Household Air Pollution (HAP) is a significant form of indoor air pollution (IAP) mostly relating to cooking and heating methods used in developing countries. Since much of the cooking is carried out with biomass fuel, in the form of wood, charcoal, dung, and crop residue, in indoor environments that lack proper ventilation, millions of people, primarily women and children face serious health risks. In total, about three billion people in developing countries are affected by this problem. The World Health Organization (WHO) estimates that cooking-related pollution causes 3.8 million annual deaths. The Global Burden of Disease study estimated the number of deaths in 2021 at 3.1 million. The problem is closely related to energy poverty and cooking.
Smoke from traditional household solid fuel combustion commonly contains a range of incomplete combustion products, including both fine and coarse particulate matter (e.g., PM2.5, PM10), carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and a variety of organic air pollutants.
Technology-based solutions to this problem tend to focus on the supply of improved cookstoves although behavioral changes can also be important.
Problem description and scale
Three billion people in developing countries rely on biomass fuel, in the form of wood, charcoal, dung, and crop residue, as their domestic cooking and heating fuel. Since much of the cooking is carried out indoors in environments that lack proper ventilation, millions of people, primarily women and children, face serious health risks from the inhalation of particulates. The major sources of indoor pollution include combustion and building materials. Globally, 4.3 million deaths were attributed to exposure to IAP in developing countries in 2012, almost all in low and middle-income countries. The South East Asian and Western Pacific regions bear most of the burden with 1.69 and 1.62 million deaths, respectively. Almost 600,000 deaths occur in Africa, 200,000 in the Eastern Mediterranean region, 99,000 in Europe and 81,000 in the Americas. The remaining 19,000 deaths occur in high-income countries.
Even though the rate of dependence on biomass fuel is declining, this dwindling resource will not keep up with population growth which could ultimately put environments at even greater risk.
Over the past several decades, there have been numerous studies investigating the air pollution generated by traditional household solid fuel combustion for space heating, lighting, and cooking in developing countries. It is now well established that, throughout much of the developing world, indoor burning of solid fuels (biomass, coal, etc.) by inefficient, often insufficiently vented, combustion devices results in elevated exposure to household air pollutants. This is due to the poor combustion efficiency of the combustion devices and the elevated nature of the emissions. In addition, they are often released directly into living areas. , Long, C., Valberg, P., 2014. Evolution of Cleaner Solid Fuel Combustion, Cornerstone, http://cornerstonemag.net/evolution-of-cleaner-solid-fuel-combustion/ Smoke from traditional household solid fuel combustion commonly contains a range of incomplete combustion products, including both fine and coarse particulate matter (e.g., PM2.5, PM10), carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and a variety of organic air pollutants (e.g., formaldehyde, 1,3-butadiene, benzene, acetaldehyde, acrolein, phenols, pyrene, and cresols, among others). In a typical solid fuel stove, about 6–20% of the solid fuel is converted into toxic emissions (by mass). The exact quantity and relative composition is determined by factors such as the fuel type and moisture content, stove type and operation influencing the amount.
Indoor gas stoves have been linked to negative health effects such as an increase in childhood asthma.
Health impacts
Most measurements have been focused on breathing-zone exposure levels of particulate matter (PM) and carbon monoxide (CO), which are the main products of incomplete combustion and are considered to pose the greatest health risks. Approximately 11% of lung cancer deaths in adults are attributed to exposure to carcinogens from household air pollution caused by using kerosene or solid fuels like wood, charcoal or coal for household energy needs. Indoor PM2.5 exposure levels have been consistently reported to be in the range of hundreds to thousands of micrograms per cubic meter (μg/m3). Similarly, CO exposure levels have been measured to be as high as hundreds to greater than 1000 milligrams per cubic meter (mg/m3). A recent study of 163 households in two rural Chinese counties reported geometric mean indoor PM2.5 concentrations of 276 μg/m3 (combinations of different plant materials, including wood, tobacco stems, and corncobs), 327 μg/m3 (wood), 144 μg/m3 (smoky coal), and 96 μg/m3 (smokeless coal) for homes using a variety of different fuel types and stove configurations (e.g., vented, unvented, portable, fire pit, mixed ventilation stove).
Rural Kenya has been the site of various applied research projects to determine the intensity of emissions that commonly occur from use of biomass fuels, particularly wood, dung, and crop residue. Smoke is the result of the incomplete combustion of solid fuel which women and children are exposed to up to seven hours each day in closed environments.Smoke's increasing cloud across the globe, Practical Action, accessed 5 May 2007. These emissions vary by day, by season, and with airflow changes in a household. Exposure in poor homes far exceeds accepted safety levels by as much as one hundred times over. Because many Kenyan women utilize a three-stone fire, the worst offender, one kilogram of burning wood produces tiny particles of soot which can clog and irritate the bronchial pathways. The smoke also contains various poisonous gases such as aldehydes, benzene, and carbon monoxide. Exposure to IAP from the combustion of solid fuels has been implicated, with varying degrees of evidence, as a causal agent of several diseases. Acute lower respiratory infections (ALRI) and chronic obstructive pulmonary disease (COPD) are the leading causes of disease and death from exposure to smoke. Cataracts and blindness, lung cancer, tuberculosis, premature births and low birth weight are also suspected of being caused by IAP.
Women and girls Women and girls are largely responsible for collecting fuel-wood for cooking in most households, particularly in rural communities and in refugee camps. Women and girls also make up the majority of deaths from household air pollution. Replacing traditional kerosene/firewood stoves with cleaner ethanol stoves in Nigeria has mitigated adverse pregnancy outcomes from HAP. Anemia, a condition in which a woman's hemoglobin levels are drastically reduced, and pregnant women's exposure to CO seem to coincide with one another. A pregnant woman with anemia seem to develop higher levels of CO pollution than those who do not.
Approaches
Early interventions Unfortunately, finding an affordable solution to address the many effects of IAP – improving combustion, reducing smoke exposure, improving safety and reducing labor, reducing fuel costs, and addressing sustainability – is complex and needs continual improvement. Efforts to improve cook stoves in the past, beginning in the 1950s, were primarily aimed at minimizing deforestation with no concern for IAP, though the effectiveness of these efforts to save firewood is debatable. Various attempts had various outcomes. For example, some improved stove designs in Kenya significantly reduced particulate emissions but produced higher CO2 and SO2 emissions. Flues to remove smoke were difficult to design and were fragile.
Improved success
Current improved interventions, however, include smoke hoods, which operate in much the same manner as flues to extract smoke but are found to reduce levels of IAP more effectively than homes that rely solely on windows for ventilation.Health, Environment And The Burden Of Disease: A Guidance Note , Cairncross, S., O'neill, D., McCoy., A., Sethi, D. 2003. DFID. Accessed 10 May 2007. Some features of newly improved stoves include a chimney, enclosing the fire to retain heat, designing a pot holder to maximize heat transfer, dampers to control airflow, a ceramic insert to reduce heat loss, and multi-pot systems for cooking multiple dishes.
Stove-related interventions are now known to be one of the least-cost means of achieving the combined objective of reducing the health burden of IAP and, in some areas, reducing environmental stress from biomass harvesting.
Sustainable energy options
Large-scale combustion of biomass is only feasible if carried out sustainably. The concern is paramount for the regeneration of renewable and sustainable fuel-wood sources if it is to continue to be available long-term. Attempts at sustainable solutions in Kenya could include developing energy crops (trees and shrubs) which would also provide additional income for farmers. This solution would benefit cropland or rangeland prone to erosion and flooding as the root systems and leaf litter would enhance soil stability.Global Village Energy Partnership, Nairobi, Kenya , UNDP. 2005. Accessed 30 April 2007. Careful selection of regenerating varieties would be most sustainable because soil stability is not disrupted due to tilling and planting. Some people view this solution as a way to further exploit forests, but with proper management of forest resources this could be a viable solution.
Fuels and cook stove technology can be assessed on two factors: energy efficiency and emissions in the household. High-performing efficient stoves can improve environmental outcomes to an extent even with unclean fuels (such as firewood and biomass). According to a study comparing environmental, social, and economic life cycle impacts of cooking fuels, with more efficient stoves "more of the heating value of the fuel is converted into useful cooking energy and therefore less fuel must be produced, transported, and burned to deliver the same amount of cooking".
Other sustainable options include liquid and gas fuels that are combusted in high-performing efficient stoves. For instance, ethanol produced from cellulosic/non-food feedstocks (wood, agricultural residue) has lower environmental life cycle impacts compared to ethanol produced from sugar and starch materials. LPG, though made from non-renewable fossil fuels, still has lower negative health impacts than traditional fuels. Thus, even though it is not a sustainable alternative, it creates far fewer emissions impacts than traditional fuels.
Challenges
Supply There exist trade-offs between efficiency and sustainability on the supply side of the cook stoves and fuels market. While developing cook stoves that use efficient and clean fuel sources is environmentally ideal, often this is not a viable solution due to barriers to scaling up production and consumption of these fuels. For instance, electric stoves are cited as emission-free 'clean' alternatives to biomass at the household level. However, negative externalities still exist – ambient air pollution in areas near power plants still poses a health risk, while the generation of electricity in India and China (countries largely dependent on coal for electricity generation) still poses significant environmental risks. Moreover, only households that are connected to the electric grid in a country or region will have access to electricity for household energy consumption, thereby excluding a large swathe of rural communities.
Demand