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239
ZHAO Yanxia and HOU Qing
Characteristics of the Acid Rain Variation in China During
1993–2006 and Associated Causes∗
ZHAO Yanxia1† (
) and HOU Qing1,2 (
)
1 Chinese Academy of Meteorological Sciences, China Meteorological Administration, Beijing 100081
2 Key Laboratory for Atmospheric Chemistry, China Meteorological Administration, Beijing 100081
(Received July 1, 2009)
ABSTRACT
The acid rain observation network of China Meteorological Administration was established in 1989 with
22 stations. From 1993 to 2005, more than 80 stations were included and maintained in the network. In
2006–2007, the number of stations in the network went up to 294. In consideration of the data continuity,
data used in this paper are the 14-yr observations of the 80 stations from 1993 to 2006. Based on the 14-yr
observation of acid rain, analysis shows that the acid rain in China dominates in the vast regions south of
the Yangtze River. Limited presence of acid rain is observed in the northern part of China. The 14-yr acid
rain data reveal an expanding tendency for acid rain area, with the north of China being a growing zone,
and the South China remaining virtually unchanged. The most severely polluted zone of acid rain gradually
moves from Southwest China to Central China and the middle part of South China. With regard to the acid
intensity of rain, the period of 1993–1998 bears the highest acid intensity; the period of 1999–2002 shows a
bit weakening intensity; and in the period of 2003–2006, the acid intensity of rain increases again, basically
up to the average acidity of the period of 1993–1998 by the end of 2006. In addition, rain acidity in the
north of China increases markedly. As to the causes of the acid rain situation in China, this paper examined
the sulfur dioxide emissions as well as the rainwater chemicals monitoring data.
Key words: China, acid rain, pH value, frequency of acid rain, sulfur dioxide emission, rainwater chemicals
Citation: Zhao Yanxia and Hou Qing, 2009: Characteristics of the acid rain variation in China during
1993–2006 and associated causes. Acta Meteor. Sinica, 24(2), 239–250.
1. Introduction
Acid rain is atmospheric precipitation with a pH
value lower than 5.6. Acidity exists in rain, freezing rain, snow, hail, dew, and so on. Acid rain is
mainly caused by sulfuric acid and nitric acid in water
droplets, converted from SO2 and NOx in the atmosphere (Fan, 2002). The term “acid rain” was first
used by Smith (Cowling, 1982). In 1972, the Swedish
government made acid rain an international environmental issue, for which the attention of governments
around the world was called (Ottar, 1976).
China started to pay more attention to acid rain
problems in the end of 1970s. Chinese environmental authorities established in the first place an acid
rain monitoring network across the country (Liu et
al., 1997). After that, Chinese meteorological authorities set up a long term acid rain monitoring network
in the country as well (Ding et al., 2004). Monitor∗ Supported
ing results show that in the mid 1980s, averaged annual rainfall with a pH value less than 5.6 was mainly
found in the southwest, south, and southeast coastal
areas of China (Dai et al., 1997). Acid rain catchments
have witnessed a noticeable change since the 1990s,
compared with the 1980s, featured with more areas
affected by acid rain. For example, acid rain areas
surrounding Nanchang and Changsha in the middle
part of the country registered a contamination level
exceeding the one that occurred in the southwest,
a traditional catchment of acid rain. The southern
part of China saw acid rain mainly in the Pearl River
Delta and the east part of Guangxi Province, with a
basic distribution pattern unchanged. The acid rain
areas in the eastern part of China, including the lower
and middle reaches of the Yangtze River and the south
coastal areas along Xiamen, had small fluctuations in
contamination patterns (Tian et al., 2001). As a
result, the areas with a pH value lower than 5.6 for
by the National Natural Science Foundation of China under Grant No. 40575058.
author: [email protected].
(Chinese version published in Vol. 66, No. 6, 2008)
† Corresponding
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ACTA METEOROLOGICA SINICA
averaged annual rainfall accounted for 40% of the Chinese territories. At least 50% of the areas in the southern part of the lower and middle reaches of the Yangtze
River were registered with a pH value even lower than
4.5, making the region an area hit harder by acid rain
in the country.
1.1 Acid rain studies in China
During the period from 1986 to 2000, Chinese scientists studied the formation of acid rain and its transport, developed numerical models, and examined its
impacts on the ecosystem and associated control measures.
During 1986–1990, an acid rain research project
was launched to investigate acid rain in the southwest
and the southern part of China in the context of the
formation of acid rain and associated transport, control methods, and impacts on the ecosystem. Study results indicate that both Chongqing and Guizhou were
seriously polluted by acid rain, with a heavy sulphate
concentration in rainwater, making the two areas a
typical case of sulfuric acid contamination. The temporal distribution shows that the southwestern part of
China saw more acid rain in winter and spring. In the
case of Sichuan and Chongqing, special meteorological
conditions and energy structures were the major contributors to the formation of acid rain.
During 1991–1995, acid rain studies started to
cover coastal areas in the east and the middle part
of the country. Two cities, Qingdao and Xiamen, were
selected as the target areas of case studies, in an attempt to understand the cause and source of acid rain
contamination, their input and output in the two areas, and their association with inland acid rain contamination (Liu et al., 1997).
During 1986–1995, Chinese scientists assessed the
impacts of acid deposition on crops and forests and
associated economic losses, identified the principles,
methodology, and indicators in evaluating and screening the technologies applicable to acid deposition control, and came up with control plans and response
strategies based on critical loads of sulfur deposition
(Hao et al., 2001). Additionally, some studies were
conducted to understand the transport process of atmospheric pollutants, and a sulfides transport model
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was developed based on the reliable SO2 emission inventory, in an attempt to calculate the transport of
the pollutants across provinces and countries (Wang
Zifa et al., 1997).
During 1996–2000, efforts were made to work on
the areas affected by SO2 and acid rain and associated control plans. An SO2 control area was defined
in northern China, and an acid rain control area was
outlined for the southern part. During 2006–2010, the
Ministry of Science and Technology kicked off an initiative to study the formation of acid rain and associated control under the national “973” program.
1.2 Formation of acid rain
One cannot understand the formation of acid rain
without sorting out its causes in the first place. Analysis of the composition of acid matters in acid rain
reveals that the acid rain that occurred in China was
mainly caused by unrestricted emission of SO2 (Fan,
2002). As a result, acid rain was also called “soot
rain” or “sulfuric acid rain”. In recent years, many
large and middle sized cities have witnessed increased
NOx emissions due to increased on-road motor vehicle
emissions. Accordingly, the composition of acid rain
saw an increased concentration of nitric acid (Mei et
al., 2005; Liu et al., 2006; Tang et al., 2005). Under
increasingly enhanced emissions of acid matters, such
as SO2 and NOx , acid rain was changing from being
mainly dominated by sulfuric acid to by both sulfuric acid and nitric acid (Liu et al., 2006; Tang et al.,
2005; and Zhu et al., 2006). Meanwhile, suspended
particulate matters that can neutralize acid rain have
gone down in concentration, which made acid rain control more complicated (Wang and Gao, 2007). Studies show that North China had more acid radical ions
in acid rain than the south, though the former had
less acid precipitation than the latter, implying that
the concentration of atmospheric SO2 is not positively
correlated with the occurrence of acid rain and associated acidity (Wang, 1993, 1994). This means the
formation of acid rain has certain precursors, such as
SO2 , though it is not a sufficient condition. Sufficient
conditions include the combined effects of a range of
natural factors (Hua et al., 1998). Natural factors, including ammonia in the atmosphere, soil acidity and
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ZHAO Yanxia and HOU Qing
alkalinity, alkaline matter concentration in atmospheric particulates, can make a difference in shaping up the regional features of acid rain (Feng, 2004).
Wang (1993, 1994) found that China had a higher concentration of atmospheric particulates, compared with
other countries, especially coarse particulate matters,
with a significant difference between the north and the
south. For example, the northern part of China was
high in alkaline matters. As a result, atmospheric particulates had more alkaline matters than acid matters.
When coming to precipitation, such atmospheric particulates were able to neutralize acid precipitation. On
the contrary, in the south, atmospheric particulates
were low in alkaline matters, with a reduced buffering
effect, compared with the north. The concentration of
alkali metal ions in soil and associated pH value was
another major player in the formation of acid rain. Alkaline matters in precipitation were mainly stemmed
from soil. In China, the concentration of alkaline particulates in soil went up from the south to the north,
which explained why acid rain mainly occurred in the
south where low soil alkalinity and pH value dominate.
Wang Wenxing et al. (1997) believed that acid
rain occurring in the east and southeast coastal areas had a complicated source, as these areas were not
only influenced by the continent in the west but also
by Japan and the Republic of Korea. In the case of
Qingdao, a coastal town that was hit hard by acid
rain, acid matters discharged from the contemporary
industrial development and from the natural release
of marine dimethylsulfide were the major causes for
the formation of acid rain. Special features of boundary layer wind and temperature fields above the Qingdao area was another major cause contributing to the
formation of acid rain (Liu et al., 1997; Feng, 2004).
However, a town located in the southern coastal area
could make a different story. For example, Xiamen
was not featured with a high concentration of SO2 ,
NOx , and PM10 , though with a high concentration of
ozone and hydroperoxide. Strong oxidation and low
concentration of ammonia resulted in reduced alkaline
concentration, which in turn contributed to the formation of acid rain there (Zhuang, 1998). Acid rain
241
that occurred in Sichuan and Chongqing were mainly
caused by high SO2 concentration in the atmosphere
as a result of high sulfur coal used in the locality,
plus special geographic environment and meteorological conditions (Xu and Lan, 2005). Poor weather
conditions, such as calm winds and temperature inversion, facilitated the formation of acid rain (Dong et al.,
2003; Wu et al., 2004; Huang et al., 2004; Lin et al.,
2005). The distribution of rainfall pH values across
China has somewhat agreed with the distribution of
surface wind fields at the same scale. The Sichuan
Basin, Yunnan-Guizhou Plateau, and some areas in
Guangxi were the calmest areas with high occurrences
of both calm winds and acid rain (Tian et al., 2001).
Other meteorological conditions, such as the amount
of rainfall, may also pose a major effect on the formation of acid rain (Lin et al., 2005). Generally speaking,
the washing-up effects of local precipitation and the
medium to long range transport constituted a decisive
source for the occurrence of acid rain in most southern
areas (Hua et al., 1998; Mao, 1992; Wang et al., 1992).
In small- and medium-sized cities and in the rural areas where pollution was relatively light, the acidity of
rainfall was mainly determined by the in-cloud process
(Huang et al., 1995).
1.3 Damage and associated control measures
Acid rain can cause damage in different forms.
In addition to its adverse effects on ecological environment, including soil, forest, agriculture, and water
body, acid rain may also erode the surface of structures, compromise people’s health, and cause huge loss
to the national economy (Feng, 1993; Cao et al., 1993;
Fan, 2003). Acid rain facilitates the release of nutritional elements, including potassium, sodium, calcium, and magnesium, from soil. The released nutrients would be washed away by rain water, making soil
barren and affecting the normal development of plants
(Fu and Tian, 2006; Xing, 2002; Chen et al., 2007).
Additionally, acid rain would result in more diseases
and pests in trees and crops, reduce yield, and deteriorate forests (Liu, 2003; Li et al., 2005). Rivers and
lakes affected by acid rain would have reduced alkaline matters in water bodies. In some serious cases,
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ACTA METEOROLOGICA SINICA
one could see fish and shrimps dying in the water affected by acid rain, with reduced biospecies of planktons. Acid rain is also a killer to building materials and cultural relics (Zhang et al., 2002). Partial
findings derived from the studies conducted during
1986–1995 show that acid rain in 11 provinces and autonomous regions, including Jiangxi, Hunan, Guangdong, Guangxi, Sichuan, Guizhou, Hubei, Jiangsu,
Zhejiang, Anhui, and Fujian, has caused annual economic and ecological loss worth RMB 45.9 billions
(Chen and Chai, 1997).
An effective approach to place acid rain under
control is to cut down SO2 and NOx emissions. Industrialized nations, where acid rain started first, have
worked on a full-fledged environmental pollution control starting from the late 1970s. Chinese government
has paid great attention to acid rain contamination
caused by emissions. For example, a policy document
on placing acid rain under control was published and
implemented in 1990. In 1992, efforts were made to
charge SO2 emissions from industrial sources and to
curb the development of acid rain in nine municipalities of two provinces (Yang, 2002). In a number of the
State policy documents, it is clearly stipulated that
the development of acid rain shall be curbed in two
major affected regions, and SO2 contamination shall
be placed under control (Liu, 2001). In January 1998,
the State Council approved the acid rain and SO2
contamination regional control plan, in a move to address the increasingly serious contamination problem
(Yang, 2002). Unfortunately, in recent years, higher
SO2 emissions outside the two major affected regions
have, to some extent, offset the control results within
the affected regions, which only account for 11.4% of
the national territories. Apparently, the spatial distribution of SO2 emissions has been changed. In addition, increased NOx emission has resulted in enhanced
concentration of acid particulates. Meanwhile, suspended particulate matters that are able to neutralize acid rain saw an annual descending trend. These
developments have made acid rain issue more complicated than 20 years ago (Wang and Gao, 2007).
In the past 30 years or so, great efforts have
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been made both at home and abroad to understand
the causes and damage of acid rain, to analyze major
chemical ions in precipitation, and to work out strategies and measures for curbing the development of acid
rain. Impressive findings have been derived from the
efforts. Some scientists made a comprehensive summary of acid rain studies (Ding et al., 1997; Xie et
al., 2004; Shannon, 1999; Menz and Seip, 2004; Wu
et al., 2006). The present study attempts to present
a general picture of the acid rain variation in China,
through objective analysis of acid rain data collected
by more than 80 acid rain monitoring stations of China
Meteorological Administration (CMA) in the past 14
years. The study is also accompanied with preliminary
analysis and discussion of the causes for the variation.
2. Data
The acid rain monitoring network, developed
by CMA, is an operational network supported by
weather stations across the country. Designed to reflect regional atmospheric acid deposition, the network has covered most provinces, municipalities, and
autonomous regions (Hong Kong, Taiwan, and Macao
are not included), and is in a position to reflect the spatial and temporal distributions of regional atmospheric
acid deposition (Ding et al., 2004). CMA launched its
acid rain monitoring operation at 22 stations in 1989.
In the early 1990s, CMA started to build a nationwide
network, with an increasing number of acid rain monitoring stations, from 81 in 1993–1996 to 85 in 1997–
2000, and further to 87 in 2001–2002. During the period of 2003–2005, stations went up to 88 in number.
In 2006, 69 national-level stations were built for the
purpose, which made the total number of stations with
acid rain monitoring reach 157. Furthermore, acid rain
monitoring stations established by provincial weather
bureaus have all been incorporated into the national
network under a unified management. In 2007, there
were 294 stations in the CMA acid rain monitoring
network. For the sake of continuity and compatibility, 14-yr observational data collected by more than
80 stations starting from 1993 were employed for
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ZHAO Yanxia and HOU Qing
events with a pH value lower than 5.6 (5.6 is excluded),
before calculating the frequency of acid rain through
the following equation:
F[<5.6] =
N[<5.6]
× 100%,
N total
(4)
Fig. 1. The acid rain observation network of China Me-
where F[<5.6] depicts the frequency of pH value <5.6,
and N[<5.6] the times of rainfall events with a pH value
lower than 5.6. Ntotal means the number of pH value
observations in the year.
The frequency of severe acid rain, whose pH value
is lower than 4.5, can be calculated similarly.
teorological Administration. Information is as accurate as
2.2 Precipitation chemistry
till June 2006.
At the present stage, only four CMA stations collect precipitation chemistry data. They are: Waliguan
Baseline Observatory in Qinghai–a global atmospheric
baseline station, and three regional atmospheric baseline stations located in Longfengshan, Heilongjiang
Province (representing the region of Northeast China),
Shangdianzi in Beijing (Beijing-Tianjin-Hebei and adjacent areas), and Lin’an in Zhejiang (the Yangtze
River Delta area), respectively. Basic facts about these
stations are summarized in Table 1. Four stations provide accurate and reliable data, thanks to the fact that
they are part of the WMO global atmospheric baseline
network operating under a unified international standard. In this study, only the precipitation chemistry
data collected by three regional baseline stations from
1999 to 2006 were used, as Waliguan Station sits in an
area without acid rain. Averaged annual ion concentration is the weighted average of individual rainfall
and ion concentration.
statistical analysis in this study. The distribution of
stations is given in Fig. 1.
2.1 Annual mean pH value and frequency of
acid rain
In this study, 14-yr daily acid rain data collected
at more than 80 stations were applied. Annual mean
pH value and averaged annual frequency of acid rain
were calculated in line with the methodologies defined
by CMA Acid Rain Observation Practice (2005).
2.1.1 Annual mean pH value
Here, the hydrogen ion concentration [H+ ]
weighted rainfall method was used. In the process,
daily rainfall pH value was converted into hydrogen
ion concentration, before being multiplied with corresponding daily rainfall. The sum was divided by
annual rainfall total to obtain averaged hydrogen ion
concentration. Negative logarithm was made to obtain
annual mean pH value. It is calculated as follows:
[H + ]i = 10−pHi ,
P +
[H ]i × Vi
P
,
[H + ] =
Vi
(1)
pH = −lg[H + ],
(3)
Table 1. Information about four stations that observe
precipitation chemistry in China
(2)
where pHi represents pH value of daily precipitation,
pH is rainfall weighted mean pH value, and [H + ]i is
hydrogen ion concentration (mol L−1 ) derived from
the calculation of daily precipitation pH value. Vi is
P
daily rainfall, and
Vi is annual rainfall in mm.
2.1.2 Frequency of acid rain attacks (F )
One has to screen out the occurrences of rainfall
Longitude
Latitude
Elevation (m)
Shangdianzi Lin’an Longfengshan Waliguan
117.07◦ E 119.04◦ E
127.36◦ E
100.54◦ E
40.39◦ N
30.18◦ N
44.44◦ N
36.17◦ N
287
139
331
3810
2.3 SO2 and NOx data
The SO2 emission data were mainly quoted from
China Environment Statistics Bulletin and the Environment Bulletin published by local provinces. The
national bulletin data cover the period from 1997 to
2005, while the provincial data from 2000 to 2005.
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ACTA METEOROLOGICA SINICA
There is no statistics for NOx emission so far, though
energy and environment authorities have published
some estimates. The estimates have shown a consistent trend, albeit with different values.
3. Acidity of precipitation
In China, acid rain mainly affects the vast region
in the south of the Yangtze River, though it also attacks some areas in the north. Averaged annual rainfall pH value shows that more areas have been affected
by acid rain in the past 14 years, with increased areas
in the north, though the southern part of the country
basically remained the same in terms of the affected
area size. With regard to the intensity of acid rain,
the period of 1993–1998 registered acid rain with the
largest intensity, though followed by a reduced intensity in 1999–2002. During the period of 2003–2006,
acid rain became more intense again, with 2006 sitting at the average level of 1993–1998. Some areas
have seen more acid rain compared with 1998, though
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a few areas have reduced occurrences of acid rain.
Figure 2 indicates that during 2003–2006, the severe acid rain area (annual mean rainfall pH < 4.5)
represented by Sichuan and Guizhou provinces had
noticeably narrowed down, and the super acid rain
area (annual mean rainfall pH < 4.0) was disappearing. Unfortunately, Hunan, Guangdong, and Jiangxi
had intensified acid rain. There even appeared some
areas in the east of Hunan and west of Jiangxi, which
had an annual average rainfall pH value lower than
3.5, implying that heavily polluted areas were shifting
from the southwest to the middle part of China and to
the middle part of South China. Additionally, some
areas in North China have been attacked by higherintensity acid rain. In Fig. 2d, the severe acid rain
area was expanding northwards.
As a matter of fact, acid rain attacks were eased
thanks to the control policies implemented by the end
of the 1990s. As of the end of 1999, 98 of 175 cities
affected by acid rain had met the SO2 emission standard (www.china5e.com). Meanwhile, CMA acid rain
Fig. 2. Average pH values of precipitation over (a) 1993–1998, (b) 1999–2002, (c) 2003–2006, and (d) the annual
average pH value of 2006.
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ZHAO Yanxia and HOU Qing
monitoring network made 1999–2002 the period enjoying the least acid rain contamination in the past
14 years. Unfortunately, the later bouncing back of
emissions (see Section 5) worsened the acid rain contamination. Therefore, the current intensity of acid
rain is only weaker than the worst period, when viewing the country’s situation as a whole.
4. Frequency of acid rain attacks
As far as the frequency of acid rain attacks is concerned, the South China saw a different story from the
north.
In the past 14 years, the eastern part of Southwest China (Yunnan, Guizhou, and Sichuan) had less
acid rain, with more acid rain in the middle part of the
country and in the middle part of South China (Hunan, Jiangxi, and Guangdong). The southern part of
East China (Zhejiang and Fujian) had kept a basically unchanged status. In Fig. 3, during the period
of 1993–1998, the areas hit hard by acid rain with a
frequency larger than 80% were located in Guizhou,
Chongqing, the northeast of Hunan, west of Jiangxi,
the middle and southern parts of Guangdong, and
some areas in Zhejiang. The areas hit hard by acid
rain started to narrow down with a reduced intensity
in the period of 1999–2002, though the west of Jiangxi
failed to see an eased situation. After 2003, Guizhou
and the western Guangxi started to enjoy a noticeably reduced attack of acid rain, while the northeast of
Hunan, Jiangxi, and Guangdong merged into a large
area with more acid rain. Changsha and Ganzhou
registered a frequency as high as 90% or more, so did
Guangzhou at 97% or more during 2004–2006. In addition, Chongqing, a traditional area hit hard by acid
rain, had a frequency of attack at 97% or more. Both
Zhejiang and Fujian basically sat around 80%, with a
few areas, such as Lin’an in Zhejiang, reaching 90%
or more. 2006 marked a year with the largest number
of areas suffering 80% or more frequency of acid rain
attacks in the history.
The northern part of China secured less attacks
of acid rain during the period of 1994–2002 except
1993. The Beijing-Tianjin-Hebei area and some parts
of Henan had increased attacks of acid rain by 20%–
245
50% from 2003. Shandong also had more areas hit by
acid rain at a frequency of 50% or more. During the
period of 2004–2005, a few areas in northwest Xinjiang and the southern Heilongjiang had recorded a
frequency of acid rain attack larger than 50%.
For acid rain attacks with a pH value less than
4.5, the southern China had seen a trend similar to the
above-mentioned variation, with a frequency ranging
from 20% to 50%. A few areas in Guizhou, Hunan,
Jiangxi, and Guangdong had recorded a frequency exceeding 80%. The northern part of China saw no large
change in the occurrence of intense acid rain, mostly
at a frequency of 20% or less.
5. Acid rain variation patterns and associated
causes
Many factors contribute to the formation of acid
rain. Local small-scale acid rain is not only associated with local emissions, but also manipulated by a
range of meteorological conditions, including wind direction, wind speed, and temperature inversion. However, when taking China as a whole, acid gas released
from human activities, such as SO2 and NOx , makes a
major contributor to the formation of acid rain. The
conclusion is confirmed by the agreement between SO2
emissions and acid rain distribution. In addition, precipitation chemistry data collected by atmospheric
baseline stations also make it a strong case. China has
so far produced no quantitative data of NOx emissions.
However, the estimates published by the State Development and Reform Commission and the former State
Environmental Protection Administration have shown
a marked ascending trend for NOx in recent years.
5.1 SO2 emissions in China
China’s total SO2 emission registered for the period of 1997–2005 (Fig. 4) shows that the period of
1999–2002 kept a lower emission level which was confirmed by observational results. Emission started to
rise in a steady manner after 2003. As a result, acid
rain monitoring stations recorded a sustained decrease
of rainfall pH value, though with enhanced acidity and
increased frequency of acid rain attacks. Apparently,
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ACTA METEOROLOGICA SINICA
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Fig. 3. Average acid rain frequency over (a) 1993–1998, (b) 1999–2002, (c) 2003–2006, and (d) the annual average pH
value of 2006.
place atmospheric pollution including acid rain contamination under control, though the economic development shall not be compromised as a precondition.
5.2 Precipitation chemistry
Fig. 4. The SO2 emission in China during 1997–2005.
the magnitude of acid rain contamination is closely
associated with regional SO2 emission. One can see
from Fig. 4 that SO2 emission released from daily life
was basically unchanged, and the general development
trend fully agreed with that of the industrial emission,
implying that acid rain control shall be focused on industry by using extensive desulphurization techniques.
Efforts shall also be made to define emission standards
and indicators for large emission sources, in order to
Of the chemical ions contributing to atmospheric
+
precipitation, a number of ions, including SO2−
4 , NH4 ,
Ca2+ , and NO−
3 , are highly concentrated, with some
others, such as Mg2+ , Na+ , K+ , Cl− , H+ , and F− , in
relatively low concentration. Of the said elements, sulfuric and nitric acids are the most important acid elements for the formation of acid rain in China. Figure 5
shows a sustained ascending trend for both SO2−
4 and
,
confirmed
by
the
observational
results
at
three
NO−
3
regional baseline stations. In Fig. 6, three stations
showed a basically descending trend for rainfall pH
value (in Figs. 5 and 6, the data collected by Shangdianzi Station in 2002 was poor in quality due to local
construction activities), which agreed with the variation of regional rain acidity in China. However, the
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ZHAO Yanxia and HOU Qing
data furnished by three regional baseline stations are
not in a position to represent the situation in the whole
country, especially the severe acid rain areas in Southwest and South China. In these areas, there are no stations designed with precipitation chemistry measurement. Monitoring results of precipitation chemistry
provided by environmental protection authorities and
research projects show that in recent years both the
eastern part of Southwest China and South China have
seen a basically ascending trend for SO2−
and NO−
4
3,
with different magnitudes in different areas. Furthermore, NO−
3 has played an increasingly large role in
shaping up acidity, though SO2−
4 remains a key player
(Mei et al., 2005; Liu et al., 2006; Zhang, 2007).
6. Case study: acid rain in North China
As it was analyzed in the above, acid rain contamination has become appreciably enhanced in the
northern part of China. To illustrate the fact in a
more objective manner, some provinces and municipalities hit but not seriously by acid rain, including
Beijing, Tianjin, Hebei, Henan, Shandong, Shanxi,
247
and Shaanxi, were selected as the targets for statistical analysis.
Figure 7 shows that even in the period of 1993–
1998 featured with rampant acid rain attacks in the
south, both North China and the Yangtze-Huai River
Valley saw light attacks of acid rain in terms of both
acidity and frequency. Unfortunately, during 2003–
2006, the same regions witnessed a rainfall pH value
that quickly dwindled, with a pronouncedly enhanced
intensity, and increased frequency for both regular and
intensified acid rain events. In 2006, the worst acid
rain contamination in the past 14 years occurred. Sixteen monitoring stations in 7 provinces and municipalities have recorded an averaged annual rainfall pH
value of 4.57 with a frequency of acid rain attacks at
45%, and severe acid rain attacks at 23%. The data
collected by the Shangdianzi Station (covering BeijingTianjin-Hebei area) showed an averaged annual rainfall pH value of 4.76, 4.43, 4.52, and 4.31, respectively,
for the period of 2003–2006, with a corresponding frequency of acid rain attacks at 40%, 47%, 51%, and
67%.
The above variation is associated with the
Fig. 5. SO2−
and NO−
4
3 concentration changes at three regional baseline stations during 1999–2006.
Fig. 6. Annual average pH changes for three baseline
Fig.
7. Rain water acidification of seven provinces in
stations during 1999–2006.
northern China in the period of 1993-2006.
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ACTA METEOROLOGICA SINICA
enhanced emissions of SO2 and NOx , a result of economic development. Both Henan and Shandong are
good examples (Fig. 8) for illustrating the increasing
SO2 emission. In 2005, Henan had a SO2 emission
that was twice the amount in 2000. Shandong has
sustained an increasingly large SO2 emission in recent
years.
In fact, Heilongjiang, Jilin, and Liaoning
provinces of Northeast China have also witnessed an
acid rain contamination that has become more severe.
No discernable improvement in the south and more
acid rain in the north characterized the variation of
acid rain in China.
7. Conclusion and discussion
Overall speaking, China has its acid rain mainly
over a vast area in the south of the Yangtze River.
Chongqing, Hunan, Jiangxi, and Guangdong are the
areas hit hard by acid rain in the country. In addition, the northern part of the country has some areas affected by acid rain that are by no means small,
mainly over the Beijing-Tianjin-Hebei area and some
areas in Shandong. When viewing the country as a
whole, more areas have been attacked by acid rain in
the past 14 years, though with a slightly weakened
intensity. The northern part of the country, in particular, has seen more areas hit by acid rain with an
enhanced intensity, though the southern part of the
VOL.24
country basically remained the same in terms of the
area size affected by acid rain. It is necessary to adopt
effective measures to control the acid rain contamination situation.
The acid rain in China is mainly caused by acid
gases released from human activities, such as SO2 and
NOx , mostly from industrial sources. The conclusion
is supported by the agreement between the variation
of SO2 emission and that of the acid rain and its distribution. In addition, the ascending trend of SO2−
4
and NO−
in
precipitation
recorded
by
the
regional
at3
mospheric baseline stations also supported this conclusion.
This study discusses the variation of acid rain in
China as a whole. Further studies and precipitation
chemistry analysis are needed to understand the impacts of on-road motor vehicle gas emission on the
development of acid rain in medium- and large-sized
cities. Unfortunately, limited precipitation chemistry
data make the investigation of the causes of acid rain
at the local or smaller scale impossible. This hampers
us from working out rational policies and measures to
deal with acid rain. It is suggested that more precipitation chemistry observation activities be initiated in
the future.
Acknowledgements. The authors would like
to thank Wang Yaqian for preparing Fig. 1. Thanks
also go to Ding Guoan for his kind review and comments.
Fig. 8. The SO2 emission in (a) Henan and (b) Shandong provinces during 2000–2005.
NO.2
ZHAO Yanxia and HOU Qing
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