According to the Environmental Protection Agency, indoor air is often more than 10 times (and sometimes more than 100 times) more polluted than outdoor air. Indoor air pollutants contribute to asthma as well as other respiratory conditions and diseases. Indoor pollutants include VOCs (volatile organic compounds) from off gassing building materials, paints and finishes, and furnishings; other toxic chemicals emitted from cleaning products, pesticides, and hazardous household supplies; mold, which grows on moist materials and surfaces; carbon monoxide and nitrogen dioxide gases, which can be released from gas-fueled combustion appliances; particulates from wood-burning fireplaces or cars running near the house; tobacco smoke; as well as asbestos, lead, and radon.  IAQ (indoor air quality) can be particularly compromised during winter and summer months when the home or building is more likely to be sealed tight to keep heated or cooled air from escaping. Darko Kapelina suggests clean energy sustainable solutions such a geothermal with air filtration systems powered by solar.