Indoor Air Pollution in the Developing World

Figure 1: Photo courtesy of Kirk Smith, PhD, UC Berkeley (released from copyright by Dr. Smith)

Many people around the world do not have electricity or gas for cooking, lighting or heating their homes. Instead, they get their energy from burning solid fuels (coal and biomass in the form of wood, crop residues and/or dung.) These materials are burned on simple stoves, and they release many particles and gases in the smoke. The accumulation of these particles and gases inside people’s homes is the main cause of indoor air pollution in the developing world. The levels of these particles and gases are highest during cooking and heating the home in cold places. Women and young children are exposed to indoor air pollution the most, and, as a result, bear the most consequences in the form of poor health and death.

Importance of indoor air pollution

About half of the world’s population and 90% of rural households in developing countries still get their energy from burning solid fuels and are thus exposed to high levels of indoor air pollution ^[1]. In an analysis of risk factors that contributed to disease in 2000 ^[2], indoor air pollution was estimated to cause 1.6 million deaths and almost 3% of all disease worldwide. More than half of these deaths occurred in children under the age of five. In poor developing countries, indoor air pollution ranked as the fourth overall cause of disease after malnutrition, unsafe sex and lack of clean water and sanitation. Use of solid fuels for energy also results in deforestation and greenhouse gas emissions that contribute to climate change ^[3].

Causes of indoor air pollution ^[4]

When people in industrialized countries think about air pollution, they tend to think of air pollution caused by emissions from cars, factories, and power plants. In developing countries, these emissions do cause air pollution that can enter people’s homes, but a much more important source of indoor air pollution is burning of solid fuels for cooking and heating the home. The burning of forests, agricultural land and household waste, as well as smoke from neighbor’s houses, also contribute to indoor air pollution but in much lower amounts.

There are multiple solid fuels: coal and biomass. Biomass refers to any plant or animal based material. The biomass fuels burned by humans include wood, crop residues, and dung. Solid fuels are burnt on stoves that are as simple as fire pits, or three large rocks under a cooking pot. These fires are very inefficient, and much of the fuel is released as small particles and gases in the form of smoke. The levels of these substances from burning solid fuels inside the home can be many times higher than levels from outside air pollution, and are well over the limits imposed by environmental agencies. For example, small particle 24-hour levels are between 300-3,000 µg/m3 and can reach peak levels of 30,000 µg/m3 during cooking; this level greatly exceed the upper limits of 150 µg/m3 (averaged over 24 hours) and 50 µg/m3 (averaged over a year.) established by the US Environmental Protection Agency ^[5]. Considering that cooking and heating the home are daily activities, we can see that people who use solid fuels for household energy are exposed to very high levels of these substances on a daily basis for years at a time.

How indoor air pollution affects health ^[4][6]

The smoke released from burning solid fuels contains many substances known to be dangerous to humans: small particles, carbon monoxide, polycyclic aromatic hydrocarbons, nitrogen oxides, sulfur oxides, formaldehyde, arsenic and others. When we breathe, we inhale the smoke into our lungs. While little research has studied the exact pathophysiological mechanisms through which smoke from solid fuels affects health, studies on exposures to air pollution and cigarette smoke performed in industrialized countries provide evidence of how the harmful substances contribute to disease. Small particles, in particular the smallest ones which can enter deep into the lungs, irritate the respiratory epithelium resulting in inflammation, increased airway reactivity, reduced muco-ciliary clearance and reduced local immune response. Carbon monoxide binds to hemoglobin reducing the oxygen delivered to organs and developing fetuses. Polycyclic aromatic hydrocarbons, like benzo[a]pyrene are carcinogenic. Nitrogen and sulfur dioxides increase bronchial reactivity; and nitrogen dioxide also increases susceptibility to viral and bacterial lung infections. Formaldehyde irritates the nasopharynx and airways.

Indoor air pollution has been linked to many diseases. Acute lower respiratory infections (ALRIs), Chronic Obstructive Pulmonary Disease (COPD refers to emphysema and chronic bronchitis) and lung cancer are the most studied and have the largest documented association with indoor air pollution from burning solid fuels.

Pneumonia

ALRIs, most commonly in the form of pneumonia, are the main cause of death for children under the age of five worldwide, and account for 1.8 million deaths in this age group each year. Indoor air pollution doubles the risk of pneumonia in children under the age of five, and is responsible for half of the 1.8 million deaths. Young children are commonly carried on their mothers’ backs resulting in high exposure to indoor air pollution during cooking. It is thought that the substances in biomass smoke, especially the small particles, cause irritation, damage and decreased immunity in the respiratory tract resulting in greater risk for infection.

COPD

There are 3 million COPD deaths in the world each year and indoor air pollution is responsible for about a third. However, when we look at the 50 poorest countries, where most of the people using solid fuels live, indoor air pollution accounts for half of COPD deaths. Most COPD cases are caused by smoking in richer, more developed countries; however, indoor air pollution is responsible for half of cases in developing countries where many cases of COPD happen in nonsmokers. Men smoke more than women throughout the world. Yet, COPD deaths are greater among men in richer countries, but greater among women in developing countries. This is because women spend much more time exposed to indoor air pollution during cooking, resulting in more COPD cases among women than men in developing countries where solid fuels are used for household energy. This also explains why exposure to indoor air pollution triples the risk of COPD for women but only doubles it for men. It is thought that the small particles, carbon monoxide and sulfur dioxide in biomass smoke cause severe damage to the respiratory tract resulting in destruction of lung tissue (as seen in emphysema) and obstruction of airways (as seen in chronic bronchitis.)

Lung Cancer

Indoor air pollution is responsible for about 3% of the 1.3 million deaths in the world each year due to lung cancer. Smoking causes the vast majority of lung cancers in richer countries, but nonsmokers, particularly women, are a larger percentage of cases in developing countries where solid fuels are used for household energy. Lung cancer causes more deaths among men than among women in both developed and developing countries. Lung cancer is thought to result from exposure to the carcinogen benzo[a]pyrene released in the smoke from burning coal. For women cooking with coal, exposure to benzo[a]pyrene for three hours a day is similar to smoking two packs a day.

Other Illnesses

There are other diseases that are suspected to be associated to indoor air pollution. The relationship between indoor air pollution and these diseases has not been studied as much or as long as that with pneumonia, COPD, or lung cancer, but the evidence continues to mount. These diseases include: asthma, low birth weight, head and neck cancers, TB, and cataracts. The 1.6 million deaths attributed to indoor air pollution by the study published in 2004 only include ALRIs, COPD and lung cancer. This number would be a lot higher were we to include these other diseases.

How indoor air pollution affects the environment ^[3]

Many of the same substances that damage health, particularly carbon monoxide, methane and nitrogen dioxide, also act as greenhouse gases and contribute to global warming. The contribution to global warming from the burning of solid fuels in developing countries is much lower than that of more developed countries but it is still important.

On a local level, the use of wood as fuel causes deforestation, especially when trees are felled to produce charcoal. Deforestation results in erosion, landslides, and depletion of nutrients from the soil. The use of dung and crop residues as fuel prevents them from being used as fertilizer, further depleting the soil.

Indoor air pollution and poverty ^[1][3]

Modern fuels (referring to electricity, liquid fuels such as kerosene, and gaseous fuels such as liquefied petroleum gas or natural gas) are cleaner and more efficient than solid fuels, but they are also more expensive. Which fuel is used for household energy is determined by availability and cost. About 1.5 billion people (22% of the world’s population) do not have access to electricity. More than 80% of these people live in the 50 poorest and least developed countries (except for Haiti, these countries are in Sub-Saharan Africa and South-Asia.) In developing countries, rural households have less access to modern fuels than urban households. However, even when modern fuels are available, many families still burn solid fuel for household energy because they cannot afford modern fuels. Most families in developing countries use a combination of fuels to meet their energy needs with wood and gas being the most common fuels.

Poverty is the main obstacle to the use of modern fuels, and the use of solid fuels perpetuates poverty resulting in what some call “the poverty trap”. Extremely poor households spend much more of their income securing fuel for household energy than better-off households leaving less money for food, health, and education. The families with the most exposure to the harmful effects of indoor air pollution are the families who have the least access to medical care (due to no availability for remote rural areas and/or cost.) More time spent being sick, taking care of a sick child, or collecting dung or wood, means less time for income-generating activities or schooling. The depletion of soil nutrients reduces agricultural harvests meaning the families will then have less food to eat and/or sell.

Solutions to indoor air pollution ^[3]

Interventions that decrease indoor air pollution must reduce the levels of smoke dramatically in order to reduce the health problems due to burning of solid fuels. Multiple strategies have been used. One of the most widespread interventions is the use of improved stoves. Improved stoves burn solid fuels more efficiently, meaning that more of the fuel is transformed into heat and less into smoke. While promising, improved stoves have not reduced smoke levels enough to prevent disease. A second strategy has been to reduce smoke levels by increasing ventilation through chimneys and smoke hoods. The reduction in smoke varies depending on the type of ventilation but has generally had the same disappointing results as improved stoves. Ventilation also results in indoor air pollution being converted into outdoor air pollution, which does not help address the environmental problem. Another strategy has been to get people to change to modern fuels for household energy. Switching to modern fuels greatly reduces indoor air pollution levels. Unfortunately, it is not an option for many due to cost or lack of availability.

While many of the past interventions have not achieved the desired reduction in indoor pollution levels, they have contributed to the understanding of the problem. Newer ideas are being implemented right now such as: subsidizing the cost of gas cookers to help poor families switch to liquefied petroleum gas, installing biogas plants which convert dung and human feces into methane which is then used in low-pressure gas burners, and the use of biofuel stoves which burn locally produced methanol (by gasifying biomass) or ethanol (from sugar production residues.)

Further Reading

WHO website: Indoor air pollution related publications

References

1. ↑ ^{1.0 1.1} UNDP and WHO. The energy access situation in developing countries: A review focusing on the least developed countries and Sub-Saharan Africa. New York: United Nations Development Program, 2009.
2. ↑ Smith KR, Mehta S, and Feuz M. Indoor air pollution from household use of solid fuels. In: Ezzati M, et al, eds. Comparative quantification of health risks: global and regional burden of disease attributable to selected major risk factors. Geneva: World Health Organization, 2004:1435-1494.
3. ↑ ^{3.0 3.1 3.2 3.3} WHO. Fuel for Life: Household energy and health. Geneva: World Health Organization, 2006.
4. ↑ ^{4.0 4.1} Bruce N.G., Perez-Padilla R., Albalak R. Indoor air pollution in developing countries: A major environmental and public health challenge. Bulletin of the World Health Organization 2000, 78(9):1078–1092.
5. ↑ US Environmental Protection Agency. Particulate Matter (PM-10). Available at: http://www.epa.gov/oaqps001/airtrends/aqtrnd95/pm10.html. Accessed on March 30, 2010.
6. ↑ WHO. The Global Burden of Disease: 2004 Update. Geneva: World Health Organization, 2008.