Indoor air pollution refers to chemical, biological and physical contamination of the air quality within and around buildings and structures that may result in adverse health effects for household inhabitants. This study sought to establish the factors both socio-demographic and structural that predispose women and children to indoor air pollution among rural families living within Kaplamai location in Trans NzoiaCounty. Historically, biomass fuels (wood, charcoal, sawdust, animal dung, and agricultural wastes) have been used for cooking, lighting and heating in developing countries. Duflo et al. , noted that the use of such fuels as sources of energy has constantly been about 25 percent since 1975. It is estimated that by 2030 over 2.7 billion people across the world will still be dependent on biomass fuels . These energy sources, which are heavily relied upon by billions of people globally, have continued to raise health and environmental concerns and are now recognized as a significant source of potential health risks to exposed populations throughout the world . It is of no wonder that the Lancet Commission on Pollution and Health endorses cleaner fuels at all levels of intervention .
In the current study, information on the age of the household head, occupation, ability to read and level of education were assessed. In addition, the marital status, main source of family income and household composition by female aged above 14 years and children aged below five years were also assessed with the aim of establishing the extent to which these factors influence household vulnerability to IAP. Given that that majority of the household heads in the current study were aged between 25 and 34 years is regarded advantageous to these families, as members in this age group are likely to be much more aware of the sources of IAP and its potential health impacts on household members. Being middle aged, this group could also be considered as mature and more likely to be financially stable compared to the younger age sets or the elderly . Financial stability is regarded as a critical determinant of the choice of fuel type used by a household. It also dictates the type, size and design of the family house as well as the location, size and design of the kitchen. The type of biomass fuel used greatly influences the levels of Indoor Air Pollution (IAP). All these factors are however determined by household income.
In the current study, 44.6% of women respondents were not employed, while another 20.7% worked as unskilled labourers with most (40.2%) households generating an average monthly income of between Ksh. 2001 and 5000. Consistent with the findings of this study, Kimani  observed that a majority of women work in the informal sector, handling small-scale businesses with meager income to even sustain their families. Insufficient household income can only allow for the most basic commodities such as food for the family forcing households to settle for the cheapest fuel sources such as plant remains and firewood that are mostly obtained for free.
Studies show that when women are overly dependent on their spouses, they are unable to make important or critical decisions especially on matters relating to the family expenditures . Poverty and illiteracy remain the key barriers to adoption of cleaner fuels, with the slow pace of development in many developing countries a further indication that the use of biomass fuels will continue for many decades to come by many poor households. Akin to other studies, the use of biomass fuels among poor households in Kenya is likely to remain stable or even increase in the near future, as few rural families can afford alternative fuel that is higher on the energy ladder (such as liquefied petroleum gas and electricity, which are regarded as being cleaner but more expensive) . Accordingly, the choice of fuel type used by a household becomes cleaner and more convenient, efficient and costly as people move up the energy ladder; a feat that can only be achieved through economic empowerment of women.
Studies show that households at the lower income levels tend to be at the bottom of the energy ladder; using fuel that is cheap and locally available but not very clean or efficient. According to the World Health Organization, over three billion people worldwide are at these lower rungs and depend on biomass fuels-crop waste, dung, wood, leaves and coal to meet their energy needs . It is estimated that globally a majority of poor households rely on biomass fuels for everyday household energy needs, with most of those exposed being women, who are normally tasked with food preparation, and children under the age of five years who are most often with their mothers in the cooking area . Consistent with the WHO  findings, the current study established that a large percentage (96.8%) of households relied on wood as the main source of fuel for cooking and heating with crop residues, charcoal and other sources being mentioned, albeit by less than 4% of the respondents. The second most preferred fuel for cooking and heating for a majority of households after wood was crop residues. These findings were also consistent with those of , who reported that approximately 3 billion people in the world use solid fuels. Precisely, 2.4 billion people use biomass (wood, charcoal, animal dung, crop wastes), and the remainder utilize coal for the majority of their household energy needs because these are relatively cheaper and thus available to a majority of the people.
Various studies [40, 41] have shown that solid fuels are extensively used for cooking and home heating in developing countries, especially in rural areas. Further, studies also show that in sub-Saharan Africa, wood fuel is acknowledged as the main source of energy in most rural communities , with an estimated daily fuel wood consumption of 500,000 tons per day in Africa. Sanders,  reported that the three-stone open fire commonly used in many developing countries is only about 10–15% efficient leaving most of the energy content of the fuel wasted. Poverty contributes highly to indoor air pollution as poor households are not able to afford alternative efficient fuel such as electricity or LPG gas and thus remain vulnerable to poor health. As such, it becomes a vicious cycle for members of the affected household as they remain trapped both in poverty and in poor health [44, 45].
Besides use of biomass fuel, several other factors at both community and household levels determine the extent of indoor air pollution among households. These factors include the design of the house, size of the kitchen and its location, availability and size of eave spaces, ventilation size and design among others. In the current study, a large proportion of respondents lived in semi permanent houses, a few others in temporary houses and only a handful in permanent houses. In terms of kitchen size, over half the households had average sized kitchen, with a small proportion (8.8%) having large sized kitchens. Kitchen size is an important contributor to indoor air pollution since burning biomass fuel indoors produces large quantities of smoke, providing a perfect avenue for human exposure to smoke especially in confined space without adequate ventilation .
In the current study, most (84.5%) kitchens were housed in a separate building from the main house, while 13.5% of the kitchens were located in a separate room within the main house and 2.0% were located in the main living area. Consistent with the current study findings, a similar study by Oguntoke et al.  in Odede area of South Africa also established that 25% of the respondents located their kitchens indoors (separate room within the main house); while a larger majority had their kitchen in a separate room outside the main house; but in close proximity to the main house. In the current study, most (84.5%) respondents had enclosed kitchens as opposed to 15.5% who had semi-closed kitchens. The state of the kitchen influences the levels of indoor air pollution, with enclosed kitchens likely to confine higher levels of smoke indoors than non-enclosed kitchens.
In the current study, most (63.3%) houses did not have any eave spaces in their kitchens, though for those that had, they were small sized ranging between 0 and 6 inches in size. Most (43.8%) eaves were the cross ventilation type, with another 31.1% being door ventilation type. In addition, the IAP was negatively associated with ventilation and education, while semi-permanent houses and age were positively associated with it. The reasons for these could be that with increase in education individual knew the effects of IAP. This was similar with age, and this enabled them to institute proper housing policy. House types included that of grass-thatched and most of them had small round windows or without one at all. Semi-permanent houses were those with corrugated iron sheets and most of them had spacious eves.
In a study on efficiency of eave spaces, Bruce et al. , observed a reduction in particulate levels from 2042 g/m3 to 766 g/m3 with a slight increase in the size of eave space. Other researchers have however argued that eave spaces alone cannot protect women and children from the effects of indoor air pollution since proximity to the fire place, duration of stay in the kitchen and length of exposure differ and these play a vital role .
Given that most households in the current study used biomass fuel most of which was burnt indoors on open fires or poorly functioning stoves, often with no or limited ventilation, a large numbers of women and young children within Kaplamai Division are therefore exposed to high levels of air pollution, every day of the year. Limited ventilation implies that free flow of smoke from the kitchen is inhibited thus exacerbating the effect of indoor air pollution. The WHO  acknowledges that the greatest global burden of air pollution exposure occurs not outdoors in the cities of the developed world, but indoors in poor rural communities. Poor ventilation coupled with incomplete combustion by most of the stoves used results in substantial emissions which in the presence of inadequate ventilation and air circulation produce very high levels of indoor pollutants . Earlier studies including those of Smith et al. , Collings et al. , Martin  and Ellegard , showed that indoor concentrations of particles usually exceed set guidelines by a large margin. For instance 24-hour mean PM10 levels are typically in the range 300–3,000 mg/m3 and may reach 30,000 mg/m3 or more during periods of cooking. The United States Environmental Protection Agency’s standards for 24-hour average PM10 and PM2.5 concentrations are 150 mg/m3 and 65 mg/m3, respectively . The current study however had a discrepancy as it did not measure the actual PM10 or PM2.5 concentration, and it would therefore be difficult to compare them against the USEPA standards.
An individual’s true exposure may vary with the size of the kitchen and an individual’s proximity to the stove during periods when the stove is in use. Saksena et al.  reported concentrations of 20,000 µg/m3 near the cooking stove and much lower concentrations in the rest of the kitchen and in other rooms within the house, while Ezzati and Kammen  reported peak concentrations greater than 50,000 µg/m3 in the immediate vicinity of the cooking stove. These two studies suggest that women, children and even girls who normally seat close to cooking stoves for extended periods of time are likely to be exposed to higher levels of carbon monoxide compared to other household members. USEPA  estimated the mean (24-hour level) of carbon monoxide in homes using biomass fuels in developing countries to range between 2 and 50 ppm, with values ranging between 10 and 500 ppm likely to be achieved during the cooking process. This is far above the 8 hour average carbon monoxide standard of 9 ppm set by the USEPA .
Health outcomes of indoor air pollution
A number of poor health outcomes result from the use of biomass fuel that is normally burnt in poorly ventilated kitchens. Other factors such as duration of time that women and children spend exposed to smoke among and the habit of opening or closing windows and doors while cookingalso exacerbate the health risk. According to Begum et al. , indoor air pollution has significant influence on women and children. In the current study, over 90% of women and children experienced coughing of varying intensities over a 12 month period, with 45.9% of the women reported coughing in the same manner for several days, while 30.3% coughed in the same manner for over 1 month. Coughing was significantly associated with IAP. Inhaled particles and gases may expose women to Acute Respiratory Infection (ARI) such as pneumonia which is one of the causes of morbidity in Kenya . It is, therefore, likely that among adults, women are particularly at higher risk of developing ARI because of the prolonged time they spend in the kitchen preparing meals for families compared to men. Children are also at a higher risk than adults because their airways are relatively narrower and more easily obstructed and their oxygen demand relative to body weight is higher resulting in relatively larger inhaled volumes [22, 58].
Furthermore, there is sufficient evidence linking smoke from solid fuel use with acute infection of lower respiratory tract, chronic obstructive pulmonary disease and lung cancer . Shabir et al.  estimates that ARI’s are the single most important cause of mortality in children aged below 5 years, and they account for between 1.9 million and 2.2 million children deaths annually. In a study of 1532 female patients above 40 years and exposed to kitchen smoke over a span of 13 years, Mishra et al.,  observed high incidence of chronic bronchitis followed by bronchial asthma, pulmonary tuberculosis and bronchiectasis. There is also evidence, mainly from China, that exposure to coal smoke in the home markedly increases the risk of lung cancer, particularly in women , while there is also mounting evidence that cooking with biomass substantially increases the risk of developing active tuberculosis [63, 64]. Another set of health problems associated with indoor air pollution reported in this study include sputum production, headaches and wheezing, all of which are as a result of IAP and which were confirmed by very recent studies in the field .
In the current study, a number of eye problems were also reported and linked to the smoke from the cooking stove. Khalequzzaman et al.  and Díaz et al.  reported that tears coming out from the eye, eye discomfort and sore eyes, redness and itching of the eye, eye irritation, muscle weakness, fatigue, sleeping problems, stomach pains, dry mouth, and blindness linked to cataracts, trachoma, and conjunctivitis are further indications of indoor air pollution within houses. The constant and continued exposure to smoke from biomass fuel continues to cause both long and short-term health threats to members of the household – hence the need to cut down on expose to IAP.
Studies show that although reducing exposure to indoor air pollution from solid fuels can be achieved through several interventions targeting emission sources through improved energy technology, well designed houses and provision of ventilations. Encouraging behavior change and time-activity budget is also a strategy that can reduce IAP. Most current studies however suggest that the main focus should be on improved (high-efficiency and low emissions) stoves and fuels, which provide more affordable options for the poor majority in developing countries as opposed to complete shift to non-solid fuels . In that regard, the Clean Cooking Alliance has singled out Kenya as one of eight priority countries for clean cookstove endowment [69, 70].
However, while use of improved stoves has been proposed as being highly reliable in reducing indoor air pollution, the challenge remains on the rate of uptake of this simple technology and its usage. Experts warn that if not properly executed, these improved stoves or any other interventions for that matter might not achieve the much-desired results. A cross-sectional population-based study of 353 households in Kasarani, Kenya, has showed that higher environmental health literacy may help improve IAP-associated health outcomes among those using solid fuel stoves . Finally, awareness campaigns on IAP exposure effects and interventions for reduce the use of biomass fuels are warranted in sub-Saharan Africa .