Indoor air pollution causes 1.6 million premature deaths every year and afflicts nearly half of the world's population, predominantly the rural poor. This makes it the second leading environmental health threat in the world and a critical barrier to poverty alleviation in low-income countries. Yet this issue is rarely discussed outside of public health circles, probably because the health consequences of indoor air pollution are not immediate and can be difficult to trace. Thus, indoor air pollution remains a quiet and neglected killer, with lack of global awareness being one of the primary obstacles to the widespread implementation of existing, proven interventions.
Indoor air pollution is a pressing health threat that, at its root, is really an energy problem. It stems from indoor burning of solid fuels, which include coal and biomass (wood, dung, crop residues, charcoal). Solid fuel burning is very inefficient, so indoor fires and traditional stoves emit a substantial amount of particulate matter and gaseous pollutants like carbon monoxide (CO), nitrogen dioxide (NO2), and hydrocarbons. Combustion of wood, one of the cleaner biomass fuels, emits 50 times more household pollution than do gas stoves (see Figure 1) (Smith et al., 2000).
Figure 1: Household Emissions of Common Cooking Fuels
(PM10 = particulate matter)
Source: Smith et al., 2000
Solid fuels are the primary fuel source for the world's poorest people. Over 3 billion people worldwide use solid fuels for cooking, boiling water, lighting, and heating (Rehfuess et al., 2006). These fuels account for more than 95% of domestic energy use in twenty-five of the world's low-income countries. In contrast, virtually no households in developed regions use solid fuel as their primary energy source (see Figure 2).
Figure 2: Percent of Population Using Solid Fuels
(Total population using solid fuels in parentheses)
Source: EarthTrends, 2007 using data from WHO Global Health Atlas, 2007
Supplementary info: EarthTrends table of solid fuel use by country
Impacts on Human Health
The relatively high emissions of solid fuel combustion are only part of the problem. Human exposure to these pollutants indoors is compounded in homes with close quarters and poor ventilation. Even low levels of indoor air pollution can negatively affect health because of the proportionally large amount of time families spend indoors. For that reason, researchers now take into account not only pollutant concentration but amount of time spent in each environment, calculating individual "time-activity patterns."
Using this metric, the number of people exposed at unacceptable levels indoors is equivalent to or greater than the number exposed to unacceptable levels outdoors in all the world's cities combined (Smith et al., 2000). Though no international standards for indoor air pollution exist, studies show that daily average levels of small particles in households that burn solid fuels are six to 60 times the World Health Organization air pollution guidelines (Rehfuess et al., 2006, WHO).
The WHO's 2002 World Health Report ranked indoor smoke from solid fuels eighth among all risk factors for global disease and death. In terms of environmental contributors to ill health, indoor smoke is responsible for one-third of premature mortality and disability worldwide, second only to unsafe water, sanitation, and hygiene (see Figure 3). Health effects associated with indoor pollution include respiratory illness and pneumonia, lung cancer, bronchitis and emphysema, weakened immune system, and reduced lung function. One analysis determined that exposure to indoor air pollution more than doubled a child's likelihood of developing pneumonia and other respiratory infections, which are the world's leading cause of illness in children and can often be fatal in rural areas with limited healthcare (Smith et al., 2000).
Figure 3: DALYs Attributed to Environmental Risk Factors
(Disability Adjusted Life Years are the sum of years lost due to disability and mortality)
Source: WRI, 2005. World Resources Report
An Uneven Distribution of Risk
Because solid fuel use is largely among poor and rural populations, the associated health risks are primarily concentrated in Africa and southeast Asia (see Figure 4). The WHO estimates that 1.6 million deaths due to indoor smoke occurred in 2000, almost all in developing countries.
Figure 4: Burden of Disease Attributable to Indoor Smoke from Solid Fuels
Source: WHO, 2002. World Health Report
Most deaths due to indoor smoke are among women and children, who are especially vulnerable to exposure. In developing countries, women are often the primary household cook, and if they have an additional occupation it's often fuel-intensive as well: brewing beer, smoking fish, or processing palm oil. Because young children are often carried on their mothers' backs or otherwise kept close by during cooking, they too are exposed. Potential harm is very great for children under one year, since their lungs and immune system are not yet fully formed. Household use of biomass fuels has been found to significantly increase the risk of acute respiratory infections, which annually kill millions of children under age five (Smith et al., 2000).
Vicious Cycle of Energy Poverty and Limited Opportunity
The social importance of solid fuel use extends beyond its impact on health to a broader cycle of energy poverty and material poverty in the world's poorest countries. Poor households can't afford kerosene, gas, or the stoves to burn them, so they collect biomass. However, the burden of time required to collect biomass is great and often falls on women. One study in rural Malawi found that women spent four to 15 hours per week collecting fuel, depending on distance from the woodland (see Box 1) (Rehfuess et al., 2006).
The time-consuming nature of fuel collection limits other opportunities for these women, such as education and income-generation. In addition, being ill or caring for children who are ill as a result of indoor smoke consumes time and money. As a result, it is difficult for these families to switch to more efficient and expensive fuels. Energy poverty and underdevelopment have thus become self-reinforcing situations in countries of the developing world.
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Box 1: Fuel Collection and Education Firewood is the primary fuel for over 90 percent of the population of Malawi, a country of about ten million people located in southeast Africa. Dependence on wood for fuel has contributed to significant deforestation, forcing residents to travel even farther to collect wood. Because the burden of fuel collection falls primarily on women and girls, probability of children's school attendance decreases with hours spent collecting fuel. School attendance also decreases with environmental degradation: children from wood-scarce districts are 10 to 15 percent less likely to attend secondary school than children from less scarce districts. Responsibility of fuel collection thus contributes to lack of education among children in Malawi. (Nankhuni and Findeis, 2003) (Map from World Resources 2005, Figure 2.6) |
Successful Intervention
Though complex, the problem of solid fuel use is not insoluble. Programs to reduce hazards of solid fuel use have been successful, most visibly the Chinese National Improved Stove Program. The program focused on improving stoves by increasing air flow or installing chimneys or flues. It accomplished an unprecedented scale of rural energy intervention, distributing more than 180 million improved stoves between the early 1980s and its end in the mid-1990s (Zhang and Smith, 2007).
Reviews of the program confirm that roughly three-fourths of China's rural households were outfitted with improved stoves, and that improved stoves did in fact improve household air quality, though not sufficiently to meet China's indoor air quality standards (Woodrow Wilson Center, Edwards et al., 2005).
Unfortunately, since the program's end, little progress has been made to improve rural energy, and rising coal use among China's rural households threatens to erode the benefits. However, its initial success reveals that a simple technological change, coupled with awareness of the social and economic factors that contribute to a household's fuel choice, can go a long way to raise families out of energy poverty.
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RELATED LINKS:
Partnership for Clean Indoor Air
EarthTrends
Solid Fuel Use by Country, in Thousand Tonnes of Oil Equivalent (ktoe)
Solid Fuel Use by Country, as Percent of Fuel
"Health, Environment, and Poverty"
"Undying Flame: The Continuing Demand for Wood as Fuel"
Other Publications
Assessing Household Solid Fuel Use: Multiple Implications for the Millennium Development Goals (Rehfuess et al., 2006)
