Module 11: Air

Air Pollution

Air pollution is a major environmental risk to health and is estimated to cause approximately 2 million deaths worldwide per year. Exposure to air pollutants is largely beyond the control of individuals and requires action by public authorities at the national, regional, and international levels. The WHO Air Quality Guidelines contain up-to-date assessments of the health effects of air pollution, and the guidelines recommend targets for air quality at which the health risks will be significantly reduced. By reducing particulate matter (PM10) pollution from 70 to 20 micrograms per cubic meter, we can reduce air quality-related deaths by around 15%. By reducing air pollution levels, we can help countries reduce the global burden of disease from respiratory infections, heart disease, and lung cancer. The WHO guidelines provide temporary targets for countries that still have very high levels of air pollution. The targets call for a maximum of three days a year with up to 150 micrograms of PM10 per cubic meter (for short term peaks of air pollution), and 70 micrograms per cubic meter for long term exposures to PM10.(1)

Wood Burning Stoves(2)

Approximately 50% of people, almost all in developing countries, rely on coal and biomass in the form of wood and crop residues for domestic energy. These materials are typically burned in simple stoves with very incomplete combustion. Consequently, women and children are exposed to high levels of indoor air pollution every day, which increases the risk of chronic obstructive pulmonary disease and of acute respiratory infection in childhood. It is the greatest cause of death among children under 5 years of age in developing countries. Evidence also shows associations with low birth weight, increased infant and perinatal mortality, pulmonary tuberculosis, nasopharyngeal and laryngeal cancer, and cataract. Indoor air pollution is a major global public health threat requiring increased efforts in the areas of research and policy-making. There should be more research on its health effects, particularly in relation to respiratory infections.

Poverty is one of the main barriers to the adoption of cleaner fuels. Wood is the most common example of biomass fuel, but the use of animal dung and crop residues is also widespread. Many of the substances in biomass smoke can harm human health. The most toxic byproducts are particles, carbon monoxide, nitrous oxides, sulphur oxides (principally from coal), formaldehyde, and polycyclic organic matter. The majority of households in developing countries burn biomass fuels in open fireplaces, or in a poorly functioning earth or metal stove. Combustion is very incomplete in most of these stoves, resulting in substantial emissions which, in the presence of poor ventilation, produce very high levels of indoor pollution.

Exposure can be reduced by using improved stoves, better housing, cleaner fuels, and behavioral changes. Cleaner fuels, especially liquefied petroleum gas, offer the best long-term option in terms of reducing pollution and protecting the environment, but most poor communities using biomass are unlikely to be able to make the transition to these types of cleaner fuels. The use of improved biomass stoves has given varying results and has often been unsuccessful. Until recently, the main emphasis of stove programs has been to reduce the use of wood, and consequently there has been relatively little evaluation of reductions in exposure. Other factors such as seasonal energy requirements and cultural beliefs are also important considerations.(3)


Indoor Pollution

More than half of the world’s population relies on dung, wood, crop waste or coal to meet their most basic energy needs. Cooking and heating with such solid fuels on open fires or stoves without chimneys leads to indoor air pollution. This indoor smoke contains a range of health-damaging pollutants, including small soot or dust particles that are able to penetrate deep into the lungs. People in developing countries are commonly exposed to very high levels of pollution for 3-7 hours daily over many years. During the winter in cold and mountainous areas, exposure may occur over a substantial portion of each 24-hour period. Because of their customary involvement in cooking, women’s exposure is much higher than men’s. Young children are often carried on their mothers’ backs while cooking is in progress, and they therefore spend many hours breathing smoke. Pollution attributable to the use of biomass fuel also causes eye irritation and may cause cataract. (4) 

One study found that less than 20 % of homes in poor areas of northeastern Brazil and central Mexico were safe for living. Wood smoke contains many chemical products such carcinogens, carbon monoxide, and hydrocarbons that negatively impact human health.(5) “In fact, nearly half the world's population prepares meals with wood or wood-replacement fuels on primitive stoves without chimneys.”(6) The consequences of indoor air pollution are revealed in a study conducted in Nepal and India which examined the association between cooking with unflued indoor stoves and development of cataract. This study found that the use of solid fuel indoor stoves is associated with increased risk of developing cataract in women.(7)

Outdoor Air Pollution

Outdoor air pollution results largely from the combustion of fossil fuels for transport, power generation, and other human activities. Combustion processes produce a mixture of pollutants that comprise both primary emissions, such as diesel soot particles and lead, and the products of atmospheric transformation, such as ozone and sulfate particles that form from the burning of sulfur-containing fuel. Urban air pollution is primarily generated by transportation vehicles and energy production, and this form of pollution kills an estimated 1.2 million people annually. Today, many developing world cities face very severe levels of urban air pollution.(8)

Cigarette Smoke

Smoking impacts many forms of human health, including increased risk for lung disease and heart disease. It has also been shown that exposure to cigarette smoke can contribute to the development of cataracts later in life. One third of all women and two thirds of men in India use tobacco in some form, such as smoking tobacco in cigarettes. This statistic is cause for concern since smoking is reported to be a risk factor in eye diseases such as cataract, age-related macular degeneration, and glaucoma.(9) Studies show that cigarettes contribute to the formation of cataracts in two ways. First, free radicals present in tobacco smoke attack the eye directly, potentially damaging lens proteins and the fiber cell membrane in the lens.(10),(11) Second, smoking reduces the body's levels of antioxidants and certain enzymes which may help remove damaged protein from the lens.(12),(13) Over time, this damage can double or triple the risk of developing cataracts versus a non-smoker from a similar background.(14)


Replacing unflued stoves with flued stoves would greatly improve ventilation. Cooking in an unventilated kitchen doubles the risk of cataract compared with cooking in a fully or partially ventilated kitchen.  Allowing smoke to exit the house, and the use of cleaner fuels, are ideal options. It is best to replace the solid-fuel stoves with stoves that use liquid fuel or gas. Since resources are limited in developing countries, vented solid-fuel stoves may be a more economic solution.(15)

Twelve studies have assessed the risk for developing cataract in ex-smokers. Ex-smokers have a reduced risk for developing cataract compared with current smokers. However, the risk is still greater than for individuals who have never smoked. Also, the greater the intensity of previous smoking, the longer it takes for the increased risk to decline. However, cessation does ultimately decrease the risk. Education and public health campaigns aimed at increasing awareness of the dangers of smoking may help to curb rates in the developing world.(16)

Go To Module 12: Innovations in Air >>


(1) “Air quality and health.” WHO. (August 2008). Accessed 10 July 2010.

(2) Bruce,N., Perez-Padilla, R., and Albalak, R. “Indoor air pollution in developing countries: a major environmental and public health challenge.” Bulletin of the World Health Organzation. (2000). 78(9). Accessed 8 July 2010.

(3) Ibid.

(4) Ibid.

(5) Fitzpatrick, T. “Cooking Smoke Serious Global Health Risk.” Albion Monitor. (7 January 1997). Accessed 11 July 2010.

(6) Ibid.

(7) Pokhrel AK, Smith KR, Khalakdina A, Deuja A, Bates MN. “Case-control study of indoor cooking smoke exposure and cataract in Nepal and India.” Int J Epidemiol. (2005). 34:702–708

(8) Bruce, N., Perez-Padilla, R., and Albalak, R. “Indoor air pollution in developing countries: a major environmental and public health challenge.” Bulletin of the World Health Organzation. (2000). 78(9). Accessed 8 July 2010.

(9) World Health Organization. Tobacco or health, a global status report. Geneva: WHO, 1997.

(10) McCarty CA, Nanjan MB, Taylor HR. “Attributable risk estimates for cataract to prioritize medical and public health action.” Invest Ophthalmol Vis Sci. (2000). 41:3720–25.

(11) Van Heyningen R, Pirie A. “Naphthalene cataract in pigmented and albino rabbits.” Exp Eye Res.1976. 22:393–94.

(12) Shalini VK, Luthra M, Srinivas L et al. “Oxidative damage to the eye lens caused by cigarette smoke and fuel smoke condensates” Indian J Biochem Biophys.(1994). 31:261–66.

(13) Wegener A, Kaegler M, Stinn W. “Frequency and nature of spontaneous age-related eye lesions observed in a 2-year inhalation toxicity study in rats.” Ophthalmic Res.(2002). 34:281–87.

(14) Kelly SP, Thornton J, Edwards R, et al. “Smoking and cataract: review of causal association.” J Cataract Refract Surg. (2005). 31:2395–404.

(15) “Module 12: Smoke Exposure and Cataract.” Accessed 10 July 2010.

(16) Kelly SP, Thornton J, Edwards R, et al. “Smoking and cataract: review of causal association.” J Cataract Refract Surg. (2005). 31:2395–404.