Smoke from biomass and coal combustion contains a large number of pollutants with known health hazards, including particulate matter, carbon monoxide, nitrogen dioxide, sulfur oxides (mainly from coal), formaldehyde, and polycyclic organic compounds (e.g., carcinogens such as benzo[a]pyrene). The concentrations of each of these pollutants vary among the different forms of solid fuels, with animal dung and crop residues having some of the highest level emissions to environment of particulate matter, one of the important indicator pollutants for health effects.
Pollution levels are especially high when burning is done using simple technologies such as open ‘‘three stone’’ fires, which result in incomplete and inefficient combustion emisisons(Fig. bellow). Monitoring of pollutants and personal exposures in biomass-burning households has shown concentrations many times higher than those observed in industrialized countries. The latest National Ambient Air Quality Standards of the U.S. Environmental Protection Agency, for instance, required that the daily average concentration of particles below 10 mm in diameter (PM 10 ) be less than 150 mg/m 3 (annual average below 50 mg/m 3 ). In contrast, typical 24-hour average concentrations of PM 10 in homes using biofuels may range from 200 to 5000 mg/m 3 or more throughout the year, depending on the exact type of fuel, stove, and housing. Levels of carbon monoxide and other pollutants also often exceed international guidelines.
Improving air quality is important for occupant health, contributing to a favorable working or home environment and a sense of comfort, health, and well being; when indoor air pollutants are present, however, indoor air quality deteriorates. To date, much of the attention relating to air pollution has focused on the risk and health effects of outdoor air quality, despite the fact that indoor levels of air pollutants are often 2–5 (and occasionally more than 100) times higher than outdoor concentrations. Recently, though, comparative risk studies such as those performed by the U.S. Environmental Protection Agency (EPA) have consistently ranked indoor air pollution among the top five environmental risks to public health. Furthermore, in industrialized countries, people spend the majority of time indoors, thereby increasing their exposure to indoor air pollutants relative to outdoor air pollutants.
A typical adult spends approximately 60% of their time at home; 25% is spent in the workplace; 5%, at public places, shops, leisure pursuits, etc.; 5%, within transport vehicles; and 5–10%, outdoors. Some populations, often those most susceptible to health effects, such as the elderly, infants, the sick, and their caregivers, spend even more time indoors, usually in the home. However, within the general public, there is a notable lack of appreciation of this risk; the level of education regarding indoor air quality issues is low and the indoor environment is considered a place of refuge and safety. Furthermore, unlike outdoor air quality, indoor air problems are often subtle and do not always produce easily recognized impacts.
