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INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 5, No 4, 2015
© Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0
Research article
ISSN 0976 – 4402
Comparison of particulate matter levels in major urban centres in Eastern
Nigeria
Ngele, S.O1, Onwu, F.K 2
1- Department of Industrial Chemistry, Ebonyi State University, Abakaliki, Nigeria
2- Department of Chemistry, Michael Okpara University of Agriculture, Umudike,
Abia State, Nigeria.
[email protected]
doi:10.6088/ijes.2014050100071
ABSTRACT
This study investigated the particulate matter (PM) load, total suspended particulate matter
(TSP) and PM of diameter ≤ ten micrometers (PM10)) in ten urban centres in South-Eastern
Nigeria in the dry and wet seasons from December, 2008 to September, 2009 using
particulate counter instrument. The results showed that the cities' seasonal mean TSP ranged
from103.31±22.26 to1260.25±608.59 and 28.69±4.77 to 555.13±304.57 µg.m- 3 in the dry
and wet seasons respectively. The corresponding range for the dry and wet seasonal means of
PM10 was 14.38±3.01 to 288.06±129.79 µg.m-3 respectively. Comparatively the cities had
PM load in the order: Onitsha > Aba > Umuahia > Owerri > Enugu > Nsukka > Abakaliki >
Nnewi > Afikpo > Orlu. Four cities representing 40% of the cities studied namely: Nnewi,
Abakaliki, Afikpo and Orlu recorded dry seasonal mean TSP values within the WHO annual
guideline limit of 150-230 µgm-3 for combined exposure to TSP and SO2 , while other cities
had dry seasonal TSP mean values above the limit. The dry seasonal mean PM10 levels in all
the cities exceeded the US annual National Ambient Air Quality Standard (NAAQS) of 50
µg.m-3. The Correlation matrix showed that the TSP seasonal means (dry and wet) correlated
positively with that of the PM10 (p<0.05) while the student t-test statistics showed that the dry
seasonal means (TSP and PM10) were statistically significant from that of the wet season
(p<0.05). The study concluded that recording high values (which exceeded the recommended
annual guideline limit) of these pollutants in these cities portends public health risk
particularly to people dwelling in the affected cities.
Keywords: Ambient air, Environmental pollution, monitoring, particulate matter, SouthEastern Nigeria.
1. Introduction
Nigeria presently has neither National ambient air quality standard (NAAQS) nor air
monitoring stations for measuring the concentration of pollutants in the ambient air as
obtainable in most developed countries. The availability of base line data on regional and
national levels is necessary for the establishment of NAAQS and air quality management and
control. The paucity of information regarding air quality in major cities in Nigerian
environment has attracted researchers’ attention of late. Majority of the previously published
works on environmental issues tilted greatly in favour of the water and soil segment of the
environment. This development is in line with what the World Bank research group observed,
that starting from the lowest level of development, environmental regulation increases
steadily with income per capita and follow a characteristic trend of natural resources
protection through regulation of water pollution to air pollution control (World bank policy
Received on December 2014 Published on January 2015
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Comparison of particulate matter levels in major urban centres in Eastern Nigeria
working paper, 1995). The recent upsurge in the quantum of research in the air environment
may stem from increased awareness on the negative consequences of air pollution on public
health, biotic and material component of the environment. For instance, air pollution
particularly particulate matter has been implicated in the aggravation of respiratory and
cardiovascular diseases (philip and Graham, 2005; Norris et al., 1999; Pope, 2000; Samet et
al., 2000; Ong et al., 1991), retardation in growth and yield of plants (Prajapati, 2008),
reduction in visibility (EPA, 1979; Kim et al., 2006) and deterioration of the physical
environment (Ferm et al., 2006). This awareness has been powered more by the globalization
of information made possible by the advent of internet communication technology (ICT).
Furthermore, researchers assume that as developing countries strive to develop and expand
their industries, the developed multinationals shift their production /manufacturing activities
to developing economies in search of relatively cheaper labour and less stiff environmental
regulations and as a result air pollution is most likely to progressively increase in the
developing countries.
Air pollution has been simply defined as the presence in the ambient (outdoor) atmosphere of
one or more contaminants or combination thereof in such quantities and of such duration as
may be or tend to be injurious to humans, plants, property or animal life, or which
unreasonably interfere with the comfort of life, property or the conduct of business (US
public Health service). Air pollutants include: sulphur oxides, nitrogen oxides, carbon
monoxide, gaseous hydrocarbons, dust, smoke, fumes, aerosols (particulates) and radioactive
materials. These potential air pollutants are usually present in the atmosphere at low level
concentration (background level) and are considered to be harmless but are regarded as
pollutants when their levels in atmosphere relatively exceed the background level and hence
become harmful (RAO, 1991; Mirslav and Vladimir, 1998). Air pollutants are categorized as
primary and secondary. Primary pollutants are those that are emitted directly from the sources
while secondary pollutants are those that are formed in the atmosphere by chemical and
photochemical interactions among primary pollutants and normal atmospheric constituents
(Miroslav and Vladimir, 1998; Sodhi, 2005). The sources of these air pollutants are grouped
into natural and anthropogenic sources. Typical natural sources include: volcanoes (SO2, HCl,
CO2, dust particles), bog and marshes (H2S), lightning (NOx) and sea spray (sea salts). The
anthropogenic sources include: vehicular traffic emissions (CO, SO2, NOx, hydrocarbons),
emissions from electric power generation plants (SO2,NOx), volatile organic compounds
(VOCs), emissions from agricultural activities and solid waste burning, emissions from bush
and forest fires, emissions from mining and quarry activities, emissions from domestic
heating and alternative electric power generation during power outages from public power
supply (Gomez et al., 2005; EU, 1997; Oluyemi et al., 1994; Fennelly, 1976).
Suspended particulate matter is an important source of air pollutant (Miroslav and Vladimir,
1998). It consists of finely divided solids or liquids such as smoke, dust, fumes, mist, smog
and sprays (Sodhi, 2005). Particulate matter in the ambient air usually consists of discrete
particles ranging in size from molecular clusters of 0.005 µm to coarse particles in the order
of 100 µm (Sodhi 2005; Shendell and Naeher, 2002). Processes that emit particulate matter
into the atmosphere include: volcanic eruptions, geochemical sources, windblown dust, soil
re-suspension, spray from marine sources, power plant emissions, agricultural and industrial
emissions, vehicular emissions (Commission of European communities, 2005; Sodhi, 2005;
Gomez et al., 2005). In Nigeria, data on ambient air concentration of particulate matter is
lacking for many urban cities and scanty for some others, hence the need to monitor it to
build baseline data for the south-eastern part of the country. Available data of random
sampling by researchers and consultants in some urban centres in the country showed that
Ngele, S.O, Onwu, F.K
International Journal of Environmental Sciences, Volume 5 No.4, 2015
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Comparison of particulate matter levels in major urban centres in Eastern Nigeria
while some cities such as Lagos, Kano, PortHarcourt, Calabar etc., have PM load above the
WHO recommended limit (Olukayode, 2005; Akeredolu, 1989; Koku and Osuntogun, 1999;
Ikamaise et al., 2001; Azuka, 1985), other cities such as Abakaliki and Ogoja have PM levels
within the limit (Ngele, 2009; Ngele, 2012). This study aims at providing baseline data on the
PM levels (TSP andPM10) of ten major cities in south- eastern part of Nigeria.
2. Material and methods
2.1 The study area
The study covered two major cities each in Anambra, Enugu, Ebonyi, Abia, Imo (all in
south- eastern Nigeria). The area is located within latitudes (4º-6.5º) N and longitudes (5º-9º)
E (Microsoft Ecanta, 2007). The area has an approximate population of 16,382,029 according
to the 2006 census figure. The climatic condition is tropical, characterized by wet and dry
seasons. The wet season sets in between April and October while the dry season is usually
between November and March (Strachler and Strahler, 1977)
Table 1: Sampling Location, Name and GPS Coordinates
S/No
1
City
Aba
Site Name
Osisioma junction
2
Umuahia
Gate / Warri Street
3
Nnewi
Izuchukwu junction
4
Onitsha
Upper Iweka
5
Abakaliki
Akanu Ibiam Roundabout
6
Afikpo
Eke Market
7
Enugu
8
Nsukka
Chris Chemist/Ogbete
market Junction
Peace Mass Park, Nsukka
9
Orlu
10
Owerri
Owerri Road /
International Market
junction
Govt House / Modotel
Junction
Coordinates
N050 07.051
E0070 19.811
N050 32.061
E0070 29.651
N060 01.101
E0060 55.091
N060 08.041
E0060 47.481
N060 18.581
E0080 05.411
N050 52.961
E0070 56.181
N060 26.321
E0070 29.241
N060 50.921
E0070 23.901
N050 47.331
E0070 01.901
N050 30.541
E0070 02.181
2.2 Sampling site selection
In each of the States, two major cities were selected for study. The cities studied were
Abakaliki and Afikpo (Ebonyi State), Enugu and Nsukka (Enugu State), Onitsha and Nnewi
(Anambra State), Owerri and Orlu (Imo State), Umuahia and Aba (Abia State). In each of the
cities, a site was chosen in the ‘heart’ of the city based on visible human activities, high
population density and traffic volume. The coordinates of each site was measured with
Garmin global position system, model etrex H (Taiwan).
Ngele, S.O, Onwu, F.K
International Journal of Environmental Sciences, Volume 5 No.4, 2015
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Comparison of particulate matter levels in major urban centres in Eastern Nigeria
2.3 Monitoring protocol
The suspended particulate matter (SPM) concentration in the ambient air of the monitored
sites was determined by means of a digital read out photometric -laser particle counter,
Aerocet Model 531-9800 Rev. C (Metone Inc. U.S.A.). The instrument has in-built particle
count data for eight different particle size ranges including total suspended particulate (TSP),
PM10, PM2.5 and proprietary algorithm to derive the mass concentration for particulate
sampled. The sampler was held at a height of 2 m above ground level, human breathing zone
(EC, 2005) and the ambient air PM concentration reading recorded as displayed on the
instrument's screen. Sampling time for each parameter was two minutes (that is time taken
from switch on of parameter nub to display of reading on the screen). The frequency of the
monitoring was such that a site was monitored one day in a week for twelve hours (6.00 am6.00 pm) at an interval of thirty minutes for four months (16 weeks) in the dry season,
December, 2008 to March, 2009 and four months in the wet season, June-September, 2009.
The hourly mean level for the twelve hours per day per week of each parameter was averaged
and the mean for the 16 weeks computed to obtain the seasonal mean for the parameters
using statistical package for social science (SPSS) software, version 17. Invernizi et al., 2011,
had earlier reported the use of the Aerocet-531 instrument in the measurement of black
carbon concentration (of the following PM sizes: PM10, PM2.5 and PM1) as an indicator of air
quality benefits of traffic restriction policies within the ecopass zone in Milan, Italy
3. Result and Conclusion
The results of the TSP and PM10 concentrations and their computed seasonal means are
presented in Tables 2 and 3 and their seasonal variations depicted in Figs. 1A and 2A, while
their trends across the cities within the period of the study are shown in Figs. 1B, 1C and 2B,
2C.
Figure 1A: Variations of TSP concentrations in Ambient Air between the dry and wet
seasons across cities in South-Eastern Nigeria.
Ngele, S.O, Onwu, F.K
International Journal of Environmental Sciences, Volume 5 No.4, 2015
768
Comparison of particulate matter levels in major urban centres in Eastern Nigeria
Figure 1B: Comparison of Dry Season TSP concentration within the months of Dec. 2008 to
March 2009.
Figure 1C: Comparison of Wet Season TSP concentration within the months of June –
September, 2009.
Table 2: Weekly levels and seasonal mean TSP (µg m-3) in dry and wet seasons in the cities
monitored
Week
1
2
3
4
5
6
7
8
9
10
ABA
D
W
704
180
721
186
924
185
960
121
1786
156
1088
63
829
84
913
103
692
86
652
97
UMU
D
W
446
114
476
126
517
106
1006
86
1551
100
1314
70
422
55
476
80
517
68
421
90
NNEWI
D
W
142
60
126
55
134
38
127
25
162
67
141
60
156
54
133
26
141
80
128
70
ONITSHA
D
W
1271
581
1211
627
1200
608
2379
781
2408
779
2244
813
1564
981
1034
841
1126
801
1231
807
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International Journal of Environmental Sciences, Volume 5 No.4, 2015
ABAKALIKI
D
W
211
121
179
89
182
124
400
76
377
86
364
40
257
46
120
48
140
50
150
45
769
Comparison of particulate matter levels in major urban centres in Eastern Nigeria
11
12
13
14
15
16
x
S
1036
101
463
76
104
61
1028
510
132
28
840
80
385
60
96
49
960
136
100
54
345
112
426
43
73
50
641
121
150
21
385
68
345
53
81
60
437
141
96
65
312
75
107
50
76
62
556
229
120
56
318
118
186
44
99
58
874
126
98
52
781.56 113.44 566.13 76.31 119.94 54.69 1260.25 555.13 192.25 62.56
370.61 41.69 388.79 25.62 28.14 14.73 608.59 304.57 102.84 29.71
Table 2 Continued
Week
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
x
S
AFIKPO
D
W
101
40
115
42
96
45
120
50
150
52
130
41
124
43
102
32
122
37
98
22
86
25
64
30
75
36
97
33
88
34
85
32
103.31 37.13
22.26
8.32
ENUGU
D
W
550
120
560
160
427
122
533
150
450
108
315
104
325
102
307
121
146
133
130
50
180
40
150
42
120
46
150
37
130
22
140
30
288.31 86.69
167.46 46.97
NSUK
D
W
201
53
221
60
302
70
365
46
249
170
280
86
267
109
239
120
206
42
246
53
224
42
326
60
208
40
156
36
127
38
121
46
233.63 66.94
66.82 37.15
ORLU
D
W
150
32
160
30
165
32
172
37
180
35
216
25
165
30
157
24
148
28
146
32
140
20
130
25
125
30
105
32
100
25
108
22
147.94 28.69
30.23
4.77
OWERRI
D
W
290
50
308
45
296
38
314
37
360
40
380
35
443
36
460
40
413
42
390
35
313
45
321
30
296
30
240
28
248
28
236
30
331.75 36.81
69.37
6.63
Foot note: D = Dry Season; W = Wet season, x = mean and S = Standard deviation.
Figure 2A: Variations of PM10 concentrations in Ambient Air between the dry and wet
seasons across cities in South-Eastern Nigeria
Ngele, S.O, Onwu, F.K
International Journal of Environmental Sciences, Volume 5 No.4, 2015
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Comparison of particulate matter levels in major urban centres in Eastern Nigeria
Figure 2B: Comparison of Dry Season PM10 concentration within the months of Dec. 2008
to March 2009
Figure 2C: Comparison of Wet Season PM10 concentration within the months of June –
September, 2009
Table 3: Weekly levels and seasonal mean PM10 (µg m-3) in dry and wet seasons in the cities
monitored
Week
1
2
3
4
5
6
7
8
9
ABA
D
W
604
106
678
124
727
117
711
121
901
107
975
106
811
120
846
100
684
90
UMUAHIA
D
W
376
120
481
134
810
106
840
100
889
90
720
60
911
80
387
60
312
70
NNEWI
D
W
106
44
122
51
87
24
98
30
96
31
89
34
96
29
78
30
73
28
ONITSHA
D
W
1320
427
1460
408
1600
419
1433
400
1283
383
1109
375
1175
364
1086
208
1101
276
ABAKALIKI
D
W
107
82
100
73
148
76
155
68
158
48
147
41
123
64
126
60
128
58
Ngele, S.O, Onwu, F.K
International Journal of Environmental Sciences, Volume 5 No.4, 2015
771
Comparison of particulate matter levels in major urban centres in Eastern Nigeria
10
11
12
13
14
15
16
x
S
637
580
564
498
367
470
335
649.25
181.47
83
83
87
79
75
89
66
97.06
18.04
354
287
248
172
180
243
271
467.56
269.08
75
66
60
51
85
72
53
80.13
24.32
78
76
80
70
74
63
64
84.38
16.03
25
24
28
26
25
23
21
29.56
7.87
896
235
120
982
211
115
960
136
106
96
121
112
88
101
82
81
98
120
81
95
117
921.34 266.06 122.75
532.60 129.79 20.78
45
41
40
39
38
36
29
52.38
16.36
Table 3 Continued
Week
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
x
S
AFIKPO
D
W
128
60
100
64
136
61
140
58
142
54
152
50
102
52
96
48
95
47
90
42
84
38
76
29
72
32
70
24
56
25
52
21
99.44 44.06
31.67 14.29
ENUGU
D
W
247
46
253
48
270
48
308
60
309
51
233
40
207
42
362
30
172
29
162
30
108
20
107
18
152
20
90
18
75
16
96
18
196.94 33.38
89.77 14.46
NSUKKA
D
W
170
60
200
71
206
80
220
68
200
62
210
65
286
60
301
40
254
36
100
32
100
30
120
42
190
28
180
27
110
23
146
21
187.06 46.56
61.75 19.51
ORLU
D
W
105
12
100
10
120
14
102
14
120
18
90
15
88
12
86
18
86
14
80
15
80
12
60
20
70
18
68
16
80
10
86
12
88.81 14.38
17.09
3.01
OWERRI
D
W
110
120
121
100
136
102
160
102
158
101
171
90
280
83
310
86
323
82
286
76
260
85
277
75
240
98
236
90
285
85
244
78
224.81 90.81
70.90 12.13
The highest dry and wet seasonal mean TSP concentrations of 1260.25±608.59 and
555.13±304.37 µg.m-3 were recorded in Onitsha Urban, while the least values of
103.31±22.26 and 37.13±8.32 µg.m-3 and 119.94±28.14 and 54.69±14.73 µg.m-3 were
recorded at Afikpo and Nnewi urbans respectively (Table 2).
It can be seen from the results of TSP that urban areas that are relatively larger in size, higher
in traffic volume, population density and built-up areas (Onitsha, Aba, Umuahia, Owerri and
Enugu) ranked higher in their TSP levels whereas the smaller cities (Orlu, Afikpo and
Nnewi) trail behind. This is in agreement with similar study which reported higher TSP
values in Lagos, Nigeria relative to less urbanized city of Ile-Ife, south-west Nigeria
(Ikamaise et al, 2001). The general (with few irregularities) dry season trends of the TSP
levels across the cities within the period of the study showed gradual rise within the first eight
weeks with the peaking in the fourth to sixth week followed by dipping from tenth week (Fig.
1B). The peaking of the TSP in this study corresponds with the peak of harmattan (usually
between the middle of December to January ending in the south-east Nigeria) characterized
by high levels of dust in the ambient air due to the dust laden south-east trade wind from the
sahara desert that prevails within this period. Similarly, in the wet season, the TSP presented
higher levels in the first four weeks (June) (Fig. 1C) corresponding to the commencement of
Ngele, S.O, Onwu, F.K
International Journal of Environmental Sciences, Volume 5 No.4, 2015
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Comparison of particulate matter levels in major urban centres in Eastern Nigeria
the rainy season and dipping afterwards as the rainy season deepens due to wet precipitation.
The levels of TSP obtained in this study (in most of the cities) were generally above those
recorded in European countries (European Commission, 1997) but within those reported in
Pakistan (JICA/PAKEPA Report, 2002; Masfin, 2005) but below that reported for Lagos,
Nigeria (koku and osuntogun, 2007; Akeredolu et al., 2004). Onitsha also recorded the
highest seasonal mean PM10 values of 921.34±532.60 and 266.08±129.79 µg.m-3 during the
dry and wet seasons respectively while the least seasonal mean values were obtained in
Nnewi and Orlu for the dry and wet seasons respectively (Table 3). The trends of the PM10
(Figs. 2B and 2C) during the study period across the cities were similar to that exhibited by
the TSP. The dry and wet seasonal levels of PM10 correlates significantly with TSP (P< 0.05)
in all the cities monitored while the student t-test statistics showed significant difference
between the dry and wet seasonal mean level across the cities (p<0.05). The PM10 seasonal
mean in all the cities (except Orlu in the wet season) exceeded the WHO annual average
guideline value of 20 µg.m-3. The seasonal mean range of PM10 in this study (14.38±3.01921.34±532.60 µg.m-3) was above the values reported for various European Countries
(European Commission Report, 1997) and 170-260 µg.m-3 reported in Calabar, Cross River
State, Nigeria (Abam and Unachukwu, 2009) but were within the 24-hour mean levels of
149-340 µg.m-3 reported for cities in Pakistan with the exceptions of Onitsha, Aba and
Umuahia (JICA/PAKEPA Report, 2002).
It can be concluded that within the period of the study, Onitsha urban relative to other cities
studied had the highest ambient air level of the coarse particulate. It is noteworthy that
greater percentage of the cities studied had particulate matter load that were above the
guideline limit and this calls for concern in view of the human health risk associated with
particulate matter pollution.
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Ngele, S.O, Onwu, F.K
International Journal of Environmental Sciences, Volume 5 No.4, 2015
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Comparison of particulate matter levels in major urban centres in Eastern Nigeria
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