Acid deposition and its e�ects in China: an overview

Thorjùrn Larssen a, *, Hans Martin Seip a, 1, Arne Sembb, 2, Jan Mulder c, 3,Ivar P. Muniz d, 4, Rolf D. Vogt a, 5, Espen Lydersen e, 6, Valter Angell f, 7,

Tang Dagangg, 8, Odd Eilertsend, 9

aDepartment of Chemistry, University of Oslo, P.O. Box 1033, Blindern, 0315 Oslo, NorwaybNorwegian Institute for Air Research, P.O. Box 100, 2007 Kjeller, Norway

cDepartment of Soil and Water Sciences, Agricultural University of Norway, P.O. Box 5028, 1432 AÊs, NorwaydNorwegian Institute for Nature Research, P.O. Box 736, Sentrum, 0105 Oslo, NorwayeNorwegian Institute for Water Research, P.O. Box 173, KjelsaÊs, 0411 Oslo, NorwayfNorwegian Institute of International A�airs, P.O. Box 8159, Dep. 0033 Oslo, Norway

gAtmospheric Environment Institute, China Research Academy of Environmental Science (CRAES), Beiyuan,

Beijing 100012, People's Republic of China

Abstract

Acid rain is an increasing environmental problem in China. At present SO2 emission is about 20±22 million tons. Howeverwith a growing number of large power plants the long-range transport of air pollutants is expected to increase. The highest acid

deposition is near the emission sources. Wind-blown, alkaline soil dust is important in neutralizing the acidity of the emissions,especially in large parts of northern China. In the south, where alkaline soil dust contributes less to acid neutralization, theannual pH in precipitation was below 4.5 at monitoring stations in several provinces and as low as 4.1 in some urban areas.

Total sulfur deposition has been estimated to be about 10 g S mÿ2 yearÿ1 in heavily exposed areas. Negative e�ects on forests,including die-back, have been reported for relatively small areas near large cities. Since large, regional surveys have not beencarried out, there are large uncertainties about e�ects on a regional level. The high concentrations of gaseous pollutants,especially within and near the cities, are likely to have severe e�ects on human health as well as on materials and vegetation.

Several ®eld and laboratory studies, as well as computer simulations, indicate that acidi®cation of soil and soil water hasoccurred in the past few decades. This has probably caused elevated concentrations of toxic aluminum in soil water. At present,the toxic e�ect of Al is likely to be counteracted by high concentrations of calcium at many places. The Chinese authorities have

recognized air pollution and acid rain as serious environmental problems, however, there are di�culties in implementing e�ectivemeasures to reduce the problems. With respect to ecological e�ects we lack a comprehensive regional overview of the extent ofthe acid deposition problem in China. Such information is necessary before e�ective countermeasures can be developed. # 1999

Elsevier Science Ltd. All rights reserved.

Keywords: Acid rain; Air pollution; Acidi®cation; Ecosystem e�ects; China; Soil; Water

1. Introduction

Acid deposition was recognized as a potential en-

vironmental problem in China in the late 1970s and

early 1980s (Zhao and Sun, 1986; Zhao et al., 1988;

Wang et al., 1996, 1997a). The First National

Symposium on Acid Rain was convened in November

1981. In 1982 the National Environmental Protection

Agency (NEPA) organized and sponsored the National

Environmental Science & Policy 2 (1999) 9±24

1462-9011/99 $ - see front matter # 1999 Elsevier Science Ltd. All rights reserved.

PII: S1462-9011(98 )00043 -4

* Corresponding author. Tel.: +47-22-855-659; fax: +47-22-855-

441; e-mail: thorjorn.larssen@kjemi.uio.no.1 E-mail: h.m.seip@kjemi.uio.no2 E-mail: arne.semb@nilu.no3 E-mail: jan.mulder@ijvf.nlh.no4 E-mail: ivar.muniz@ninaosl.ninaniku.no5 E-mail: r.d.vogt@kjemi.uio.no6 E-mail: espen.lydersen@niva.no7 E-mail: valter.angell@nupi.no8 E-mail: tangdg@sun.ihep.ac.cn9 E-mail: odd.eilertsen@ninaosl.ninaniku.no

Survey of Acid Rain, in addition to local research pro-

jects in several provinces (Zhao et al., 1988). Based on

the ®ndings of the ®rst survey, the Second National

Survey on Acid Rain was initiated in 1985 and lasted

for two years; the third national acid rain research

project lasted from 1986 to 1990 (the 7th ®ve-year

plan) and the fourth national project from 1991 to

1995 (the 8th ®ve-year plan) (Wang et al., 1997a). The

two ®rst projects focused mainly on emission of SO2

and distribution and deposition of acid rain, while the

two subsequent projects also involved studies of

e�ects.

China's energy consumption increased 5.3%

annually over the period 1980±1991 (Byrne et al.,

1996). Coal accounted for more than 34 of the commer-

cial energy production and it is likely that coal will

remain the major energy carrier in the next decades.

The SO2 emissions have recently shown a lower

growth rate than in previous years due to cleaner tech-

nology on new power plants and boilers and legal pro-

visions. O�cial plans aim at stabilizing the emissions

at about present values (NEPA, 1997), but other scen-

arios suggest that the Chinese SO2 emissions will con-

tinue to increase. A considerable increase is expected

in the NOx emission due to the fast increasing number

of motor vehicles. Hence, acid deposition in China is

likely to become more serious in large areas (Rodhe

et al., 1992; Seip et al., 1995; Foell et al., 1995).

Preliminary calculations, e.g. by the RAINS-Asia

model (Downing et al., 1997), suggest that the critical

loads of forest ecosystems are seriously exceeded in

many areas (Hettelingh et al., 1995). However, as will

be discussed later, no thorough studies of critical loads

have been carried out for Chinese conditions and the

values are highly uncertain.

The combination of high emissions of acid gasesand acid sensitive ecosystems requires a betterunderstanding of the relationship between emissionsand environmental e�ects than what is availabletoday.

Here we give an overview of the current knowledgerelated to acid rain in China. The focus is on emissionsof acidifying and acid-neutralizing substances and ondeposition and e�ects of acid rain. We concentrate onecosystem e�ects rather than e�ects on health and ma-terials because the latter two are largely local e�ects,particularly health e�ects which are primarily causedby the acid rain precursor SO2 (and particles) ratherthan the acidity of rain.

2. Emissions

Estimated total SO2 emissions in China vary from16 to 22 million tons per year (see e.g. Cao, 1989;Akimoto and Narita, 1994; Wang et al., 1996;Arndt et al., 1997). The o�cial ®gure for 1995 is019 million tons SO2, while the RAINS-Asia modelused 22 million tons for 1990 (Wang et al., 1996).The di�erences in the emission ®gures may bepartly due to di�erent average sulfur content ofcoal used in the calculations (Akimoto and Narita,1994) and partly to exclusion of small domesticsources in the o�cial ®gures (Wang et al., 1996).The annual total SO2 emission has been increasingthe last decades (Fig. 1) and is likely to increasefurther in the near future. The average sulfur con-tent of the coal consumed is 1.2%, but in Guizhouand Sichuan provinces the averages are 3.2 and2.8%, respectively.

Fig. 1. Sulfur emission in China from 1982 to 1995 (Statistics China, 1983±1996).

T. Larssen et al. / Environmental Science & Policy 2 (1999) 9±2410

The nitrogen emissions in China are dominated byNH3 from fertilizer and domestic animal waste (Zhaoand Wang, 1994; Galloway et al., 1996). Commercialfertilizers account for about 80% of China's total 20Tg N yearÿ1 ¯ux to the atmosphere. The nitrogen mo-bilization is expected to increase signi®cantly in thecoming decades due to increased use of fertilizers aswell as enhanced fossil fuel combustion (Gallowayet al., 1996).

3. Geographical distribution

According to Zhao and Sun (1986), two core areasfor acid rain were identi®ed in the beginning of the1980s: the Chongqing-Guiyang and the Nanchang corezones (Fig. 2). In the beginning of the 1990s two morecore zones were observed: one in the southeast coastalarea (Fuzhou±Xiamen±Shanghai) and one in thecoastal north area surrounding Qingdao in ShandongProvince (Wang et al., 1996).

4. Atmospheric dispersion and deposition

4.1. Atmospheric concentrations of SO2

Monitoring of SO2 in 88 Chinese cities in 1994showed that annual average concentrations variedfrom 2 to 472 mg/m3 (Wang et al., 1996). Averageconcentrations were 89 mg/m3 in northern cities and83 mg/m3 in southern cities. Forty-eight of the 88 citiesexceeded the Chinese National Air Quality StandardClass II (60 mg/m3 annual avg.) for SO2 (Wang et al.,1996). High SO2 concentrations are observed in bothsouthern and northern China, while acid rain is mainlyobserved in the south. SO2 concentrations in Chinesecities, from di�erent sources, are given in Table 1.

4.2. Measurements and monitoring of precipitationchemistry

In the 1980s, most of the acid rain research wasfocused on the situation in the Sichuan, Guizhou,Guangxi and Guangdong provinces, and information

Fig. 2. Map of the People's Republic of China.

T. Larssen et al. / Environmental Science & Policy 2 (1999) 9±24 11

on precipitation chemistry are available from severalsources (e.g. Zhao and Sun, 1986; Zhao et al., 1988;Zhao and Xiong, 1988; Zhao and Zhang, 1990; Qi andWang, 1990; Xue and Schnoor, 1994; Zhang et al.,1996; Wang et al., 1997a). In the beginning of the1990s, the National Acid Deposition MonitoringNetwork (NADMN) was established, with the purposeof increasing the knowledge about acid deposition inother provinces than those in the south and southwest,especially in the southeast.

In general, sulfate is the dominating anion in pre-cipitation and calcium and/or ammonium are thedominant cations (Table 2). The pH is relatively low,with weighted averages less than 4.5 in several pro-

vinces. The acid rain situation in Chongqing andGuiyang has been and still is particularly serious, witha volume-weighted average pH of about 4.1 in theurban areas. However, it is likely that the situation hasbeen improved recently in Guiyang, due to counter-measures induced by the local government (Lydersenet al., 1997). The information on acid deposition inrural areas is relatively scarce since little monitoringdata are available.

Some data are available from rural areas nearChongqing and Guiyang and a decrease in total ionconcentration out from the urban areas can been beseen (Fig. 3). This clear trend can be explained by thehigh emission from small, domestic sources inside the

Table 1

Concentrations of SO2 and total suspended particles (TSP) in air at di�erent sites in China

Place SO2

concentration

(mg/m3)

TSP

(mg/m3)

Average

period

Year

measured

No. of measure

sites included

Reference

Northern 110 740 24 h 1985 31 Cao, 1989

Southern 100 444 24 h 1985 33 Cao, 1989

Beijing 115 380 1 year 1991 1 Wells et al., 1994

Chengdu., urban 85 658 annual 1985±1989 1 Lei et al., 1997

Chongq., Jiulongpo district 280 annual 1990 ? Ma, 1990

Chongq., Ba county 240 annual 1990 ? Ma, 1990

Chongq., Dadukou district 320 annual 1990 ? Ma, 1990

Chongq., Jiangbei district 400 annual 1988±1989 ? Ma, 1990

Chongq., Nanan district 310 annual 1990 ? Ma, 1990

Chongq., Nanshan park 50 1 month Jan. 1989 1 Ma, 1990

Chongq., Nanshan, Huangshan 130 1 month Jan. 1989 1 Ma, 1990

Chongq., Nanshan, Tieliao 450 1 month Jan. 1989 1 Ma, 1990

Chongq., Nanshan, Wenfongtai 133 24 h Sept 1986 1 Bian and Yu, 1992

Chongq., Nanshan, Wenfongtai 254 24 h July 1988 1 Bian and Yu, 1992

Chongq., Nanshan, Zhenwushan 400 1 month Jan. 1989 1 Ma, 1990

Chongq., Shizhong district 540 annual 1990 ? Ma, 1990

Chongq., Simian shan 5 100 annual 1985±1989 1 Lei et al., 1997

Chongq., Simian shan 8 annual 1989±1990 1 Ma, 1990

Chongqing 422 annual 1990 ? Zhao et al., 1995b

Chongqing, Nanshan park 40 24 h Sept 1986 1 Bian and Yu, 1992

Chongqing, Nanshan park 100 24 h July 1988 1 Bian and Yu, 1992

Chongqing, Nanshan, Zhenwushan 126 24 h Sept 1986 1 Bian and Yu, 1992

Chongqing, Nanshan, Zhenwushan 214 24 h July 1988 1 Bian and Yu, 1992

Chongqing, suburb 1 138 500 annual 1985±1989 1 Lei et al., 1997

Chongqing, suburb 2 27 300 annual 1985±1989 1 Lei et al., 1997

Chongqing, urban 402 690 annual 1985±1989 1 Lei et al., 1997

Guangzhou 90 annual 1988 ? Cao, 1991

Guangzhou 47 180 annual 1991 1 Wells et al., 1994

Guiyang 504 496 winter season 1990 6 UNDP, 1991

Guiyang 356 annual 1990 ? Zhao et al., 1995b

Guiyang catchment 44 1 month 1993 1 Larssen et al., 1998

Guiyang, suburb 1 40 500 annual 1985±1989 1 Lei et al., 1997

Guiyang, suburb 2 48 300 annual 1985±1989 1 Lei et al., 1997

Guiyang, urban 157 1 month 1993 1 Larssen et al., 1998

Guiyang, urban 423 970 annual 1985±1989 1 Lei et al., 1997

Huhot 119 375 winter season 1990 5 UNDP, 1991

Qingdao 470 335 winter season 1990 4 UNDP, 1991

Qingdao 233 annual 1990 ? Zhao et al., 1995b

Shanghai 85 220 1 year 1991 1 Wells et al., 1994

Shenyang 152 380 1 year 1991 1 Wells et al., 1994

Xian 47 510 1 year 1991 1 Wells et al., 1994

T. Larssen et al. / Environmental Science & Policy 2 (1999) 9±2412

city centers, with large emissions of both SO2 anddust. A study on fog chemistry was conducted at thetop of Emei mountain (3099 m above sea level, 300 kmwest of Chongqing) in Sichuan in 1980; the averagepH was 4.64, with a minimum of 3.77, maybe due tolong range transport (Wang et al., 1991). Some modelstudies indicate the level of air pollution in rural areasand the degree of long range transport: Meng et al.(1996) and Meng et al. (1997) combined use of a sim-pli®ed three-dimensional Eulerian model and aLagrangian trajectory model to study the transportand deposition of sulfur in the Minnan area in Fujianprovince. They concluded that long range transport(i.e. from sources outside Fujian province), accountedfor almost 60% of the total sulfur deposition.

In most parts of northern China, the pH of precipi-tation is generally above 6, due to the high levels ofneutralizing soil dust in the atmosphere (e.g. Zhaoet al., 1988; Wang et al., 1997b). Hence acid rain isprobably not an important problem in this area.However, direct e�ects from acid gases (and particles)may be of great importance to both human health andvegetation.

The composition of the rain samples from China dif-fers from the composition of precipitation in Europemainly in that the concentrations of calcium relative tosulfate are very high, and the concentrations of nitraterelative to the other components are low. However,nitrate is expected to become increasingly important asthe emissions from motor vehicles increase rapidly.

Possible e�ects of the large emissions of ammoniahave not been studied in detail in China. However,these emissions are of importance, through neutralizingacidity of the rain, but causing acidi®cation of soilsafter deposition due to nitri®cation.

Also the concentration of ¯uoride in precipitationappears to be high in China, e.g. mean values of 0.5±0.7 mg/L in precipitation in Chongqing was reported(Zhao et al., 1994; Lei et al., 1997). This may be linkedto combustion of coal with high ¯uoride contents, butalso to production of brick and tiles from clay withhigh ¯uoride contents. Emissions are primarily ashydrogen ¯uoride (HF), which is very toxic to plants.

4.3. Dust and particles in the atmosphere

Wind-blown soil dust is an important feature in theChinese atmosphere (Chang et al., 1996). In addition,there are high concentrations of anthropogenically de-rived aerosol particles. Based on the work of Wanget al. (1981), Zhao et al. (1988) suggested that theratio of dust derived from coal burning to that derivedfrom soils is about 2:1 in southern China and between2:3 and 3:2 in northern China. Zhao et al. (1994) esti-mated 40% of the dust in Chongqing to originatefrom coal burning, however, the authors pointed outT

able

2

Volumeweightedannualaverageconcentrationsofionsin

precipitationin

China(concentrationsin

meq/l)

Fujiana

average

Jiangxia

average

Hunana

average

Zhejianga

average

Hubeia

average

Anhuia

average

Jiangsu

a

average

Shangdonga

average

Chongqingb

urban

Chongqingc

urban

Chongqingb

rural

Chongqingc

rural

Guiyangb

urban

Guiyangb

suburban

Guiyangd

suburban

Guiyangb

rural

Period

1992±1993

1992±1993

1992±1993

1992±1993

1992±1993

1992±1993

1992±1993

1992±1993

1982±1984

1987

±1989

1982±1984

1987±1989

1982±1984

1982±1984

1992±1995

1982±1984

Rainfall(m

m)

1379

1555

1274

1550

1108

1020

1212

597

700

1200

1175

pH

4.48

4.49

4.78

4.69

4.47

5.37

5.48

6.10

4.14

4.11

4.44

4.33

4.07

4.42

4.43

4.58

H+

33.2

32.4

16.6

20.5

34.0

4.3

3.3

0.8

72.4

77

36.3

47

84.5

37.9

37.2

26.3

NH

4+70.1

51.3

81.7

68.5

100.5

58.5

60.2

52.4

106

123

64.1

116

78.9

49.2

23.9

50.6

Ca2+

52.3

64.5

63.0

49.3

64.8

65.2

116.7

167.6

110

125

42.0

74

231.2

198

125.3

87.7

Mg2+

7.3

11.5

10.1

9.6

9.5

8.6

14.0

52.9

48.3

31

18.3

15

56.5

44.6

26.6

29.4

Na+

14.8

22.5

8.9

24.5

8.9

18.6

29.6

41.4

51.4

17

45.4

22

10.1

11.2

6.7

5.9

K+

5.1

10.42

7.8

8.4

7.3

10.8

8.9

28.0

7.4

17

23.4

17

26.4

10.5

6.0

7.0

SO

42ÿ

104

100

128

110

129

107

166

161

307

299

165

200

411

281

188

167

NO

3ÿ14.0

19.6

18.1

18.0

22.4

21.4

20.9

22.6

31.6

23

18.0

20

21.0

25.3

15.2

15.9

Clÿ

19.3

14.9

16.3

20.3

16.4

24.4

28.0

91.4

15.0

30

23.9

21

8.2

11.8

10.1

21.1

Fÿ

11.0

16.4

11.7

8.3

3.2

1.0

10.7

21.5

35

33

4.8

acations

182

192

188

180

225

166

232

343

395

390

229

291

488

351

226

207

aanions

149

151

174

156

171

154

226

297

354

387

207

274

440

318

218

204

anionde®ciency

(%)

10.2

12.0

3.8

7.3

13.5

3.9

1.5

7.2

5.6

0.4

5.2

3.0

5.11

4.97

1.7

0.71

aFrom

Wanget

al.(1997a),

bFrom

Zhaoet

al.(1988),

cFrom

Zhaoet

al.(1994),

dFrom

Larssenet

al.(1998).

T. Larssen et al. / Environmental Science & Policy 2 (1999) 9±24 13

that the estimate was uncertain. Shao et al. (1995)

found that 50% of the particles in Beijing originated

from soils: soils were important source for metal ions,

while local combustion was the dominating source for

carbon in particles. In accordance with Shao et al.

(1995), Wang and Wang (1996) suggested that gener-

ally 30±70% of the particulate matter in urban areas

originate from soils. Several authors have discussed the

long-range transport of dust from the northern

Chinese deserts to Korea, Japan and the South China

Sea, which in parts of the year, especially the spring,

may be considerable (e.g. Suzuki et al., 1993;

Hashimoto et al., 1994; Chang et al., 1996).

The airborne anthropogenically derived particles are

generally smaller than the soil dust particles (Ning et

al., 1996; Yin et al., 1996). Ning et al. (1996) compared

the size of aerosol particles in a rural area (outside

Shenyang) with urban areas in cities in northern China

(Beijing, Shenyang, Lanzhou and Taiyuan). At the

rural site, most of the particles had an aerodynamic di-

ameter larger than 10 mm, in the cities, a large fraction

was particles smaller than 10 mm. They also found the

pH and Ca2+ content of the particles to decrease and

SO42ÿ and NH4

+ content to increase with decreasing

particle size. In northern China the content of base

cations in airborne soil particles is considerably larger

than in southern China. According to Wang and

Wang (1996) the contents of calcium and sodium are,

respectively, about 3 and 1.5% in the north and about

0.1 and 0.5% in the south.

Yin et al. (1996) compared the chemical composition

of the aerosol particles in Beijing, Chongqing and

Guiyang. As can be seen from Table 3, the pH of theparticles dissolved in water was much lower inChongqing and Guiyang than in Beijing, while thebase cation concentration, particularly Ca2+, washigher in Beijing. The sulfur content was high all threeplaces, though there are pronounced temporal vari-ations. These results clearly show that the atmosphericparticles in northern China have a large ability to neu-tralize acid rain, compared to the situation in thesouthwest. To what extent aerosols in the southwesthave an alkalizing e�ect on the precipitation is notclear, although, Liu and Huang (1993) showed that inChongqing the aerosols have some neutralizing e�ecton the precipitation. However, it is not clear in whatforms Ca2+ is bound in the particles, e.g. as nonneu-tralizing CaSO4 or as neutralizing CaO, CaCO3

(Chang et al., 1996). In addition to the possible neutra-lizing e�ect of the aerosol particles, the particle sur-faces also play an important role in sulfate and nitrateformation (Chang et al., 1996).

Fig. 3. Spatial trend in precipitation chemistry from the city center to rural areas for the cities Chongqing and Guiyang. Sodium, potassium and

¯uoride concentrations were small and are neglected in the ®gure for simplicity.

Table 3

Content of sulfur (S), potassium (K) and calcium (Ca) (in percent,

based on mass) and pH in aerosol particles dissolved in water (from

Yin et al., 1996)

Element Chongqing Guiyang Beijing

S(March) 4.2 2.8 3.2

S(Sept.) 2.2 0.8 4.5

K 0.7 0.3 1

Ca 1.3 1 4

pH 4.1 4.3 6.8

T. Larssen et al. / Environmental Science & Policy 2 (1999) 9±2414

4.4. Evaluation of the monitoring

The acid rain monitoring in China was evaluated byan expert group at the Fourth Expert Meeting on AcidDeposition and Monitoring Network in East Asia inFebruary, 1997 (EMAD, 1997). The expert group con-cluded that it is necessary to further optimize the acidrain monitoring network in China and that there cur-rently are some gaps between the state's needs and theactual situation. As the weakest points in the presentmonitoring network they identi®ed the use of non-state-of-the-art technology, unsatisfactory regionalrepresentativity of the selected sites, lack of data frombackground stations, measurement of too few par-ameters and the quality assurance. They concludedthat the ®nancial support to acid rain monitoring wastoo low and should be increased.

Variable quality of chemical analyses of monitoringsamples has also been pointed out by Larssen et al.(1998) and Lydersen et al. (1997); a problem whichshould be followed up in the future.

Ions transported as particles, especially calcium inthe Chinese atmosphere, may in¯uence strongly theprecipitation samples; the contribution depends on thelocation of the collection site and the sampling pro-cedures. In cities and industrial areas with emissions ofdust and particles, settling of coarse particles may beconsiderable. It is therefore important to assess care-fully what deposition is collected and the in¯uence ofparticulate deposition. To get better knowledge aboutlong-range transport of both pollutants and naturaldust, more monitoring stations in rural areas are im-portant.

5. Studies of e�ects on ecosystems

5.1. Forest

Damages to forests may be due to direct e�ects ofthe acid rain precursors SO2 and NOx, or to indirecte�ects involving soil acidi®cation and mobilization oftoxic metals as aluminum. Events with extremely acidicrain may also cause direct damages of leave surfaces.Most research on forest damage in China has been re-lated to direct e�ects from SO2, acid mist or extremelyacid rain events.

Forest decline in large areas has up to now not beenreported in China (Bian and Yu, 1992). However, for-est decline in smaller areas, particularly near cities andindustrial areas is observed. In the early 1980s seriousforest damage was observed on Nanshan mountain,just outside Chongqing city. More than 50% of a1800-ha Masson pine (Pinus massoniana) stand died(Wang et al., 1996). Several researchers have discussedthe reason for the forest decline (e.g. Liu and Du,

1991; Bian and Yu, 1992; Totsuka et al., 1994).Important factors are considered to be high concen-trations of SO2 and hydrogen ¯uoride (HF), acid rainand attacks by insects and fungi. Several di�erentsymptoms were observed on trees, as tip necrosis ofneedles, reduced needle length, premature abscission,crown thinning, branch die-back and reduced radialgrowth. Bian and Yu (1992) investigated three siteswith di�erent pollution loading at Nanshan. Theyfound good correlations between the air concentrationof SO2, the sulfur content of the needles and the extentof damage. However, even better correlation wasfound between ¯uorine content in needles and damage.Unfortunately the HF concentration in air was notdetermined. Di�erences in soil properties at sites withhealthy and damaged pine were not observed; on thisbasis Bian and Yu (1992) concluded that direct e�ectsfrom the gases and not acidi®cation of soils were im-portant for the observed damage. Other scientistsbelieve that soil acidi®cation has been of major im-portance (Ma, 1990). The ®nal die-back of the trees isbelieved to be caused by insect pests (Bian and Yu,1992).

Regarding the discussions about the causes of theNanshan forest decline, Totsuka et al. (1994) com-pared the conditions of Masson pine and camphor treeat one heavily polluted and one lightly polluted areaoutside Chongqing. They also conducted laboratoryexperiments to clarify interactive e�ects of SO2 andsoil acidi®cation on tree growth. They found a slowergrowth with high SO2 concentration and acid soil, butthey did not try to generalize the observations e.g. interms of dose±response relationships.

Cao et al. (1988) and Wang et al. (1988) discussedthe relationship between acid precipitation and declineof ®r at high elevations at Emei mountain and con-clude that acid rain and acid fog may result in bothdirect and indirect e�ects.

A forest damage assessment study was carried out inLiuzhou, Guangxi province (Wang et al., 1996). Of436 tree species investigated, 84 were a�ected; 30 ofthese seriously. P. massoniana and Cinnamonum bur-mannii were the two most heavily damaged treespecies. Wang et al. (1996) did not discuss the relation-ship between the observed damages and the pollutiontypes and levels.

According to Wang et al. (1996) 32% (280,000 ha)of the forested area in Sichuan province (includingChongqing) is in¯uenced by air pollutants and acidrain. In Guizhou province, 15,000 ha are in¯uenced.Loss of Masson pine was estimated from results show-ing di�erences in growth in supposedly clean and pol-luted areas in 11 Chinese provinces. The annualgrowth rate in acidi®ed areas was found to be 40±50%relative to rural, supposedly nonacidi®ed, areas (Wanget al., 1996).

T. Larssen et al. / Environmental Science & Policy 2 (1999) 9±24 15

Cao (1991) and Shu et al. (1993) presented a mul-tiple regression equation for yield loss of coniferoustrees as a function of rain pH, SO2 concentration andsoil depth. They did not report details about modeldevelopment and did not discuss uncertainties, whichobviously are large.

5.2. Crops

E�ects of SO2 and HF on crops have been studiedin China since the 1970s (Cao, 1989). Cao (1989)reported short-term exposure concentrations of SO2

and HF causing 5% injury to three sensitivity groupsof crops. The sensitive species are reported to have a5% injury at 880±1430 mg/m3 SO2 and 12±48 mg/m3

HF during 8 h exposure (Cao, 1989). How the injurywas measured was not reported. Dose±response curvesfor yield loss caused by SO2 were given for short-termexposure, the investigated plants have decreasing sensi-tivity as follows (Cao, 1989):

cabbage > pinto bean > potato > wheat > soybean

> corn > rice

For long-term exposure of SO2, a yield loss of 5% isreported for 30±50 mg/m3 SO2 for sensitive species(potato, bean, Chinese cabbage). In the most pollutedChinese cities a yield loss of 5±25% should beexpected for the most common crops (Cao, 1989).Chang and Hu (1996) reported that the average yieldreduction for vegetables in Chongqing is 24.4%. AlsoCao (1989) studied e�ects of both SO2 and acid rain inopen top chambers. Rice was among the most resistantspecies both to SO2, acid rain and the combination ofthe two. `Most vegetables' were classi®ed as sensitive.

A ranking of the sensitivity of acid rain for the mostcommon crops in China is also given by Wang et al.(1996)

rape > wheat > corn > barley > soybean > rice

> tobacco > jute

Of the most common vegetables, tomato, eggplant andcucumber are among the most sensitive, while cabbage,spinach and carrot are among the least sensitive toacid rain (Wang et al., 1996). The sensitivity rankingfrom Cao (1989) and from Wang et al. (1996) arerather di�erent. It is not clear if the discrepancies aredue to di�erences between SO2 and acid rain e�ects,or if they are due to experimental uncertainties. Innone of the above-mentioned studies, the e�ects havebeen related to soil properties, which are of majorimportance for the growth.

Chameides et al. (1994) estimated that 10±35% ofthe World's grain producing areas, including the den-sely populated part of China, may be exposed toozone levels large enough to reduce crop yields. As

e�ects of SO2 and HF have been in focus, very littleresearch has been done on the e�ects of other gaseouspollutants, as ozone and NOx, on vegetation in China.

5.3. Other natural vegetation

We have found very little information about possiblee�ects of air pollution and acid rain in China on veg-etation other than crops and the most common treespecies. Studies of for example some wild herbs andferns collected for food, medicine and fodder and oflichens or other indicator species particularly sensitiveto air pollution would be valuable.

6. Soils and soil water

Direct e�ects of air pollutants on vegetation aremost commonly used to explain damages in China.However, changes in soils caused by acidi®cation are alikely long-term e�ect of acid rain. Dai et al. (1997)and Pan (1992) compared soil analyses conducted 30years ago with recent results from several sites insouthern China. They found the soil pH to havedecreased considerably; between 0.1 and 1.0 pH units.These results clearly suggest that soil acidi®cation hasoccurred and may become a serious problem in Chinain the future. This is in agreement with modelingresults (Zhao and Seip, 1991). However, experimentaland modeling studies involve relatively large uncertain-ties, particularly when used in large areas with lowspatial resolution. Furthermore acid deposition is notthe only possible cause of soil acidi®cation; forexample changes in vegetation type, ecosystem succes-sion etc. may have similar e�ects (e.g. logging ofbroad-leaved vegetation followed by planting of coni-ferous trees, as was the case in large areas of China inthe late 50s and early 60s). In addition, many of theforests in China are intensively used, for example col-lection of mushrooms and herbs, as well as dead woodand litter, are quite common.

Liao et al. (1997, 1998) conducted laboratory exper-iments in which forest soils from ®ve sites in southernChina (Chongqing, Guiyang, Fujian, Hunan andNanchang) were extracted with di�erent salt and acidsolutions. The experiments showed that severe de-pletion of soil base cations is likely to occur in themost sensitive soils, if the acid deposition continues atcurrent level or increases. The soils from the Fujianand Nanchang were found to be the most sensitive ofthese soils. However, one must be careful in generaliz-ing to larger geographical scales because of the hetero-geneity of soils even within small geographical areas(Larssen et al., 1998). To what extent e�ects on veg-etation via soil acidi®cation may occur in the futurewill depend strongly on the development of both the

T. Larssen et al. / Environmental Science & Policy 2 (1999) 9±2416

sulfur and the base cation deposition. Lin et al. (1992)studied the bu�ering capacity of soils from severalplaces in China. They concluded that soils fromNanshan (outside of Chongqing) had low bu�ering ca-pacity, the soils from Guiyang and Hunan were rela-tively well bu�ered, while the soils from Hebei andXian had the highest bu�er capacity. Such soil exper-iments give valuable information about the particularsoil sampled, but generalizations are di�cult also heredue to large spatial variability.

Sulfate absorption in soils is a process which mayretard the acidi®cation process. Liao et al. (1994) stu-died this process in soils from Guiyang and Nanchangin laboratory experiments and found that the sulfateadsorption was relatively low (50±200 mg/kg) at sul-fate concentrations corresponding to ambient sulfatedeposition. Larssen et al. (1998) estimated the sulfateretention in a catchment outside Guiyang to be 30±40% of the input.

Results from studies of soil water have been pub-lished from sites in Chongqing (Xu et al., 1994a) andGuiyang (Larssen et al., 1998). In Chongqing, highconcentrations of sulfate (80±335 mg/l) and calcium(10±51 mg/l) were found. However, concentrations ofaluminum were rather low (38±150 mg/l) (Xu et al.,1994a). In the Guiyang study concentrations of allthese three components were high (SO4

2ÿ: 18±111 mg/l,Ca2+: 3±25 mg/l and Al3+: 0.4±13 mg/l) (Larssen etal., 1998). The chemical composition of precipitation,soil and soil water in the Guiyang catchment werecompared with several catchments in Poland andNorway, showing that concentrations of sulfate, alumi-num and calcium were especially high in Guiyang(Larssen et al., 1996).

7. Surface water

Xue and Schnoor (1994) published results from asurvey of 16 streams and lakes in southwestern China.All investigated waters had a pH above 6.5 and basecation concentration above 300 meq/l, due to consider-able acid neutralization in the soils and high depo-sition of alkaline dust. At high elevation, Xue andSchnoor (1994) found some waters that may be sensi-tive to acidi®cation (ANC<150 meq/l), but not acidi-®ed at present. Williams et al. (1995) studied the ionconcentration in the UÈ ruÈ mqi river in northwest Chinaand concluded that this river is not sensitive to acidi®-cation. Larssen et al. (1998) reported rather low pH intwo small headwater streams outside Guiyang.However, the water is rapidly neutralized downstream,probably due to mixing with drainage water frommore alkaline soils. Based on this limited amount ofinformation surface water acidi®cation in China is con-sidered to be a minor problem at present. Model stu-

dies by Zhao and Seip (1991) using the MAGIC model(Cosby et al., 1985) also indicated that acidi®cation ofsurface water is not likely to become a serious pro-blem. However, one should be aware of possible futureacidi®cation in some sensitive areas. Lydersen et al.(1997) identi®ed waterbodies with low acid neutraliz-ation capcity in mountainous areas in Guizhou andGuangdong provinces. At present the deposition ofacidifying compounds is quite low. However, if thepresent low loadings are replaced by higher inputs ofacid rain, surface water acidi®cation is likely.

There are very few studies on the ecological e�ectsof high acidity on Chinese freshwater ecosystems. Xiaet al. (1994) studied e�ects on freshwater biota in foursmall ponds and two lakes in the Chongqing area andconcluded that the most acid ponds had higher trans-parency, fewer species of phytoplankton and loweralgal cell-density and biomass. Experimental evidencesuggested that low pH and low phosphorous levelswere limiting factors for these primary producers.

8. Integrated studies

In order to understand the acidi®cation processes inone of the most exposed areas in China in more detail,a small catchment outside Guiyang, dominated by yel-low soil (Haplic Alisol in the FAO classi®cation sys-tem), was equipped for sampling of SO2 gas,precipitation, throughfall, soil water and surface waterin 1992. The results from the ®rst years of samplingare given in Larssen et al. (1998). The relatively lowpH in the precipitation (average 4.4) causes high con-centration (1.6±4.6 mg/l) of inorganic aluminum in soilwater. However, possible toxic e�ects of aluminum areprobably counteracted by high concentration of basecations, in particular calcium (8±19 mg/l), as pro-nounced e�ects on vegetation were not seen. Theauthors concluded that the present high base cationdeposition seems to counteract potential e�ects to veg-etation of elevated aluminum concentration in soilwater.

9. Critical loads

Critical load is often de®ned as ``the maximum inputof acid deposition to an ecosystem which will notcause long-term damage to ecosystem structure andfunction'' (Nilsson and Grennfelt, 1988). In the criticalload concept, toxic aluminum concentrations play akey role. It is assumed that damage to biota occursabove a threshold value for the molar Ca2+/Al3+

ratio in soil water. For forests in temporate and borealareas the critical Ca2+/Al3+ ratio at which treedamage is expected, is assumed to be 1.0 (see e.g.

T. Larssen et al. / Environmental Science & Policy 2 (1999) 9±24 17

Cronan and Grigal, 1995). The scienti®c basis for set-

ting absolute values for critical loads is weak and the

estimates are highly dependent on soil base cation

weathering rates and base cation deposition (e.g.

Lùkke et al., 1996). Nevertheless the concept of critical

loads is widely used in Europe and estimation of criti-

cal loads has also been performed for China. The criti-

cal loads for China at present are highly uncertain, as

estimates for weathering rates are based on soil pH

maps (with some adjustments for other factors). Also

the estimated rates of base cation deposition are not

well known. According to estimates done in the

RAINS-Asia project, the areas most sensitive to acid

deposition in China are, as expected, in the south

(Hettelingh et al., 1995; Downing et al., 1997). The

exceedances of the critical loads are largest in the

Chongqing-Guiyang area, but the values are also

exceeded in large areas in the south and south east

according to the RAINS-Asia model (Downing et al.,

1997).

Zhao et al. (1995a) made a critical load case study

for Guizhou province. Based on the same critical load

approximations and maps as used in RAINS-Asia,

large parts of the province were found to have a criti-

cal load of 200±500 eq/ha/year (approximately 0.3±0.8

g S mÿ2 yearÿ1).

It is also uncertain if the critical Ca2+/Al3+ ratios

in temperate and boreal forests are relevant in China

as well. Gao and Cao (1989) conducted laboratory ex-

periments in which aluminum toxicity to Masson pine

seedlings was related to ionic strength, pH and Ca2+/

Al3+ ratio. The results indicated that the aluminum

toxicity increased with decreasing pH and decreasing

ion strength and Ca2+-concentration. In another study

aluminum toxicity to Masson pine seedlings was re-

lated to biophysiological parameters and growth; the

growth was inhibited markedly at an aluminum con-

centration of 15 mg/l (Cao et al., 1992).

Traditional use of forests in China has been gather-

ing of edible plants as well as collection of litter and

understory vegetation for use both as domestic fuel

and for fertilizing of cultivated land, usually after com-

posting. This practice reduces the fertility of the forests

and increases the rate of soil acidi®cation because of

the removal of plant nutrients which would otherwise

be returned to the soil with the litterfall. This problem

has been addressed by scientists in the Dinghushan

biosphere reserve, who have conducted mass balance

studies of nutrients in litterfall and material removed

by local residents (Brown et al., 1995; Mo et al., 1995).

The removal of nutrients, particularly potassium and

calcium by harvesting and litter-collection, should also

be considered in connection with estimation of critical

loads.

10. E�ects on health

In discussing health e�ects the focus is not on acid

rain per se, but on the gaseous precursors (SO2, NOx)or pollutants which to a large degree originate from

the same sources (e.g. particles).

WHO (1995) has given air quality guidelines for

Europe for some pollutants and for di�erent averagingtimes. The maximum allowable annual average for

SO2 is 50 mg/m3 and for NO2 40±50 mg/m3. For par-ticles WHO has decided not to give guidelines, since

there is no evident threshold for e�ects, while US EPArecently proposed that daily average concentration of

particles with diameter less than 2.5 mm (PM2.5)should not exceed 50 mg/m3 (Reichhardt, 1996).

Comparing with Table 1, it is clear that the SO2

guideline is exceeded in many places in China, theexceedance may be up to eight times. In comparison,

NOx poses a minor problem at present, but NOx con-centrations are increasing. The concentrations of air-

borne particles in many Chinese cities are very largeand accordingly serious health e�ects are expected.

A large number of epidemiological studies in Europeand the USA have shown a signi®cant correlation

between level of air pollution and mortality. The corre-lation seems to be stronger between particles and mor-

tality than between SO2 and mortality (Aunan, 1996).In contrast, Wells et al. (1994) found the highest corre-

lation between SO2 and mortality in Beijing andShenyang.

Concerning morbidity, there seems to be a clear

e�ect of air pollution on respiratory diseases. It ishighly probable that air pollution also may increase

the frequency of lung cancer, but quantitative relation-ships are di�cult to obtain.

Studies in Western Europe and the USA generallysupport a linear relationship between SO2 (or particles)

and health e�ects. There are indications that thesefunctions overstate the response in areas with high pol-

lution levels (WHO, 1995); i.e. the dose±response func-tion levels o� as the pollution increases. Studies in

Beijing and Shenyang seem to support this conclusion(Wells et al., 1994; Xu et al., 1994b).

In a World Bank study in Chongqing, air pollution

was found to be signi®cantly associated with daily

mortality from cardiovascular diseases and increasedfrequency of hospital visits (Xu, 1996). The prevalence

of respiratory system illness in the downtown area ofChongqing is very high being 34.3%, according to

Chang and Hu (1996). Pope and Xu (1993) found asigni®cant, and nearly additive, e�ect of passive ciga-

rette smoke and coal heating on respiratory symptomsin a study in Anhui Province. Indoor pollution may be

particularly important as a cause of lung cancer inmany places in China (Xu et al., 1989).

T. Larssen et al. / Environmental Science & Policy 2 (1999) 9±2418

11. E�ects on materials

The reactivity to various air pollutants varies greatlyfor di�erent materials and pollutants. High concen-trations of sulfur dioxide and high deposition aciditycause increased corrosion of metals, and deteriorationof calcareous building materials, including concreteand marble (see e.g. Kucera and Fitz, 1995).

Tsujino et al. (1995) compared corrosion rates fordi�erent materials in Shanghai and Chongqing inChina with rates at several Japanese cities and oneKorean city. Chongqing had the highest sulfur pol-lution load, followed by Shanghai. For all the ma-terials investigated, the corrosion rates wereconsiderably larger in the Chinese cities than theJapanese and Korean cities. The corrosion rates ofsteel, copper and bronze were 3.9±4.5 times higher inChongqing than the average of the Japanese cities, formarble the rate was 2.7 times higher in Chongqing. InShanghai, the metals corroded 1.5±2.5 times fasterthan the Japanese average.

Wang et al. (1995) developed dose±response func-tions for material damage based on experiments atdi�erent levels of SO2 and pH in China. Chang andHu (1996) reported that life-times of outdoor paintingin Chongqing are only 1

2 to13 of that found under back-

ground conditions.Costs associated with material damage may be esti-

mated from assessments of exposed material, and thecosts of early replacements or maintenance, e.g. paint-ing. In many European cities, reduced sulfur dioxideconcentration levels have resulted in substantial re-ductions in building maintenance costs, and savings inthis sector are often comparable to the costs of redu-cing emissions (e.g. Kucera et al., 1993). Based on theresults referred to above, it is likely that this is also thecase in many Chinese cities.

12. Economic losses caused by acid rain and relatedpollutants

Estimates of the economic losses from pollution maybe useful guidelines for environmental policy makingand may also draw attention to certain environmentalissues. Economic valuation of human life and naturalecosystems is controversial, and large variations in esti-mated values will occur depending on the methodapplied.

Cao (1989) estimated that 2.66 million ha crops area�ected by SO2 pollution and an area about half aslarge by hydrogen ¯uoride pollution causing an econ-omic loss of US$ 550 million annually. Cao et al.(1990) estimated the yield loss of grain and vegetablesto be 2530 and 536 thousand tons in Guangxi andGuangdong provinces. Based on a multiple regression

model they further estimated loss of timber to about 4million tons in the same provinces. Shu et al. (1993)estimated the annual cost of forest damage by acidrain in Guangxi province to US$ 80 million. Ou et al.(1996) estimated the economic loss due to acid raindamages to crops and materials in the Xiamen area toabout US$ 6 million, which equal about 1% of thegross product for the area. Chang and Hu (1996)reported that the annual damage from air pollution inChongqing in 1993 was about US$ 220 million whichis 4.4% of the gross product. They included damagesto health, agriculture, forestry, materials and increasedtransportation costs due to reduced visibility.

The World Bank (1997) has estimated the cost ofdamages to crop, forest, ecosystems and materialsfrom acid rain in China to about US$ 5000 millionannually, corresponding to about 0.75% of the grossdomestic product (GDP). The World Bank (1997) alsoestimated the costs of urban air pollution to health tobe almost 5% of GDP, based on a willingness-to-payapproach. Due to methodological problems in valua-tion as well as lack of knowledge concerning actualdamages of various kinds, such estimates are highlyuncertain.

13. Policy issues

Coal will continue to be the major energy carrier inChina the next few decades (Xie and Kuby, 1997; Lin,1998). The fast growth in rural and small town indus-tries in China strongly a�ects the energy use and re-lated pollution problems (Bradbury et al., 1996). If nomeasures are taken to reduce the sulfur emissions, thee�ects seen today are likely to increase to large areaswith impacts on health, natural ecosystems and cropyields (Chang et al., 1998). Hence, the emissions mustbe controlled, preferably reduced, from present levels;this is also recognized by the Chinese authorities(NEPA, 1997). In order to ®nd the best possiblemeasures against increased sulfur emissions and poss-ible severe e�ects, important patterns in the energyproduction and demand must be recognized: Themajor coal producing regions are in the north whilethe major coal consuming regions are in the south andalong the east coast. Hence coal must be transported,and the transport system, i.e. the railway, has not su�-cient capacity, which is an important reason for energyshortages (Xie and Kuby, 1997). Up to now, mostinvestments in the energy sector have been in new ca-pacity development (US$ 93,000 million from 1985 to1990) rather than energy conservation (US$ 5000million) (Lin, 1998). China's total energy intensitydecreased with about 50% from 1980 to 1995, but atabout 1.8 coal equivalents consumed per US$ 1000 in

T. Larssen et al. / Environmental Science & Policy 2 (1999) 9±24 19

China it is still four times higher than in USA and 13times higher than in Japan (World Bank, 1997).

The combination of high coal dependency, in-adequate transportation capacity and low energy e�-ciency suggests that energy conservation is a major keyfor future energy planning even without taking intoaccount environmental e�ects. Hence an almost freeenvironmental bene®t can be achieved. Xie and Kuby(1997) calculated that a 10% reduction in sulfur andparticle emission using coal washing can be reached ata 2% increase in cost, without taking savings fromreduced pollutant levels into account. In estimating thebene®t of measures it is important to consider allmajor e�ects, i.e. locally on health and materials dueto reduced particle and SO2 concentrations, regionallyon crops, forests and waters and globally due toreduced emissions of greenhouse gases (WorkingGroup on Public Health and Fossil Fuel Combustion,1997; Aaheim et al., 1998). Strong sector barriers inthe present administrative system (cf. Lin, 1998) andstate-owned enterprises still protected by subsidies andhence without a motive to save energy (cf. Xie andKuby, 1997), slow down the process of energy conser-vation and emission reduction.

The bureaucratic and administrative structure inChina is important in understanding some of the pro-blems in implementing measures. National emissionstandards and other regulations exist, but there seemsto be lack of power in the environmental protectionagencies in forcing implementation of adequatemeasures (Lin, 1998). In many cases there is a con¯ictbetween business interests and environmental protec-tion in the administration. More clearly separatedbusiness and government functions in energy supplyand demand may ease the enforcement of emissionstandards (Xie and Kuby, 1997).

The direct in¯uence of the central power on thelocal communities in China has decreased in recentyears, giving more responsibility to local governmentsin enforcing environmental emission standards.Therefore one must expect large di�erences in howmeasures are implemented locally. There is also adanger of polarization between town o�cials and en-vironmental protection agencies in small towns anddistricts with economically important, but heavily pol-luting, small industries (Bradbury et al., 1996).

14. Conclusions

China's economy is rapidly developing and theenergy demand in the coming decades is likely toincrease substantially. There is little doubt that coalwill account for most of the increase since other energycarriers will generally be more expensive in China.Hence the sulfur emissions from coal combustion most

probably will continue to increase in the coming dec-ades, even if several countermeasures are taken toreduce the emission per energy unit produced. In thissituation it is important to present assessments of thee�ects of acid rain as complete and detailed as poss-ible.

This paper shows that considerable research on acidrain and related issues has been carried out in China.However, it is also clear that the available informationis incomplete and there still is a strong need forincreased knowledge within many ®elds of acid rainand its e�ects. Major tasks for acid rain research inChina, all essential for choosing adequate countermea-sures, include studies of many aspects of this environ-mental problem.

. The relationships between anthropogenic emissions,natural emissions (particularly dust) and the chemi-cal composition of precipitation should be betterunderstood. One important aspect is to expand thefocus from only pH and sulfate to also include theother major components, as calcium, magnesium,ammonium and nitrate. Another important aspect isthe transportation to, and deposition in, rural areas.With an increasing tendency to move industry outof the cities and building tall stacks, acid depositionwill most likely increase in more rural areas.

. Long-term changes in the soil chemistry is a seriousthreat to forest-ecosystems and cropland. Littlequalitative information about soil acidi®cation isavailable at present, which in turn means that esti-mates of future exceedances of critical loads are veryuncertain. Deposition of base cations is very import-ant in mitigating soil acidi®cation in most areas inChina. Reduced emissions of alkaline dust maytherefore increase soil acidi®cation.

. A combination of regional surveys, integrated moni-toring sites (including deposition, soils and soilwater), laboratory experiments with soils and model-ing is necessary to make better predictions of futuresoil acidi®cation.

. The critical load concept should be improved andmodi®ed to ®t Chinese ecosystems better. A fewwell-designed and controlled experiments with aselection of vegetation species should be carried out,in addition to careful long-term monitoring ofchanges on several ecosystem levels.

. Little is known about e�ects of long range trans-ported air pollutants on forest and agro-ecosystems.A systematic inventory of e�ects on forest ecosys-tems using standardized techniques should be carriedout at the national level.

. Water acidi®cation has up to now received lessattention and only been observed in very limitedareas. Although at this point in time not recognizedas a de®nite environmental problem, it may, given

T. Larssen et al. / Environmental Science & Policy 2 (1999) 9±2420

acid loading in excess of neutralizing-bu�eringcapacity, become a problem in sensitive areas.Identi®cation of biological indicators of early acidi®-cation may here prove useful as prognostic tools. Insome areas with surface waters sensitive to acidi®ca-tion, careful monitoring is recommended.

. Improving energy e�ciency will be very importantin e�orts to reduce emissions. In estimating net costsof measures, all major e�ects on environment andhealth should be considered.

Acknowledgements

We appreciate the assistance of several Chinesescientists, in particular Senior Engineer Zhao Dawei,Chongqing Institute of Environmental Science inChongqing, Dr. Xiong Jiling and Mr. Xiao Jinshong,Guizhou Institute of Environmental Sciences inGuiyang and Professor Zhou Guoyi, South ChinaInstitute of Botany, Chinese Academy of Sciences,Guangzhou. An earlier version of this manuscript wasprepared for the Environmental and Natural ResourceDivision, Asia Technical Department, the World Bankand The Norwegian Agency for DevelopmentCooperation as a part of the project Planning of anIntegrated Acidi®cation Study and Survey on Acid RainImpacts in China (PIAC).

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Thorjùrn Larssen is Research Fellow in Environmental Chemistry

at the University of Oslo, Norway. His ®elds of interest include

biogeochemistry and metals mobilization in soils e�ects on veg-

etation from air pollutants as acid rain and photochemical oxi-

dants and environmental problems in fast developing countries.

He earned an M.Sc. degree in environmental chemistry from the

University of Oslo in 1994 and is currently working on a Ph.D.

at the same university focusing on acid deposition and acidi®ca-

tion in China.

Hans Martin Seip is Professor at the Department of Chemistry,

University of Oslo; he also has a part-time position at Center for

Climate and Environmental Research Ð Oslo (CICERO). Fields

of interest include modeling of acidi®cation, e�ects of air pollu-

tants on local, regional and global scales, and cost±bene®t ana-

lyses. He has cooperated with Chinese scientists for about 10

years. He earned a degree as graduate chemical engineer at the

Technical University of Norway in 1961 and a Ph.D. at

University of Oslo in 1967.

Arne Semb is a Senior Research Scientist at the Norwegian Institute

of Air Research.

Jan Mulder is Professor in Soil and Water Sciences at the

Agricultural University of Norway. His ®elds of interest include

hydrochemistry in catchments, interactions between metals and

humic substances in soils and soil plant relationships. He earned an

M.Sc. degree in soil science from the Wageningen Agricultural

University, The Netherlands in 1982 and a Ph.D. in Agricultural and

Environmental Sciences from the same University in 1988. Professor

Mulder is Associate Editor of the European Journal of Soil Science.

Ivar Pors Muniz holds a Ph.D. in biology and is working in the ®eld

of applied ecology and chemistry at NINA Ð Norwegian Institute

for Nature Research, Department of Landscape Ecology in Oslo,

Norway. His ®elds of interest are in environmental physiology/toxi-

cology and chemistry, aquatic and terrestrial ecology, particularly

ecosystem interactions. He received his B.Sc. in zoology from the

University of Bergen, in 1974 and his Ph.D. in zoophysiology from

the University of Oslo in 1986.

Rolf D. Vogt is an Assistant Professor at the Environmental

Chemistry group at the University of Oslo, Norway. His ®elds of

interest include biogeochemistry and metals mobilization in soil by

long range transported air pollutants and environmental problems in

fast developing countries. He earned an M.Sc. degree in environmen-

tal chemistry from the University of Oslo in 1989 and a Ph.D. at the

same university in 1996.

Espen Lydersen is Research Leader at the Norwegian Institute for

Water Research. His ®elds of interest are water acidi®cation, aquatic

chemistry and toxicity. He earned a M.Sc. degree in limnology at the

University of Oslo in 1985 and a Ph.D. in limnology at the same uni-

versity in 1992.

Valter Angell is director of the Information Department at the

Norwegian Institute of International A�airs (NIIA). His ®elds of

interest include international trade, development issues and environ-

mental problems. He received the Cand. Oecon. degree from the

University of Oslo in 1969. He has been a Research Fellow at the

NIIA and Senior Economist in the World Bank.

Tang Dagang is Director and Associate Researcher at the

Atmospheric Environment Institute at the Chinese Research

Academy of Environmental Sciences, Beijing. He graduated from

Department of Technical Physics, Peking University and has been

working at the Particle Technology Laboratory at, University of

Minnesota, USA. His research interests includes aerosols and emis-

sion control of coal vehicles and coal combustion sources. He is a

committee member of the Aerosol Committee, the Chinese Society

of Particles and the Chinese Society of Chemical Engineering.

T. Larssen et al. / Environmental Science & Policy 2 (1999) 9±24 23

Odd Eilertsen is Assistant Research Director and scienti®c researcher

in vegetation ecology at NINA, Norwegian Institute for Nature

Research. His ®elds of interest and expertise are in biodiversity and

spatio-temporal dynamics on ground vegetation and e�ects and

counteractions of acidi®cation. He received a M.Sc. degree at the

Faculty of Mathematics and Natural Science, University of Oslo.

T. Larssen et al. / Environmental Science & Policy 2 (1999) 9±2424