Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954
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Understanding the Nature of Wet Air Deposition on Rooftops in Uyo Metropolis
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Ihom A.P.1, Uko D.K. 1, Markson I.E. 1, Eleghasim O.C. 1
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1 – Department of Mechanical Engineering, University of Uyo, Uyo, PMB, Uyo, Nigeria
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a – ihom@uniuyo.edu.ng
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DOI 10.2412/mmse. provided by Seo4U.link
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Keywords: wet air, nature, pollutants, particulates, deposition, rooftops, Uyo metropolis.
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ABSTRACT. The work titled Understanding the Nature of Wet Air Deposition on Rooftops in Uyo Metropolis was Carried out by determining the extent of air pollution in four different places in Uyo metropolis. Attair 5X was used to determine the gaseous pollutants in the wet air, while filtration technique using High Volume Sampler was used to determine the suspended particulates in the air, and the concentration was calculated in mg/l over a 24hrs period. The composition of the deposition on the rooftops was analysed using EDX-X-Ray Fluorescence (EDX-XRF) and the characterization of the deposit was done using Scanning Electron Microscope (SEM). The result of the work showed that gas pollutants existed in all the four stations but were not to the level of health concern since air quality standard specifications were not exceeded. However, impact on rooftop was noted since SO3 was in the composition of the deposit on the rooftops. The suspended particulate matter exceeded air quality standard value of 200 µg/m3 in all the four stations, and so was of both health and environmental concern since it influenced the deposition on the rooftops. The SPM composition elements were also found in the composition of the deposits on the rooftops. SEM characterized the darkblack deposit on the rooftop and the micrograph showed areas of high and low deposition on the roofs. The study concluded that a better understanding of the nature of wet air deposition on rooftops in Uyo metropolis has now been established.
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Introduction. The quantity of atmospheric deposition depends on the amount and types of air pollutants emitted in the vicinity and upwind of a site [15], and the length of time between precipitation events [11]. A recent study of the Puget Sound Basin evaluated heavy metals, polycyclic hydrocarbons (PAHs), and other compounds in wet and dry atmospheric depositions. This study found that concentrations of the chemicals of concern in the highly urbanized area sampled were an order of magnitude greater than outside the urban area [17]. To differentiate between materials leaching and air deposition, recent studies have attempted to control for the contribution of air deposition, thereby evaluating the concentrations that leach from the roofing materials themselves.
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Wet and dry deposition contributes to the contaminants from commercial, residential and industrial roofs. Plate I with dark-black deposit on the rooftop is a typical building in Uyo metropolis. Contaminants associated with wet air deposition on rooftops comprise a portion of roof runoff. For example, Sabin [10] found that more than 50% of the metals in storm water runoff in Los Angeles were associated with air deposition. In a Swiss study, the ratio of the concentrations of metals in runoff compared to wet and dry atmosphere deposition ranged from as high as 27: 1 for copper to less than 1:1 for zinc depending on the roofing type and the location [16].
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© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/
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Fig. 1. Building Roof Completely Covered with Dark-Black Coating/Deposit.
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The dispersion of air pollutants at a particular place are influenced by meteorological factors, such as wind speed, wind direction, and turbulence. Precipitation and humidity also influence the pollution potential. Air quality standards indicate the levels of pollutants that cannot be exceeded during a specified time period in a specified geographic area with due reference to the method of measurement, units of measurement, concentration, and time of exposure. The primary air-quality standards define the levels judged necessary to protect the public health with, an adequate safety margin. Air pollutants affect man and his environment. The materials that may be affected by air pollutants include metals, building materials, rubbers, elastomers, paper, textiles, leather, dyes, glass, enamels, and surface coatings. The types of possible damage to these materials by air pollutants include corrosion, abrasion, deposition, direct chemical attack and indirect chemical attack. Air pollutants, such as sulphurdioxide, HF, particulate, fluorides, smog, oxidants like ozone, ethylene (from automobiles), NOx, chlorine, herbicide and weedicide sprays exert toxic effects on vegetation. Arsenic, lead and fluorides are the main pollutants which cause damage to livestock. These air-borne contaminants accumulate in vegetation and forage and poison the animals when they eat the contaminated vegetation [1]-[3], [5]-[9].
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Particulates (solid or liquid) are one important constituent of the atmosphere. About 2000 million tonnes of particulate matter per year are released from natural agencies such as volcanic eruptions, wind and dust, storms, salt sprays etc. man-made activities, such as burning of wood, coal, oil and gaseous fuels, industrial processes, smelting and mining operations, fly-ash emissions from power plants, forest fires, burning of coal refuse and agricultural refuse etc. release about 450 million tonnes of particulates per year. The diameter of particulates may range from 2 x10-4 to 5 x 102 Âľm with varying life times depending upon the size and density of the particles and turbulence of air which control their settling rate. Fine particulates having size of < 3 Âľ (such as air-borne toxic metals like Be and air-borne asbestos) which can penetrate through nose and throat, reach the lungs and cause breathing problems and irritation of the lungs capillaries. Similarly pulmonary fibrosis in asbestos mine workers, black-lung disease in coal miners and emphysema in urban population are attributed to the particulate pollution. Further, air-borne particulate such as dust, mist, fumes, and soot can cause damage to various materials; particulates may accelerate corrosion of metals and cause damage to roofs, paints and sculptures. Solid particles or liquid droplets including fumes, smoke, dust and aerosols. Solid particles can adsorb various chemicals. Effect of particulate matter vary with the MMSE Journal. Open Access www.mmse.xyz
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nature of the particulates; carbon particles and other particles cause scarring of lungs via complex walling off and fibrogenic reactions leading to a disease condition known as ‘’pneumoconiosis’’. Cadmium inhalation of fumes and vapours causes kidney damage, bronchitis, gastric and intestinal disorders, cancer, disorders of heart, liver, and brain, renal dysfunction, anaemia, hypertension, bonemarrow disorder and cancer with chronic and acute poisoning. Lead absorption through gastrointestinal and respiratory tract and deposition in mucous membranes, cause liver and kidney damage, mental retardation in children, abnormalities in fertility and pregnancy. Zinc fumes have corrosive effect on skin and can cause irritation and damage mucous membrane [1]-[3], [5]-[6].
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This present work is particularly focused on understanding the nature of wet air deposition on rooftops in Uyo metropolis and the effects of the wet air deposition on the roofs and human beings. The wet air comes into contact with the roofs creating various effects like deposition, roof leaching, biological organisms’ growth, corrosion, surface erosion and discoloration. This effects are caused by SOx, NOx, COx and other acid gases, acid mist, sticky particulate matter. Other environmental factors influencing the rate of attack include moisture, freezing, and temperature [2]-[3].
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Materials and method
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Materials. The materials used for this research work included the following: the sampled air in raining season, dark-black deposit from the rooftops, chemicals used for the analysis and specimens cut from the rooftops.
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Equipment. The equipment used for the work included Attair 5x Multigas detector, EDX-X Ray Fluorescence, Scanning Electron Microscope, scissors, petri dish, filter paper, analytical weighing balance, electric oven, desicator with silica gel, thongs, sample collectors and ladder.
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The Study Area. The study area of this research work is Uyo metropolis. Uyo is the Capital of Akwa Ibom state. It is a major oil producing state in Nigeria, with a lot of gas flaring activities going on from the oil exploiting companies. The population of Uyo according to the 2006 Nigerian census which comprises Uyo and Itu is 436,606. The metropolitan area covers an estimated area of 168 km 2 (65sq.mi). Uyo is a fast-growing city and has witnessed some infrastructural growth in recent years. It is located on coordinates 502`N and 7056’E.
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The average annual rainfall in the study area is between 2000-4000mm with the period of fall usually between April and October. The rainfall reaches its peak in the months of June and September, while the dry period falls between November to March. The relative humidity of the area varies between 75% and 95% with mean annual temperatures of about 26 to 36oC. Fig.1 is the map of the study area. The samples for the work were taken in different areas of the metropolis covering, Use Offot on Nwanniba road (station 2), University of Uyo, main campus on Nwanniba road (station 1), IkotOkubo on Abak road (station 3), and Mbaibong on Oron road (station 4). The town is characterized by high usage of generators as a result of incessant power failure from the national grid and high vehicular traffic typical of a growing metropolis.
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Fig. 2. The Map of Uyo Metropolis the Study Area.
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Method. Air sampling in the four stations was made possible through the use of Attair 5X Multigas detector. The device is equipped with catalytic sensor that detect a variety of gases in the atmosphere and displays the reading. Fig. 3 shows the technologist sampling the air at station 1 (University of Uyo, Main campus). The sampling of the wet air took place 10th September, 2016 during the peak of raining season period in Uyo metropolis.
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The High Volume Sampler was used to determine the Suspended Particulate Matter in the air that remained for extended periods. Sampling was done for 24 hrs. Particulate matter collected on the filter paper was extracted and digested with acid mixture for chemical analysis of some selected elements like iron, lead, cadmium, copper, zinc, and sodium. The SPM was determined according to specifications by Ambient Air specification methods and American Society for Testing Materials (ASTM). The dark-black deposit on the rooftops was scraped for analysis using EDX-X Ray Fluorescence. Specimens were equally cut from the roofs for SEM analysis using Scanning Electron Microscope.
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Fig. 3. Show the Technologist Sampling the Air at Station 1using Attair 5X (University of Uyo, Main campus).
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Results and discussion
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Results. The results of this research work are as presented in Tables 1-2. Table 1 is the quality of the dry air, which was sampled in the dry season in four different locations of Uyo metropolis. Table 2 is the elemental composition of the suspended particulate matter which was measured in dry season in four different locations of Uyo metropolis. Table 3 is the air quality standard Table. Table 4 is the EDX-X-Ray Fluorescence analysis of the dark-black deposit on the rooftops of buildings in Uyo metropolis. Fig. 4 is the SEM micrograph of the dark-black deposit on the rooftops in Uyo metropolis.
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Table 1. Analysis of Air Pollutants in Four Different Stations in Uyo Metropolis. S/No Parameter
Station 1
Station 2
Station 3
Station 4
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SOX (ppm)
< 0.01
< 0.01
< 0.01
< 0.01
2
NOX (ppm)
< 0.01
< 0.01
< 0.01
< 0.01
3
CO (ppm)
< 0.01
0.02
0.01
0.05
4
CO2 (ppm)
272.0
276.0
274.0
278.0
5
H2S (ppm)
<0.01
<0.01
<0.01
<0.01
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SPM (Âľg/m3)
0.68
3.25
2.91
3.15
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Table 2. Chemical Analysis of Suspended Particulate Matter (SPM) from Four Stations in Uyo Metropolis. S/No Parameter
Station 1
Station 2
Station 3
Station 4
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Lead (Pb) mg/l
<0.0001
0.0002
0.0002
<0.0001
2
Iron (Fe) mg/l
0.0008
0.0008
0.0009
0.0008
3
Copper (Cu) mg/l
0.0027
0.0026
0.0028
0.0026
4
Zinc (Zn) mg/l
0.0029
0.0031
0.0036
0.0003
5
Cadmium (Cd) mg/l
<0.0001
0.0002
0.0004
0.0003
6
Sodium (Na) mg/l
0.0002
0.0003
0.0005
0.0002
Key: Station 1: University of Uyo, main campus on Nwanniba road. Station 2: Use Offot on Nwanniba road. Station 3:Ikot-Okubo on Abak road. Station 4: Mbaibong on Oron road.
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Table 3. Ambient Air Quality Standards. Pollutant
Time weighted average
Residential, Rural and mixed used area
Sulphur dioxide
Annual average
60µg/m3 (0.023 ppm)
(SO2)
24hrs
80µg/m3
Oxides of Nitrogen
Annual average
60µg/m3
(NOx)
24hrs
80µg/m3
Carbon Monoxide
Annual average
2.0mg/m3
(CO)
1 hr
4.0 mg/m3
Suspended Particulate
Annual average
140µg/m3
Matter (SPM)
24 hrs
200µg/m3 (0.077ppm)
Respirable Particulate
Annual average
60µg/m3
Matter (size less than 0µm), RPM
24 hrs
1000µg/m3 (0.38 ppm)
Lead (Pb)
Annual average
0.75µg/m3
24 hrs
1.00µg/m3 (0.00038 ppm)
Annual average
80µg/m3 (0.03ppm)
24 hrs
365µg/m3 (0.14 ppm)
H2S
Annual average
-
CO2
24 hr
600 ppm
Oxidants
1 hr
160µg/m3 (0.08 ppm)
Sox
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Source: Dara [3]
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Table 4. Chemical Composition of Dark-Black Material Scrapped from Roof-Tops (Analysed at NMDC Jos). S/No Sample
Al2O3
SiO2
P2O5
SO3
K2O
CaO
TiO2
V2O5
1
Blackish powder from roof-top
16.00
43.80
1.20
2.71
3.20
1.62
2.93
0.11
Cr2O3
MnO
Fe2O3
NiO
Co2O3
CuO
ZnO
Br
Rb2O
SrO
0.10
0.31
10.55
0.05
ND
0.09
0.22
0.07
0.03
0.05
ZrO2
Yb2O3
Re2O7
PbO
Carbonaceous and volatile matter
0.20
0.001
0.06
0.11
16.59
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Fig. 4. Scanning Electron Microscope (SEM) Micrograph of Dark-Black Deposit on Zinc-Coated Base Roofing Sheet. The light areas have low deposit of the material; the substrate is still shining and the dark areas have large deposit of the material; the substrate is covered.
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Discussion
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Table 1 is the Analysis of Air Pollutants in four different stations in Uyo metropolis. The Table shows that the values of the gaseous pollutants are actually lower than the standard specification for residential and mixed used area in all the four stations of the wet air sampling. This may not really pose any health challenge. According to several researcher the pollutants can affect the roofs of buildings and other materials. The wet air comes into contact with the roofs creating various effects like deposition, roof leaching, biological organismâ&#x20AC;&#x2122;s growth, corrosion, surface erosion and discoloration. These effects are caused by SOx, NOx, COx and other acid gases, acid mist, sticky particulate matter. Other environmental factors influencing the rate of attack include moisture, freezing, and temperature [1]-[3], [5]-[6].
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The SPM in all the four stations were higher than the standard specification for air quality in residential and mixed used area of 200 µg/m3. This can be attributed to gas flaring activities, automobiles exhaust fumes and emissions, particulates (generating sets and others) the health implications needs to be investigated, but according to Dara [3] Solid particles or liquid droplets including fumes, smoke, dust and aerosols. Solid particles can adsorb various chemicals. Effect of particulate matter vary with the nature of the particulates. Carbon particles and other particles cause scarring of lungs via complex walling off and fibrogenic reactions leading to a disease condition known as “pneumoconiosis”. Cadmium inhalation of fumes and vapours causes kidney damage, bronchitis, gastric and intestinal disorders, cancer, disorders of heart, liver, and brain, renal dysfunction, anaemia, hypertension, bone-marrow disorder and cancer with chronic and acute poisoning. Lead absorption through gastro-intestinal and respiratory tract and deposition in mucous membranes, cause liver and kidney damage, mental retardation in children, abnormalities in fertility and pregnancy. Zinc fumes have corrosive effect on skin and can cause irritation and damage mucous membrane [1]-[3], [5]-[9].
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The effect of the pollution in Table 1 can be noticed by the presence of SO3 in Table 4, which is the composition of the deposit on the rooftops of buildings in all the four stations. Table 2 is the chemical composition of the SPM from the four stations in Uyo metropolis. Some of the values of the elements in the SPM actually exceeds standard specifications a little and may have some health implications particularly the lead and the cadmium but not in all stations. Stations 2 and 3 for lead and stations 23 for cadmium. The health implications of these metals have been clearly stated by these authors [2][3], [8]. On the impact of the SPM on the rooftops of building in Uyo metropolis; some of the elements in Table 2 are found in the chemical analysis of the deposit on the rooftops presented in Table 4. This agrees with the effects of SPM on building rooftops as shown by several authors [4], [10], [15], [17]. These researchers have argued that, air-borne particulate such as dust, mist, fumes, and soot can cause damage to various materials; particulates may accelerate corrosion of metals and cause damage to roofs, paints and sculptures [12], [14], [16]. Solid particles or liquid droplets include fumes, smoke, dust and aerosols. Solid particles can adsorb various chemicals and also produce depositions on rooftops. Sticky particulate matter from the wet air settles on rooftops producing dark black deposit on the roofs [2], [3]. The characterization of the SPM deposit on rooftops in Uyo metropolis is shown in Plate III. The dark areas indicate thick deposit of the SPM and light shining areas indicate thin deposit of the SPM on the roof. This study has explicitly thrown light on the nature of wet air deposition on rooftops in Uyo metropolis. Table 1 has highlighted the gaseous pollutants in the wet air and Table 2 the particulate pollutants associated with the wet air and the impact of the wet air on rooftops is the dark-black deposition on the rooftops. Table 3 is the ambient air quality standard with which the analyses in Tables 1-2 were compared with.
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Summary. This study “Understanding the nature of wet air deposition on rooftops in Uyo metropolis” has been executed and the following conclusions drawn from the study
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1. Study has shown that the deposition from the wet air unto the rooftops is in two parts the deposit from gaseous pollutants and deposits from particulate matter.
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2. Gaseous pollutants and the particulate matter from the wet air affect the rooftops in different ways, which include, corrosion, deposition of sticky matter, erosion and leaching.
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3. Deposit on the rooftops contain compounds and elements from both the gaseous and particulate matter pollutants
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4. Scanning Electron Microscope micrograph showed that the distribution of the deposit on the rooftops is not uniform
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5. Suspended particulate matter may have some health implications since in all the four stations it was higher than standard specification and therefore there may be need for relevant government agencies to investigate the health implications.
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Sponsorship MMSE Journal. Open Access www.mmse.xyz
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This work is part of a major work that has been sponsored by TETFUND Institutional based Research Grant for University of Uyo-Uyo-Nigeria.
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