While people tend to believe that air pollution is an outdoor urban problem, the indoor environment in rural areas experience the highest pollution levels. Many rural residents in developing countries rely on coal and unprocessed biomass fuels (wood, cattle dung and crop residues) as the primary energy source for cooking and heating.
When these solid fuels are burned in traditional stoves, high concentrations of multiple pollutants are generated. Air pollution emanating from fuels used for cooking and heating (including kerosene) has been termed “household air pollution (HAP)” and this presents a major public health hazard for the rural population in developing countries. Women and children generally spend more time indoors and are exposed to HAP daily. Interventions are needed in terms of dissemination of improved stoves and clean fuels, improvement of kitchen ventilation and behavioural change to reduce exposure to HAP.
Globally, almost three billion people, mostly in developing countries depend on solid fuels for cooking (~2.6 billion on traditional biomass and 0.4 billion on coal) . These solid fuels are mostly burned in inefficient traditional cookstoves, without proper smoke venting systems, and often in poorly ventilated kitchens. The incomplete combustion of solid fuels promoted by inefficient household stoves result in much of the fuel energy being emitted as particles of varying sizes and range of gaseous pollutants. Cattle dung and agricultural residues emit significantly higher concentrations of respirable particles compared to firewood and other solid fuels . Although the number of households relying on solid fuels is decreasing, for example globally some 21 percent between 1980 and 2010, the number of people exposed to HAP has remained same due to growth in population .
In Bhutan, the residential sector is the highest consumer of energy with 48.7 percent, and 91 percent of this constitutes biomass, placing the country in the top list in terms of per-capita firewood usage . Electrified houses in Bhutan use only 25 percent less firewood than un-electrified houses .
A comprehensive documentation of studies providing an overview of methods and results of HAP measurements in developing countries is available in the World Health Organisation (WHO) HAP database . These studies have reported particulate matter and gaseous pollutant concentrations exceeding the WHO guidelines by several orders of magnitude. For example, in houses using biomass fuels the mean 24-hour indoor PM10 (particles < 10 μm) concentrations were found to range from 200 – 5,000 µg/m3. The recommended WHO guideline is 50 µg/m3. My own study in Bhutan has found ultra-fine particles (UFP, < 0.1 μm) concentrations (during cooking time) comparable to typical concentrations inside road tunnels . Thus, many people in developing countries face severe energy poverty and therefore live in highly polluted homes.
In terms of health impacts, 99 percent of the almost two million deaths that occur annually in developing countries from pneumonia, chronic lung disease and lung cancer have been attributed to exposure to HAP . For the year 2012, the WHO has estimated 4.3 million premature deaths from exposure to HAP, mostly in low and middle-income countries . This makes HAP from solid fuels combustion one of the top three risk factors for global burden of disease, next to the high blood pressure and tobacco smoking . Women and children are the most affected demographic groups since they spend maximum time at home and indoors. In 2014, the WHO has published a new guideline on “indoor air quality, household fuel combustion” to help countries reduce emissions and public health burden from exposure to HAP .
The dissemination of improved biomass cookstove has the potential to substantially reduce HAP levels. For example, in Nepal more than 60 percent reduction in concentrations of PM2.5 (particles < 2.5 μm) and carbon monoxide (CO) were reported once houses have been disseminated with improved cookstoves . In Tibet up to 90 percent lower PM2.5 and CO was observed in houses using improved stoves compared to houses using traditional open-fire stoves . Likewise, many studies have reported significant reduction in HAP levels and exposure once improved cookstoves have been disseminated in rural homes. However, pollution levels were still found to be higher than the WHO guidelines, which means improved cookstoves do not lower the pollutant concentrations to a safe level.
Although there are health benefits from use of improved cookstoves, a desired health benefit can only be realised by switching to clean fuels such as LPG and electricity. Like in other developing countries, for a rural community in Bhutan, shifting to clean fuels (LPG or electricity) as primary energy source will remain a challenge. The prevalence of customary intensive cooking practices, such as liquor distillation and cattle feed preparation, limit their use as a primary fuel. More importantly, accessibility and affordability associated with LPG in rural areas will compel people to continue using firewood and other solid fuels. Therefore, improved cookstoves are important considerations for reducing exposure to HAP, if proper and sustained use is adopted by users. Alternatively, other strategies such as improving kitchen ventilation and changing cooking behaviour can contribute to lower health risks. Educating parents to minimise the time spent by children inside kitchens during cooking will lower exposure since pollutant concentrations are high closer to the source and rapidly decay with distance from the source. Interventions should not only target on reduction of firewood usage and greenhouse gas emissions but also to optimise the health benefits from the same.
 Legros, et al., 2011. Global changes in household access to electricity and modern fuels: regional variations and patterns. Current Opinion in Environmental Sustainability 3:241-247.
 Balakrishnan, et al., 2004. Exposure assessment for respirable particulates associated with household fuel use in rural districts of Andhra Pradesh, India. Journal of Exposure Analysis and Environmental Epidemiology 14:S14-S25.
 Bonjour, et al. 2013. Solid fuel use for household cooking: country and regional estimates for 1980-2010. Environment Health Perspectives 121:784-790.
 DoE. 2009. Overview of Energy Policy of Bhutan. Thimphu: Ministry of Economic Affairs, Royal Government of Bhutan.
 DoE. 2005. Bhutan Energy Data Directory 2005. Thimphu: Ministry of Economic Affairs, Royal Government of Bhutan.
 WHO. Global Database of Household Air Pollution Measurements. Available: http://www.who.int/indoorair/health_impacts/databases_iap/en
 Wangchuk, et al., 2015. Children’s personal exposure to air pollution in rural villages in Bhutan. Environmental Research 140: 691-698.
 WHO. 2014. World Health Organization Burden of Disease from Household Air Pollution for 2012 Geneva, Switzerland: World Health Organization.
 Lim, et al., 2013. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010. The Lancet. 380, 2224-2260.
 WHO. 2014. WHO Indoor Air Quality Guidelines: Household Fuel Combustion. Geneva, Switzerland: World Health Organisation.
 Singh et al., 2012. Assessment of effectiveness of improved cook stoves in reducing indoor air pollution and improving health in Nepal. Energy for Sustainable Development 16(4): 406-414.
 Li et al., 2012. Personal PM2.5 and indoor CO in nomadic tents using open and chimney biomass stoves on the Tibetan plateau. Atmospheric Environment 59: 207-213.
Tenzin Wangchuk (PhD)
Sherubtse College, Royal University of Bhutan