Indoor air pollutants associated with combustion of solid fuels in households of developing countries are now recognized as a major source of health risks to the exposed populations. Use of open fires with simple solid fuels, biomass, or coal for cooking and heating exposes an estimated 2 billion
people worldwide to concentrations of particulate matter and gases that are 10 to 20 times higher than health guidelines for typical urban outdoor concentrations. Although biomass makes up only 10 to 15 percent of total human fuel use, since nearly half the world’s population cooks and heats their homes with biomass fuels on a daily basis, indoor exposures are likely to exceed outdoor exposures to some major pollutants on a global scale. Use of traditional biomass fuels—wood, dung, and crop residues is widespread in rural India. According to the 55th round of the National Sample Survey conducted in 1999–2000, which covered 120,000 households, 86 percent of rural households and 24 percent of urban households rely on biomass as their primary cooking fuel.