Long-term trend of aerosol composition and direct radiative forcing due to aerosols over Gosan: TSP, PM10, and PM2.5 data between 1992 and 2008

Long-term trend of aerosol composition and direct radiative forcing due to aerosols over Gosan: TSP, PM10, and PM2.5 data between 1992 and 2008

Atmospheric Environment 45 (2011) 6107e6115 Contents lists available at SciVerse ScienceDirect Atmospheric Environment journal homepage: www.elsevie...

380KB Sizes 0 Downloads 5 Views

Atmospheric Environment 45 (2011) 6107e6115

Contents lists available at SciVerse ScienceDirect

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

Long-term trend of aerosol composition and direct radiative forcing due to aerosols over Gosan: TSP, PM10, and PM2.5 data between 1992 and 2008 N.K. Kima, Y.P. Kima, *, C.-H. Kangb a b

Dept. of Environmental Science and Engineering, Ewha Womans University, 11-1, Daehyun-Dong, Seodaemun-Gu, Seoul 120-750, Republic of Korea Dept. of Chemistry, Jeju National University, 1-Ara-Dong, Jeju, Republic of Korea

a r t i c l e i n f o

a b s t r a c t

Article history: Received 11 May 2011 Received in revised form 2 August 2011 Accepted 17 August 2011

In this study, size segregated measurement data between 1992 and 2008 at Gosan, Jeju, Korea were analyzed. Long-term trend of aerosol composition changes related to the emission change was analyzed and direct radiative forcing due to aerosols over Gosan was calculated. The concentration variations of ion components and carbonaceous aerosols matched well to the emission changes in Northeast Asia, and the concentration variations of the elements with natural origin were highly correlated to the frequency of dust storms in the region. The net aerosol forcing varied from 4.48 W m2 to 0.53 W m2 at Gosan and it was increasing. This was mainly because of continuous decrease of sulfate concentration and steady increase of EC concentration in the region. It was found that for the determination of the direct aerosol radiative forcing, relative humidity (RH) was most critical during summer season when it was high (over 75%), and EC was most critical during spring and fall. Ó 2011 Elsevier Ltd. All rights reserved.

Keywords: Size segregated aerosols Ions Elements Carbonaceous aerosols Direct aerosol radiative forcing Air pollutant emissions

1. Introduction Northeast Asia is characterized by high energy consumption. China, Japan, and South Korea consumed 19.5%, 4.2%, and 2.1% of the world total primary energy, respectively in 2009 (BP, 2010). Consequently, resultant emissions of anthropogenic air pollutants are huge. Based on the satellite observation data of NOx which is emitted by all combustion processes, significant concentration increase of about 50% over the industrial areas of China was observed (Richter et al., 2005). The emission of SO2, another major pollutant emitted by fossil fuel combustion, decreased from 23.7 to 19.3 Mt between 1995 and 2002 in China, but started to increase again since 2003 and reached to 25.9 Mt in 2006 (State Environmental Protection Administration, 2008). Also, organic aerosols are emitted into the atmosphere through incomplete combustion of biomass and fossil fuel. These emission changes affect the concentrations of ambient aerosols. Recently, the effect of aerosols on the climate change is becoming more prominent because these aerosols play an important role in regulating the amount of solar radiation absorbed by the earth atmosphere (Charlson et al., 1992; Jacobson, 2004; Khan et al., 2010). Elemental carbon (EC) or Black carbon (BC) is known for the direct warming by absorbing solar radiation, and particulate sulfate

* Corresponding author. Tel.: þ822 3277 2832; fax: þ822 3277 3275. E-mail address: [email protected] (Y.P. Kim). 1352-2310/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2011.08.051

(SO2 4 ) transformed by SO2 oxidation is known to contribute to cool the air by scattering solar radiation. The aerosols are both temporally and spatially variable, and therefore, the effect on climate change by aerosols are even more important in Northeast Asia region. Gosan is one of the cleanest areas in Korea and an excellent location to study the ambient aerosols in Northeast Asia (Kim et al., 2009). Gosan has been a supersite during several international intensive measurement studies such as ACE-Asia, and important results about the characteristics of chemical composition of ambient particles and direct aerosol radiative forcing exist. However, the study periods of those studies were rather short since most studies were based on episodic measurements. There is a few multi-year study results (Park et al., 2004; Kim et al., 2009), but only the ion components or the elements in Total Suspended Particles (TSP) were analyzed in those studies. In this study, long-term trend of aerosol composition changes related to the emission changes based on the size segregated measurement data between 1992 and 2008 at Gosan, Jeju, Korea were analyzed. Then, direct aerosol radiative forcing due to aerosols over Gosan was calculated. Also, the relationship between the direct aerosol radiative forcing and the aerosol chemical components, relative humidity were discussed. This is the first study to summarize the characteristics of long term measurement data in all particle sizes including the concentrations of ions, elements, carbonaceous species measured at Gosan during last 16 years. The data summarized in this study will be very

6108

N.K. Kim et al. / Atmospheric Environment 45 (2011) 6107e6115

Table 1 The sampling periods and the numbers of data used in this study.

Ions

Elements Elemental carbon (EC) Organic carbon (OC)

Size

Sampling period

Number of data

TSP PM10 PM2.5 TSP PM10 PM2.5

1992. 3.e2008. 12. 2000.3.e2008. 2. 1994. 7.e2008. 2. 1993. 4.e2008. 12. 2000.3.e2006. 4. 1994. 7.e2007. 1.

Before QA/QC

PM2.5

1994. 7.e2007. 1.

316

2478 315 855

Table 3 The annual mean concentrations of mass and ionic components in PM10 (unit: mg m3). After QA/QC

2264 235 648

1475 166 316

useful to find out the change of air quality in Northeast Asia during last two decades because Gosan is a very important background site in this region. Also, the investigation of the direct aerosol radiative forcing using this long term measurement data is meaningful since it is rare and important to find out the aerosol effect on climate change in this region. 2. Measurements The measurement site is located on the western tip of Jeju (126 100 E, 33 170 N). A trailer containing the TSP, PM10 (Particulate Matter with a diameter of 10 mm or less) and PM2.5 samplers is situated about 10 m inside of cliff, which is about 70 m above sea level. Sampling inlet is located about 6 m above the ground. Jeju upper air meteorological station is located 100 m northeast of the site and upper air meteorological parameters are measured twice a day and surface meteorological parameters are measured continuously. The detailed map of the measurement site is shown in Kim et al. (2009). TSP were collected by a high volume tape sampler (Kimoto Electric Co., Model 195A), which is an automatic sampling system with roll type PTFE filters (Sumitomo Electric, 100 mm  10 m). Particles were collected for either 6 or 24 h and then a new clean filter surface was moved to the sampling area on which particles were collected. The flow rate was about 170 LPM. All the data presented in this work are 24 h averaged results. The mass concentration could not be analyzed with this instrument since the collected particles are rolled in the tape. After the sampling, the Teflon filters were divided into two sections: one part for elemental analysis and the other part for ion analysis. The PM10 sampler consisted of a Teflon-coated aluminum cyclone with a cut size of 10 mm at a flow rate of 16.71 LPM (URG, USA), a Teflon filter holder for 47 mm filters (Sarvillex, USA),

2000 2001 2002 2003 2004 2005 2006 2007

þ Mass NHþ 4 Na

 NO 3 Cl

nss-SO2 nss-Kþ nss-Ca2þ nss-Mg2þ 4

29.6 32.3 26.3 22.9 32.0 38.0 27.6 20.7

2.27 1.23 1.41 1.38 4.05 2.63 1.83 1.52

7.04 5.81 2.90 2.90 4.19 9.32 7.40 5.59

2.63 1.93 1.01 1.35 2.01 3.74 2.72 1.85

0.35 0.47 0.52 0.31 0.55 0.27 0.49 0.41

0.20 0.36 0.46 0.27 0.35 0.16 0.38 0.28

0.57 0.24 0.15 0.07 0.22 0.40 0.38 0.20

0.12 0.27 0.23 0.06 0.18 0.29 0.34 0.13

0.03 0.05 0.02 0.02 0.02 0.14 0.03 0.03

a critical orifice (BGI, USA) and a pump (Dayton, USA). Two PM10 samplers were used; one for the elements and the other for the ion components. The PM2.5 sampler consisted of a Teflon-coated aluminum cyclone with a cut size of 2.5 mm at a flow rate of 16.7 LPM (URG, USA), a Teflon filter holder for 47 mm filters (Sarvillex, USA), a critical orifice (BGI, USA) and a pump (Dayton, USA). Also, two PM2.5 samplers were used; one for the carbonaceous aerosols, and the other for the ion components. Eight ions in TSP, PM10, and PM2.5 were analyzed. NHþ 4 ion was analyzed by the indophenol method with a UV visible spectrophotometer (Kontron, Model Uvikon 860) and Naþ, Kþ, Ca2þ, and Mg2þ by the atomic absorption spectroscopy (GBC, Model   Avanta-P). Anions, SO2 4 , NO3 , and Cl were analyzed by the ion chromatography (Dionex, Model DX-500). Non-sea salt (nss)-Kþ, nss-Ca2þ, nss-Mg2þ, and nss-SO2 4 concentrations were estimated by assuming all Naþ was from sea salt and subtracting sea salt composition. Details on the ion analysis were given elsewhere (Kim et al., 1998; Park et al., 2004). To ensure the quality of the ion data, two steps of quality control procedures were taken for the whole data set. First, instrument quality check and the sampling and analysis QA/QC had been carried out. Second, ion balance was used to check the validity of the data. The data with the ratio of the sum of the cation concentrations to the anion concentrations being within 30% was used for further data analysis (Park et al., 2004). The criterion of 30% was chosen since organic ions and carbonates could be up to 30% of the total ion concentrations at Gosan. Inductively coupled plasma (ICP) spectrophotometer (JobinYvon Emission Instruments, Model JY 38S till 1997 and Thermo Jarrel Ash, Model Iris-duo from 1998) with a polychromator (PMT) detector was used for elemental analysis. Twelve elements in TSP (Cr, Ca, Zn, Cd, Ni, Fe, Al, Cu, Ti, Mn, Pb, and V) were analyzed until 1997, and twenty elements in TSP (Al, Fe, Ca, Mg, Na, K, S, Ti, Mn, Ba, Sr, Zn, V, Cr, Pb, Cu, Ni, Co, Mo, and Cd) were analyzed from 1998.

Table 2 The annual mean concentrations of ionic components in TSP (unit: mg m3).

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

NHþ 4

Naþ

NO 3

Cl

nss-SO2 4

nss-Kþ

nss-Ca2þ

nss-Mg2þ

1.65 1.56 1.85 1.16 1.55 1.39 1.49 1.25 1.74 1.43 1.43 1.32 1.34 2.39 2.80 2.30 2.34

1.60 1.76 1.66 1.97 1.70 1.53 1.84 1.91 1.76 2.66 1.84 1.70 1.86 2.67 2.11 1.89 1.52

0.81 1.38 1.19 1.61 2.25 1.36 1.86 1.91 2.18 2.19 1.96 1.81 1.88 2.07 2.57 2.05 1.68

1.88 1.89 1.53 2.00 1.67 1.39 1.67 1.86 1.50 2.69 1.89 1.48 1.46 2.25 1.69 1.74 1.43

6.78 6.96 8.00 6.55 7.61 6.56 6.60 5.90 6.70 5.90 5.97 4.82 5.43 7.95 8.62 7.67 8.28

0.30 0.29 0.38 0.38 0.37 0.46 0.38 0.27 0.31 0.28 0.25 0.25 0.24 0.34 0.34 0.29 0.32

0.25 0.46 0.42 0.48 0.51 0.40 0.53 0.36 0.53 0.74 0.50 0.21 0.22 0.37 0.30 0.25 0.27

0.05 0.08 0.06 0.13 0.08 0.03 0.06 0.05 0.05 0.05 0.08 0.10 0.09 0.03 0.11 0.20 0.02

Table 4 The annual mean concentrations of mass and ionic components in PM2.5 (unit: mg m3).

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

þ Mass NHþ 4 Na

 NO 3 Cl

29.2 16.3 19.5 17.6 15.5 20.2 21.7 26.4 19.5 19.0 24.0 23.9 22.7 18.9

0.10 0.67 0.79 0.37 0.44 0.91 1.76 1.18 1.01 1.14 2.06 1.67 1.12 1.45

4.24 1.82 1.60 1.50 1.17 1.38 1.94 1.73 1.00 1.22 1.58 2.15 1.96 1.97

0.47 0.45 0.55 0.47 0.32 0.43 0.37 0.46 0.40 0.29 0.46 0.39 0.54 0.38

nss-SO2 nss-Kþ nss-Ca2þ nss-Mg2þ 4

0.76 13.44 0.84 6.80 0.26 5.54 0.38 5.11 0.20 4.25 0.33 4.30 0.22 5.38 0.36 4.83 0.29 3.03 0.21 2.85 0.26 3.95 0.14 5.23 0.31 5.91 0.34 5.42

0.27 0.11 0.29 0.29 0.29 0.27 0.33 0.25 0.13 0.10 0.17 0.14 0.25 0.18

0.04 0.22 0.17 0.10 0.11 0.09 0.12 0.19 0.14 0.05 0.10 0.09 0.23 0.24

0.00 0.04 0.00 0.02 0.02 0.03 0.02 0.04 0.01 0.03 0.04 0.04 0.04 0.04

N.K. Kim et al. / Atmospheric Environment 45 (2011) 6107e6115

Twenty elements in PM10 (Al, Fe, Ca, Mg, Na, K, S, Ti, Mn, Ba, Sr, Zn, V, Cr, Pb, Cu, Ni, Co, Mo, and Cd) were analyzed until 2006. Details on the elemental analysis were given in Kim et al. (2009). Carbonaceous aerosols (EC and Organic Carbon (OC)) in PM2.5 were analyzed by three different methods. From 1994 to 2000, they were analyzed by Thermal Manganese dioxide Oxidation (TMO) method (Kim et al., 1999; NIER, 2007). From 2001 to 2004, they were analyzed by thermal conductivity detector, and from 2005, they were analyzed by Thermal Optical Transmittance (TOT) methods (NIER, 2007). The total number of data was reduced from 314 to 176, because the data between 2001 and 2004 was removed due to the verification problem of the analytical method.

a

The sampling periods and the numbers of data used in this study are shown in Table 1. 3. Result 3.1. Ion composition changes of TSP, PM10, and PM2.5 The annual mean concentrations of eight ions for TSP, PM10 and PM2.5 are shown in Tables 2e4, respectively. In this work, the annual mean concentration is defined as the mean value from March of that year to February of the next year except TSP annual mean of 2008 (March 2008 to December 2008). Among the ions,

10

-3

Concentration (μg m )

8

6

4

2

TSP PM10 PM2.5

0 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

b

5

TSP PM10 PM2.5

-3

Concentration (μg m )

4

6109

3

2

1

0 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

 Fig. 1. The variations of the annual mean concentrations of (a) nss-SO2 4 and (b) NO3 in TSP, PM10, and PM2.5.

30

3.0

25

2.5

20

2.0

15

1.5

10

1.0 SO2 (China)

Emission in Korea (Mt)

N.K. Kim et al. / Atmospheric Environment 45 (2011) 6107e6115

Emission in China (Mt)

6110

SO2 (S. Korea) NOx (S. Korea)

5

0.5

0

0.0 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Fig. 2. The emission changes of total SO2 in China (State Environmental Protection Administration, 1998, 2000, 2002, 2006, 2008), and the emission changes of total SO2 and total NOx in Korea (NIER, 2009).

the mass concentration of nss-SO2 4 was the highest, followed by  þ NHþ 4 and NO3 . The concentrations of sea salt components (Na and Cl) were high only in TSP because those sea salts are mainly in coarse particles. The concentrations of nss-Kþ, nss-Ca2þ, nss-Mg2þ were low compared to other ions. The variations of the annual mean concentrations of nss-SO2 4 2 and NO 3 are shown in Fig. 1. The concentrations of nss-SO4 decreased continuously till 2003. The nss-SO2 concentration in TSP 4 decreased by 60.2% (8.00 mg m3 in 1994 to 4.82 mg m3 in 2003), that in PM10 decreased by 41.2% (7.04 mg m3 in 2000 to 2.90 mg m3 in 2003) and that in PM2.5 decreased by 51.4% (5.54 mg m3 in 1996 to 2.85 mg m3 in 2003). However, after 2003, it started to rapidly increase and showed a peak concentration in 2006 and kept high until 2008 in TSP and PM2.5. The concentration in PM10 also increased since 2003 and showed a peak concentration in 2005. The nss-SO2 4 concentration change at Gosan between 1992 and 2002 was highly related to the emission change of China (Park et al., 2004). According to the reports on the state of the environment in China (State Environmental Protection Administration, 1998, 2000, 2002, 2006, 2008), the emission of SO2, major pollutant emitted by fossil fuel combustion and the precursor of nss-SO2 4 , has decreased

from 23.7 to 19.3 Mt between 1995 and 2002 in China, but started to increase since 2003 and reached to 25.9 Mt in 2006 and kept high in 2007 and 2008 as 24.7 Mt and 23.2 Mt, respectively (Fig. 2). Compared to the SO2 emission in China, the SO2 emissions in South Korea was very small (1e2% of the emission in China) and kept the almost same emission level during last 8 years (Fig. 2). It was 0.48 Mt in 1999, and kept decreasing by 0.40 Mt in 2007 (NIER, 2009). Thus, the concentration change of nss-SO2 4 at Gosan during last 14 years is well matched by the SO2 emission trend in China rather than the SO2 emission trend in South Korea. The concentrations of NO 3 increased continuously at all size particles, and showed the peak concentration in 2006 in TSP and in 2004 in PM10 and PM2.5. The NO 3 concentration in TSP increased by 317% (0.81 mg m3 in 1992 to 2.57 mg m3 in 2006), that in PM10 increased by 178% (2.27 mg m3 in 2000 to 4.05 mg m3 in 2004) and that in PM2.5 increased by 261% (0.79 mg m3 in 1996 to 2.06 mg m3 in 2004). After that, the concentrations of NO 3 slightly decreased at all size. In 2004, NO 3 concentration in PM10 was higher than that of TSP. It was caused by the high concentration events in October. The NO 3 concentrations in TSP and PM2.5 were also high in those days, but there are more data of TSP and PM2.5

Table 5 The annual mean concentrations of the elements in TSP (unit: ng m3).

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Al

Fe

Ca

Mg

Na

K

S

Ti

Mn

Ba

Sr

Zn

V

Cr

Pb

Cu

Ni

Co

Mo

Cd

422.2 244.1 509.4 618.2 e 1124.7 402.8 626.2 821.3 1254.4 290.6 355.9 350.7 691.3 383.1 311.1

605.8 343.3 483.6 688.1 e 787.6 371.6 561.0 703.7 1023.3 233.1 200.5 260.6 410.2 356.4 253.2

637.3 527.8 506.6 613.2 e 939.4 530.7 635.5 731.4 1215.8 284.2 279.9 248.1 359.9 424.7 211.8

e e e e e 487.7 336.1 499.6 440.8 621.4 204.8 164.7 188.2 326.3 260.2 177.0

e e e e e 1352.6 1408.0 1409.0 1668.9 1797.6 1216.0 855.1 1210.0 1338.5 1060.8 899.1

e e e e e 623.4 284.5 400.8 496.6 611.1 344.9 242.3 232.2 427.7 336.6 284.1

e e e e e 1964.3 1838.5 2189.4 1707.0 2193.1 1643.1 1754.7 1655.0 2689.2 2042.0 2178.5

21.0 11.4 17.0 21.2 e 40.0 30.4 31.8 40.7 36.3 14.2 14.5 30.0 24.0 16.2 13.1

12.8 13.5 13.7 18.9 e 24.4 16.2 20.1 23.9 32.1 10.5 15.0 16.4 20.8 15.8 10.5

e e e e e 7.5 4.6 6.5 6.5 9.2 3.4 3.1 3.5 7.9 8.4 3.0

e e e e e 6.2 4.0 5.2 5.2 5.8 2.3 2.2 2.4 4.2 3.3 2.7

62.5 44.9 61.7 69.5 e 46.9 39.0 45.0 45.7 55.3 41.9 41.3 48.5 63.6 53.3 35.2

5.6 9.7 3.9 3.1 e 8.9 7.1 8.0 8.0 9.5 4.4 4.8 7.0 8.1 3.4 2.1

2.3 2.4 4.6 4.2 e 2.4 2.8 2.9 2.6 4.4 1.2 0.9 1.6 2.9 2.3 2.0

21.6 18.4 19.4 31.3 e 37.7 46.1 40.1 39.4 41.1 26.4 19.6 18.5 74.8 80.5 17.2

4.5 4.3 6.7 8.7 e 3.5 3.7 4.9 4.0 4.8 3.6 4.0 4.7 5.7 4.5 2.5

3.7 8.1 6.6 15.4 e 3.4 2.9 4.9 4.3 5.7 2.9 3.1 6.6 3.5 2.8 3.1

e e e e e 0.8 0.6 0.6 0.6 0.9 0.2 0.2 0.9 1.5 0.5 0.6

e e e e e 1.2 1.1 0.9 0.8 0.8 1.0 1.6 0.6 0.9 1.0 0.4

1.0 3.1 1.2 1.3 e 0.7 0.8 1.2 0.9 0.9 0.8 0.7 0.8 1.1 0.9 0.6

N.K. Kim et al. / Atmospheric Environment 45 (2011) 6107e6115

6111

Table 6 The annual mean concentrations of the elements in PM10 (unit: ng m3).

2000 2001 2002 2003 2004 2005 2006

Al

Fe

Ca

Mg

Na

K

S

Ti

Mn

Ba

Sr

Zn

V

Cr

Pb

Cu

Ni

Co

Mo

Cd

279.1 1000.2 597.1 367.0 332.8 52.2 245.1

346.9 1102.4 725.2 353.1 250.6 82.4 310.8

376.2 699.5 1011.4 383.3 304.5 109.3 159.4

658.4 622.2 471.4 267.3 186.5 96.2 110.9

1526.2 1564.2 1869.8 1298.4 977.1 97.2 191.4

380.6 494.4 468.2 395.5 266.4 106.0 218.9

2348.9 1623.7 1837.8 1558.2 1363.9 466.5 931.4

10.3 39.6 26.5 18.4 14.1 3.8 8.1

9.4 36.3 23.9 14.5 17.5 3.0 4.2

4.6 12.9 6.1 5.0 3.4 1.7 2.8

4.4 9.7 5.1 2.7 2.6 0.8 1.3

44.0 49.1 41.3 51.5 39.1 27.4 33.4

5.5 5.4 6.8 5.2 2.3 0.6 3.5

1.1 6.4 3.2 1.6 0.7 2.4 1.7

30.5 39.7 42.3 31.2 27.4 7.3 8.0

8.0 7.0 4.2 3.7 5.5 2.4 2.8

3.9 52.2 4.5 4.8 2.4 2.5 5.0

0.5 0.4 0.9 0.3 0.1 0.7 1.3

1.3 0.8 0.7 0.8 0.7 0.3 0.3

0.9 2.0 1.0 0.9 0.8 0.6 0.5

than PM10 throughout the whole year, so the high concentration peaks of TSP and PM2.5 were much smoothed than PM10. The concentration change of NO 3 at Gosan was also well matched to the NOx emission trends in China and South Korea. The emission of NOx from China is drastically increasing. Streets and Waldhoff (2000) predicted the NOx emission from China will increase by 122% from 1995 to 2020. According to Ohara et al. (2007), total emissions of NOx in Asia increased by 2.8 times from 1980 to 2003, and the Chinese NOx emissions increased by 3.8 times from 3.77 Mt in 1980 to 14.5 Mt in 2003 in particular. These NOx trends in the period 1996e2003 over China were also validated by comparison with column NO2 data from the GOME (Global Ozone Monitoring Experiment) satellite by Akimoto et al. (2006). Also, He et al. (2007) found a continuous increase of NO2 concentration during the past decade with a sharp linear increase rate of 14.1e20.5%/year after the year 2000 in satellite observation data. The emission on NOx in South Korea also increased from 1.07 Mt in 1999 to 1.37 Mt in 2004, and slightly decreased to 1.18 Mt in 2007 (NIER, 2009). 3.2. Elemental concentration changes of TSP and PM10 The annual mean concentrations of the elements in TSP and PM10 are shown in Table 5 and Table 6. The concentrations of the elements with natural dust origin such as Al, Ca, Fe, K, Mg were high both in TSP and PM10. The concentrations of Zn, Mn, Pb, Ti were in the middle and the concentrations of V, Cr, Cu, Cd were very low. The concentration variations of the elements with natural dust origin are highly correlated to the frequency of dust storm in this region. The number of days that dust storm occurred at Gosan last 16 years are shown in Table 7. The concentrations of natural origin species were high in 1998, 2001, 2002, and 2006 when there were frequent dust storms. Also, in the previous studies with the same kind of data (Park et al., 2003; Kim et al., 2009), it was found that the concentrations of elements with natural origin increased during dust storm period. 3.3. EC and OC concentration changes in PM2.5 intensive measurements The mean concentrations of OC and EC for each intensive measurement period are shown in Fig. 3. The OC concentrations were 2e4 mg m3 and didn’t show any obvious increasing or decreasing trend. Compared to other background areas, the OC concentrations at Gosan were higher than the background areas in Japan (Hatakeyama, 1993), and similar to the background area in the U.S.A. (Malm et al., 1994; Khan et al., 2010). Table 7 Number of dust storm days at Gosan, Korea (KMA, 2011). Year No. of days Year No. of days

1993 5 2001 21

1994 1 2002 12

1995 4 2003 4

1996 4 2004 6

1997 1 2005 7

The EC concentrations were below 0.5 mg m3 (0.09e0.42 mg m3) before 1999, but they showed continuous increasing trend after the year 2000. To compare to other background areas, the EC concentrations at Gosan were lower than the background areas in Japan (Hatakeyama, 1993), and higher than the background areas in the U.S.A. (Malm et al., 1994; Khan et al., 2010). As it is mentioned in Chapter 2, the OC and EC analysis methods before 2001 and after 2005 were different (TMO and TOT), and therefore, the increasing trend of EC after the year 2000 might be considered to be uncertain because the EC concentrations varies widely by analysis methods. According to Fung et al. (2002), the EC concentrations analyzed by the TMO and TOR methods were comparable, and according to Chow et al. (2001), the EC concentrations analyzed by the TOT method were lower than the half of the EC concentrations analyzed by the TOR method. It means, the EC concentrations after 2005 were the lower limit values, and the increasing trend of EC can be considered as the real one. According to Ohara et al. (2007), BC and OC emissions in China showed decreasing trend from 1996 to 2000 because of the reduced use of biofuels and coal in the domestic and industry sectors. However, since 2000, the Chinese emissions of these species have begun to increase. According to the other studies about the emissions in East Asia (Streets et al., 2003; Zhang et al., 2009), BC emission was 1049 Gg yr1 in 2000 and increased to 1811 Gg yr1 in 2006 in China. During the same period, the BC emission in South Korea was 22 Gg yr1 in 2000 and slightly decreased to 17 Gg yr1 in 2006. Therefore, the increasing trend of the EC concentration at Gosan after 2000 can be explained by these regional emission trends. Both EC and OC showed maximum concentrations in spring 2000, especially EC showed about 3 times higher concentration compared to other measurement periods. According to Kim and Kim (2006), during this measurement period, Gosan was affected by severely contaminated air mass stagnated over Southern China, and all other ions representing anthropogenic pollution such as  2 þ NHþ 4 , NO3 , nss-SO4 , nss-K were also very high compared to other measurement periods. The OC to EC ratios for each intensive measurement period are shown in Fig. 4. The OC to EC ratio shows a decreasing trend due to steady increase of EC concentrations. OC to EC ratio were 20e30 before the year 1999, but after the year 2000, the ratio decreased to 3e7. The correlation coefficient values between OC and EC are shown in Table 8. The correlations between OC and EC were high throughout all the sampling periods except in spring 1999. Since the relationship between EC and OC concentrations was good, majority of the OC measured at Gosan was considered to be emitted and/or transported along with EC. 3.4. Direct aerosol radiative forcing due to aerosol over Gosan

1998 12 2006 9

1999 0 2007 5

2000 13 2008 3

Atmospheric aerosols are known to cool or warm the atmosphere directly by absorption, scattering and emission of solar and terrestrial radiation and indirectly by changing the albedo and the

6112

10 N.K. Kim et al. / Atmospheric Environment 45 (2011) 6107e6115

spring 1996

winter 1996

winter 1996

fall 1997 winter 1997

fall 1997

fall 1998

winter 1997

spring 1999

fall 1998

spring 2000

spring 1999

summer 2000

spring 2000

OC

fall 2000 fall 2005

summer 2000 fall 2000

winter 2005

fall 2005

spring 2006

winter 2005

summer 2006 fall 2006

spring 2006

winter 2006

summer 2006

Okinawa, Japan

fall 2006

Nagano, Japan

winter 2006

Marblemount, USA

Okinawa, Japan Nagano, Japan Marblemount, USA

TMO TOT

TMO TOT

Lye brook, USA

8

winter 1995

spring 1996

Acadia National Park, USA

6

summer 1995

4

summer 1994

summer 1995

2

0

3.0

2.5

2.0

1.5

1.0

0.5

0.0 summer 1994

Whiteface mountain, USA

a

b

-3

OC Concentration (μg m )

winter 1995

EC

Fig. 3. The temporal trend of the OC and EC concentrations for each intensive measurement period (Okinawa and Nagano: Hatakeyama, 1993; Marblemount: Malm et al., 1994; Whiteface mountain, Acadia National Park, and Lye brook: Khan et al., 2010).

-3

EC Concentration (μg m )

N.K. Kim et al. / Atmospheric Environment 45 (2011) 6107e6115 100

6113

3 2 1 0

ΔFr (W m-2)

OC/EC (Log)

-1

10

-2 -3 -4 -5 -6 -7 -8

fall 2006

winter 2006

summer 2006

fall 2005

spring 2006

fall 2000

summer 2000

spring 2000

fall 1998

spring 1999

fall 1997

winter 1997

winter 1996

summer 1995

spring 1996

-9

summer 1994

fall 2006

winter 2006

spring 2006

summer 2006

fall 2005

winter 2005

fall 2000

spring 2000

summer 2000

fall 1998

spring 1999

fall 1997

winter 1997

winter 1996

winter 1995

spring 1996

summer 1995

summer 1994

1

Fig. 4. The OC to EC ratios for each intensive measurement period.

Fig. 5. The net direct aerosol radiative forcing due to aerosols over Gosan, Korea.

life time of clouds by acting as cloud condensation nuclei (Charlson et al., 1992; Chang and Park, 2004). A large positive component of radiative forcing from aerosols is due to BC (similar to EC) that is released from the burning of fossil fuel and biomass, and, natural fires (Jacobson, 2001b). Sulfate particles are non absorptive in the visible region of the electromagnetic spectrum, they provide the most significant anthropogenic cooling contribution to global direct radiative forcing (Charlson et al., 1992; Jacobson, 2001a; Martin et al., 2004). In this study, we tried to find out long term regional characteristics of direct aerosol radiative forcing based on the 13 year measurement data measured at Gosan from 1994 to 2007 To calculate direct aerosol forcing, the following equation derived by Charlson et al. (1991) and modified by Chýlek and Wong (1995) was used. This equation was chosen since it is easy to calculate with the surface measurement data, and widely used in many other studies (Charlson et al., 1991, 1992; Chýlek and Wong, 1995; Haywood and Shine, 1995; Khan et al., 2010).

efficiency per mass, m2 g1) ¼ Qsc þ Qabs; B (aerosol burden, g m2); *Parameters (except N and z) are from Seinfeld and Pandis (2006). The direct aerosol radiative forcing calculated by this equation is the radiative forcing at the top of atmosphere (TOA), not the surface even though all the calculations are based on the surface measurement data. We assumed vertical profiles of aerosols to be uniformly mixed to the 1000 m from surface. The calculation results are only valid under those conditions. Although, this equation is very simplified one and includes many assumptions, it is considered that there’s enough reliability in the calculation results within the assumptions. To get the Qext, Qsc, and Qabs, the ELSIE (Elastic Light Scattering Interactive Efficiency) model (Sloane, 1984, 1986) was used. The ELSIE model is based on MIE theory extended to concentric sphere scatterers. Optical equation for the light scattering coefficient is as follows:

i h S 2 DFR ¼  0 Tatm ð1  NÞ ð1  aÞ2 2bzsc  4azabs 4

bscat ðlÞ ¼ (1)

2

Where, S0: Solar constant, 1370 (W m ); S0/4 is the globally averaged incident solar flux at the top of the atmosphere; Tatm: Transmittance of the atmosphere above the aerosol layer, 0.76; N: Fraction of sky covered by clouds, from Gosan meteorological observatory data for each sampling day; a: Albedo of underlying surface, 0.3; b: Fraction of radiation scattered by aerosol into the upper hemisphere, 0.125; z: Optical depth; z ¼ QextB; Qext (scattering

Table 8 The correlation coefficient values (r) between OC and EC for each intensive measurement period. Sampling period

r

Sampling period

r

Summer 1994 Summer 1995 Winter 1995 Spring 1996 Winter 1996 Fall 1997 Winter 1997 Fall 1998 Spring 1999

0.83 0.90 e 0.05 0.68 0.90 0.96 0.91 0.27

Spring 2000 Summer 2000 Fall 2000 Fall 2005 Winter 2005 Spring 2006 Summer 2006 Fall 2006 Winter 2006

0.99 0.82 0.90 0.93 0.91 0.75 0.86 0.97 0.96

D Zmax

pD2 4

Qscat ðm; aÞnðDÞdD

0

Where, l: wave length of the light; Qscat: Scattering efficiency; m: the index of refraction; D: particle diameter; a: pD/L; n(D)dD: particle number density. In this model, the aerosols are considered to have a mixed chemical composition which varies with particle size. In this study, we used fixed sized particles, PM2.5 because OC and EC were analyzed only in PM2.5. There might be some errors by fixing the particle size to PM2.5, but the calculation results seem to be reliable because EC and SO2 4 , two major aerosols affecting on the direct aerosol radiative forcing mainly exist in fine particles. The core of each particle is primarily taken to be nonvolatile carbon, and enclosed in a water-soluble exterior. The soluble layer responds to changes in the relative humidity (RH) by absorbing (or releasing) water. The water content of the aerosol particles is derived from a semi-empirical application of the thermodynamic equations for particle growth. The model is valid for all range of RH. Light scattering efficiencies, the change in the amount of light scattered with a change in mass of an aerosol constituent. Input data is consisted of 2 2 the concentrations of PM2.5 mass, NO 3 , SO4 (nss-SO4 ), OC, EC, and RH. As an output data, we can get the Qext, Qscat, and Qabs (m2 g1) of each component. The direct aerosol radiative forcing

6114

N.K. Kim et al. / Atmospheric Environment 45 (2011) 6107e6115

was calculated for each measurement day, and averaged for each measurement periods. As it is shown in Fig. 5, the net aerosol forcing averaged for each measurement period varied from 4.48 W m2 to 0.53 W m2 at Gosan and it was increasing. This was mainly because of continuous decrease of the sulfate concentrations and steady increase of the EC concentrations. These results are comparable to other study results carried out at Gosan. Yoon and Kim (2006) calculated the aerosol radiative forcing for the Asian dust event in 2002, and the result was 5.60 W m2 at surface, 3.81 W m2 at TOA, and 1.79 W m2 in the atmosphere when the RH was 80%. Also, Park et al. (2005)

calculated the aerosol radiative forcing for the Asian dust event in 2002, and the aerosol radiative forcing was 11 W m2 at surface and 6 W m2 at TOA. Kim et al. (2006) calculated direct aerosol radiative forcing at the surface. The values contributed by watersoluble components were 14.1 to 13.7 W m2 and the values contributed by EC were 11.1 to 9.3 W m2, respectively. To find out the most effective factor affecting on direct aerosol forcing, a sensitivity analysis, 50%, þ50%, and þ100% changes of 2 measured mass concentrations of 5 species (NO 3 , nss-SO4 , OC, EC, residue) and 50% and 75% changes of RH affecting on the radiative 2 forcing were carried out (Fig. 6). Among the 5 species (NO 3 , nss-SO4 , 3

3

0

-3

-3

No change -50% +50% +100%

No change -50% +50% +100%

-6

-6

-9

-9

3

3

EC

0

0

-3

-3 No change -50% +50% +100%

No change -50% +50% +100%

-6

-6

-9

-9 3

3

RH

Residue 0

0

-3

-3

No change -50% -75%

No change -50% +50% +100%

-6

-6

Fig. 6. Changes of DFr for the changes of measured mass concentrations of each factors and RH.

fall 2006

winter 2006

summer 2006

fall 2005

spring 2006

fall 2000

spring 2000

summer 2000

fall 1998

spring 1999

fall 1997

winter 1997

winter 1996

spring 1996

summer 1995

summer 1994

fall 2006

winter 2006

summer 2006

fall 2005

spring 2006

fall 2000

spring 2000

summer 2000

fall 1998

spring 1999

fall 1997

winter 1997

winter 1996

spring 1996

-9 summer 1995

-9 summer 1994

ΔFr (W m-2)

Δ Fr (W m-2)

ΔFr (W m-2)

OC

Δ Fr (W m-2)

ΔFr (W m-2)

0

Δ Fr (W m-2)

nss-SO42-

NO3-

N.K. Kim et al. / Atmospheric Environment 45 (2011) 6107e6115

OC, EC, residue and RH), only EC contributed to warming, and others contributed to increase cooling effect. RH, EC, and nss-SO2 4 were the major factors for the determination of the direct aerosol radiative forcing and NO 3 barely affected on the radiative forcing. RH was most critical during summer season when it was high (over 75%), and concentrations due to it was more effective with high nss-SO2 4 the hygroscopicity of nss-SO2 4 along with the result of Choi and Kim (2010). However, when EC concentration was higher than nss-SO2 4 , RH was not critical even it was high because EC doesn’t grow by absorbing water. During spring and fall, EC was most critical. 4. Summary In this study, size segregated measurement data between 1992 and 2008 at Gosan, Jeju, Korea was analyzed. The concentration variations of ion components and carbonaceous aerosols were well matched to the emission changes in this region. The concentrations of nss-SO2 4 showed decreasing trend until 2003, but it started to increase and kept high concentration until 2008 in TSP and 2006 in PM10 and PM2.5. The concentrations of NO 3 increased continuously at all size, and showed the peak concentration in 2006 in TSP and in 2004 in PM10 and PM2.5. The NO 3 concentrations in TSP, PM10 and PM2.5 increased by 317%, 178% and 261%, respectively. The concentrations of the elements with natural origin such as Al, Ca, Fe, K, Mg were high both in TSP and PM10, and the concentrations of the elements with anthropogenic origins were relatively low. The concentrations variations of the elements with natural origin were highly correlated to the frequency of dust storm in this region. The net aerosol forcing varied from 4.48 W m2 to 0.53 W m2 at Gosan and it was increasing. This was mainly because of continuous decrease of sulfate concentrations and steady increase of EC concentrations in this region. For the determination of the direct aerosol radiative forcing, RH was most critical during summer season when it was high (over 75%), and EC was most critical during spring and fall. Acknowledgements This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. 2011-0016297) and the Korea Meteorological Administration Research and Development Program under Grant RACS_2010-3006. References Akimoto, H., Ohara, T., Kurokawa, J., Horii, N., 2006. Verification of energy consumption in China during 1996e2003 by using satellite observation data. Atmospheric Environment 40, 7663e7667. British Petroleum, 2010. Statistical Review of World Energy June 2010. London, UK. Chang, L.S., Park, S.U., 2004. Direct radiative forcing due to anthropogenic aerosols in East Asia during April 2001. Atmospheric Environment 38, 4467e4482. Charlson, R.J., Laugher, J., Rodhe, H., Leovy, C.B., Warren, S.G., 1991. Perturbation of the northern hemisphere radiative balance by backscattering from anthropogenic sulfate aerosols. Tellus J3AB, 152e163. Charlson, R.J., Schwartz, S.E., Hales, J.M., Cess, R.D., Coakley Jr., J.A., Hansen, J.E., Hofmann, D.J., 1992. Climate forcing by anthropogenic aerosols. Science 255, 423e430. Choi, E.K., Kim, Y.P., 2010. Effects of aerosol hygroscopicity on fine particle mass concentration and light extinction coefficient at Seoul and Gosan in Korea. Asian Journal of Atmospheric Environment 4, 55e61. Chow, J.C., Watson, J.G., Crow, D., Lowenthal, D.H., Merrifield, T., 2001. Comparison of IMPROVE and NIOSH carbon measurements. Aerosol Science and Technology 34, 23e34. Chýlek, P., Wong, J., 1995. Effect of absorbing aerosol on global radiation budget. Geophysical Ressearch Letters 22, 929e931. Fung, K., Chow, J.C., Watson, J.G., 2002. Evaluation of OC/EC speciation by thermal manganese dioxide oxidation and the IMPROVE method. Journal of Air & Waste Management Association 52 (11), 1333e1341.

6115

Hatakeyama, S., 1993. Data of ’91 IGAG/APARE/PEACAMPOT Survey. ISSN 1341e4356. National Institute for Environmental Studies (NIES), Japan. Haywood, J.M., Shine, K.P., 1995. The effect of anthropogenic sulfate and soot aerosol on the clear sky planetary radiation budget. Geophysical Research Letters 22, 603e606. He, Y., Uno, I., Wang, Z., Ohara, T., Sugimoto, N., Shimizu, A., Richter, A., Burrows, J.P., 2007. Variations of the increasing trend of tropospheric NO2 over central east China during the past decade. Atmospheric Environment 41, 4865e4876. Jacobson, M.Z., 2001a. Global direct radiative forcing due to multicomponent anthropogenic and natural aerosols. Journal of Geophysical Research 106, 1551e1568. Jacobson, M.Z., 2001b. Strong radiative heating due to the mixing state of black carbon in atmospheric aerosols. Nature 409, 695e697. Jacobson, M.Z., 2004. Climate response of fossil fuel and biofuel soot, accounting for soot’s feedback to snow and sea ice albedo and emissivity. Journal of Geophysical Research 109, D21201. doi:10.1029/2004JD004945. Khan, A.J., Li, J., Dutkiewicz, V.A., Husain, L., 2010. Elemental carbon and sulfate aerosols over a rural mountain site in the northeastern United States: regional emissions and implications for climate change. Atmospheric Environment 44, 2364e2371. Kim, J., Yoon, S.-C., Kim, S.-W., Brechtel, F., Jefferson, A., Dutton, E.G., Bower, K.N., Cliff, S., Schauer, J.J., 2006. Chemical apportionment of shortwave direct aerosol radiative forcing at the Gosan super-site, Korea during ACE-Asia. Atmospehric Environment 40, 6718e6729. Kim, N.K., Kim, Y.P., 2006. The effect of Local air pollutants in a background area: measurements at Gosan in March 2000. Journal of Korean Society for Atmospheric Environment 22 (6), 821e830 (in Korean). Kim, N.K., Park, H.-J., Kim, Y.P., 2009. Chemical composition change in TSP due to dust storm at Gosan, Korea: do the concentrations of anthropogenic species increase due to dust storm? Water, Air, & Soil Pollution 204, 165e175. Kim, Y.P., Shim, S.G., Moon, K.C., 1998. Monitoring of air pollutants at Kosan, Cheju Island, Korea, during March-April 1994. Journal of Applied Meteorology 37, 1117e1126. Kim, Y.P., Moon, K.C., Lee, J.H., Baik, N.J., 1999. Concentrations of carbonaceous species in particles at Seoul and Cheju in Korea. Atmospheric Environment 33, 2751e2758. Korea Meteorological Administration, 2011. http://www.kma.go.kr/weather/ asiandust/observday.jsp. Malm, W.C., Gebhart, K.A., Molenar, J., Cahill, T., Eldred, R., Huffman, D., 1994. Examining the relationship between atmospheric aerosols and light extinction at Mount Rainer and North Cascade National Parks. Atmospheric Environment 28, 347e360. Martin, S.T., Hung, H.M., Park, R.J., Jacob, D.J., Spurr, R.J.D., Chance, K.V., Chin, M., 2004. Effects of the physical state of tropospheric ammonium-sulfate-nitrate particles on global aerosol direct radiative forcing. Atmospheric Chemistry and Physics 4, 83e214. NIER, National Institute of Environmental Research, 2007. Study on the Chemical Properties and the Characteristics of the Long-range Transported Aerosols Incheon, Korea. NIER, National Institute of Environmental Research, 2009. National Air Pollutants Emission 2007 Incheon, Korea. Ohara, T., Akimoto, H., Kurokawa, J., Horii, N., Yamaji, K., Yan, X., Hayasaka, T., 2007. An Asian emission inventory of anthropogenic emission sources for the period 1980e2020. Atmospheric Chemistry and Physics 7, 4419e4444. Park, M.H., Kim, Y.P., Kang, C.H., 2003. Aerosol composition change due to dust storm: measurements between 1992 and 1999 at Gosan, Korea. Water, Air, and Soil Pollution: Focus 3, 117e128. Park, M.H., Kim, Y.P., Kang, C.H., Shim, S.G., 2004. Aerosol composition change between 1992 and 2002 at Gosan, Korea. Journal of Geophysical Research 109. doi:10.1029/2003JD004110. Park, S.U., Chang, L.S., Lee, E.H., 2005. Direct radiative forcing due to aerosols in East Asia during a Hwangsa (Asian dust) event observed on 19e23 March 2002 in Korea. Atmospheric Environment 39, 2593e2606. Richter, A., Burrows, J., Nub, H., Granier, C., Niemeier, U., 2005. Increase in tropospheric nitrogen dioxide over China observed from space. Nature 437, 129e132. Seinfeld, J.H., Pandis, S.N., 2006. Atmospheric Chemistry and Physics. Wiley, New York, U.S.A. State Environmental Protection Administration, 1998, 2000, 2002, 2006, 2008. http://english.mep.gov.cn/standards_reports/soe/SOE2006/200711/t20071106_ 112569.htm. Streets, D.G., Waldhoff, S.T., 2000. Present and future emissions of air pollutants in China: SO2, NOx, and CO. Atmospheric Environment 34, 363e374. Streets, D.G., Bond, T.C., Carmichael, G.R., Fernandes, S.D., Fu, Q., He, D., Kilmont, Z., Nelson, S.M., Tsai, N.Y., 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. doi:10.1029/2002JD003093. Sloane, C.S., 1984. Optical properties of aerosols of mixed composition. Atmospheric Environment 18, 871e878. Sloane, C.S., 1986. Effects of composition on aerosol light scattering efficiencies. Atmospheric Environment 20, 1025e1037. Yoon, S.C., Kim, J.Y., 2006. Influences of relative humidity on aerosol optical properties and aerosol radiative forcing during ACE-Asia. Atmospheric Environment 40, 4328e4338. Zhang, Q., Streets, D.G., Carmichael, G.R., He, K.B., Huo, H., Kannari, A., Kilmont, Z., Park, I.S., Reddy, S., Fu, J.S., Chen, D., Duan, L., Lei, Y., Wang, L.T., Yao, Z.L., 2009. Asian emissions in 2006 for the NASA INTEX-B mission. Atmospheric Chemistry and Physics 9, 5131e5153.