Author: Antonio Da Roza
Carbon dioxide 
A survey of indoor air pollutants in public places (restaurants, cinemas and shopping malls) showed a high concentration of carbon dioxide.
Restaurants have more pollutants with an elevated level than cinemas and shopping malls. A particularly high level of carbon dioxide was recorded at restaurants and cinemas.
Carbon dioxide per se is not an important pollutant in terms of its adverse health effect. Its concentration in an indoor environment is, however, a good indicator of the effectiveness of ventilation systems and adequacy of fresh air.
High concentration of carbon dioxide is not uncommon for enclosed places containing many people. Prolonged exposure to this or higher level may make people tired and sleepy but poses no significant health risks.
Other pollutants with measured concentrations higher than the proposed indoor air quality objectives are formaldehyde, nitrogen dioxide, ozone, respirable suspended particulates, nicotine, benzene, and counts of bacteria and fungi. 
Formaldehyde – comes mainly from new furniture or materials used in renovation work
Nicotine – and often respirable suspended particulates, are indicators of level of cigarette smoking.
Nitrogen dioxide – usually comes from cooking stoves.
Ozone – comes from photocopiers or other devices that may emit ultra violet light.
Bacteria and fungi – people exposed to elevated bacteria and fungi counts will have an increased chance of being affected. Bacteria and fungi counts are usually indicators of the cleanliness of ventilation systems, particularly the filters, and sometimes indicators of the cleanliness of carpets. In addition to fresh air volume, cleanliness of ventilation systems and carpets is also an important issue
Volatile organic compounds – lifetime cancer risk from exposure to volatile organic compounds in indoor and commuting environments was found to be greatest for housewives, followed by food service and office workers, and then school children. 
In the longer term, exposure to these indoor air pollutants at high levels may impair lung function, cause respiratory disease, and enhance the probability of contracting cancer.