$0.21 1.78$0.38 0.74$0.13 0.36$0.05 0.70$0.13 0.90$0.10

Mass 25.7$2.54 51.7$9.08 26.5$5.04 21.2$3.68 30.4$2.99 29.1$2.23Total N"50

!Mar/96: 28 Feb.}12 Mar. 1996; Dec/96: 11}17 Dec. 1996; Jan/97: 9}20 Jan. 1997; Sep/97: 26 Sep.}6 Oct. 1997; Dec/97: 11}21 Dec.1997; OC: organic carbon; EC: elemental carbon.

train consists of a Te#on-coated aluminum cyclone witha cut size of 2.5lm at a #ow rate of 16.7 lmin~1 (URG,USA), a Te#on "lter holder (Sarvillex, USA), and a criti-cal ori"ce with an air #ow rate of 16.7 l min~1 (BGI,USA). In one sampling train, a three-stage "lter holderwas used. In the other sampling train a one-stage "lterholder was used.

In the three-stage "lter holder, Te#on membrane "lters(Gelman, Ze#uor) were used at the "rst stage to collect"ne particles. Nylon membrane "lters (Gelman, Nylar-sorb) pre-washed by ion chromatography (IC) eluent(1.7mM NaHCO

3/1.8mM Na

2CO

3) and citric acid im-

pregnated quartz "ber "lters (Whatman, QM-A) wereused at the second and third stages for nitric acid andammonia, respectively. The collection e$ciency of gas-eous species by a three-stage "lter pack was known to belower than that of a denuder. Also, sampling artifacts

were likely to occur due to acid}base interactions be-tween air pollutants, especially, in marine environment.Therefore, the values reported in this paper for somevolatile gaseous species should be considered as conser-vative values, i.e., lower limit values (Kim et al., 1998b). Inthe second sampling train, quartz "ber "lters (Whatman,QM-A) pre-"red at 8503C for 90min were used to collect"ne particles for analyzing carbonaceous species. Aftersampling, all "lters were put in clean petridishes and thenthe petridishes were sealed with Te#on tape and wrappedwith aluminum foil to prevent contamination by gaseousorganics. Analysis of carbonaceous species, organic car-bon (OC) and elemental carbon (EC), was carried out atAtmAA, Calabasas, CA, USA by the selective thermalmanganese oxidation (TMO) method (Fung, 1990). Thelower detection limit was 0.02lgm~3 for the atmosphericconditions. Detailed descriptions of the measurement

Aea=3117=Durai=VVC

J.H. Lee et al. / Atmospheric Environment 35 (2001) 635}643 637

Fig. 2. Mass fraction of major components to PM2.5

: (a) Kosan;(b) Kangwha.

and analysis of carbonaceous species are given by Kimet al. (2000).

Filters were stored in a freezer at }183C until analysis.Particle mass concentrations were obtained from theTe#on "lters by gravimetry. The "lters were stored ina desiccator with 40% relative humidity and room tem-perature for 24 h before weighing. The "lter samples fromKosan were analyzed by KIST and those from Kangwhawere analyzed by Konkuk University (KKU) for majorions. For quality assurance, standard solutions were ex-changed and analyzed by both institutes twice between1996 and 1997.

Te#on "lters were wetted by a small amount of ethanoland were extracted using an ultrasonic device with puredeionized water to analyze water-soluble ionic species.The citric acid impregnated quartz "lters and nylon "l-ters were extracted with 10ml of deionized water and10ml of IC eluent, respectively, using the same way as forTe#on "lters.

Anions in the samples from Kosan site were analyzedby an IC (Dionex 2000i/sp), and NH`

4by the indophenol

colorimetric method using a spectrophotometer (HACHDR-3000). Other cations, Na`, K`, Ca2`, and Mg2`

were analyzed by atomic absorption spectroscopy(Hitachi 8200). All ionic species of the samples fromKangwha were analyzed by an IC (Dionex DX-100). Thelower detection limits were 0.01}0.08lgm~3 for anionsand less than 0.02lgm~3 for cations. Details are given inMoon et al. (1998).

Four-day backward air trajectory analyses were car-ried out to identify the transport pattern of the air parcelsarriving at Kosan and Kangwha by Kangwon NationalUniversity, Korea. The hybrid single particle Lagrangianintegrated trajectories (HY-SPLIT) (Draxler, 1992) wereused. Isentropic trajectory results at 1000m level wereused in this study. The Global Data Assimilation andPrediction System (GDAPS) data from the Korea Me-teorological Administration were used. The GDAPSdata are meteorological data at 1.8753 grid points within20}603N and 90}1503E in which Korea, China, andJapan are included.

3. Results and discussion

3.1. General characteristics

The mean concentrations and standard errors of ionicspecies of "ne particles (PM

2.5) and nitric acid at Kosan

and Kangwha between 1996 and 1997 are presented inTable 2. Since Kosan is one of the background areas inKorea while Kangwha is a background area of the MSA,the mean concentrations of the major anthropogenicspecies in PM

2.5at Kosan were generally lower than

those at Kangwha.

At each site, the mean concentrations of mass andmajor species for each period were comparable exceptduring December 1996. The usual weather pattern dur-ing winter in the region is a strong anticyclone systemover northern China or eastern Russia with high windspeed. However, backward trajectory analysis shows thatduring the December 1996 measurement period, a migra-tory anticyclone system moved to the east and windspeed was low. This weather pattern might contribute tothe high concentrations of anthropogenic air pollutants.

Fig. 2 shows the chemical compositions of PM2.5

at Kosan and Kangwha. Even though the sites are in thecoastal areas, the concentrations of major sea-saltspecies, Na` and Cl~, at both sites were low. The massfraction of sea salts based on the Na` concentrations andsea water composition in Horne (1969) was 4}8wt% tothe PM

2.5mass concentrations at both sites. This is

because sea-salts particles are mainly in coarse mode.At Kosan, the fraction of nss SO2~

4(30 wt%) is higher

than that of OC (20wt%) while at Kangwha, the frac-tions of nss SO2~

4(20 wt%) and OC (22wt%) are compa-

rable to each other. The fractions of the nss SO2~4

andOC at Kosan and Kangwha are quite high compared tothe values in remote regions reported by Heintzenberg(1989), 22 and 11wt% for SO2~

4and OC, respectively.

Aea=3117=Durai=VVC


Tab

le3

Mea

nco

ncen

trat

ion

ofm

ajor

spec

ies

atm

onitoring

site

sin

the

wor

ld(u

nit:lg

m}

3)!

SO

2~ 4N

O~ 3

HN

O3

NH

` 4O

CEC

Mas

sA

rea

type

Par

ticl

esize

Ref

eren

ces

Kosa

n,K

orea

5.13

0.67

0.77

1.48

3.26

0.34

16.6

Bac

kgr

oun

dPM

2.5

This

stud

y(5

.04)

Kan

gwha

,Kor

ea5.

983.

350.

903.

616.

450.

9829

.1U

rban

back

ground

PM

2.5

This

stud

y(5

.87)

Nag

ano,

Japan

(Oct

.19

91)

1.22

0.37

*0.

361.

021.

078.

04Bac

kgr

ound

TSP

Hat

akey

ama

(199

3)San

Nic

ola

sIs

.,U

SA(S

ep.}

Oct

.19

87)

2.77

0.46

*0.

680.

810.

109.

7U

rban

back

groun

dPM

2.5

Cho

wet

al.(1

994)

Qin

gdao

,C

hina

(Sep

.}O

ct.19

97)

11.6

3.07

*3.

94*

*38

.2U

rban

back

ground

PM

2.5

Moo

net

al.(1

998)

!Num

ber

sin

par

enth

eses

are

non-

sea-

salt

SO

2~ 4va

lues

;O

C:org

anic

carb

on;EC

:el

emen

talca

rbon

.

These results indicate that the concentrations of nssSO2~

4and OC in PM

2.5at Kosan are highly a!ected by

continental out#ow as described by Chen et al. (1997)and Kim et al. (1998a). Kim et al. (2000) found that OC atKosan are mainly from anthropogenic sources outside ofCheju Island except during summer. During summer,biogenic sources become important.

The fractions of unidenti"ed materials (called residuein Fig. 2) at both sites are about a quarter of the totalmass concentrations. It is likely that most of the residuesare soil dust species with some water (Meng et al., 1995).At Kangwha, the fractions of the nitrogen compounds,NH`

4and NO~

3, are higher than those at Kosan. Nss

SO2~4

, OC, NO~3, and NH`

4were major components of

PM2.5

and the sum of the mass fractions of these speciesaccounted for 63 and 68 wt% of the PM

2.5mass concen-

tration at Kosan and Kangwha, respectively. Therefore,it can be concluded that "ne particles at both sites areheavily a!ected by anthropogenic species.

The mean concentrations of major anthropogenic spe-cies at both sites are compared with those at otherbackground areas in Table 3. The overall mean concen-trations of SO2~

4are 5.13 and 5.98lgm}3 at Kosan and

Kangwha, respectively. These values are far higher thanthose at Nagano, Japan (1.22lgm}3) and San Nicolas Is.,USA (2.77lgm}3). Nagano is a mountainous region incentral Japan, Japan Alps (Hatakeyama, 1993). SanNicolas Is. is a background area in Los Angeles, USA(Chow et al., 1994). The same trend was found for theconcentrations of other anthropogenic air pollutants andparticulate mass except NO~

3and NH`

4for Kangwha

and EC for both sites. However, the concentrations ofSO2~

4and mass at these sites are far lower than those at

Qingdao, China. The average concentrations of SO2~4

and mass at Qingdao are 11.6 and 38.2lg m}3, respec-tively (Moon et al., 1998). The Qingdao site is located ata coastal area and can be considered as a backgroundarea of Qingdao with about seven million inhabitants.

The average concentrations of NO~3

and NH`4

atKangwha are higher than those at Kosan, Nagano, andSan Nicolas Is. but comparable to those at Qingdao.There are three possible sources for these high concentra-tions; local emission/transformation, transport from theMSA, and transport from outside of the MSA.

Particulate NH`4

is formed from gaseous NH3

emittedfrom various natural and anthropogenic sources. Impor-tant emission sources of NH

3around Kangwha site and

the MSA are livestock, fertilizer application, and fossilfuel burning. Since the site is surrounded by an agricul-tural area, a sizable fraction of NH`

4at Kangwha seemed

to be from compost scattered near the site for agricul-tural activity. Particulate NO~

3is either transformed

through the photo-oxidation of NO2

derived from com-bustion of fossil fuels (Logan, 1983) or emitted fromfertilizer applications. At Kangwha, both sources mightnot be negligible. In a marine environment, conversion to

Aea=3117=Durai=VVC


Table 4Correlation coe$cients among major species of PM

2.5at Kosan

and Kangwha!

Nss SO2~4

NH`4

NO~3

Nss K` OC EC Na`

(a) KosanNss SO2~

40.79 0.50 0.66 0.63 0.37 0.30

NH`4

0.42 0.66 0.78 0.68 0.09NO~

30.63 0.42 0.39 0.18

Nss K` 0.63 0.55 0.34OC 0.78 !0.01EC 0.08Na`

(b) KangwhaNss SO2~

40.49 0.78 0.74 0.76 0.68 0.07

NH`4

0.47 0.41 0.43 0.43 0.05NO~

30.74 0.80 0.76 0.20

Nss K` 0.69 0.66 0.19OC 0.88 0.32EC 0.37Na`

!OC: organic carbon; EC: elemental carbon.

NO~3

via surface interaction on sea-salt particles may beimportant (Song and Carmichael, 1999). But as discussedearlier in this section, the fraction of sea salt in PM

2.5collected at Kangwha is small and surface interactionsseem to be unimportant.

The concentrations of EC at both sites are lower thanthat at Nagano, Japan, but far higher than that at SanNicolas Is., USA. As suggested by Kim et al. (2000), thesedi!erences might be due to the di!erences in the analyti-cal methods used at Nagano and other sites. The sameanalytical method was used for the sites in Korea andSan Nicolas Is.

The fractions of nss sulfate over the total sulfate in "neparticles at both sites were about 97 wt% as shown inTable 3. Thus, though Kangwha and Kosan sites arelocated in coastal areas, the contribution of sea salts tosulfate in "ne particles was small. Arimoto et al. (1996)reported that the contribution from the emissions ofbiogenic nss SO2~

4was about 11% of the nss SO2~

4measured at Cheju Island. Thus, the contribution ofbiogenic emissions to nss SO2~

4at the sites is likely to be

small. Since anthropogenic emission sources and ambi-ent concentration of SO

2at the sites are low, nss SO2~

4measured at both sites should be transported out of thesites.

3.2. Behavior of the anthropogenic species of PM2.5

In remote marine regions, it was reported that theNH`

4to nss SO2~

4equivalent ratio is signi"cantly less

than one (Parungo et al., 1986; Quinn et al., 1990), indic-ating partial neutralization of sulfuric acid by am-monium. The average equivalent ratio of NH`

4to nss

SO2~4

was approximately 0.87$0.04 at Kosan, indicat-ing that nss SO2~

4was not completely neutralized by

NH`4

due to the high concentrations of SO2~4

rather thanthe weak source strength of NH

3. Thus NH`

4-containing

particles at Kosan could be in the form between(NH

4)2SO

4and (NH

4)3H(SO

4)2

but not with NO~3

(Kim et al., 1994). At Kangwha, the average equivalentratio of NH`

4to nss SO2~

4was about 1.42$0.07. The

average equivalent ratio of NH`4

to the sum of nss SO2~4

and NO~3

was about 1.02. It suggests high sourcestrength of NH

3to neutralize not only sulfuric acid

completely but also HNO3

almost completely. From thisresult, NH`

4-containing particles at Kangwha could exist

as forms of (NH4)2SO

4and NH

4NO

3.

One way of studying the behavior of anthropogenicspecies is to "nd the relationship among them.Table 4 shows correlation coe$cients among major an-thropogenic species and Na`, a typical sea-salt species inPM

2.5measured at Kosan and Kangwha.

At Kosan, good correlations are observed amongnss SO2~

4, NH`

4, nss K`, OC, and EC while NO~

3and

Na` showed weak correlation with other species. Thereason that NO~

3shows poor relationship with other

anthropogenic species might be related with the de-pletion of nitrate in the "ne particles and formation ofcoarse nitrate. As shown earlier, the equivalent ratio ofNH`

4to nss SO2~

4was approximately 0.87 at Kosan.

Thus, nitrate in "ne particles should evaporate to satisfycharge neutrality in the particles (Song and Carmichael,1999). NO~

3in the "ne mode can be mainly generated by

the reactions between HNO3

and NH3

while, in thecoarse mode, by the reactions between HNO

3and/or

NO2, and sea salt in a marine environment (Gao et al.,

1996; Pakkanen et al., 1996). Kim et al. (1999) measuredaerosol size distribution at Kosan in April 1998 andreported that NO~

3was mainly in the coarse mode while

SO2~4

and NH`4

were mainly in the "ne mode. Thus, theevaporation of nitrate from "ne particles and the interac-tions between the oxides of nitrogen and alkaline sea-saltparticles could possibly lead to the weak correlationbetween NO~

3and other anthropogenic species in PM

2.5particles at Kosan.

Good correlations are also observed among anthropo-genic species in PM

2.5of Kangwha. Good correlation

between NO~3

and other major anthropogenic species atKangwha is mainly due to the high concentrations ofNO~

3in the "ne mode in contrast with that at Kosan.

The NH`4

to the sum of nss SO2~4

and NO~3

was 1.02and, thus, NH`

4neutralized NO~

3in "ne particles.

3.3. Nss sulfate to nitrate ratio

The molar ratio of nss SO2~4

and NO~3

could be usedas an index to explain major sources of sulfur and nitro-gen compounds in the atmosphere (Carmichael et al.,

Aea=3117=Durai=VVC


Table 5Molar ratios of non-sea-salt sulfate to total nitrate concentration and of SO

2to NO

xemission

Nss SO2~4

/T-NO~3

! SO2/NO

x" Reference

Kosan, Korea 2.77 This studyKangwha, Korea 1.16 This studyNagano, Japan 2.15# Hatakeyama (1993)Korea 0.5 MOE (1998)Japan 0.4 Akimoto and Narita (1994)Northern China 1.59 Akimoto and Narita (1994)Southern China 2.34 Akimoto and Narita (1994)Beijing, China 1.32# 1.7 Huebert et al. (1988)

!T-NO~3

means the sum of the particulate NO~3

and gaseous HNO3

concentrations."Assuming that NO

xis emitted in the form of NO.

#Ratio of SO2~4

to T-NO~3

.

1997). Following the approach by Huebert et al.(1988), the mean nss SO2~

4to T-NO~

3(the sum of

NO~3

and HNO3) molar ratios at Kosan and Kangwha

were estimated and are presented in Table 5 with SO2

to NOx

molar emission ratios in Korea, Japan, andsouthern and northern China. Huebert et al. (1988) com-pared the nss sulfate to nitrate ratio and SO

2to NO

xemission ratio around Beijing with the approximationthat the conversion rates of SO

2to SO2~

4and NO

xto

NO~3

are comparable. Evidently, it is a "rst approxima-tion with large uncertainties. However, this approach isa useful one to further study the relationship betweenemission and ambient levels of anthropogenic air pollu-tants. Arimoto et al. (1996) also used this approach tostudy the transport characteristics of air pollutants in theregion.

The mean nss SO2~4

to T-NO~3

molar ratios were 2.77and 1.16 at Kosan and Kangwha, respectively. If weassume that NO

xis largely emitted in the form of NO,

molar ratio of SO2

to NOx

emission in Korean peninsulais about 0.5 (MOE, 1998) and this value is much lowerthan the molar ratio of nss SO2~

4to T-NO~

3in particles

observed at Kosan and Kangwha. Note that the molarratio of nss SO2~

4to T-NO~

3at Kangwha is a lower limit

since the e!ects of local NO~3

are not negligible. Thus, theratio value when the air parcels arrive at the site shouldbe higher than 1.16. Therefore, majority of nss SO2~

4and

NO~3

observed at these sites are likely from outside ofKorea. The molar ratios of SO

2to NO

xin southern and

northern China are about 2.34 and 1.59, respectively(Akimoto and Narita, 1994).

The major uncertainty sources for this analysis arethree. First, generally, the oxidation rate of NO

xto NO~

3or HNO

3is higher than that of SO

2to SO2~

4, thus,

lowering the aerosol nss SO2~4

to T-NO~3

ratio. Thesecond factor is the tendency of rapid dry deposition ofHNO

3. This would tend to increase the nss SO2~

4to

T-NO~3

ratio. The third factor is that the air in southernChina is generally warmer and wetter than that in north-ern China and, thus, the oxidation of SO

2could be

accelerated. It increases the ratio values. Finally, theT-NO~

3concentrations at Kangwha are a!ected by local

emissions from the MSA.

3.4. Backward trajectory analysis

Based on the backward trajectory analysis of air par-cels, it was observed that more than 95% of air parcelsarriving at Kosan and Kangwha were coming fromChina during the measurement periods. The other 5%were coming from Korean peninsula. Further, air parcelsfrom China were divided into two sections, northern andsouthern China based on 353N. About half of the airparcels arriving at Kosan from China was from southernChina and the other half was from northern China asshown in Table 6. The air pollutants' concentrationswhen air parcels were from southern China are higherthan when air parcels were from northern China. Thedi!erences between the average concentrations ofSO2~

4, NH`

4, OC, and EC at Kosan when air parcels

were from southern and northern China are signi"cantwith 90% con"dence level while the di!erences for theconcentrations of NO~

3and Ca2` at Kosan were not

signi"cant.In the case of Kangwha, most trajectories arriving at

the site were from northern China and the frequency ofair parcels from southern China was just about 10%. Theaverage concentrations of SO2~

4, NO~

3, Ca2`, NH`

4, OC,

and EC at Kangwha were higher in air parcels fromsouthern China than in air parcels from northern China.But the di!erences between the two averages were notstatistically signi"cant at 90% con"dence level. This isdue to the small number of air parcels from southernChina compared to that from northern China.

Aea=3117=Durai=VVC


Table 6Concentrations and standard error of the major species forPM

2.5based on air trajectories at Kosan and Kanghwa!

Concentration (lg m}3) Signi"cance"

Northern China(N"20)

Southern China(N"18)

(a) KosanSO2~

43.69$0.59 6.58$0.68 Y

NO~3

0.75$0.21 0.60$0.14 NNH`

41.11$0.17 1.83$0.18 Y

OC 2.70$0.29 3.93$0.38 YEC 0.29$0.04 0.39$0.05 YCa2` 0.17$0.05 0.12$0.03 N

Concentration (lg m}3) Signi"cance"

Northern China(N"41)

Southern China(N"7)

(b) KangwhaSO2~

45.90$0.66 7.43$1.06 N

NO~3

3.23$0.52 4.83$1.41 NNH`

43.49$0.37 4.53$0.86 N

OC 6.46$0.55 7.06$1.20 NEC 0.94$0.13 1.27$0.29 NCa2` 0.37$0.10 0.43$0.18 N

!OC: organic carbon, EC: elemental carbon."Y means two mean values are di!erent with 90% con"dence level;

N means two mean values are not di!erent with 90% con"dence level.

4. Summary

Five intensive time series measurements had been car-ried out to investigate the characteristics of "ne particles(PM

2.5) at two background sites, Kosan and Kangwha,

Korea.The mean concentrations of anthropogenic species of

PM2.5

at Kosan and Kangwha were higher than those atremote areas in Japan and USA, but lower than those inan urban background area in China. Based on the ambi-ent concentrations of SO

2and NO

2at both sites and "ne

particle compositions, it is concluded that the majorfraction of anthropogenic species in PM

2.5at both sites

is a!ected by the transport from outside the sites. Fur-ther, it was found that Kangwha is a background area ofthe Metropolitan Seoul Area. The correlation amonganthropogenic species in PM

2.5was good at both sites.

The equivalent ratios of ammonium to nss sulfate werecomparable to and over 1 at Kosan and Kangwha, re-spectively. The results of backward air trajectory ana-lyses showed that more than 95% of air parcels at Kosanand Kangwha originated from China. The concentra-tions of sulfate, ammonium, organic and elemental car-bons at Kosan were higher when air parcels were fromsouthern China than when the air parcels were fromnorthern China. At Kangwha, however, the di!erences

between mean concentrations based on the air parceltrajectories were not statistically signi"cant.

Based on the molar ratio of nss sulfate to total nitrate(sum of particulate nitrate and gaseous nitric acid con-centrations) and the molar ratio of sulfur dioxide andnitrogen oxides, backward trajectory analysis, and therelationship among anthropogenic species, it was foundthat the major fractions of sulfate and nitrate at Kosanare from China. At Kangwha, the major fraction ofsulfate is from China, but the local contributions to thenitrate and ammonium levels are high.

Acknowledgements

This work was supported by National Institute ofEnvironmental Research, Korea. The authors thank Dr.Fung at AtmAA, USA for organic and elemental carbonanalyses.

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