1. Introduction

Besides just looking at the clean and decorative facades of the buildings in a city, a closer look reveals a darker aspect of the urban scenario – the presence of squatter settlements or slums. Although the concept of slums or squatter settlements and its definition vary from country to country depending upon the socio-economic conditions of the society, slums are generally regarded as neglected parts of cities where housing and living conditions are appallingly poor. Slum household as a group of individuals living under the same roof that lack one or more of the following conditions; access to safe water; access to sanitation; secure tenure; durability of housing; and sufficient living area [1]. Slumshave also been viewed as areas where building are in any respect unfit for human habitation by reason of dilapidation, overcrowding, faulty arrangement and design of such buildings, narrowness or faulty arrangement of streets, lack of ventilation, light, sanitation facilities or any combination of these factors which are detrimental to safety, health and morals [2].Economically slums are areas inhabited by the poor in the urban system [3]. The poor are the unemployed, the unskilled, and illiterate and often the alcoholics, the vagabond and the delinquent [3].

The basic characteristics of slums are visually unpleasant buildings, lack of basic amenities (water supply, sanitary, electricity etc), acute overcrowding, services used illegally, high birth rate, high mortality rate, high infant mortality, unhealthy environment, low socio-economic conditions, environmental (land, air, water and noise) pollution, frustration among people, lack of civic sense and knowledge, grossly congested area and unsecured life. The living conditions in slums are usually unhygienic and contrary to all norms of planned urban growth [4].

The origin of slum settlements can be traced to the great industrial revolution in Britain [5]. The development of the wheel machine in London created opportunities for job and thus lured people who then settled themselves near to the factory. The limited residences built around the factory could not provide shelter for all the workers. Some people adjusted themselves in congested spaces although basic amenities were not available, thus a ‘slumdon’ was created. Today, slums are fast becoming major characteristics of an industrial growing city. There is no likelihood that the present trend of increasing urban population growth in Nigeria can be changed for some time to come. This is because for many Nigerians there is the belief that the only hope of improving their standard of living is to live in an urban environment.

Living conditions have a direct impact on public health. Slum dwellers usually experience a high rate of disease [6]. Diseases that have been reported in slums include cholera [7], HIV/AIDS, [8], measles [9], malaria, [10] dengue [11], typhoid [12], drug resistant tuberculosis [13], and other epidemics [14]. Slum dwellers have also been reported to be affected by indoor air pollution. Examples of short-term effects of indoor air pollutants include irritation to the eyes, nose and throat, and upper respiratory infections such as bronchitis, and pneumonia [15-18]. Long-term effects of poor indoor air quality include chronic respiratory disease, lung cancer, heart disease and even damage to the brain, nerves, liver or kidneys [19], [20]. Researchers have found that radon gas is responsible for over 1,800 deaths annually in United Kingdom [21].

Relative small-scale studies of indoor PM₁₀ exposure from woodfuel combustion have been conducted in Kenya [22], Guatemala [23], Mexico [24] and Gambia [25]. Recently, a larger sample of houses has been studied in rural India [26], [27]. In Nigeria there is little or no empirical database. This fact has being collaborated [28]. In Nigeria, interdisciplinary studies of slum areas are very limited. An early attempt in indoor air pollution studies in Nigeria, paid attention on the physical aspects of slums [29]. This paper provides empirical evidence on the levels of indoor air quality insome households in squatter settlements within Warri metropolis. The general aim of the current study was to create a database of the indoor airconcentrations for suspended particulate matter, carbon monoxide ozone, sulphur dioxide and nitrogen dioxide insquatter settlement in Warri, Nigeria. This study was designed to answer several questions about air quality exposure in poor households. First, is the assessment of indoor air quality monitoring. Second, how different is indoor pollution in kitchen area and living room area? Are these concentrations significantly affected by typical variations in cooking practices, cooking locations, structural characteristics and ventilation practice (opening doors and windows)? If such effects are large, then simple alterations in household arrangements may provide a cost-effective alternative to fuel switching or investment in clean stoves. Thirdly, what is the health implication for the households. Finally, what are the prospects for increased use of improved stoves and clean fuels in Nigeria?

2. Materials and Methods

2.1. Study Area

The study area is Warri, which is located in the Southern part of Delta State, Nigeria (Figure 1). It is a major urban city in the Niger Delta area, where a number of industries such as Delta Steel Company, Shell Petroleum and Development Company (SPDC), Chervron Nig. Ltd., Warri refinery and Petrochemical companies, Nigeria Gas Company are located.

Figure 1. Google map of Delta State showing Warri

The study area is inundated with a number of squatter settlements (slums) that are usually located by river banksand on pipeline right of way. Examples of such slums are Maroko slum, Igbuduslum, Marcaver slum, Waterside slum, Hausa quarter etc. Geographically, the area is enclosed between latitude 4°40′N and 4°30′N and longitude 6°12′E and 6°20′E.The area is within the humid tropical zone with defined dry (November – March) and rainy (April – October) seasons. The rainy season is brought about by the south-west trade wind blowing across the Atlantic Ocean. The dry, dusty and often cold north-east trade wind blowing across the Sahara desert dominates the dry season and brings a short spell of harmattan, [30]. The relative humidity of the area is very high, with values ranging from 74.7% in January to 88.7% in July.

2.2. Methodology

Three (3) slums (Maroko, Igbudu and Marcaver) were selected for the study. The choice of the selected slums is based on their large sizes and high population. At each of the selected slum, twenty (20) households were randomly selected, bringing the total households investigated in the study to sixty (60). In each of the randomly selected household air quality was monitored in the living room and kitchen areas. In each household, six (6) air quality monitoring parameters; suspended particulate matter (SPM_2.5), suspended particulate matter (SPM₁₀), nitrogen dioxide (NO₂), carbon monoxide (CO), sulphur dioxide (SO₂), and ozone, (O₃) were determined using a series of hand held air quality monitoring equipment. These monitors include: An industrial scientificcorporation ITX Multi gas monitor for NO₂,SO₂, and CO. O₃ concentration was measured with Ebara Jitsugyo EG-2001 high-accuracy O₃ monitor, which provided O₃ mixingratio referenced to 1 atm and 295 K conditions with a1-ppb resolution. The GT-331 VI.04 A Met One Instrument, Inc. Aerosol Mass Monitor Model GT-331 was used in determination of suspended particulate matter (SPM). The monitor uses light scatter to measure individual particles instead of clouds like other monitors. The particle information is then grouped into size ranges and converted to mass concentration over 4 minutes at a flow rate of 2.83L/min into measuring ranges of: SPM_2.5 and SPM₁₀ mass concentration. Measurements were done by holding the sensor to a height of about two meters in the direction of the prevailing wind and readings recorded at stability. The eight-hour monitoring period was carried out from early morning to evening during the monitoring period. The study was carried during thedry season of January, 2014.

2.3. Statistical Analysis

Obtained data were statistically analysed using the following statistical tools:

Correlation Coefficient (r): It is a measure of the strength and direction of the linear relationship between two variables that is defined as the (sample) covariance of the variables divided by the product of their (sample) standard deviations. Correlation values are bound between a value of -1 and +1. A correlation of +1 can be interpreted to suggest that both variables move perfectly positively with each other, and a -1 implies they are perfectly negatively correlated. Specifically, a correlation of 0.7 – 1.0 is describe as a strongly positive; 0.5 – 0.69 is described as moderately positive and 0.0 – 0.49 is described as weakly positive [31].

The coefficient of determination (R²) is a measure of how well the regression line represents the data. If the regression line passes exactly through every point on the scatter plot, it would be able to explain all of the variation. The further the line is away from the points, the less it is able to explain.

Mean and Standard Deviations: The sample mean is the average and is computed as the sum of all the observed outcomes from the sample divided by the total number of events. We use x as the symbol for the sample mean. In mathematical terms,

where n is the sample size and the x correspond to the observed valued.

The Standard Deviation is a measure of how spread out numbers are. The symbol for Standard Deviation is σ (the Greek letter sigma).

This is the formula for Standard Deviation:

3. Results and Discussion

3.1. Results

Results of air quality monitored in the randomly selected households in the three squatter settlements (slums) are as presented in Tables 1-3. Results of the air quality for the houses in which kitchens and living rooms were concurrently monitored are included.

Table 1. Air Quality in the Kitchen and Living Rooms in the Maroko Slum

Table 2. Air Quality in the Kitchen and Living Rooms in the Makaver Slum

Table 3. Air Quality in the Kitchen and Living Rooms in the Igbudu Slum

3.2. Discussion

Range of values of indoor air quality in the selected households in the squatter settlements and regulatory limits is presented in Table 4.

Table 4. Range of Values of Air Quality in the Kitchen and Living Rooms in the Selected Households

From the results as presented in Table 4, measured levels of NO₂, CO and SPM in all sampled households were above regulatory limits of 0.06ppm, 10ppm and 250µg/m³ respectively [33]. Although, the levels of CO are higher than the regulatory limits, much higher levels of 50 ppm of CO have been recorded in Kenyan Masai homes [34]. Concentrations of 300 µg/m³or greater for respirable airborne particulates (PM10) are common in Bangladeshi households [35]. This is in sharp contrast with houses in non-slum areas where almost 91% of the houses are of a permanent nature and indoor air quality are below regulatory limits [2]. A pollutant measurement surpassing national ambient air quality standards for a specific averaging time is referred to as exceedance. Adopting the Nepal, Ministry of Population and Environment categorization of five different types of air quality based on the levels of PM₁₀: 0-6µg/m³ as good, 60-120µg/m³ as moderate, 121-350µg/m³ as unhealthy, 351-425µg/m³ as very unhealthy and greater than 425µg/m³ as hazardous [36]. The indoor air quality in squatter settlement located in Warri metropolis can be described as unhealthy.

Figure 2. Correlation of SPM and CO values in the kitchen and living room in Marako Slum

Figure 3. Correlation of SPM and CO in the kitchen and living room in Igbudu Slum

Figure 4. Correlation of SPMand CO values in the kitchen and living room in Makaver Slum

Measured levels of O₃in all sampled households were below regulatory limits of 100 (µg/m³) [32]. Although, there are no known sources of ozone in the area, it is assumed that the obtained values of 44 – 67 (µg/m³) may have been created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. As have been similarly observed [37]. Levels of SO₂ in all sampled households were below equipment detection limits of 0.1ppm [33].

Obtained values of NO₂, CO and SPM in this study may have resulted from the form of domestic fuels use for cooking. Field observation shows that common sources of fuel are firewood, wood charcoal and sawdust. This observation is consistent with that reportedin literature [38], [39-41]. Biomass and coal smoke have been reported to emit many health-damaging pollutants, including particulate matter (PM), carbon monoxide (CO), sulphur oxides, nitrogen oxides, aldehydes, benzene, and polyaromatic compounds [42], [43].

The distribution of the measured air quality parameters (PM₁₀ and CO) in the living (parlour) room and in the kitchen area, was computed using the Pearson Momentcorrelation. A correlation (r) of 0.571 and 0.756 were obtained for SPM and CO respectively for households in Marako slum. In Igbudu slum a correlation (r) of 0.455 and 0.447 were obtained for SPM and CO respectively, while in Makaver slum a correlation (r) of 0.510 and 0.784 were obtained for SPM and CO respectively. Computed values shows strong positive correlation between the air quality monitored in the kitchen and living room areas for the measured parameters. When the values of the correlation were squared, coefficient of determination of 57.10% and 68.23% were obtained for the levels of SPM and CO respectively for households in Marako slum. At Igbudu slum, coefficient of determination of 20.70% and 19.98% were obtained for SPM and CO respectively while at Makaver slum coefficient of determination of 26.01% and 61.47% for SPM and CO respectively. Obtained values of measured parameters in both the living room (parlour) and kitchen area of the selected households were subjected to significance test using a two-tailed under a probability of 0.01, calculated valuesindicate signicant difference in some cases as presented in Tables 1-3.

The strong positive correlation between the concentrations of SPM and CO in the kitchen and living areas may be attributed to the characteristics of houses that are similar in structure in the study slums. Such structural arrangement of the houses affects ventilation. In most of the households that were randomly selected for the study, structural configurations show that kitchen are located within dwelling and attached. They do not have separate kitchens; cooking takes place inside the single dwelling room during the rainy season and outside during the dry season. Similar structural arrangements of poor households in Bangladesh have been reported [35]. This kind of structural arrangement promotes the amount of smoke diffusing from the kitchen into the living spaces.

Health risk assessment of the results was explored using the guidelines for reporting of daily air quality - air quality index (AQI) (see equation 1) [44]. The descriptor of air quality index is presented in Table 5 and illustrated in Figure 5.

Table 5. Air Quality Index descriptor

Figure 5. Air Quality Index Descriptor

(1)

Where: I_P = the index for pollutant P

CP = the rounded concentration of pollutant P

BP_Hi = the breakpoint that is greater than or equal to C_P

BP_Lo = the breakpoint that is less than or equal to C_P

I_Hi = the AQI value corresponding to BP_Hi

I_Lo = the AQI value corresponding to BP_Lo

The air quality index (AQI) calculated for the squatter settlements in Warri metropolis for Particulate matter (PM_2.5 and PM₁₀), Ozone (O₃), and Carbon monoxide (CO) is presented in Table 6.

Table 6. Air Quality Index of Studied Squatter Settlements

Using carbon monoxide, the air quality can be described as unhealthy for active children, women and adults, and people with respiratory disease such as asthma. Since today’s air quality is expected to be the same as long as the source and forms of fuel remain the same, sensitive groups should consider limiting staying indoor especially during cooking periods.

4. Policy Implications

At the policy level, the study has identified several sources of indoor air pollution exposure risk that can be mitigated bythe dwellers of squatter settlements in Nigeriaat feasible cost. I strongly believe that self-interest will motivate the slum dwellers to act, once they become convinced that the problem is serious, and that their actions will be cost-effective. The following should form the policy thrust:

Ø Restructuring of the buildings using porous construction material and providing proper ventilation in cooking areas. This will yield a better indoor health environment. The use of chimneys or vent-holes may improve indoor air in individual households.

Ø The use of wood, dung and other biomass fuels should be discouraged.

Ø Results imply that measures that could significantly reduce indoor air pollution exposure would be; use of cleaner fuels; purchase of more fuel-efficient stoves; peripheral location of cooking facilities; and ventilation of cooking smoke through astack tall enough to reduce the particulate concentration, by dispersing smoke over a relatively broad area.

5. Conclusions

Findings of the study show that measured levels of NO₂, CO and SPM in all sampled households were above regulatory limits which may have resulted from the form of domestic fuels (firewood, wood charcoal and sawdust) use for cooking. Air quality index (AQI) indicates that the indoor air can be described as unhealthy for active children, women and adults, and people with respiratory disease such as asthma. At the policy level, the study has identified several sources of indoor air pollution exposure risk that can be mitigated by the dwellers of squatter settlements. Alternatively, cooking smoke could be ventilated through a stack tall enough to disperse smoke over a broad area, thereby reducing particulate concentration in slum households. In addition, the solution is to switch to cleaner-burning stoves and modern fuels andto increase their affordability. This work would be an important supply to the indoor air pollution studies, and would be helpful in policy making.