Indoor Air Quality

According to the World Health Organization (WHO), indoor air pollution associated with solid fuel use kills approximately 1.6 million people each year and represented 2.7 percent of the global burden of disease (in disability-adjusted life years, or DALYs). Hence, poor indoor air quality is the second-biggest environmental contributor to morbidity and mortality, behind unsafe water and poor sanitation. In several regions of the world, people spend most of their time indoors. The building design and ventilation in most of the cases influence the indoor air quality concentrations. Due to high population density and land scarcity, and as an effort to conserve energy, building designs are compact, with lower rates of ventilation in some places. While some buildings have natural ventilation, others have mechanical ventilation. Also, the outdoor air enters indoors by infiltration, natural ventilation, and forced ventilation. The natural air exchange through cracks and leaks, such as through door and window frames, chimneys, and exhaust vents, is called infiltration. The exchange of air resulting from opening and closing of windows is termed natural ventilation, while forced ventilation is the air exchange resulting from the use of whole-house fans or blowers.

Gases include the following:

• Carbon dioxide: Sources include combustion, tobacco smoke, metabolic activities, garage exhaust, and so forth. Concentrations of carbon dioxide above 15,000 parts per million volume (ppmv) can cause respiratory problems.
• Carbon monoxide: The primary sources include boilers, gas or kerosene heaters, gas stoves, wood stoves, fireplaces, tobacco smoke, garage exhaust, outdoor air, and so on. Exposure to carbon monoxide concentrations greater than 700 ppmv causes headache; concentrations greater than 700 ppmv for one hour cause death.
• Nitrogen dioxide: Sources include outdoor air, garage exhaust, kerosene and gas space heaters, wood stoves, gas stoves, tobacco smoke, and so on. Concentrations greater than 900 parts per billion volume (ppbv) impact respiratory function.
• Ozone: Sources include outdoor air, photocopy machines, electrostatic air cleaners, and so on. At concentrations greater than 0.15 ppmv, ozone causes headaches; concentrations greater than 0.25 ppmv cause chest pains; and concentrations greater than 0.30 ppmv lead to sore throat, cough, and breathing discomfort.
• Sulfur dioxide: Important sources include outdoor air, kerosene space heaters, gas stoves, coal appliances, and so on. Concentrations greater than 1.5 ppmv can lead to respiratory infections and impaired lung function.
• Formaldehyde: Sources include particle board, insulation, furnishings, paneling, plywood, carpets, tobacco smoke, and so on. Concentrations greater than 0.01 to 2.0 ppm can cause irritation of eyes; greater than 1 to 30 ppm causes respiratory problems; greater than 100 ppmv can cause coma and be fatal.
• Volatile organic compounds (VOCs): Important sources include adhesives, solvents, building materials, combustion appliances, paints, varnishes, tobacco smoke, room deodorizers, cooking, carpets, furniture, draperies, and so on. Some common VOCs include propane, butane, pentane, hexane, n-decane, benzene, toluene, xylene, styrene, and so on. High concentrations can lead to health problems that range from sensory irritation to behavioral, neurotoxic, hepatoxic, and genotoxic effects.
• Radon: Diffusion from soil is an important source. A combination of radon and cigarette smoking increases cancer risk.

Aerosol particles include the following:

• Allergens: Sources include house dust, domestic animals, insects, pollens, and so on. Allergens cause asthmatic problems.
• Asbestos: Sources include fire retardant materials, insulation, and the like. Primary health effects include lung cancer, mesothelioma (cancer of mesothelial membrane lining lungs), and asbestosis (slow degeneration of lungs).
• Fungal spores, bacteria, and viruses: Sources include soil, plants, food, human transmission, and so on. Several respiratory diseases and skin allergies are associated with fungal spores, bacteria, and viruses.
• Environmental tobacco smoke (ETS): This is a combination of inhaled and exhaled smoke from cigarettes. ETS consists of a mixture of aerosol particles and gases and is mostly carcinogens.
• Polycyclic aromatic hydrocarbons (PAHs): Sources include fuel combustion, tobacco smoke, mothballs, blacktop, wood preservatives, and so on. Most PAHs are carcinogens.
• Other: Sources include combustion processes associated with cooking with wood stoves, fireplaces, outdoor air, and more. Pollutants from these sources cause respiratory ailments.

For evaluating and regulating indoor air quality, pollution standards and guidelines are in use in several countries. Most of them are based on WHO air quality guidelines. In the [Page 229]United States, the Occupational Safety and Health Administration (OSHA) sets the indoor air pollution standards. Also, several countries follow their own nationally determined minimum guidelines for indoor air pollution control. A multidisciplinary approach involving engineers, material manufacturers, architects, air pollution experts, and other professionals is needed to tackle the indoor air pollution problem.

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