Source contributions to black carbon mass fractions in aerosol particles over the northwestern Pacific

ARTICLE IN PRESS

Atmospheric Environment 42 (2008) 800–814 www.elsevier.com/locate/atmosenv

Source contributions to black carbon mass fractions in aerosol particles over the northwestern Pacific Seizi Koga, Takahisa Maeda, Naoki Kaneyasu National Institute of Advanced Industrial Science and Technology (AIST), Research Institute for Environmental Management Technology, AIST Tsukuba West, 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan Received 18 February 2007; received in revised form 20 July 2007; accepted 24 September 2007

Abstract Aerosol particle number size distributions above 0.3 mm in diameter and black carbon mass concentrations in aerosols were observed on Chichi-jima of the Ogasawara Islands in the northwestern Pacific from January 2000 to December 2002. Chichi-jima is suitable to observe polluted air masses from East Asia in winter and clean air masses over the western North Pacific in summer. In winter, aerosols over Chichi-jima were strongly affected by anthropogenic emissions in East Asia. The form of energy consumption in East Asia varies in various regions. Hence, each source region is expected to be characterized by an individual black carbon mass fraction. A three-dimensional Eulerian transport model was used to estimate contribution rates to air pollutants from each source region in East Asia. Because the Miyake-jima eruption began at the end of June 2000, the influence of smokes from Miyake-jima was also considered in the model calculation. The results of model calculations represent what must be noticed about smokes from volcanoes including Miyake-jima to interpret temporal variations of sulfur compounds over the northwestern Pacific. To evaluate black carbon mass fractions in anthropogenic aerosols as a function of source region, the relationships between the volume concentration of aerosol particles and the black carbon mass concentration in the winter were classified under each source region in East Asia. Consequently, the black carbon mass fractions in aerosols from China, Japan and the Korean Peninsula, and other regions were estimated to be 9–13%, 5–7%, and 4–5%, respectively. r 2007 Elsevier Ltd. All rights reserved. Keywords: Aerosol; Black carbon; Number size distribution; Black carbon fraction; Source contribution

1. Introduction The participation in climate influences by aerosols is divided roughly into two effects. The first is the extinction of the solar radiation. Aerosols including non-absorbing species such as sulfate (SO2 4 ) scatter solar radiation, and black carbon absorbs solar Corresponding author. Tel.: +81 29 861 8388; fax: +81 29 861 8358. E-mail address: [email protected] (S. Koga).

1352-2310/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2007.09.052

radiation. The second is that the change of aerosol particle number concentrations alters radiative properties of clouds and a water cycle by interactions with clouds because part of aerosol particles work as cloud condensation nuclei (CCN). Furthermore, the mixing state of black carbon with other chemical compounds strongly affects radiative properties of aerosols. The light absorption coefficient of a mixture of black carbon and nonabsorbing species is higher for internal than for external mixtures (Ackerman and Toon, 1981;

ARTICLE IN PRESS S. Koga et al. / Atmospheric Environment 42 (2008) 800–814

Horvath, 1993). There is much less confidence to quantify the radiative forcing by aerosols due mainly to a high spatial and temporal variability (Penner et al., 2001). Evaluating radiative forcing by aerosols necessitates further understanding of spatial and temporal variations of the number size distribution and chemical composition of aerosol particles. Processes causing the release of sulfur dioxide (SO2) from anthropogenic activities in East Asia are primarily the combustion of coal and the secondarily that of petroleum (Streets et al., 2000). Half of anthropogenic sulfur emitted from East Asia is transported to an easterly direction in winter and spring (Tan et al., 2002). Emissions of black carbon in China arise primarily from the uses of raw coal, coal briquettes, and biofuels in the residence. The regional distribution pattern of black carbon emissions obviously differs from that of other species such as SO2 and NOx (Streets et al., 2001). China, South Korea, and Japan differ widely in the rates of coal and oil consumptions to the total energy amount of consumption. China consumes the most amount of

801

coal in the world. As of 2002, the consumption of coal including lignite in China is 4.7 times larger than the sum of coal consumptions in the Korean Peninsula and Japan. The consumption of petroleum in Japan is equivalent to that in China, and is 1.9 times larger than that in South Korea. Japan also consumes the most amount of natural gas in East Asia (United Nations, 2005). Anthropogenic emissions of SO2 and black carbon are considered to differ widely in each country and region. Furthermore, the export efficiency of black carbon is higher than that of SO2 and NOx (Park et al., 2005). Hence, black carbon mass fractions in aerosol particles are expected to be a function of source region. The present study is concerned with aerosol particle number size distributions above 0.3 mm in diameter and black carbon mass concentrations on Chichi-jima (271040 N, 1421130 E) of the Ogasawara Islands in the northwestern Pacific from January 2000 to December 2002 (see Fig. 1). This period corresponds to the early eruption stage of Miyakejima volcano (341050 N, 1391320 E, 775 m above sea

40

Northern part of China 30 Japanese Archipelago Korean Peninsula Miyake-jima Southern part of China

20

Futami harbor

10

Weather station

Ogasawara downrange station (27°04’N, 142°13’E, 230m a.s.l.)

0 100

110

130

170

Chichi-jima

Fig. 1. Locations of the Ogasawara downrange station of the Japan aerospace exploration agency and Miyake-jima, and the domain for the calculation of the transport model.

ARTICLE IN PRESS 802

S. Koga et al. / Atmospheric Environment 42 (2008) 800–814

level) in the Izu Islands about 180 km south–southwest of Tokyo. The area of Chici-jima is about 24 km2. This island has a population of about 2000 and most people live in the waterfront between the weather station and Hutami harbor. The observation base is the Ogasawara downrange station (ODRS, 230 m a.s.l.) of the Japan aerospace exploration agency (JAXA). Chichi-jima is approximately 1000 km south of Tokyo and is an ideal site to monitor both polluted continental air masses and clean air masses over the western North Pacific. During summer months when high pressure is centered over the North Pacific, southerly or easterly winds dominate over this island, but in contrast, northwesterly winds persistently blow during winter months. This interchange of predominant air masses is responsible for a distinct seasonal change of air quality in this region (Matsumoto et al., 1998). The purpose of the present study is to examine the difference of aerosol particle number size distributions between polluted and clean air masses, and to evaluate black carbon mass fractions in aerosol particles as a function of source region. 2. Experiment 2.1. Instrumentation Number size distributions of particles above 0.3 mm in diameter were obtained from a laser particle counter (Model TF-500, Kanomax Japan, Co., Inc.). Measurements of the number concentrations were automatically repeated every 10 min by classifying into five classes of 0.3 mmoD, 0.5 mmoD, 1 mmoD, 3 mmoD, and 5 mmoD. Sample air was directly drawn into TF-500 through a conductive silicon tubing of 0.85 m in length and 4 mm in inside diameter and was collected at ambient temperature (typically 17 1C in winter and 25 1C in summer) and relative humidity (typically 74% in winter and 88% in summer). The light source is a semiconductor laser of 780 nm in wavelength. Laser light is scattered to all space by a single aerosol particle attracted from the sampling hole. The scattered light condensed by a pair of wide angle condensing ellipsoidal mirrors is converted to an electrical signal by two photodiodes. A voltage of the electrical signal depends on a scattering cross section, because the scattered light is condensed covering almost all solid angles. The coincidence error leads to an underestimation of the number

concentration and an overestimation of the particle size. When the number concentration of particles above 0.3 mm in diameter is 100 cm3, the coincidence error is 5% in nominal value. The number concentrations in this size range were usually o100 cm3 during the observation. Black carbon mass concentrations were obtained from an aethalometer using optical absorption at 880 nm in wavelength (AE-16U, Magee Scientific, Co., Inc.) with 1 h interval. The aethalometer measures the attenuation of a light beam transmitted through a web-reinforce quarts fiber tape (e.g. Hansen et al., 1984). The optical attenuation is linearly proportional to the black carbon mass concentration. The black carbon mass concentrations were calculated with the assumption of the mass specific attenuation cross-section (sATN) of 16.6 m2 g1 recommended by the manufacturer. More details of black carbon mass concentrations on Chichi-jima will be the subject of a separate paper. 2.2. Data screening The number concentration of aerosol particles is strongly affected by precipitation events. Hence, based on precipitation records of 10 min intervals at Chichijima meteorological station (see Fig. 1) in monthly observation reports issued by the Japan meteorological agency (JMA), the data of particle number and black carbon during precipitation events were excluded from analyses. The coefficients of variation in the number concentrations (s/x; x is an arithmetic mean of the number concentrations and s is a population standard deviation) were calculated from the moving average for 1 h in four classes of 0.3 mmoDo0.5 mm, 0.5 mmoDo1 mm, 1 mmo Do3 mm, and 3 mmoD. When the coefficients of variation in one or more classes at a certain time were 40.5, the values of all the five classes at that time were also excluded. The influence of nearby sources can be removed by this procedure. The 1 h-averaged values were calculated when data were obtained six times in a row. The diurnal averages were calculated when data were 496 a day. 3. Results 3.1. High number concentrations of aerosol particles in summer Fig. 2 shows the diurnal averages of aerosol particle number concentrations in two classes from

ARTICLE IN PRESS S. Koga et al. / Atmospheric Environment 42 (2008) 800–814 2000

0.3
100 ΔN/Δ ln(D) (cm-3)

100

Date

12/31

12/3

11/5

10/8

9/10

8/13

7/16

6/18

5/21

1/1

12/2

12/30

11/4

10/7

9/9

8/12

7/15

6/17

5/20

4/22

0.01 3/25

0.01 2/26

0.1

1/1

0.1

4/23

1

3/26

1

2001

1.0
10

2/26

10

1/29

1.0
1000

1/29

ΔN/Δ ln(D) (cm-3)

0.3
803

Date

0.3
2002

1.0
1000

ΔN/Δ ln(D) (cm-3)

100 10 1 0.1

12/31

12/3

11/5

10/8

9/10

8/13

7/16

6/18

5/21

4/23

3/26

2/26

1/29

1/1

0.01

Date

Fig. 2. Variations of aerosol particle number concentrations (diurnal average) in two classes from January 2000 to December 2002.

January 2000 to December 2002. In spite of the summer season, the total number concentrations above 0.3 mm in diameter were frequently 4100 cm3 for a few days. Correlations between the volume concentration of aerosol particles and the black carbon mass concentration were examined by using the winter data from December 2000 to January 2001 and from December 2001 to January 2002. Volume concentrations of aerosol particles in four classes of 0.3 mmoDo0.5 mm, 0.5 mmoDo1 mm, 1 mmo Do3 mm, and 3 mmoDo5 mm were estimated from 1 h-averaged number concentrations. There are good positive correlations between the black carbon mass concentration and the volume concentrations of aerosol particles from 0.3 to 0.5 mm and from 0.5 to 1 mm. The correlation coefficients of monthly data in these classes are in the range of 0.48–0.84 with the typical value of 0.7, except for 0.37 from

0.3 to 0.5 mm in January 2001. In larger size classes, the correlation coefficients are o0.35. These coefficients suggest that black carbon mainly exists in aerosol particles below 1 mm in diameter. It is wellknown that black carbon mass concentrations are generally found in submicron particles (e.g. van Dingenen et al., 2004). Therefore, the number concentration ratio of 0.3–1 to 1–5 mm can be regarded as an indicator of the degree of pollution in an air mass. Ratios of the number concentration of 0.3 mmo Do1 mm (N0.31 ¼ DN0.30.5/Dln(D0.30.5)+DN0.51/ Dln(D0.51)) to 1 mmoDo5 mm (N15 ¼ DN13/ Dln(D13)+DN35/Dln(D35)) were calculated. Fig. 3 shows the variation of diurnally averaged ratios from January 2000 to December 2002. Most of the ratios in winter range from 10 to 300. In summer, the ratios dramatically vary from 3 to 600. To examine causes of these variations, back trajectories

ARTICLE IN PRESS S. Koga et al. / Atmospheric Environment 42 (2008) 800–814

804

2000

2001

2002

10000 Sep.13, 2000 Aug.20, 2002 Sep.25, 2002

Ratio of N0.3-1 to N1-5

1000

100

10

Aug.10, 2000

Sep.30, 2002

Aug. 29, 2002

12/30

12/2

11/4

10/7

9/9

8/12

7/15

6/17

5/20

4/22

3/25

2/26

1/29

1/1

1

Date

Fig. 3. Ratios of the number concentration of 0.3–1 mm (N0.31) to 1–5 mm (N15).

were computed about six samples in the summer as shown in Fig. 3, using the hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) model based on the meteorological model’s vertical velocity fields of FNL archive data (Draxler and Rolph, 2003; Rolph, 2003) (available from; http://www.arl. noaa.gov/ready/hysplit4.html). When Chichi-jima is covered with clean air masses in the marine atmosphere, ratios of the number concentration are generally o10. The air parcels that arrived on Chichi-jima on 10 August 2000, 29 August 2002, and 30 September 2002 are estimated to have been over the western North Pacific for at least 5 days before arriving on Chichijima, as shown in Fig. 4. From 12 to 13 September 2000, the number concentrations of aerosol particles from 0.3 to 1 mm in diameter were substantially high. This would result from the influence of smokes from the Miyake-jima volcano. The air parcel encountered on Chichi-jima on 20 August 2002 was probably influenced by the smoke from Sakurajima volcano (311340 N, 1301400 E, 1060 m a.s.l.). The high ratio on 25 September 2002 is associated with the polluted air mass from Japan. Even in summer, Chichi-jima is frequently influenced by not only anthropogenic pollutions from Japan but also smokes from volcanoes in Japan.

3.2. Number size distribution Ratios o7 and 430 of N0.31 to N15 can be defined as typical values in clean and polluted air masses, respectively, although these values are decided arbitrarily. Aerosol particle number size distributions in clean and polluted air masses can be obtained from the data satisfying these conditions. The number size distribution in the ratios o7 is shown in Fig. 5A. The ratios were calculated from 1 h-averaged concentrations from July to October in 2000, 2001, and 2002. Fig. 5B shows the number size distribution in the ratios 430 in the same period. Fig. 5C also shows the number size distribution in the ratios 430, although the periods are from December 2000 to January 2001 and from December 2001 to January 2002. The number size distribution in Fig. 5C, similar to that in Fig. 5B, is completely different from that in Fig. 5A. The sum of n log-normal distributions is often used to describe atmospheric aerosol size distributions. Jaenicke (1993) divided tropospheric aerosols into seven types. Fig. 5 also shows the model size distributions for maritime, rural, and background aerosols. The appearance of the observed number size distribution in Fig. 5A is very close to that of the number size distribution for the background

ARTICLE IN PRESS S. Koga et al. / Atmospheric Environment 42 (2008) 800–814

805

30 Sep.13, 2000 00

2

Sep.25, 2002

.1 ug ug

.2

9,

20

Aug.20, 2002

02

10

A

Se

p.

0,

30

20

,2

00

20

A

Chichi-jima

0

20 100

120

140

160

180

Fig. 4. Backward trajectories for the past 5 days of air parcels arrived on Chichi-jima. Arrival time: 12:00 of each date (Japan Standard Time); attainment altitude: 230 m (altitude at ODRS). The trajectory of air parcel arrived on Chichi-jima on 13 September 2000 is the arrival time of 6:00 a.m. and goes back in the past 7 days.

aerosols rather than the maritime aerosols. The observed concentrations, however, are 6.5 times as small as the background values. Reasons of this difference are unknown. Most measurements of the background aerosols have been carried out at mountain sites or in subsiding air masses reflecting mid-tropospheric conditions (Jaenicke, 1993). The ratios o7 of N0.31 to N15 suggest the subsidence of air masses from the free troposphere due to the North Pacific anticyclone. The rural model distribution is mainly continental but with a moderate influence from anthropogenic sources (Jaenicke, 1993). The observed number size distributions in Fig. 5B and C are roughly the same as the rural model distribution. The ratios of 7 and 30 are appropriate selection as threshold values classifying air masses into clean and polluted air masses. The number size distribution in Fig. 5B would mainly be affected by the inflows of anthropogenic pollutions from Japan and smokes from volcanoes in Japan (see Fig. 4). In winter, aerosols encountered on Chichi-jima would be a complex mixture of chemical components from various anthropogenic and volcanic sources. The number size distribution in Fig. 5C is very similar to that in Fig. 5B. Even if the degree of pollution in any air mass can be estimated from ratios of N0.31 to N15, source regions cannot be estimated from the ratios.

Nevertheless, if Chichi-jima is strongly affected by a specific source region, some characteristic relations should be observed between volume concentrations of aerosol particles and black carbon mass concentrations. These relations should be concerned with emission rates of SO2 and black carbon from anthropogenic sources. It is useful to look more closely at some features of the relationship between the volume concentration of aerosol particles and the black carbon mass concentration as a function of source region. These features will be discussed in detail using a transport model of air pollution. 4. Transport model Sulfur dioxide is produced from such human activities as fossil fuel combustion and industry emissions. Volcanic activities are also significant sources of SO2. Sulfur dioxide is readily converted to SO2 4 in the atmosphere. Sulfate concentrations were not measured in the present study. Nevertheless, the estimation of SO2 concentration is 4 useful to evaluate the influence from volcanic activities, and also to demonstrate the observed temporal variations of particle volumes and black carbon mass concentrations. A three-dimensional Eulerian transport model developed by Maeda et al. (2001) is used to

ARTICLE IN PRESS S. Koga et al. / Atmospheric Environment 42 (2008) 800–814

806

B Less than 7 of N0.3-1 to N1-5

More than 30 of N0.3-1 to N1-5 103

103 Maritime Rural Background Background*1/6.5

102

ΔN/Δ ln(D) (cm-3)

ΔN/Δ ln(D) (cm-3)

Rural Background

101

101 100 Range

10-1

Average Median

10-2

100 Range

10-1

Average Median

10-2 10-3

10-3 Jul. - Oct. 2000, 2001, 2002

10-4 10-5

Maritime

102

0.1

Jul. - Oct. 2000, 2001, 2002

10-4

1248 data of 1 hr. average 1 Diameter (μm)

10-5

10

1222 data of 1 hr. average 0.1

1 Diameter (μm)

10

More than 30 of N0.3-1 to N1-5 103 Maritime

102

Rural Background

ΔN/Δ ln(D) (cm-3)

101 100 Range Average Median

10-1 10-2 10-3

Dec. 2000 - Jan. 2001 Dec. 2001- Jan. 2002

10-4

1524 data of 1 hr. average

10-5 0.1

1 Diameter (μm)

10

Fig. 5. Aerosol particle number size distributions in clean (A) and polluted (B and C) air masses. The model size distributions for maritime, rural, and background aerosols (Jaenicke, 1993) are also displayed. The vertical axis is in natural logarithm.

discriminate SO2 4 concentrations derived from the northern part of China (north of 351N, the NC), the southern part of China including Taiwan (south of 351N, the SC), the Korean Peninsula, Japan, volcanoes in Japan, and other regions (see Fig. 1).

The discrimination is performed by the following procedure. First, SO2 emissions are provided for all the regions in the calculation domain. Secondly, a certain specific region or a source point such as the volcano is assumed to be the zero emission of SO2,

ARTICLE IN PRESS S. Koga et al. / Atmospheric Environment 42 (2008) 800–814

but at this time SO2 emissions are given for the other regions. The following formula, then, is defined to calculate contribution rates (RA) from a region A to SO2 4 concentrations: RA ¼

C all  C A0  100: C all

(1)

In this formula, when SO2 is emitted from all the regions, Call represents an estimated SO2 4 concentration at an arbitrary time. CA0 represents an estimated SO2 4 concentration at an arbitrary time under the zero emission of SO2 in the region A. Contribution rates to SO2 concentrations on 4 Chichi-jima can be computed as a function of source region at 1 h interval, according to this definition. The present model covers the periods from December 2000 to January 2001 and from December 2001 to January 2002 when northwesterly winds persistently blew. The present study utilizes Global SOx Inventory version 1B, compiled by Global Emissions Inventory Activity (GEIA), as the emission source distribution of anthropogenic sulfur (SO2) (Benkovitz et al., 1996). The SO2 emission rates mentioned here are the estimated values as of 1985. The original emission rates from China are multiplied by 1.5 to apply to model calculations from 2000 to 2002. This is because the coal consumption in 2000 increased 1.5 times compared with that in 1985 (China Statistical Yearbook, 2002, available from: http://www.stats.gov.cn/english/statisticaldata/ yearlydata/YB2002e/ml/indexE.htm). From 1985 to 2000, the SO2 emission rate also increased as the same value as the increase rate of the coal consumption (China Environment Yearbook, 1990–2003). The change of the geographical distributions of the emission sources and factors, however, is not taken into consideration. The SO2 emission rates from the NC and the SC are supposed to be 5.35 and 9.05 TgS yr1, respectively. The sum of these values is 410.4 TgS yr1 estimated by Streets et al. (2003). From the comparison of the concentrations from field observations with model predictions, Streets et al. (2003) suggests an underestimation of local coal use and emissions from significant sources omitted from their inventory. The original values are applicable to the SO2 emission rates of the Korean Peninsula and Japan, without correcting. The environmental agencies of governments report that the anthropogenic SO2 emission rates and the monitored SO2 concentrations in urban areas are the same as or below those

807

in 1985. The SO2 emission rate in the Korean Peninsula is supposed to be 0.84 TgS yr1 which is 40.53 TgS yr1 estimated by Streets et al. (2003). The SO2 emission rate in Japan is supposed to be 0.42 TgS yr1. This value is roughly the same as the value estimated by Streets et al. (2003). The SO2 emission rates from active volcanoes are also quoted from the GEIA data. The SO2 emission rate from Sakura-jima had been the maximum among Japanese volcanoes until Miyake-jima erupted. The emission rate of 0.35 TgS yr1 from Sakura-jima is roughly the same as the total emission from anthropogenic sources in Japan and is about half of 0.64 TgS yr1 from all the volcanoes in Japan. The Miyake-jima eruption began at the end of June 2000. The SO2 emission from Miyakejima is also considered in this model calculation. The sulfur emission on 16 November 2000 amounted to 36,400 ton a day, being comparable to the emission rate of anthropogenic sulfur from the whole of China. The diurnally averaged emission rates of SO2 from Miyake-jima can be calculated from the values in the following web page (in Japanese) of the JMA: http://www.seisvol. kishou.go.jp/tokyo/320_Miyakejima/320_So2emission. htm (this web page is renewed). The altitudes from the mountain summit that SO2 was ejected are assumed to be 1000 m from December 2000 to January 2001, and to be 500 m from December 2001 to Janaury 2002, on the basis of the volcanic activity description data (in Japanese; available from: http://www.seisvol.kishou.go.jp/tokyo/STOCK/ monthly_v-act_doc/monthly_vact.htm) edited by the JMA. Dimethylsulfide (DMS) is a major contributor of SO2 over the ocean (Koga and Tanaka, 1999; 4 Georgii and Warneck, 1999). Emissions of DMS to the atmosphere are estimated to be considerable low in areas surrounding Chichi-jima in winter (Koga et al., 1993). Here, the DMS emission is excluded to simplify the calculations. Emissions of other sulfur compounds are also disregarded. 5. Discussion 5.1. Model evaluation To evaluate the accuracy of the present model, it is necessary to compare results of calculation with those of observation. Sulfate concentrations in aerosol particles o2.5 mm in diameter were observed on Amami-Oshima from 11 to 29 April 2001

ARTICLE IN PRESS S. Koga et al. / Atmospheric Environment 42 (2008) 800–814

808

in the APEX field campaign (Tsuruta et al., 2003). To begin with, a comparison of the observed SO2 4 concentrations with the predicted SO2 4 concentrations can be made. Although there is a systematic underestimation in the predicted concentrations, the observed and predicted concentrations show a good temporal correlation with a correlation coefficient of 0.72. The observed SO2 4 concentrations from 11 to 16 April were quite high with an average value of 8.4 mg m3. The predicted SO2 4 concentration during the same term was an average of 5.7 mg m3. In this term, the concentration ratios of Si, Al, and Ti to the total mass decreased with time, whereas those of Pb and Zn increased. Si, Al, and Ti are soil components, and Pb and Zn are associated with cars and industry emissions. Back trajectories suggest that the air masses in the former part of this term included a mixture of dust particles from the inland China and anthropogenic pollutants from the NC. The predicted contribution rates show that air

masses were transported from the NC in the former part of this term and from the SC in the latter part of the same term. The variations of the contribution rates are consistent with the variations of trace elements. Next, the data obtained on Chichi-jima in December 2000 are taken as the object of comparison. Fig. 6A shows the estimated SO2 4 concentrations on Chichi-jima in December 2000 and also that Chichi-jima in this month must be strongly affected by the SO2 emission from Miyake-jima. Fig. 6B shows that the contribution rates to SO2 4 concentrations from each source region on Chichijima vary severely with several hours. The variations of black carbon mass concentrations (see Fig. 6C) and particle volumes (see Fig. 6D) observed on Chichi-jima can be explained, as follows. The black carbon mass concentrations from 4 to 8 December were noticeably high with the two peaks from 200 to 400 ng m3 (see Fig. 6C). The

Black carbon concentration (ng m-3)

Sulfate concentration (μg m-3)

12 with Miyakejima eruption without Miyakejima eruption

10 8 6 4 2 0

1000 800 600 400 200 0

1

3

5

7

9

11 13 15 17 19 21 23 25 27 29 31

1

3

5

7

9

Day

Day

Korean Peninsula Volcanoes

North China South China Japan

5000 Volume concentration

75

50

25

0

of aerosol particles (μm3 L-1)

100 Relative contribution (%)

11 13 15 17 19 21 23 25 27 29 31

0.3
4000 3000 2000 1000 0

1

3

5

7

9

11 13 15 17 19 21 23 25 27 29 31

1

Day

SO2 4

3

5

7

9

11 13 15 17 19 21 23 25 27 29 31

Day

SO2 4

Fig. 6. Estimated values of concentration (A) and contribution rates to concentration for each emission source (B), observed values of black carbon mass concentration (C) and aerosol particle volumes of 0.3–0.5 and 0.5–1 mm in diameter (D) in December 2000.

ARTICLE IN PRESS S. Koga et al. / Atmospheric Environment 42 (2008) 800–814

volume concentrations of aerosol particles were also rather high (see Fig. 6D). Clearly, the advection of air masses from East Asia occurred during this term. The increase rate of particle volumes on 5 December was larger than that of black carbon mass concentrations. As shown in Fig. 6A and B, the great portion of contribution to SO2 on 5 4 December is occupied by the smoke from Miyakejima. This appears to cause very high volume concentrations of aerosol particles on this day (see Fig. 6D). The contribution rate from anthropogenic emissions on 7 December, however, is estimated to be higher than that from Mityake-jima (see Fig. 6B). The high black carbon mass concentrations on 7 December are related with polluted air masses from anthropogenic emissions. The inflow of volcanic smokes leads to the increase of the particle volume rather than the black carbon mass concentration. The variation of the black carbon mass concentrations from 11 to 12 December synchronizes with the variations of particle volumes from 0.3 to 1 mm in diameter (see Fig. 6C and D). These variations would be attributed to polluted air masses from anthropogenic sources, as shown in Fig. 6B. The black carbon mass concentration and the particle volume abruptly increased in the afternoon of 15 December. This would be associated with the advection of polluted air masses from Japan and the NC (see Fig. 6B). The black carbon mass concentrations and the particle volumes from 25 to 26 December varied with the two peaks (see Fig. 6C and D). From the contribution rates as shown in Fig. 6B, the high particle volumes on 25 December appear to be caused by polluted air masses from the SC, whereas those on 26 December would be due mainly to the influence of polluted air masses from the NC. Although the appreciably high concentrations of SO2 4 from 28 to 29 December in Fig. 6A are mainly produced by the smoke from Miyakejima, as shown in Fig. 6B, the observed particle volumes hardly change as shown in Fig. 6D. The smoke from Miyake-jima seems not to affect actually the variation of the particle volumes from 28 to 29 December. Concentrations of chemical compounds strongly depend on the intensity, formation process, and type of rain, and the land use situation and vegetation state related to dry deposition rates. The small-scale turbulence o1  11 of latitude–longitude and 1 h temporal resolution cannot be reproduced correctly in the present model. These result in differences between the predicted and observed concentrations.

809

Inflows of anthropogenically polluted air masses give rise to the simultaneous increase of the aerosol particle number concentration and the black carbon mass concentration. Volcanic smokes tend to make the aerosol particle number concentration increase rather than the black carbon mass concentration. Unlike back trajectory analysis estimating transportation paths of air masses, the present model can numerically express contribution rates from each source region. As shown in Fig. 3, the remarkable high ratios of N0.31 to N15 were observed in the summer. The contribution rate from Miyake-jima on from 12 to 13 September 2000 accounts for 60% at the maximum. On 20 August 2002, the smokes from Sakura-jima contribute to the production of SO2 4 at the rate of 80% at the maximum. The high ratios on 25 September 2002 can be interpreted to be produced by the contribution rate of 70% of anthropogenic pollutions from Japan. Such an interpretation of observation results was unavailable until this model was used. Estimations of contribution rates from each source region are likely to be helpful to explain causes of the temporal variations of aerosol particle and black carbon. 5.2. Contributions from each source region Here, when a contribution rate from a certain region at an arbitrary time is 450% (cr50), it is presumed that the air pollution from this region most affect aerosols over Chichi-jima. From December 2000 to January 2001 and from December 2001 to January 2002, the frequency of the cr50 of volcanic emissions is half of the total frequency of the cr50 from every source region. The frequency of the cr50 of Miyake-jima accounts for 86% of that of the cr50 of volcanic emissions in East Asia. This represents that the Miyake-jima smoke strongly affected SO2 4 concentrations during these periods. The frequency of the cr50 of anthropogenic emissions can be obtained by subtracting the frequency of the cr50 of volcanic emissions from the total frequency of the cr50. The frequencies of the cr50 of the NC and the Korean Peninsula are 38% and 34% of the frequencies of the cr50 of anthropogenic emissions, respectively. The frequencies of the cr50 of the SC, Japan, and other source regions, are 6%, 13%, and 9% of the frequencies of the cr50 of anthropogenic emissions, respectively. Therefore, Chichi-jima appears to be mainly influenced by anthropogenic emissions from the NC and the Korean Peninsula. The influence from the Korean

ARTICLE IN PRESS S. Koga et al. / Atmospheric Environment 42 (2008) 800–814

810

Peninsula more frequently than from Japan is due to higher SO2 emission from the Korean Peninsula than from Japan and the influence from the western part of Japan instead of the whole of Japan (see Fig. 7). 5.3. Black carbon mass fraction Fig. 8 shows the relationships between particle volumes from 0.3 to 1 mm in diameter and black carbon mass concentrations in ratios 430 of N0.31 to N15 besides the cr50, from December 2000 to January 2001 and from December 2001 to January 2002. Data points are classified under each source region by five different symbols. The data in air masses from volcanoes are excluded from this figure. Under conditions of the ratios and the cr50, averaged black carbon mass concentrations are 266 ng m3 (median, 210 ng m3) in air masses from the NC, 474 ng m3 (median, 397 ng m3) from the SC, 181 ng m3 (median, 157 ng m3) from Japan, 193 ng m3 (median, 160 ng m3) from the Korean Peninsula, and 157 ng m3 (median, 134 ng m3) from other regions. There is a little contribution from the SC as mentioned above but then concentrations of aerosol particle number and black carbon mass tend to increase when polluted air masses from the SC arrive on Chichi-jima. Least-squares fit to lines are calculated from the data points for each source region. There is very good correlation between the particle volume and

the black carbon mass concentration in air masses from China (see Fig. 8A). The slope of the regression line from the SC data is larger than that from the NC data but then the difference is slight. The slope of the regression line from both the NC and SC data is calculated to be 0.12670.005 with a coefficient of determination (R2) of 0.74. Fairly good correlations can be seen in the data for Japan, the Korean Peninsula, and other regions (see Fig. 8B). The regression line from the data for Japan is substantially the same as that for the Korean Peninsula. Thus, the regression line can be calculated by using the data for Japan and the Korean Peninsula. The slope of this regression line, 0.07170.007 (R2 ¼ 0.45), is considerably smaller than that of the lines from the China data. The minimum slope value of 0.05370.008 (R2 ¼ 0.44) is calculated in the regression line from the data for other regions. These differences of slope indicate that the black carbon mass fraction depends on source regions. This result is consistent with the advance expectation. Kaneyasu and Murayama (2000) found that the mass size distribution of black carbon over the North Pacific was extremely similar to that of non2 sea-salt SO2 4 (nss-SO4 ) with the maxima concentrations near 0.5–0.7 mm in aerodynamic diameter. Chowdhury et al. (2001) reported that black carbon over the Indian Ocean was predominant in the size range between 0.32 and 1.0 mm in aerodynamic diameter and accounted for 6–11% of the fine

50° N

40° N

30° N

20° N

100° E

50 GgS month-1 120° E

140° E

160° E

Fig. 7. Addition flux of sulfur (SO2+SO2 4 ) throughout December 2001 from the surface of the earth to s ¼ 0.75 (about 2400 m in altitude). To decipher easy, the arrows of o5 and 4100 GgS month1 are excluded.

ARTICLE IN PRESS S. Koga et al. / Atmospheric Environment 42 (2008) 800–814

811

BC= 78.7 + 0.13V0.3-1.0 R2 = 0.74 1200

1200

Japan

1000

800

BC = 83.3 + 0.12V0.3-1.0

600

R2 = 0.73

400

Northern part of China

200

Black carbon concentration (ngm-3)

Black carbon concentration (ng m-3)

BC= 49.7 + 0.15V0.3-1.0 R2 = 0.72

Korean Peninsula

1000

Other regions Japan and Korean Peninsula BC = 98.2 + 0.07V0.3-1.0

800

R2 = 0.45 600

400 Other regions BC = 90.4 + 0.05V0.3-1.0

200

Southern part of China

R2 = 0.44 0

0 0

2000

4000

6000

8000

10000

0

2000

4000

6000

8000

Volume concentration of aerosol particles

Volume concentration of aerosol particles

from 0.3 to 1.0 μm in diameter (μm3 L-1)

from 0.3 to 1.0 μm in diameter (μm3 L-1)

10000

Fig. 8. Relationships between black carbon mass concentrations and particle volumes from 0.3 to 1 mm in diameter as a function of source region.

particle mass concentration. The peak in the mass size distribution occurred in the size range of 0.56–1.0 mm in aerodynamic diameter. The predominant size range of black carbon was identical to this size range. The unit of mm3 L1 in the horizontal axis in Fig. 8 represents the volume of particles per liter of air. If all aerosol particles have a density of 1 g cm3, 1 mm3 L1 corresponds to 1 ng m3 representing the mass of particles per m3 of air. Suppose the great portion of black carbon mass is in the size range from 0.3 to 1 mm in diameter, the black carbon mass fractions in aerosol particles from China, Japan and the Korean Peninsula, and other regions, then, are estimated to be 13%, 7%, and 5%, respectively, from the slope values of the regression lines. If a density of 1.4 g cm3 obtained by Quinn et al. (2004) is applicable to estimate mass concentrations of aerosol particles, the black carbon mass fractions from China, Japan and the Korean Peninsula, and other regions are 9%, 5%, and 4%, respectively. From the long-term monitoring of aerosol chemical properties on Hong Kong (22.221N, 114.251E), Cheju Island (33.301N, 126.151E) in South Korea, and Sado Island (38.201N, 138.351E) in Japan, Cohen et al. (2004) found that the average fractions of black carbon over these three sites were

well alike mutually with 8–9% of the total mass concentration in aerosol particles below 2.5 mm in diameter. Quinn et al. (2004) measured aerosol properties in the surrounding waters of the Japanese Islands and showed that the black carbon mass fraction in aerosol particles below 1.1 mm in diameter was a fairly constant value from 2% to 4%. These results appear to be misread as a rather uniform proportion of black carbon in spite of different source regions. The uniformity of black carbon mass fraction is probably a superficial relationship. Source regions that affect aerosols over Chichi-jima alternate with a short time interval (see Fig. 6B). Therefore, black carbon mass fractions are probably equalized during aerosol collections even if the fractions differ from each other as a function of source region. In parentheses, when least-squares fit is applied to all the data in Fig. 8, the slope of the regression line is calculated to be 0.09370.002 (R2 ¼ 0.46). The black carbon mass fraction from this slope is estimated to be 7–9%, equivalent to the values obtained by Cohen et al. (2004). Measurements with high temporal resolution are required to investigate black carbon mass fractions as a function of source region. In the optical measurements with an aethalometer, sATN strongly depends on the state of

ARTICLE IN PRESS 812

S. Koga et al. / Atmospheric Environment 42 (2008) 800–814

aerosol mixture and the atmospheric condition (Liousse et al., 1993; Weingartner et al., 2003). The low values of sATN especially were obtained at remote locations (Liousse et al., 1993). In the present study, the data used to determine the black carbon mass fraction were obtained under atmospheric conditions moderately influenced from anthropogenic sources (see Fig. 5C) rather than remote locations. The difference of black carbon mass fractions, however, cannot quite deny a possibility of having yielded by the effect of the sATN variation. It needs further investigation to discriminate definitely the black carbon mass fraction as a function of source region. Although black carbon hardly contributes to CCN (Ishizaka and Adhikari, 2003), aerosol particles will absorb significant amounts of water when hydrophobic carbon particles are coated with organic compounds that act as surfactants (Andrews and Larson, 1993). According to Hasegawa and Ohta (2002), black carbon mass fractions at the non-urban sites, Fukue Island (32.731N, 128.731E), Japan, and Poker Flat (65.121N, 147.331W), Alaska, were 6–13% in fine particles below 2 mm in diameter, whereas mass fractions at the urban site, Sapporo (43.721N, 141.371E), Japan, were very high, approximately 40%. In marked contrast to the mass fractions, the number fractions of internally mixed soot-containing aerosols were much higher at non-urban sites than at the urban site. These results suggest that the accumulation of secondary aerosols on soot-containing aerosols and the subsequent growth of particles result in an internal aerosol mixture. On the basis of microphysical and optical properties of aerosols from East Asia, Clarke et al. (2004) estimated that black carbon was internally mixed with volatile components. Black carbon mass fractions are high values in urban areas neighboring emission sources (e.g. Hasegawa and Ohta, 2002), but over the ocean near the Asian Continent decrease in the range of 2–15% (Kaneyasu et al., 2000; Hasegawa and Ohta, 2002; Cohen et al., 2004; Quinn et al., 2004; Clarke et al., 2004). Black carbon emitted from emission sources is immediately mixed with other compounds, and then the black carbon mass fraction is thought to decrease gradually with the aging of air mass. The black carbon mass fractions on Chichi-jima, however, are in the range of values observed near the Asian Continent and also appear to depend on source regions. These results suggest that the aging of aerosol

particles containing black carbon rapidly declines over the ocean. 6. Conclusions Aerosol particle number size distributions above 0.3 mm in diameter and black carbon mass concentrations in aerosols were observed on Chichi-jima of the Ogasawara Islands in the northwestern Pacific from January 2000 to December 2002. This island is a favorable site to observe polluted air masses from East Asia in winter and clean air masses over the western North Pacific in summer. Typical aerosol number size distributions in clean and polluted air masses were obtained by classifying air masses into clean and polluted air masses, by the number concentration ratio of 0.3–1 to 1–5 mm as an indicator of the degree of pollution. The aerosol particle number size distributions in clean air masses, in appearance, were very close to those in the free troposphere rather than the maritime aerosols. This shows the subsidence of air masses from the free troposphere due to the North Pacific anticyclone. In polluted air masses, the number size distributions were roughly the same as the rural distributions obtained in the previous studies by other investigators. The contribution rates on Chichi-jima to SO2 4 concentrations from the northern (north of 351N) and southern (south of 351N) parts of China, the Korean Peninsula, Japan, volcanoes in Japan, and other regions were computed by the three dimensional Eulerian transport model. Data from December 2000 to January 2001 and from December 2001 to January 2002 were classified under each source region on the basis of contribution rates 450% from each source region. The results of model calculations represent that smokes from volcanoes including Miyake-jima strongly affected the production of SO2 4 . To ignore this fact is to miss the accurate interpretation of temporal variations of sulfur compounds in East Asia. The results also show that Chichi-jima is mainly influenced by anthropogenic emissions from the northern part of China and the Korean Peninsula. Contributions of air masses from the southern part of China are slightly frequent. Aerosol number concentrations and black carbon mass concentrations, however, show the tendency to increase when these air masses arrive on Chichi-jima. Relationships between the volume concentration of aerosol particles and the black carbon mass concentration were obtained as

ARTICLE IN PRESS S. Koga et al. / Atmospheric Environment 42 (2008) 800–814

a function of source region. As a result, black carbon mass fractions were different from each other in aerosol particles from each source region. Assuming a particle density of 1–1.4 g cm3, the black carbon mass fractions in aerosol particles from China, Japan and the Korean Peninsula, and other regions were estimated to be 9–13%, 5–7%, and 4–5%, respectively. Here, a question remains unsettled; how black carbon is internally mixed with other aerosols. There is room for argument on the formation process that determines the fraction. The study of aging process of black carbon over the ocean especially is necessary to assess the lifetime of black carbon. Acknowledgments We are grateful to the staff of Tokyo bika Corporation in the Ogasawara downrange station of the Japan aerospace exploration agency (JAXA). This research owes much to their kind assistance and maintenance. This research was supported in part by a grant from Variability of Marine Aerosol Properties (VMAP) project of the Core Research for Evaluation Science and Technology (CREST) of the Japan Science and Technology Agency (JST) (Chief scientist: M. Uematsu, Ocean Research Institute, University of Tokyo). We also gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and/or READY website (http://www.arl.noaa.gov/ready.html) used in this paper. References Ackerman, T.P., Toon, O.B., 1981. Absorption of visible radiation in atmosphere containing mixtures of absorbing and nonabsorbing particles. Applied Optics 20, 3661–3668. Andrews, E., Larson, S.M., 1993. Effect of surfactant layers on the size changes of aerosol particles as a function of relative humidity. Environmental Science and Technology 27, 857–865. Benkovitz, C.M., Scholtz, M.T., Pacyna, J., Tarrasen, L., Dignon, J., Voldner, E.C., Spiro, P.A., Logan, J.A., Graedel, T.E., 1996. Global gridded inventories of anthropogenic emissions of sulfur and nitrogen. Journal of Geophysical Research 101, 29239–29253. China Environment Yearbook 1990–2003. The Editorial Committee of China Environment Yearbook. China Environment Yearbook Press (in Chinese). China Statistical Yearbook 2002. National Bureau of Statistics of China, China Statistics Press, Website: /http://www.stats.

813

gov.cn/english/statisticaldata/yearlydata/YB2002e/ml/indexE. htmS. Chowdhury, Z., Hughes, L.S., Salmon, L.G., Cass, G.R., 2001. Atmospheric particle size and composition measurements to support light extinction calculations over the Indian Ocean. Journal of Geophysical Research 106, 28597–28605. Clarke, A.D., Shinozuka, Y., Kapustin, V.N., Howell, S., Huebert, B., Doherty, S., Anderson, T., Covert, D., Anderson, J., Hua, X., Moore Jr II, K.G., McNaughton, C., Carmichael, G., Weber, R., 2004. Size distributions and mixtures of dust and black carbon aerosol in Asian outflow: physiochemistry and optical properties. Journal of Geophysical Research 109, D15S09. Cohen, D.D., Garton, D., Stelcer, E., Hawas, O., Wang, T., Poon, S., Kim, J., Choi, B.C., Oh, S.N., Shin, H.-J., Ko, M.Y., Uematsu, M., 2004. Multielemental analysis and characterization of fine aerosols at several key ACE-Asia sites. Journal of Geophysical Research 109, D19S12. Draxler, R.R., Rolph, G.D., 2003. HYSPLIT (HYbrid SingleParticle Lagrangian Integrated Trajectory) Model access via NOAA ARL READY Website: /http://www.arl.noaa.gov/ ready/hysplit4.htmlS. NOAA Air Resources Laboratory, Silver Spring, MD. Georgii, H.W., Warneck, P., 1999. Chemistry of the tropospheric aerosol and of clouds. In: Zellner, R. (Guest Ed.), Global Aspects of Atmospheric Chemistry. Springer, pp. 111–179. Hansen, A.D.A., Rosen, H., Novakov, T., 1984. The aethalometer—an instrument for the real-time measurement of optical absorption by aerosol particles. Science of the Total Environment 36, 191–196. Hasegawa, S., Ohta, S., 2002. Some measurements of the mixing state of soot-containing particles at urban and non-urban sites. Atmospheric Environment 36, 3899–3908. Horvath, H., 1993. Atmospheric light absorption—a review. Atmospheric Environment 27A, 293–317. Ishizaka, Y., Adhikari, M., 2003. Composition of cloud condensation nuclei. Journal of Geophysical Research 108, D44138. Jaenicke, R., 1993. Tropospheric aerosols. In: Hobbs, P.V. (Ed.), Aerosol-Cloud-Climate Interactions. Academic Press, San Diego, CA, pp. 1–31. Kaneyasu, N., Murayama, S., 2000. High concentrations of black carbon over middle latitudes in the North Pacific Ocean. Journal of Geophysical Research 105, 19881–19890. Kaneyasu, N., Takeuchi, K., Hayashi, M., Fujita, S., Uno, I., Sasaki, H., 2000. Outflow patterns of pollutants from East Asia to the North Pacific in the winter monsoon. Journal of Geophysical Research 105, 17361–17377. Koga, S., Tanaka, H., 1999. Modeling the methanesulfonate to non-sea-salt sulfate molar ratio and dimethylsulfide oxidation in the atmosphere. Journal of Geophysical Research 104, 13735–13747. Koga, S., Tanaka, H., Hayashi, M., 1993. Dimethylsulfide measured in the western Pacific and the southern Indian Ocean. Journal of the Meteorological Society of Japan 71, 183–194. Liousse, C., Cachier, H., Jennings, S.G., 1993. Optical and thermal measurements of black carbon aerosol content in different environments: variation of the specific attenuation cross-section, sigma (s). Atmospheric Environment 27, 1203–1211.

ARTICLE IN PRESS 814

S. Koga et al. / Atmospheric Environment 42 (2008) 800–814

Maeda, T., Hayashi, M., Imasu, R., Wang, Z., 2001. A model analysis of transport of sulfur oxides in China and outflow to the sea. Water, Air, and Soil Pollution 130, 355–360. Matsumoto, K., Nagao, I., Tanaka, H., Miyaji, H., Iida, T., Ikebe, Y., 1998. Seasonal characteristics of organic and inorganic species and their size distributions in atmospheric aerosols over the northwestern Pacific Ocean. Atmospheric Environment 32, 1931–1944. Park, R.J., Jacob, D.J., Palmer, P.I., Clarke, A.D., Weber, R.J., Zondlo, M.A., Eisele, F.L., Bandy, A.R., Thornton, D.C., Sachse, G.W., Bond, T.C., 2005. Export efficiency of black carbon aerosol in continental outflow: global implications. Journal of Geophysical Research 110, D11205. Penner, J.E., Andreae, M., Annegarn, H., Barrie, L., Feichter, J., Hegg, D., Jayaraman, A., Leaitch, R., Murphy, D., Nganga, J., Pitari, G., 2001. Aerosols, their direct and indirect effects. In: Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., van der Linden, P.J., Dai, X., Maskell, K., Johnson, C.A. (Eds.), Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 881pp. Quinn, P.K., Coffman, D.J., Bates, T.S., Welton, E.J., Covert, D.S., Miller, T.L., Johnson, J.E., Maria, S., Russell, L., Arimoto, R., Carrico, C.M., Rood, M.J., Anderson, J., 2004. Aerosol optical properties measured on board the Ronald H. Brown during ACE-Asia as a function of aerosol chemical composition and source region. Journal of Geophysical Research 109, D19S01. Rolph, G.D., 2003. Real-time Environmental Applications and Display sYstem (READY) Website: /http://www.arl.noaa. gov/ready/hysplit4.htmlS. NOAA Air Resources Laboratory, Silver Spring, MD. Streets, D.G., Tsai, N.Y., Akimoto, H., Oka, K., 2000. Sulfur dioxide emissions in Asia in the period 1985–1997. Atmospheric Environment 34, 4413–4424.

Streets, D.G., Gupta, S., Waldhoff, S.T., Wang, M.Q., Bond, T.C., Yiyun, B., 2001. Black carbon emissions in China. Atmospheric Environment 35, 4281–4296. Streets, D.G., Bond, T.C., Carmichael, G.R., Fernandes, S.D., Fu, Q., He, D., Klimont, Z., Nelson, S.M., Tsai, Y.N., Wang, M.Q., Woo, J.-H., Yarber, K.F., 2003. An inventory of gaseous and primary aerosol emissions in Asia in the year 2000. Journal of Geophysical Research 108 (D21), 8809. Tan, Q., Huang, Y., Chameides, W.L., 2002. Budget and export of anthropogenic SOx from East Asia during continental outflow conditions. Journal of Geophysical Research 107 (D13), 4167. Tsuruta, H., Sudo, S., Yonemura, S., Shirasuna, Y., Hirano, K., Sera, K., Futatsugawa, S., Maeda, T., Kaneyasu, N., Takeuchi, N., Takamura, T., Nakajima, T., 2003. Characterization, source identification, and optical properties of atmospheric aerosols measured at Amami-Oshima, southwest Japan, during spring seasons under the APEX field campaign program. Findings and current problems in the Asian particle environmental change studies: 2003. JST/CREST/APEX 2003 interim report, 21–40. United Nations, 2005. Energy Statistics Yearbook 2002, 47th issue. United Nations, 604pp. Van Dingenen, R., Raes, F., Putaud, J.-P., Baltensperger, U., Charron, A., Facchini, M.-C., Decesari, S., Fuzzi, S., Gehrige, R., Hansson, H.-C., Harrison, R.M., Hugline, C., Jones, A.M., Lajg, P., Lorbeer, G., Maenhaut, W., Palmgren, F., Querol, X., Rodriguez, S., Schneider, J., ten Brink, H., Tunved, P., Torseth, K., Wehner, B., Weingartner, E., Wiedensohler, A., Wahlin, P., 2004. A European aerosol phenomenology—1: Physical characteristics of particulate matter at kerbside, urban, rural and background sites in Europe. Atmospheric Environment 38, 2561–2577. Weingartner, E., Saathoff, H., Schnaiter, M., Streit, N., Bitnar, B., Baltensperger, U., 2003. Absorption of light by soot particles: determination of the absorption coefficient by means of aethalometers. Atmospheric Environment 34, 1445–1463.