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Sampling and Analytical Techniques for Indoor-Air Pollution Studies of Local Kitchen.
D. I. Malgwi Department of Physiscs, University of Maiduguri. P. M. B. 1069 Maiduguri, Borno State, Nigeria.
Abstract In this paper, model instrumentation for smoke sampling and wet analysis procedure in indoor air pollution studies for a local kitchen condition has been devised, applied and discussed. Indoor air sampling was carried out from burning of common fuelwood species using the simple traditional tripod woodstove in a model kitchen of size 8.6 x 6.75 x 2.8m at Maiduguri, Northeastern Nigeria. Experimental set-up for investigating indoor dispersion of pollutants and space-heating arising from woodstove fire are also presented. Methods for the determination of levels of exposure experienced by cooks in typical working condition were also considered. Key Words: Indoor-air Pollution, Sampling, Analysis, Techniques.
Introduction The atmosphere provides a sink for gaseous and particulate waste arising from natural and human activities. Air pollution studies have shown that levels of toxic elements and compounds in air are increasing with negative impact on environment and human health (Stern et al, 1973; Meetham et al, 1981; Ogugbuaja and Barsisa, 1993; Malgwi, 2000). Air pollution has serious impacts on weather and climate and on biogeochemical cycling of elements (Okunade, 1992; Botkin and Keller, 1998; Utah and Malgwi, 2001). Air pollution affect atmospheric visibility, vegetation, animals, soils, water quality, natural and artificial structures, and human health. Recent studies have shown that concentrations of indoor air pollutants may be greater than outdoor concentrations of the same pollutants found (Botkin and Keller, 1998; Parker, 1978; Malgwi, 2000; Utah and Malgwi 2001). A number of sampling techniques have been developed to facilitate collection of suspended particulate matter in the air for subsequent analysis. A typical ambient air-sampling system often consists of vacuum pumps, flowmeter, air flow regulators, connecting glass and rubber tubes, funnel and filter papers (Stern et al, 1973; Okunade, 1992). The general approach is to pump a known volume of air through a filter paper so as to collect the particles which might be present in the air. Although some samplers may be equipped with certain devices which have the ability to select particles of certain size ranges and to remove reactive gases, many of the samplers can be modified to realize the set objectives. The choice of sampling technique is determined mostly by the research objectives, analytical technique to be employed, cost and availability of sampling device, type of collection medium and occasionally on the pollutants to be analysed (Meetham et al, 1981; Maenhaut, 1989; Okunade, 1992; Ogugbuaja and Barsisa, 1993, Malgwi, 2000). After sampling of particulate matter in the air, analysis of the gaseous pollutants is achieved by three standard methods which are categorized into Physical Methods, Wet Analytical Methods and Thermal Analytical Procedure. Commonly employed physical methods include Nuclear and other related techniques such as Atomic Absorption Spectrometry (AAS), X-Ray Fluorescence (XRF), Proton Induced X-Ray Emission (PIXE), Instrumental Neutron Activation Analysis (INAA), Flame Ionization Analyzer (FIA), Flame Photometry, Infrared Absorption and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Wet analysis is the standard procedure for classical analytical chemistry. The concentrations (mg/m3) of the pollutant at standard temperature and pressure are determined either titrametrically, conductometrically, or tubidimetrically. In thermal analysis, most instruments and procedures are based on thermal properties for gas analysis (either on thermal conductivity or by heat of combustion from gases) (Stern et al, 1973; Okunade, 1992; Utah and Malgwi, 2001). If the objectives of the analysis is to determine the weight of particulate matter in the air, filtration method is the best means and chemical analysis of the collected sample is possible. If, on the other hand, it is desired to ascertain particle size or other physical characteristics, then the inertial sampler, electrostatic or thermal collector, greased slides, and photometric methods are used. In any case, special (or alternative) experimental sampling and analytical methods may be devised depending on specific problems (Stern et al, 1973; Okunade, 1992; Ogugbuaja and Barsisa, 1993). This paper, presents a simple set-up for smoke sampling and analysis in indoor air pollution studies. Information on the background concentration levels of indoor air quality (IAQ); the concentration and dispersion of total suspended particles (TSP) derived from fuelwood combustion; and the identification of pollutants such as SO2, COx, NOx. along with their concentrations had been the subject of other papers in the series of our investigations on indoor air pollution from fuelwood combustion in a local kitchen (Utah and Malgwi, 2001). Data collection and analysis Materials used for this study include fabricated metallic stove (made of iron scraps), aluminium pot (of known thermal capacity), vacuum pump. The model kitchen had a dimension of 8.6 x 6.75m and a height of 2.8m with adequate ventilation source (1-window) typical of normal village kitchen. Air pollution sampling and analysis The theoretical framework for sampling of particulate matter and the analysis of indoor-air pollutants are based on the standard methods reported by Dobbins (1979); Stern et al (1973); Meetham et al, (1981); Ibeanu, (1992); Okunade, (1992); Oguguaja and Barsisa (1993); and, Malgwi, (2000). Air samples collected mostly by filtration were used in determining the concentration of the dissolved pollutants in the bubbler by titration and, the constituent of the gaseous pollutants were computed as: Concentration = MR x MW x OV x CF (1) per weight of fuelwood burnt (WFB) (in mg). Here; MR = mole ratio (or the number of moles from NaOH reaction with H2SO4) formed; MW = molecular weight of probed pollutants ; OV = obtained value from titration or, the volume of base (0.004M NaOH/Vol. of air (m3). Volume of air (m3) here represents rate of collection of air (1.5m3/min) multiplied by sampling time (50min); CF = conversion factor. The total suspended particulate (TSP) matter emitted in the kitchen is computed as weight in (mg or mg) per volume of air (m3) (or in parts per million, ppm). The concentrations of air pollutants for example, are calculated from the expressions given by equation 1 above, and thus, the computation of obtained value (OV), and conversion factor (CF) are as follows: OV = (titre value)/volume of air (m3) thus OV = titre value (for each fuelwood sample used) .(2) (rate of collection of air) x (sampling time) In order to obtain a generalized expression for the conversion of concentrations of air pollutants from part per million by volume ppm (vol) to micrograms per cubic metre of air (mg/m3) which is the standard unit for concentration of air pollutants, a multiplication factor (MF) is required. This is obtained by assuming that the ideal gas law is accurate under ambient conditions as reported by Stern et al 1973. Here, CF was computed at fixed temperature and pressure of 250C and 760mmHg respectively as follows: 1ppm (vol) pollutant = 1 litre pollutant .. . (3) 106 litre air = (1litre) / 22.4 x MW x 106 mg/g ... (4) 106 litre x 298K/273K x 10-3 m3 = 40.9 x MW mg/m3 where MW is the molecular weight in gramme. The conversion factor (CF) obtained for common pollutants using the above correction factors at fixed temperature and pressure are given in Table 1. Indoor-air sampling Smoke sampling was conducted for the subsequent determination of emission and pollutants from fuelwood burning for a specific cooking task (WBT) in a specified time. Three separate sampling experiments were conducted as described below. These modified experimental set-up in the model kitchen are shown in Fig. 1. Background indoor-air qualityPre-weighed filter (Whatman No.1) paper firmly inserted in a funnel was connected directly to the vacuum pump by a glass tubing. The air in the room was drawn continuously for 50min before the ignition of the wood and, the suspended particulate matter in the kitchen space was captured on the exposed filter paper. The filter paper was reweighed and, the mean difference in weight noted as the normal background concentration level of the total suspended indoor-air particles. The ambient air quality in the model kitchen was determined in this manner and is considered as the reference level for the indoor air quality index. Total emissions and pollutants from fuelwood A filter paper was firmly inserted in a funnel, in an enclosed gas chamber-like protector to permit smoke accumulation and, at the same time to provide good air circulation to allow the fire support full combustion of the wood (Fig. 1). The apparatus was arranged in such a way that solid particulate matter emitted from the fuelwood sample burnt was deposited on the filter paper. Smoky air was drawn by the vacuum pump and, pollutants were trapped inside flasks A and B which contained solutions of H2O2 and NaOH, respectively. Flask A contained 100cm3 of H2O2 solution, flask B 250cm3 base solution of NaOH, while flask C contained drying agent CaO powder which served as the vacuum pump protector in the event of any likely moisture penetration which might arise from flask A and B. Smoke from the fuelwood combustion chamber was sucked continuously for 50 min, and in each case, the exposed filter papers were reweighed after burning was completed. The quantity of fuelwood burnt was also determined in a similar manner. An average of 3-burning tests were conducted for each fuelwood species and, the mixtures in the bubblers (flask A and B) were collected for the subsequent determination of constituent pollutants (SO2 and CO2) levels. Emissions in a normal combustion The set up was similar to experiment II described above but without the carton protection for the fire (i.e the burning was free in the model kitchen). Samples collected from both the filters and bubblers were kept for analysis of the constituent pollutants (SO2 and CO2), and TSP matter. An additional bubbler, flask D, containing distilled water (H2O) was also placed in- between flask B and C, so that the total acid formed can be determined in the wet analysis. Wet analysis of indoor-air pollutants The set-up for the collection of both SO2 and CO2 is the same as that in Fig. 1, except that for the collection of SO2, flask A contains 100cm3 of 0.03% (v/v) hydrogen peroxide (H2O2) whose pH value was adjusted to 4.5 using NaOH Solution. Flask B contained NaOH (0.05M), which was used to trap CO2 while flask C contained distilled water, which trapped CO, NO2 , carbonic, sulphuric, and nitrous acids. Determination of SO2 from samples collected Hydrogen peroxide (H2O2) absorption and volumetric analysis method, as reported by Meetham et al, 1981; Ogugbuaja and Barsisa, 1993; and Malgwi, 2000, were adopted. The pH of 50cm3, 0.03% (v/v) H2O2 was adjusted to 4.5 by adding requisite volumes of 0.1 NaOH solution and placed in flask A. This was used to absorb any SO2 that was sucked according to the following reaction: SO2 + H2O2 H2SO4 (5 The resulting H2SO4 was titrated with 0.004M NaOH solutions to pH 4.5. H2SO4 + 2NaOH Na2SO4 + 2H2O . . (6) The initial and final pH values set at 4.5 helped to eliminate possible interferences from carbonic acids formed from the reaction of CO2 and the moisture from the air. The second method used was that of a blank titration carried out between the sample and 0.004M NaOH to obtain a titre value. The blank value was then subtracted from the sample volume to obtain the actual volume of SO2 converted to H2SO4. Determination of CO2 A blank titration between NaOH and 0.1M HCl was carried out using phenolphthalein indicator. NaOH + HCl NaCl + H2O ....(7) 100cm3 of NaOH (0.05M) was used to absorb the CO2 in flask according to the reaction 2NaOH+ CO2 Na2CO3 + H2O . ....(8) The Na2CO3 formed in equation 8 by passing CO2 was then titrated against HCl (0.1M) using methyl orange as indicator to obtain a titre value. Na2CO3 + 2HCl NaCl + CO2 + H2O ... (9). Dispersion of indoor-air pollutants and space heating from woodstove Wind direction determines who or what part of the landscape is to be affected when a specific quantity of wood species is burnt during cooking in an enclosed environment. The behaviour of a plume of smoke coming out of a woodstove is dependent on the strength of the wind and stability of the atmosphere in the kitchen (Dobbins, 1979; Malgwi, 2000; Utah and Malgwi, 2001). Horizontal and vertical movements are sufficient to disperse the pollutants which are released into the air. The concept of dispersion can therefore be visualized by comparing transportation of heat and smoke (pollutants) released from a woodstove. Although there are a number of modern equipment which can sense the concentration of pollutants and the intensity of heat released from fire at variable distances away from the woodstove, an alternative method that is cheap and affordable was devised due to lack of standard facility on ground. This method (Fig. 2) is typical of the standard method used for air-quality determination and is considered appropriate for such research investigations (Stern et al, 1973; Okunade, 1993; Malgwi, 2000). Filter papers and thermometers were displayed at various locations (along horizontal and vertical distances 25cm, 50cm, 75cm, 100cm, 125cm, and 150cm) away from the stove (or fire) in this part of the experiment. A maximum of 50 minutes was taken to burn each fuelwood species, after which the fire was put-off (with water) and the left over (unburnt wood) was dried (under sunshine) and reweighed. The difference between the initial and final weights of the filter papers in both horizontal and vertical direction were recorded for statistical computation of the dispersion pattern of the total suspended particulate (TSP) matter. Similarly, the difference between the initial and final room temperatures, as observed on the exposed thermometers at various locations within the model kitchen gave the change in the indoor temperature. This indoor temperature change can be directly correlated to the space heating characteristics of fuelwood species burnt as reported in our earlier research findings in the series of our publications (Malgwi, 2000). Levels of exposure experienced by cooks A vacuum pump was introduced for sucking air from the woodstove through the filter paper firmly inserted in the funnel depicting typical breathing mechanism by humans during such exposure in a cooking task (Fig. 3). The concentration of the total suspended (TSP) matter in the kitchen space was monitored at 10minutes interval by replacing the exposed filters without varying their distance at both horizontal distances of 50cm from the stove (source) and a vertical distance of 70cm (above the floor level). The monitoring of the exposure to pollutants at a fixed position represents the way and manner in which cooks are positioned near the stove while cooking in the kitchen. Conclusion In this paper, model instrumentation and experimental set-up for indoor-air pollution sampling and analysis are presented. Experimental set-up for investigating dispersion of pollutants and space heating arising from woodstoves fire in the kitchen was also presented. Methods for the determination of levels of indoor air pollutant exposure experienced by cooks in a typical working condition were also examined. Application of these model sampling and analytical procedures by research scientists in developing countries where modern facilities and analytical labs are inadequate or unavailable would compensate the dearth of required data for the validation of acceptable standards of indoor air quality (IAQ) especially in local kitchens where woodstoves are used. Concentrations of pollutants arising from the use of fuelwood in local kitchens can thus be annexed to global environmental air quality index (Dounis et al, 1996; Botkin and Keller, 1998; Utah and Malgwi, 2001)
Acknowledgment The author is grateful to his Ph.D. Supervisors at University of Jos (Professor E.U. Utah, K.I. Ekpenyong and S.F. Akande). I wish to extend my sincere thanks to Late Prof. M.B. Ahmed (the former H.O.D. Chemistry, and D.V.C. (Admin). University of Maiduguri) for releasing the vacuum pump used in this study and for permitting his research laboratory staff Merss. J.N. Onah and F. Akawu to assist with some miscellaneous chores. I am also grateful to Dr. V.O. Ogugbuaja (the H.O.D. Chemistry, University of Maiduguri) who critically reviewed some of the experiments and made reasonable and positive suggestions on alternative to some measurement techniques. I remain grateful to, the Dean Faculty of Science, Professor M.Y Balla, and the Department of Physics at the University of Maiduguri for providing one of its rooms as a model kitchen. Finally, to my students (past and present) for continually providing a challenge, which made the effort, seem worthwhile.
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