<P> Indoor air pollution in developing nations is a significant form of indoor air pollution (IAP) that is little known to those in the developed world . </P> <P> Three billion people in developing countries across the globe rely on biomass, in the form of wood, charcoal, dung, and crop residue, as their domestic cooking fuel . Because much of the cooking is carried out indoors in environments that lack proper ventilation, millions of people, primarily poor women and children face serious health risks . 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 . </P> <P> 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 . </P> <P> 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 exposures 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 . Smoke from traditional household solid fuel combustion commonly contains a range of incomplete combustion products, including both fine and coarse particulate matter (e.g., PM, PM), carbon monoxide (CO), nitrogen dioxide (NO), sulfur dioxide (SO), and a variety of organic air pollutants (e.g., formaldehyde, 1, 3 - butadiene, benzene, acetaldehyde, acrolein, phenols, pyrene, benzopyrene, benzo (a) pyrene, dibenzopyrenes, dibenzocarbazoles, and cresols). 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 . </P>

What is the most common indoor air pollutant in the developed world