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Update on the health and climate impacts of household solid fuels
[top] [end]BackgroundIt has been estimated that nearly half the world’s population still uses solid fuels (biomass and coal) for household cooking and space heating, mostly in developing countries. In the proper conditions, biomass (wood and agricultural residues) can be burned quite cleanly, producing mostly carbon dioxide and water. Such conditions are difficult to achieve in inexpensive household stoves, however, and the actual emissions of health-damaging pollutants are quite large per unit of fuel, although the total emissions are not large in the context of overall fuel use.[top] [end]Combustion of fuelStudies in India and China, for example, show that the percentage of fuel carbon fully burned to carbon dioxide is typically only 90 percent, with some fuel/stove combinations doing as poorly as 80 percent. This means that 5–20 percent of the fuel carbon is diverted into products of incomplete combustion – primarily carbon monoxide, but including benzene, butadiene, formaldehyde, polyaromatic hydrocarbons, and many other compounds posing health hazards. The best single indicator of the health hazard of combustion smoke is thought to be small particles, which contain many chemicals. Household coal use, largely found in China today, can present additional hazards because of the toxic contaminants in some coals, including sulfur, arsenic, fluorine, mercury, and selenium.[top] [end]Exposure to smokeMillions of people inhale significant amounts of seriously health-damaging pollutants from household stoves on a daily basis. The exposures are highest in poor women and young children of developing countries, both rural and urban, who are the groups most often present during cooking with solid fuels (Figure 1).
[top] [end]Evidence for ill-healthSince the mid-1980s, and more frequently since the mid-1990s, there have been many dozens of published epidemiological (population-based) studies examining a range of health effects from indoor air pollution due to solid fuel use. Because of the difficulty and expense of exposure assessment in households, however, most have used a surrogate (or proxy) for true exposure, often simply whether the households are using solid fuels or not. Even with such an imprecise measure, however, health effects of several sorts have repeatedly been found. The best evidence is for (a) acute lower respiratory infections (pneumonia) in young children, the chief killer of children worldwide and the disease responsible for the most lost life years in the world; (b) chronic obstructive pulmonary disease, such as chronic bronchitis and emphysema, in adult women who have cooked over unvented solid fuel stoves for many years; and (c) lung cancer, though the best evidence is only for coal smoke.[top] [end]Comparison with other health risksThe World Health Organization, in a risk assessment that combined the results of many studies, compared the burden of illness and premature death from solid fuel use along with other major risk factors, including outdoor air pollution, tobacco smoking, hypertension, etc. The results indicate that solid fuel use may be responsible for 0.8–2.4 million premature deaths each year. As shown in Figure 2, using the central (‘best’) estimates for the risk factors examined puts solid fuel use approximately tenth among major health risks in the world in terms of potentially preventable healthy lost life-years (DALYs – a measure that combines healthy years lost due to premature death and healthy years lost due to ill-health). Of this data, those marked * are based on outcomes in the Global Burden of Disease database of the World Health ganization (WHO). The remaining estimates are from the Comparative Risk Assessment managed by WHO (Ezzati et al., 2004).
[top] [end]Linking reduced exposure with improved healthIt is one thing to determine that illhealth is associated with a particular risk factor, but quite another sometimes to show that reduction in the risk factor will actually produce an improvement in health. There have been two very large cases to date, one in south China with coal and another in Guatemala with wood. The China study, done in retrospect, showed reduction in lung cancer and chronic obstructive pulmonary disease due to the introduction of improved stoves in the late 1970s. The other, a randomized trial of improved stoves in highland Guatemala, is just now being completed. It focused on childhood pneumonia, but also examined heart and lung effects in women.[top] [end]Finding a solution to indoor air pollutionAlthough the risk estimates will continue to be refined and new health effects probably will be added, the challenge for development practitioners is to find a viable intervention that can be relied on to reduce exposures and improve health cost-effectively. Improved fuels, such as liquefied petroleum gas (LPG), undoubtedly produce fewer emissions and exposure themselves, but are expensive and, at least at first, populations generally do not completely switch away from solid fuels but continue to use them for some tasks. Well-designed, built, and operated improved stoves with chimneys do reduce kitchen pollution substantially, but produce much lower reductions in human exposures because the smoke is still released in the vicinity of the household. In addition, successful dissemination of welloperating and durable stoves in large populations has not been easy. That such stoves may also have social and economic benefits, however, encourages further work to find ways to disseminate them widely.[top] [end]Stoves and greenhouse gasesIt is perhaps surprising that biomass stoves also contribute to global warming even when the fuel is harvested renewably and is thus ‘carbon neutral’, i.e., the fuel carbon released into the atmosphere is captured by regrowth of the biomass. This is because the products of incomplete combustion are more powerful greenhouse pollutants than carbon dioxide (CO2),the primary greenhouse gas. In addition to methane and other gases, a particularly powerful greenhouse pollutant from small-scale biomass combustion is now thought to be black carbon particles. Thus, the 5–20 percent of carbon that is not converted into CO2 adds to global warming even if the CO2 is completely recycled by re-growth of biomass. To be truly greenhouse-neutral, a biomass fuel cycle must not only be renewable, but also be based on efficient combustion, which is not the case in simple biomass stoves. With much of the carbon being converted to powerful greenhouse pollutants in many household biomass stoves, it is even possible to argue that an efficient clean-burning fossil fuel such as LPG could be introduced as a way of reducing greenhouse gases. The attractiveness of this approach, however, depends on assumptions related to discount rates (the way pollutants which take effect over different time periods are compared) and the amount of atmospheric warming for which each of the different pollutants is responsible.[top] [end]Benefiting the poor and reducing greenhouse gasesThis is not to say that the growing risk of global climate change is due to the stoves of the poor. Far from it! To slow down global warming, it is the world’s use of fossil fuels that needs to be addressed. However, since small inefficient stoves are responsible for both high greenhouse emissions and health-damaging pollutants (incomplete combustion), there is scope for introducing improved stoves and fuels that reduce both risks at once, i.e. produce substantial ‘co-benefits’. A stove that burns fuel efficiently is said to have high combustion efficiency. The costs of reducing carbon emissions from stoves with higher combustion efficiencies look to be well within those now being considered in various carbon trading or Clean Development Mechanism (CDM) schemes. These schemes work by funds from wealthy nations paying other countries for reducing the amount of carbon dioxide that they produce. Thus, it may be possible to purchase carbon savings at a reasonable price and achieve substantial health benefits as a side product, or vice versa. What has not been shown, however, is whether it is possible to introduce high-efficiency stoves to large populations such that they are built, operated, and maintained for long-term reliable performance. In addition, current rules or official CDM projects do not seem to allow for inclusion of stoves. The only large-scale successful improved stove effort to date was in China, which facilitated the introduction of perhaps 180 million improved stoves in the 1980s and 90s without any foreign involvement. It focused on fuel savings, but did apparently achieve some reduction in pollution air pollution levels as well, by use of chimneys, although there was little if any improvement in combustion efficiencies. Nepal is currently engaged in a national programme that promotes improved stoves as well as biogas plants, but no air pollution or health assessments of the results have been done to date . Since better tandard methods and new equipment for assessing the pollution and health implications of improved stove programmes are now being developed and field-tested, however, there should be reliable information soon about the actual changes produced by this and other improved stove and fuel programmes around the world.A national competition is now under way in China to find the best of a new generation of biomass ‘gasifier’ stoves that are now starting to be sold in the country. These are designed to produce extremely low emissions as well as having chimneys. The designs promote internal secondary combustion of the partially combusted smoke (see Spautz et al. in this edition). Designing these to be reliable in household use as well as inexpensive is a challenge, but these stoves show promise as a second generation of improved stoves that not only have high energy efficiency but the potential to substantially reduce air pollution exposures. Measurements in households over time, however, will be needed to verify these benefits.[top] [end]Recent References1). Ezzati, M. and others, eds. 2004. Comparative Quantification of Health Risks:Global and Regional Burden of Disease due to Selected Major Risk Factors. Geneva: World Health Organization, 2 vols.2). Sinton, J.E., and others. 2004. “An Assessment of Programs to Promote Improved Household Stoves in China.” Energy for Sustainable Development 8(3):33–52. 3). Smith. K.R. and others. 2004. “Indoor smoke from household solid fuels,” in Ezzati,M., and others (eds), op cit., pp. 1435–93. 4). Smith, K.R., J. Rogers, and S.C. Cowlin.2005. Household Fuels and Ill-Health in Developing Countries: What Improvements can be Brought by LP Gas (LPG)? Paris: World LP Gas Association and Intermediate Technology Development Group (in press). 5). Smith-Siversten T. and others. 2004, Reducing indoor air pollution with a randomized intervention design – A presentation of the Stove Intervention Study in the Guatemalan Highlands, Norsk Epidemiologi 14(2): 137–143. 6). Venkataraman C. and others. 2005. Residential biofuels in South Asia: Carbonaceous aerosol emissions and climate impacts. Science 307: 1454–1456. [top] [end]Download the original article Update on the health and climate impacts of household solid fuels by Kirk R. Smith (322 KB)[top] [end]Contents: Boiling Point 52 - Health, safety and household energy
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26 June 2007; Last edited:
26 June 2007; Version: 1 | |||||||||||
Pagename: UpdateOnTheHealthAndClimateImpactsOfHouseholdSolidFuels @HEDON: PBFA | |||||||||||
