A relative comparison of acid rain quality changes in quang ngai, Nha Trang and Da Lat during 2007 – 2016
Nghiên cứu khoa học công nghệ
A RELATIVE COMPARISON OF ACID RAIN QUALITY CHANGES
IN QUANG NGAI, NHA TRANG AND DA LAT DURING 2007 – 2016
Tran Tuan Viet1*, Nguyen Thi Bich Ngoc1, Dinh Mau Hoa2,
Nguyen The Tien1, Pham Hong Nhat1
Abstract: This study aims to compare the acid rain changes in three cities
including Quang Ngai, Nha Trang and Da Lat, which are different in both weather
conditions and industrial development. A set of combined data on the
characteristics of both rain water and meteorology for the last ten years was
employed for assessment. Rain water samples were collected during all the rain
events and measured on-site for the determination of pH, electrical conductivity and
temperature before delivery to the laboratory for the analysis of major anions and
cations. Data on industrial development in the study areas have also been used for
reference and discussion. According to the monitoring data, the frequency of acid
rain in Quang Ngai has decreased for the last 10 years. While the rain events with
pH < 5.6 appeared in Nha Trang from 2010 and their frequency has increased until
2015, they appeared in Da Lat only in 2009, 2010 and 2016. In addition, however,
the concentration of ions in rain water samples collected at all the three stations
seemed to show an increasing tendency of acid rain potential.
Keywords: Acid rain, Rain water, pH below 5.6, Rain event, Monitoring.
1. INTRODUCTION
The impact of air pollution from industrial and economic growth have resulted
in severe acid rain [1]. In theory, the acidity and alkalinity of rain are measured
using a pH scale for which pH = 7 is neutral. The normal rain usually has a pH
about 5.6, it is rather acidic because of carbonic acid which is formed by CO2.
Therefore, rainwater with pH below 5.6 is considered as acid rain [2,3,4]. The
oxides of sulphur, nitrogen or ozone are widely believed that they are the primary
cause of acid rain [1,3,4,5]. The acid rain may cause vegetation damage, health
effects, material corrosion, soil acidification, aquatic ecosystems harm, forest
damage, etc. [5].
Quang Ngai, Da Lat and Nha Trang locate in Central and Highland of Viet
Nam which play a very important role in economic and industrial growth as well
as national defense and security. Economic development grows with a
surprisingly fast rate for the last decade in the whole country in general and in
this part in particular. Therefore, from 1999, three acid rain monitoring stations
were established in this area and has since then been run to observe the rainwater
quality change. This study aims to presents the changes of acid deposition from
2007 to 2016.
2. METHOD AND MATERIAL
2.1. Study area
Three monitoring stations, which are presented in Figure 1, locates in three
cities in middle of Viet Nam:
- Quang Ngai Station (True altitude is 7.16 m): 108048’00’’E; 15007’00’’N.
This station is placed at the coastal province of Quang Ngai, which is very famous
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with Dung Quat Refinery for contributing upto 81.6 % of the whole province’s
industrial production value [6].
- Nha Trang Station (True altitude is 4.09 m): 109012’00” E; 12013’00” N. This
station is located at Khanh Hoa, which is another coastal province in the middle of
Viet Nam where tourism, a green industry, has a great advantage over other
industries in the area.
- Da Lat Station (True altitude: 1,508.6 m): 108027’00’’E; 11057’00’’N. This
station is situated at Da Lat, which is the capital city of Lam Dong Province in the
central Highlands and which is also famous for tourism.
Both the provinces of Quang Ngai and Khanh Hoa are situated at the central
coast of Viet Nam. They therefore have similar climate condition such as average
temperature (of 25-260C) and seasonal changes (e.g. wet season from September to
December). Though, the annual average precipitation in Quang Ngai is about 2,100
mm/year, a little higher than in Khanh Hoa which is about 1,500 to 2,000 mm/year.
In contrary, the climate in Lam Dong Province is quite different from that in the
above-mentioned two provinces due to its high altitude. Its average temperature is
only 180C to 250C and annual average precipitation is about 2,000-3,000 mm with
the wet season from May to November.
Figure 1. Study area.
2.2. Sampling and analysis
Rainwater samples have been collected during all the rain events by a semi-auto
rainwater sampling tool as following ISO 5667-8:1993 guide. The collected
samples have been measured on-site for the determination of pH, EC and
temperature before being filtered by 0.45 µm filter papers. The filtrate has then
been stored in cold P.E. bottle and delivered within 28 days to the laboratory for
-
-
2-
+
the analysis of Cl-; NO2 ; NO3 ; SO4 ; Na+; NH4 ; K+; Mg2+ and Ca2+ using an Ion
Chromatography System (Waters, detector conductivity 432). The deionized water
used for analysis has always been controlled to have an EC value below 0.5 µS/cm.
2.3. Data analysis
The results in every analysis batch have been validated by calculating the ion
balance. In other words, the total anion and cation equivalents should be equal. For
calculating ion balances, the following equation has been used [7]:
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T. T. Viet, N. T. B. Ngoc, …, “A relative comparison of acid … Da lat during 2007 - 2016.”
Nghiên cứu khoa học công nghệ
(
(
)) 100
ꢂꢃꢄ
ꢀꢁ =
(1)
ꢂꢅꢄ
where R1 is balance error (%); C and A represent anion and cation equivalents,
respectively.
C and A values are calculated by the following equations:
ꢃ
ꢃ
ꢍꢃ
ꢃ
∑
ꢁꢑ
[
]
[
]
[
]
[
]
(2)
(3)
ꢆ = ꢇꢄꢈꢉ = ꢇꢊ + ꢋꢌꢍ + ꢋꢌꢎ + 2 ꢏꢌꢐ
ꢈ
(
)
(
)
ꢒꢓꢔꢕ
ꢒꢓꢔꢕ
ꢁꢑ
ꢅ
∑
[
]
ꢇ =
+
ꢇꢂꢈꢉ =
+ ꢋꢗ
+
ꢈ
ꢁ.ꢑꢑꢖ
ꢁ.ꢑꢑꢖ
ꢍꢅ
ꢅ
ꢅ
ꢍꢅ
[
]
[
]
[
]
[
]
ꢋꢘꢐ + ꢙ + 2 ꢚꢛ
+ 2 ꢇꢗ
where CAi and CCi are the concentration (µeq/L) of i-th anion and cation,
respectively. Because the unit mg/L is used, it should be converted to µmol/L as
follows:
ꢁꢑꢑꢑ
(
)
(
)
ꢜꢝꢞꢊ/ꢟ = ꢝꢛ/ꢟ
(4)
ꢠꢡꢢꢣꢤꢥꢢꢦꢧ ꢨꢣꢈꢩꢪꢫ
The required ion balance of rainwater sample analyses is given in Table 1. If the
R1 values did not meet the criteria, the sample would have been re-analyzed or a
note flag would have been added into the database indicating that the results had
not meet the required criteria.
Table 1. Required criteria for R1.
(C+A), µeq/L
<50
R1, %
±30
±15
±8
50-100
>100
When pH is greater than 6 and R1 is significantly greater than zero, bicarbonate
concentration should be included for computation of R1. The concentration (µeq/L)
of bicarbonate would then be calculated from the dissociation constant of H2CO3
(Ka = 10-6.35), CO2 concentration in atmosphere (360 ppm) and pH as follows:
ꢱ
ꢵ
ꢶ
ꢷ
ꢴ
ꢭꢣꢮꢰ =
= 1.24 ∗ 10ꢹꢵꢃꢺ.ꢎꢺ
ꢲꢳ
ꢲꢳ
ꢃ
ꢴ
[
]
ꢘꢇꢌꢎ
ꢬ
(5)
ꢸ
[
]
ꢯ
ꢵ
To assess the potential of acid rain, the T value is calculated as follows [8]:
ꢸ
ꢸ
ꢴꢸ
ꢴꢸ
ꢸ
[
]
ꢼꢽꢵ ꢿꢅ ꣀꣁꣁꢼꢂꢦ
ꢾ
ꢿ
ꢼꢽꢵ ꢿꢅ ꣅꢼꢂꢦ ꢿꢃ ꢑ,ꢑꢎꢖ ꢽꢦ
ꢾ
ꢻ =
=
(6)
ꢓ
ꢴꢓ
ꢾ
ꢓ
ꢴꢓ
ꢾ
ꢸ
[
]
[
]
[
]
ꢽꣂ ꢅ ꣀꣁꣁꢼ꣄ꣂ
ꢿ
ꢽꣂ ꢅ ꣅꢼ꣄ꣂ ꢿꢃ ꢑ,ꢍꢺꢁ ꢽꢦ
ꣃ
ꣃ
2-
Where nss[Ca2+] is non-seasalt calcium ion concentration; and nss[SO4 ] are
non-seasalt sulfate concentration.
When T value is lower than 1, the major cation is insufficient to neutralize the
nitrate and sulfate. Those anions might then be combined with ion H+ to formulate
an acid property in rainwater.
3. RESULTS AND DISCUSSIONS
The pH changes recorded at the three study stations from 2007 to 2016 are
shown in Figure 2. According to the results, rainwater collected in Da Lat had the
monthly mean pH ranging between 5.15 and 6.5. In more details, only two mean
pH values recorded in April 2010 and April 2016 were below 5.6. In contrast,
rainwater collected at stations in Nha Trang and Quang Ngai had a higher number
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of monthly mean pH values below 5.6. In Nha Trang, rainwater pH significantly
decreased from 2009 to 2013 and varied widely around 5.6 from 2014 to 2016.
Meanwhile, monthly mean pH values in rainwater samples collected at Quang
Ngai showed a more complicate change pattern in the study period 2007 to 2010,
slightly increasing during 2011 to 2014, then rapidly increasing in 2015 and
quickly decreasing in 2016.
One-way ANOVA was used for analysis of the data. The data analysis results
showed that there was a statistically significant difference between the pH mean
values of Nha Trang, Da Lat and Quang Ngai (with p = 0.039). The 10-year pH
mean values of the three stations can be placed in an order as: Da Lat > Quang
Ngai > Nha Trang.
Figure 2. Monthly pH changes during 2007 to 2016 at Da Lat (a), Nha Trang (b),
and Quang Ngai (c).
The yearly average pH of rainwater monitored in this study ranged from 5.61 to
6.98. They seem to be higher than pH of rainwater in other wet deposition
monitoring stations in East Asia. In the latest publication in 2011, EANET (Acid
deposition Monitoring Network in East Asia) presented the five-year average pH
(2005-2009) of rainwater of all monitoring sites ranging from 4.4 to 6.2, with 62%
of values having pH value below 5.0 [9].
The frequency of rainwater with pH below 5.6 seems to slightly correlate with
industrial growth of those three cities. More specifically, the industrial production
(IP) value of Lam Dong province (ranging from VND 3,400 billion in 2007 [10] to
about VND 13,000 billion in 2016 [11]) is the smallest among those three study
provinces. As a result, almost rainwater samples collected in Da Lat had pH values
exceeding 5.6 in the last ten year. In the meantime, the slight increase of IP value
in Khanh Hoa (ranging from VND 11,300 billion in 2007 [12] to about VND
19,300 billion in 2012 [13] and to VND 44,500 billion in 2016 [14]) seems to be
related with the increasing trend of acid rain as shown in Figure 3(b). Although
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T. T. Viet, N. T. B. Ngoc, …, “A relative comparison of acid … Da lat during 2007 - 2016.”
Nghiên cứu khoa học công nghệ
Quang Ngai’s IP value increased very quickly from 2009 mostly due to the
operational commencement of Dung Quat Refinery (IP values increased from
about VND 2,000 billion in 2007 and 2008 to VND 9,000 billion in 2009 [15] and
approximate VND 109,000 billion in 2016 [6]), the frequency of rainwater with pH
values below 5.6 did not change much til 2012. This suggests that the acid rain in
Quang Ngai might have been influenced by some other sources of air pollution.
Figure 3. Number of rain events and pH<5.6 rainwater samples during 2007 to
2016 at Da Lat (a), Nha Trang (b), and Quang Ngai (c).
Figure 4. The T values during 2007 to 2016 at Da Lat (a),
Nha Trang (b), and Quang Ngai (c).
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Although the rainwater samples collected in Da Lat had high pH values during
2007 to 2016, the T values have been lower than 1 since 2012 and have just
slightly increased in 2016. This means that an increasing tendency of acid rain
potential is observed. The trends of T values for Quang Ngai and Nha Trang are
also showed in Figure 4. While T values for Nha Trang have been lower than 1
since 2010, those in Quang Ngai have been smaller than 1 since 2012.
4. CONCLUSION
Although pH values recorded in all three study stations have been in a high
range compared with those in a number of other sites around East Asia, the ion
concentrations in the study areas have shown an increasing tendency of acid rain
potential. Moreover, the high industrial production values seem to have a positive
correlation with the number of acid rain events. In order to monitor acid deposition
in these areas, it is strongly recommended that the current acid rain monitoring
program be continued. Last but not least, it is also recommended that a dry
deposition monitoring program be run in parallel.
Acknowledgement: This study has been extracted from part of the National
Environmental Monitoring Program funded by the Ministry of Natural Resources and
Environment and implemented by the Institute for Tropicalization and Environment (ITE)
under an assignment of the Ministry of Defense, that are all much acknowledged. The
authors also thank all members of the Environmental Monitoring Division for their work
as well as other divisions within the ITE for their close cooperation.
REFERENCES
[1]. T. Larssen and G. R. Carmichael, “Acid rain and acidification in China: The
importance of base cation deposition,” Environ. Pollut., Vol. 110, no. 1, pp.
89–102, (2000).
[2]. J. N. Galloway, G. E. Likens, and E. S. Edgerton, “Acid Precipitation in the
Northeastern United States: pH and Acidity,” Science, Vol. 194, no. 4266, pp.
722–724, (1976).
[3]. P. Brimblecombe, "Acid Rain - Deposition to Recovery," Dordrecht: Springer
Netherlands, (2007).
[4]. A. Singh and M. Agrawal, “Acid rain and its ecological consequences,” J.
Environ. Biol., Vol. 29, no. 1, pp. 15–24, (2008).
[5]. F. C. Menz and H. M. Seip, “Acid rain in Europe and the United States: An
update,” Environ. Sci. Policy, Vol. 7, no. 4, pp. 253–265, (2004).
[6]. Quang Ngai People’s Committee, "Report of current social economic status
of Quang Ngai in 2016", (2017).
[7]. EANET, “Technical Manual for Wet Deposition Monitoring in East Asia,”
Measurement, Acid Deposition Monitoring Network in East Asia, p. 74,
(2000).
[8]. T. D. H. Tran, “Acid deposition in North of Viet Nam,”, Proceedings of the
scientific confference in Ha Noi, pp. 186–193, (2007).
[9]. EANET, “Second Periodic Report on the State of Acid Deposition in East
Asia. Part III - Executive Summary,” Acid Deposition Monitoring Network in
East Asia, (2011).
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[10]. Lam Dong People’s Committee, "Report of current social economic status of
Lam Dong in 2007", (2008).
[11].Lam Dong People’s Committee, "Report of current social economic status of
Lam Dong in 2016", (2017).
[12].Khanh Hoa People’s Committee, "Report of current social economic status of
Khanh Hoa in 2007", (2008).
[13].Khanh Hoa People’s Committee, "Report of current social economic status of
Khanh Hoa in 2012", (2013).
[14].Khanh Hoa People’s Committee, "Report of current social economic status of
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TÓM TẮT
SO SÁNH DIỄN BIẾN CHẤT LƯỢNG MƯA A XÍT TẠI QUẢNG NGÃI, NHA
TRANG VÀ ĐÀ LẠT TRONG GIAI ĐOẠN 2007 - 2016
Mục tiêu của nghiên cứu này là so sánh diễn biến mưa a xít tại ba
thành phố có điều kiện thời tiết khí hậu và tốc độ phát triển công nghiệp
khác nhau là Quảng Ngãi, Nha Trang và Đà Lạt. Các số liệu về đặc điểm
khí tượng khí hậu và nước mưa trong 10 năm gần đây đều được sử dụng
để đánh giá. Mẫu nước mưa thu thập theo từng trận mưa và được đo ngay
pH, độ dẫn điện và nhiệt độ trước khi chuyển về phòng thí nghiệm để phân
tích các ion dương và âm chính. Dữ liệu về phát triển công nghiệp ở khu
vực nghiên cứu cũng được sử dụng để tham khảo và thảo luận. Theo kết
quả quan trắc, tần suất xuất hiện mưa a xít tại Quảng Ngãi có xu hướng
giảm trong 10 năm gần đây. Trong khi đó số các trận mưa có pH < 5,6
xuất hiện ở Nha Trang từ năm 2010 và tăng dần đến năm 2015, còn ở Đà
Lạt thì chỉ xuất hiện ít ở các năm 2009, 2010 và 2016. Hơn nữa, nồng độ
của các ion chính trong nước mưa thu thập tại cả ba trạm lại cho thấy khả
năng xuất hiện mưa a xít xu thế tăng dần.
Từ khóa: Mưa a xít, Nước mưa, pH nhỏ hơn 5,6, Trận mưa, Quan trắc.
Received date, 11th Aug, 2017
Revised manuscript, 25th Aug, 2017
Published, 15th Sep, 2017
Author affiliations:
1 Institute for Tropicalization and Environment;
2 Meteorological Station Da Lat.
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