A National Aeronautics and Space Administration (NASA) study found that common house plants improve air quality by removing pollutants and a variety of toxic air emissions, including ammonia, formaldehyde, carbon monoxide, benzene, xylele and trichloroethylene. The study reported that house plants were able to remove up to 87 percent of airborne toxins in a 24-hour period. Additionally, a study done at the University of Agriculture in Norway found that indoor plants can reduce fatigue, coughs, sore throats and other cold-related illnesses by more than 30 percent, partially by increasing humidity levels and decreasing dust. Therefore, it is no surprise that The Clean Air Council recommends one potted plant for each 100 square feet of living space. Plants that do a particularly good job of cleaning the air are: