The impact of Indoor Ambient Quality (IAQ) on human beings may consist of undesired health effects of different types, ranging from sensory annoyance or discomfort to severe health injuries. "Health" is defined according to the well-known WHO definition
as "A state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity".
The health of susceptible and sensitive individuals can be impacted even on low air pollution days. Short-term exposure to air pollutants is closely related to COPD (Chronic Obstructive Pulmonary Disease), cough, shortness of breath, wheezing, asthma, respiratory disease, and high rates of hospitalization (a measurement of morbidity).