Firewood is an important source of household energy for the rural population of many developing countries. Approximately 2.6 billion people from developing countries fulfil a majority of their basic energy demand for cooking and space heating from fuelwood, and the practice is considered to be inefficient, unhealthy, and unsustainable [1
]. This trend is expected to continue in the future, especially in rural areas of developing countries [1
]. Nepal is one of the least developed countries that has one of the lowest per-capita energy consumption globally [2
]. The energy use and energy access levels in Nepal are significantly below the level of basic human needs, and firewood is expected to remain the dominant cooking fuel for the foreseeable future [3
]. As of 2010, over 30% households lacked in access to electricity, and 78% households relied on traditional biomass for cooking and space heating [4
]. According to the household survey 2015/16 of Nepal, firewood is a major source of cooking fuel for more than half of the households in the country and is used by 76.5% rural households and 38.0% urban households to meet their everyday cooking energy demands [5
]. Low financial income has compelled the rural population to use inefficient sources of solid biomass energy which can trigger hazardous events when it is mishandled [6
The World Health Organization (WHO) estimates that about 2.8 billion people in developing countries depend on solid fuels and traditional cook stoves for cooking and heating [7
]. Burning of solid fuel in inefficient traditional stoves is responsible for the emission of various indoor air pollutants, which have direct and indirect impacts on the health of the inhabitants. Small and improperly ventilated buildings reduce the dilution of indoor pollutants and increase the concentration of harmful gases, which creates unfavorable indoor environments.
In developing countries like Nepal, particularly in rural areas, direct firewood consumption in inefficient traditional cook stoves without chimneys in improperly ventilated buildings is considered the major cause of indoor air pollution. Exposure to indoor air pollution is one of the important risk factor of infant and child mortality. Exposure to pollutants resulting from the burning of solid fuels has been responsible for the death of at least 4.3 million people per annum worldwide [7
]. Improvements in the indoor air quality of residential buildings is important for minimizing the health burden on rural population. CO2
emissions and the concentrations resulting from firewood consumption inside buildings are the simplest indicators of indoor air quality of residential buildings in rural areas and this information can be used to monitor the indoor air quality of residential buildings.
1.1. Literature Review
Previous studies have showed that firewood consumption varies due to socio-economic circumstances, cultural backgrounds, and availability and accessibility of fuels [8
]. Fox [8
] conducted a study on firewood consumption in a Nepali village highlighting on farm size, cast and family size. That study found a mean firewood consumption of 0.95 m3
/(person·year). Bhatta and Sachan [10
] found that higher firewood consumption was mainly caused by a lack of conventional energy sources. They also concluded that firewood consumption differs according to family size: smaller families have more per capita firewood consumption than medium and large families. Bhatta and Sachan [10
] also found that firewood consumption increased with altitude.
Some studies have highlighted related health concerns, focusing on the use of traditional cooking fuels and indoor environmental conditions of houses in Nepal. Pandey et al. [14
] conducted research on domestic smoke pollution and acute respiratory infections in Nepal and found that episodes of moderate and severe acute respiratory infections increased with an increase in the level of exposure to domestic smoke pollution. Fuller et al. [15
] used measured firewood and temperature data to validate a simple and cost-effective model of rural houses. Some other studies have highlighted the firewood use patterns associated with socio-economic factors and CO2
]. However, there has been a lack of focus on hourly variation of firewood consumption patterns and associated CO2
emissions and concentrations in rural households of Nepal. These patterns offer important information for assessing indoor environmental conditions, and this information can be used to simulate the thermal environmental conditions and indoor air quality of such houses.
The above literature review indicates that there is a need to focus on hourly firewood consumption patterns and associated CO2 emission patterns of rural households to understand and minimise the associated health impacts. Thus, the present study aims to assess the effects of firewood consumption patterns on CO2 emissions and concentrations of residential buildings in rural areas of Nepal. The findings of this study can be used to understand the energy use patterns of rural households in Nepal. Furthermore, this information is important for developing effective energy policies for rural households.
The main objective of this study was to identify the hourly firewood consumption patterns and associated CO2 emission patterns from firewood consumption in rural houses. Furthermore, this study also intended to identify the effect of different factors, such as family size and number of animals reared, on firewood consumption patterns. The goal of this study was to provide information on hourly variations in firewood consumption and associated CO2 emissions to concerned stockholders such as building and cook stove designers to enable cleaner indoor environments for the betterment of the living condition of the rural population.
A large number of households in Nepal still rely on firewood for cooking fuels. There have been several studies on firewood consumption patterns in Nepal, and these studies reported that the annual per capita firewood use varies widely among different parts of the country [10
]. Table 2
shows the results of similar studies conducted in temperate regions of Nepal and India. The firewood consumption in the present study was 663 kg/(capita·year), which falls in the middle of values from previous studies. Several factors could have affected the rate of firewood consumption as there was significant variation in firewood consumption patterns within similar climatic zones [23
]. Another cause might be the difference in the research method applied. For example, some researchers measured firewood use only for a few days, but some researchers measured firewood consumption for longer periods, which can influence the firewood consumption rate in similar climatic regions.
The per-capita firewood consumption rate in this study was 1.8 kg/(capita·day), which is similar to the results of Fox [8
] and Pokharel et al. [17
], and higher than that of Rijal [9
]. The difference might be associated with differences in the socio-economic conditions of the people, availability of fuels in the locality, and family size. Other methodological differences may also have influenced these results. In this study, firewood data were collected on hourly basis for one day in each house during winter, but in the study conducted by Rijal [9
], firewood data were collected on daily basis for the whole year. Therefore, seasonal factors must have affected the results. As this study was conducted in winter, we found a marginally higher value of firewood consumption rate than the previous study [9
]. The present study shows that firewood consumption differs according to family size; i.e., per-capita firewood consumption is negatively correlated with family size and household firewood consumption is positively correlated with family size. Bhatta and Sachan [10
] also found similar results and reported that smaller families have more per capita firewood consumption than those of medium and large families. Our present study is consistent with previous studies indicating that smaller households have higher per capita firewood consumption than bigger households, and bigger households are typically efficient firewood users [9
The household firewood consumption in this study was 12 kg/family·day, which is higher than the results obtained in other studies [8
]. The cause of higher household firewood consumption in this study might be associated with family size, and the number of animals reared. We found that household firewood consumption is positively correlated with household size. This result aligns with many other studies that have also found that household firewood consumption was positively correlated with family size [8
]. Thus, we confirmed that household size was indeed an important factor of firewood consumption.
Nepal is an agriculturally dominant economy where 74% of the households rely on the subsistence-based agricultural [26
]. People living in rural areas rear many animals for energy, meat, and other economic purposes that may affect the household firewood consumption patterns. The results of this study showed a positive relationship between firewood consumption and the number of livestock reared. This is similar to many other studies that have found that households with more livestock units consume more firewood [28
]. This result is however opposite to the result obtained by Bewket [13
] in Ethiopia, where household firewood consumption was negatively correlated with the number of livestock units. The reason for lower firewood consumption by households with more livestock units was the use of animal dung as a substitute for firewood in Ethiopia [13
]. In the present study, people used animal dung only as organic fertilizer, and hence firewood consumption did not decrease with an increase in the number of livestock units. On the contrary, the amount of firewood consumption increased with the increase in the number of livestock units due to the requirement of additional firewood for preparing animal feed.
Indoor air pollution produced by the domestic combustion of solid fuels is a significant cause of morbidity and mortality across the world especially in developing countries [31
]. The present study has found that all investigated households used more firewood in the morning and evening hours. It indicates that high CO2
emissions and high indoor CO2
concentrations in the morning and evening hours may pose a serious health risk to the rural people. The health problem due to indoor air pollution in rural households becomes more severe during winter when cooking occurs in non-ventilated conditions, and people enjoy staying near the cooking place for a longer time to keep themselves warm [32
]. We can speculate that the installation and use of mechanical ventilation system in the rural households would result in some health gain, particularly in the morning and evening hours. Rijal et al. [33
] showed that installation of an improved cook stove can minimize indoor air pollution in rural areas of Nepal. Therefore, improved cooking technology and introduction of mechanical ventilation in the rural houses with necessary preventive measures would be the ideal way of dealing with indoor air pollution. To create favorable indoor environment in the rural houses, knowledge on hourly firewood consumption helps assess the influence of firewood consumption on indoor air pollution.
Average exposure on firewood consumption was found to be 8.7 and 9.9 h/day for small and big households, respectively, which is higher than the exposure time of 3–7 h/day reported by Ranavat et al. [36
]. Longer cooking time has a significant negative effect on the health condition of people who are exposed directly to firewood burning [7
]. Pandey [39
] found that significantly higher proportion of women as compared to men were exposed to household smoke pollution in Nepal which creates serious health problems especially for women and children.
emission was found 14.26 kg CO2
e/(household·day) which is more than the value of 6.4 kg CO2
e/(household·day) obtained in Bangladesh [16
]. This difference might be due to the difference in the type and rate of fuel used and the efficiency of cooking devices used between the two countries. The use of clean cooking fuel and efficient technologies can play an important role in the reduction of household CO2
emissions. Therefore, an intensive awareness program is required to improve the indoor air quality and health condition of the rural population.